Internal Channel Change B9

ED 04 RELEASED INTERNAL CHANNEL CHANGE EVOLIUM 0399_04.doc

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Site VELIZY EVOLIUM™ SAS

Originators Didier ESCLAMADON

INTERNAL CHANNEL CHANGE RELEASE B9

System : ALCATEL 900/BSS Sub-system : SYS-TLA Document Category : PRODUCT DEFINITION

ABSTRACT This document describes the protocol for execution of the internal channel changes (handover and directed retry). The following channel changes cases are covered: intra-cell, synchronous/asynchronous inter-cell and multiband inter-zone. Intra-cell swap of the main channel, pre-synchronous and pseudo-synchronous channel changes are not supported in this Alcatel BSS release.

Approvals Name App.

J. ACHARDR. MAUGER SYT CCM

ZHANG Y. DPM BSC U. TISCH

DPM BTS

Name App.

C. LEJEUNE DPM SYT


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REVIEW

Ed. 01 Proposal 01 2004/03/19 MRD/TD/SYT/rma/0121.2004

HISTORY Ed. 01 Proposal 01 2004/02/20 First version for release B9, based on B8 3BK 11202 0346 DSZZA.

Includes “Autonomous Packet Resource Allocation” feature Ed. 01 Released 2004/03/19 Updated according to review report MRD/TD/SYT/rma/0121.2004 Ed. 02 Proposal 01 2004/04/23 Updated to include the impacts of the SFD “Enhanced E-GSM band

handling” (Ref. 3BK 11204 0612 DSZZA). Ed. 02 Proposal 02 2004/09/23 Taking into account VGCS feature Ed. 02 Released 2004/10/12 TD/SYT/des/204485.04/ed1

3BKA20CBR148477 Ed. 03 Released 2005/05/31 3BKA20CBR158834 - ICC : Mode of first channel always included, due

to MS bug Ed. 04 Released 2005/11/08 3BKACBR20166773 - ICC : 2G to 3G Handover (RFD156030)


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TABLE OF CONTENTS

TABLE OF CONTENTS......................................................................................................................... 3 1 SCOPE.............................................................................................................................................. 5 2 FUNCTIONAL DESCRIPTION ......................................................................................................... 6 2.1 General description ..................................................................................................... 6

2.1.1 Phase 1 MS capabilities.................................................................................................. 7 2.1.2 Phase 2 MS capabilities.................................................................................................. 7

2.2 INTERNAL HANDOVER ENTITIES.............................................................................. 7 3 DYNAMIC BEHAVIOUR................................................................................................................... 9 3.1 GENERAL BEHAVIOUR .............................................................................................. 9

3.1.1 Successful intra-cell internal handover ........................................................................... 9 3.1.2 Successful inter-cell synchronous internal channel change ......................................... 11 3.1.3 Successful inter-cell asynchronous internal channel change ....................................... 14 3.1.4 Unsuccessful internal channel changes........................................................................ 16 3.1.5 BSC protocol failures .................................................................................................... 21 3.1.6 Target BTS protocol failures ......................................................................................... 23

3.2 DETAILED INTERNAL CHANNEL CHANGE PROTOCOL BEHAVIOUR................ 24 3.2.1 BTS internal channel change protocol .......................................................................... 24 3.2.2 BSC intra-cell internal channel change......................................................................... 24 3.2.3 BSC inter-cell internal channel change......................................................................... 37 3.2.4 PHYSICAL CONTEXT procedure................................................................................. 53 3.2.5 CHANNEL ACTIVATION message construction .......................................................... 55 3.2.6 ASSIGNMENT COMMAND message construction ...................................................... 63 3.2.7 HANDOVER COMMAND message construction ......................................................... 65 3.2.8 HANDOVER PERFORMED message construction ..................................................... 68 3.2.9 ASSIGNMENT COMPLETE message construction ..................................................... 71 3.2.10 CHANNEL MODE MODIFY message construction...................................................... 71 3.2.11 TFO MODIFICATION REQUEST message construction ............................................. 71 3.2.12 HANDOVER COMPLETE, HANDOVER FAILURE, ASSIGNMENT COMPLETE, ASSIGNMENT FAILURE messages checking........................................................................ 72 3.2.13 BTS CHANNEL ACTIVATION message checking ....................................................... 72 3.2.14 MS behaviour ................................................................................................................ 72 3.2.15 MSC behaviour.............................................................................................................. 72

3.3 INTERACTION WITH OTHER PROCEDURES.......................................................... 73 3.3.1 Internal channel change interaction with assignment, ciphering, classmark request, classmark update & DTAP ...................................................................................................... 73 3.3.2 Internal handover & power control ................................................................................ 75 3.3.3 Internal handover & SMS PP ........................................................................................ 75 3.3.4 Internal channel change & call release ......................................................................... 76 3.3.5 Internal directed retry & In-call modification.................................................................. 76 3.3.6 Internal channel change & timer T3103 ........................................................................ 77 3.3.7 Internal handover & concentric cells ............................................................................. 77 3.3.8 Internal channel change & handover algorithms .......................................................... 77 3.3.9 Internal handover & eMLPP.......................................................................................... 77

4 INTERFACE DESCRIPTIONS........................................................................................................ 78 4.1 GSM interfaces / Physical interfaces....................................................................... 78

4.1.1 Radio interface .............................................................................................................. 78 4.1.2 Abis interface................................................................................................................. 78 4.1.3 A interface ..................................................................................................................... 79

4.2 Internal interfaces...................................................................................................... 80 4.2.1 BSS internal entities ...................................................................................................... 80 4.2.2 BSS internal interfaces with Internal Channel Changes ............................................... 81

4.3 Timer list ..................................................................................................................... 82 4.4 Parameter list ............................................................................................................. 83

5 GLOSSARY .................................................................................................................................... 85


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REFERENCED DOCUMENTS

Doctree references [1] 3BK 11202 0413 DSZZA Radio and link establishment [2] 3BK 11202 0412 DSZZA Normal Assignment Procedure [3] 3BK 11202 0156 DSZZA Ciphering procedure [4] 3BK 11202 0398 DSZZA Call release [5] 3BK 11202 xxxx DSZZA Channel modification [6] 3BK 11202 0409 DSZZA Classmark Handling [7] 3BK 11202 0296 DSZZA DTX functional specification [8] 3BK 11202 0295 DSZZA Power control and radio link supervision [9] 3BK 11202 0400 DSZZA Handover preparation [10] 3BK 11202 0359 DSZZA Reset Circuit and blocking and unequipped circuit [11] 3BK 11202 0388 DSZZA Frequency encoding algorithm [12] 3BK 11202 0414 DSZZA LapDm functional specification [13] 3BK 11202 0389 DSZZA System information management [14] 3BK 11202 0387 DSZZA Resource Allocation and management [15] 3BK 11202 0411 DSZZA Handover management [16] 3BK 11202 0386 DSZZA External Channel Change [17] 3BK 11202 0096 DSZZA Alcatel BSS Application Document to GSM -General Overview [18] 3BK 11202 0403 DSZZA Radio measurements Data Processing [19] 3BK 11203 0104 DSZZA Layer 3 message dictionary - Abis interface [20] 3BK 11202 0337 DSZZA LCS Functional Specification [21] 3BK 11202 0405 DSZZA ASCI Functional Specification

3GPP References [22] 3GPP TS 44.018 Mobile radio interface layer 3 specification: Radio Resource Control

Protocol [23] 3GPP TS 48.058 Radio transmission and reception [24] 3GPP TR 29.994 Recommended infrastructure measures to overcome specific phase 1 MS

faults [25] 3GPP TS 42.068 Voice Groupe Call Service (VGCS) – Stage 1 [26] 3GPP TS 43.068 Voice Groupe Call Service (VGCS) – Stage 2 Note the versions of the 3GPP Technical Specifications are given in ref.[17]. RELATED DOCUMENTS None. PREFACE Not applicable.


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1 SCOPE

This document specifies the internal channel changes protocol of the Alcatel BSS. The channel change can be an intra-cell handover, an inter-cell handover or a directed retry. The inter-cell channel change is synchronous or asynchronous, depending on the cells synchronisation and the O&M configuration. Intra-cell swap of the main channel, pre-synchronous and pseudo-synchronous channel changes are not supported in the Alcatel BSS. The call and resource release scenarios which occur as a result of events during the protocol are specified in ref.[4]. The referencing of events in ref.[4] are provided by means of the reference and an event number. The event number is made of 1 to 4 character string followed by 4 numbers - e.g. ref.[4] IH0100 or N0200. These event numbers are to be found in ref.[4] together with the call releasing scenario.


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2 FUNCTIONAL DESCRIPTION

2.1 General description The channel change procedure is the ability of a system to change the RF channel supporting the main signalling of a transaction (FACCH or SDCCH). It can be either decided and performed autonomously by a BSS (internal channel change), either decided by an MSC or a BSS and performed under the control of an MSC (external channel change). In a first step, in the serving BSS, the Handover Preparation (HOP) or Resource Allocation Management (RAM) entity detects the need for a channel change (for the latter case, RAM requests to HOP to trigger the alarm). HOP builds a first list of possible target cells (see ref.[9]). This handover alarm and the cell list is sent to the Handover Management (HOM) entity, which decides if the channel change must be internal or external. Then the HOM entity sends a channel change request to the ICC (Internal Channel Change) or ECC (External Channel Change) entity with the possible target cells given in a filtered cell list (see ref.[15]). The external channel change protocol is described in ref.[16]. The internal channel change protocol is described in this document. Internal channel change type: The internal channel change can be one of the following: • Intra-cell internal handover: The intra-cell internal handover is a channel change performed between RF channels belonging to the same cell.

• Inter-cell internal handover: The inter-cell internal handover is a handover performed between cells controlled by the same BSS.

• Internal directed retry: The internal directed retry is a channel change from SDCCH on the serving cell to a TCH on a neighbour cell controlled by the same BSS.

Frequency bands: Inter-cell channel changes can be performed between cells belonging to the same frequency band (GSM900, GSM850, DCS1800 or DCS1900). In addition, inter-cell channel changes may be performed between GSM900 and DCS1800 cells, or between GSM850 and DCS1800 cells, or between GSM850 and DCS1900 cells, if allowed. Inter-cell channel changes cannot be performed between DCS1900 cells and cells belonging to the bands GSM900 or DCS1800, and between GSM850 and GSM900 cells. Multiband / Biband MS definition: An MS is defined as multiband if it supports at least two different frequency bands. These bands may not be compatible (e.g. GSM850 – GSM900, DCS1800 – DCS1900). In Alcatel implementation, an MS is defined as biband if it supports at least the bands given by the parameter PLMN_FREQUENCY_BANDS, i.e. : • it supports at least P-GSM AND DCS1800, and PLMN_FREQUENCY_BANDS = “GSM900 and

DCS1800 bands” • it supports at least DCS1800 AND GSM850, and PLMN_FREQUENCY_BANDS = “GSM850 and

DCS1800 bands” • it supports at least DCS1900 AND GSM850, and PLMN_FREQUENCY_BANDS = “GSM850 and

DCS1900 bands”


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Synchronisation:

Inter-cell channel changes can be synchronous or asynchronous. • Synchronous channel change is performed between synchronised cell, if allowed by an O&M parameter at cell level (serving cell and target cell are checked). The MS uses the same TA on the serving cell and on the target cell.

• Asynchronous channel changes are performed in any other cases. The MS waits the PHYSICAL INFORMATION messages from the target cell to know which TA it must use.

Synchronous channel changes operate faster than asynchronous channel changes due to the fact that the access method to the new channel is faster and simpler. This is possible as the BSS has knowledge of the synchronisation between the MS, the serving cell and the target cell. In addition, 3GPP has defined pre-synchronous and pseudo-synchronous channel changes. Pre-synchronous handovers are performed in micro cellular environments when the BSS knows the approximate Timing advance to give to a MS. Pseudo-synchronous handovers are performed when the BSS has knowledge of the timing synchronisation of the serving and target cell. These channel change types are not implemented in the Alcatel BSS. 2.1.1 Phase 1 MS capabilities It is generally agreed in 3GPP (but not actually stated) that the SDCCH -> SDCCH asynchronous handover for Phase 1 MSs is not guaranteed. This results from the setting of the MS timer (T3124) being made too short to ensure at least more than one reception of the PHYSICAL INFORMATION message. It was not foreseen for the GSM Phase 1 or GSM Phase 1 extended MSs to operate with a network which supports several ciphering algorithms. As a result, the Phase 1 MSs can not change ciphering algorithm during channel changes or turn off ciphering once ciphering has been initiated. Thus any GSM Phase 2 network will have to take into account this behaviour when performing a channel change. The Alcatel implementation of internal directed retry takes into account faulty phase 1 mobiles, with respect to [24]. 2.1.2 Phase 2 MS capabilities Phase 2 MSs may support two new channel change types: pseudo-synchronous and pre-synchronous handovers (both are not supported by the Alcatel BSS). SDCCH -> SDCCH asynchronous handovers are ensured as the value of T3124 in the MS has been increased during this type of handover. A phase 2 MS may support more than one ciphering algorithm and may stop or start or change the ciphering algorithm during channel changes (if requested by the BSS) once ciphering has already been activated by the MSC. A phase 2 MS may support channel change between frequency bands.

2.2 INTERNAL HANDOVER ENTITIES The following entities are involved in the execution of an internal channel change: BSC HOM (Handover Management) When the need for a channel change is detected, this entity manages the triggering of the channel changes protocols (requesting a handover or a directed retry), the repetition of the channel change (internal or external) in case of failure, and all the interactions with other procedures. BSC RAM (Resource Allocation and Management) When the BSC protocol needs a resource for the target channel, it will call this entity to select it.


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BSC ICC (Internal Channel Change) protocol:

When the BSC HOM entity detects the need for an internal channel change, it will call this entity and give a list of filtered target cells and the type of channel change (handover or directed retry). When the channel change is finished, the BSC Channel Change entity sends an indication to the BSC HOM with the success/failure indication. Serving cell protocol: The serving BTS plays no active role in the handover protocol. Its main function is to relay messages and events between the MS and the BSC. Target cell protocol: The target BTS controls the access of the MS to the new channel. MS Handover protocol: The MS is not aware of the on-going channel change before it receives the HANDOVER COMMAND or ASSIGNMENT COMMAND message. Then the MS must immediately switch to the new channel described in the HANDOVER COMMAND or ASSIGNMENT COMMAND messages and establish the connection. The establishment procedure depends on the channel change type: intra-cell, inter-cell synchronous or inter-cell asynchronous. MSC Handover protocol: The MSC plays no part in the internal channel change protocol. However, if the channel change is a handover, the MSC will receive an indication of the fact that it has been successfully performed. If the channel change is a directed retry, the MSC will only be aware of the successful completion of the assignment, with the new cell identity. Remark: An overview of the MS and MSC functions will be given so as to help the reader. The

behaviour may deviate due to implementation choices in the MS and MSC.


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3 DYNAMIC BEHAVIOUR

3.1 GENERAL BEHAVIOUR This section contains the successful and major failure cases of an internal channel change. The failure cases mainly consist of timer expires and errors signalled with GSM defined messages. In this section message protocol errors or internal system errors are not taken into account. These cases are dealt with in the section 3.2 on detailed dynamic behaviour where the checking and error handling is specified. Only Radio, Abis and A interface messages are used in the message sequence charts within this section. 3.1.1 Successful intra-cell internal handover The following message sequence chart shows the scenario of a successful intra-cell internal handover for a BSS. MS BTS BSC MSC ICC (intra-cell) request from HOM (1)

PHYSICAL CONTEXT REQUEST

(old main channel)

<------------------------------------------------------------ start T9108 PHYSICAL CONTEXT CONFIRM

(old main channel)

------------------------------------------------------------> stop T9108 (2) CHANNEL ACTIVATION (new channel) <------------------------------------------------------------ start T9103 CHANNEL ACTIVATION ACK

(new channel)

------------------------------------------------------------> stop T9103 (3)

I (ASSIGNMENT CMD)

DATA REQUEST (ASSIGNMENT COMMAND) (old channel)

<---------------------------- <------------------------------------------------------------ start T3107 (4) SABM ----------------------------> ESTABLISH INDICATION (new channel) UA ------------------------------------------------------------> <---------------------------- Start T_CFI_TR (5)

I (ASSIGNMENT CMP)

DATA INDICATION (ASSIGNMENT COMPLETE) (new channel)

----------------------------> ------------------------------------------------------------> stop T3107 HANDOVER PERFORMED ----------------------> ICC send success to HOM (6) RF CHANNEL RELEASE (old channel) start <------------------------------------------------------------ T_RCR_ACK RF CHANNEL RELEASE ACK

(old channel) stop

------------------------------------------------------------> T_RCR_ACK

Figure 3-1 : Successful intra-cell internal handover


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(1) The BSC ICC entity: Requests a new channel on the serving cell to the RAM entity.

When the RAM entity has successfully selected the target channel, the BSC ICC entity starts a physical context procedure towards the old channel and starts T9108.

The BTS: Builds a PHYSICAL CONTEXT CONFIRM message and sends it to the BSC.

The BSC ICC entity: Stops T9108. (2) The BSC ICC entity: Activates the new channel (see section 3.2.5.1 “CHANNEL

ACTIVATION message construction”), starts T9103 and starts ignoring CONNECTION FAILURE INDICATION cause “Remote transcoder failure” from the BTS.

The BTS: For the new channel: - starts ciphering and deciphering immediately, - starts transmitting on the SACCH, using the power and timing

advance indicated in the CHANNEL ACTIVATION message, dedicated system information messages.

- sends CHANNEL ACTIVATION ACK and starts the synchronisation with the transcoder. As long as the synchronisation is not good, the BTS will send every T_SYNC expiry CONNECTION FAILURE INDICATION messages to the BSC, with cause “Remote transcoder failure”.

The BSC ICC entity: When CHANNEL ACTIVATION ACK message is received, stops T9103.

In case of TCH-call, sets up the internal path across the switch and switches the downlink direction (see Note) taking into account the full rate / half rate requirements of the new channel.

(3) The BSC ICC entity: Sends via the old channel an ASSIGNMENT COMMAND to the MS. Starts T3107 to supervise the procedure and starts to queue DTAP

messages. The BTS: Passes the ASSIGNMENT COMMAND message transparently on the

old channel. (4) The MS: On reception of the ASSIGNMENT COMMAND, disconnects the old

channel, connects to the new channel and establishes the new channel at SAPI 0 via the exchange of SABM and UA.

The BTS: Relays the SABM as an ESTABLISH INDICATION to the BSC, starts T_CFI_TR and resynchronises system information messages on the main channel (restarts at SYSTEM INFORMATION TYPE 5 message),

starts the reporting of the measurements to the BSC, starts TA computation, starts radiolink failure detection. The BSC ICC entity: Switches (TCH only) the uplink direction of the internal path set up in

(2) on a per call basis, depending on the full rate / half rate requirements of the connection and starts MS and BS power control (if appropriate).

(5) The MS: Sends the ASSIGNMENT COMPLETE to the BSS. The BTS: Passes the ASSIGNMENT COMPLETE transparently. The BSC ICC entity: Stops the timer T3107, sends a HANDOVER PERFORMED to the MSC, sends a success indication to the BSC HOM entity, starts sending queued DTAP messages to the MS. (6) The BSC ICC entity: Releases the old channel by use of the RF channel release procedure -

ref.[4] IH0700. Note: In case of TCH to TCH channel change, the BSC performs a “Y” connection in the downlink direction.


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3.1.2 Successful inter-cell synchronous internal channel change

The following message sequence chart shows the scenario of a successful inter-cell synchronous internal channel change for a BSS. The HOM entity requests either a handover, either a directed retry. Serving Target MS BTS BTS BSC MSC Directed Retry case ASSIGNMENT

REQUEST

<-------------------------

Start T11 or

Start T11 Forced

Handover and Directed Retry common procedure ICC (inter-cell) request from HOM

- Synchronous ICC -

(1) PHYSICAL CONTEXT REQUEST <---------------------------------------------------------- start T9108 PHYSICAL CONTEXT CONFIRM ----------------------------------------------------------> stop T9108 (2) CHANNEL ACTIVATION <-------------------------- start T9103 CHAN ACTIV ACK --------------------------> stop T9103

(2a) (opt) TFO MODIFICATION REQUEST <---------------------------------------------------------- (3) I (HO CMD) DATA REQUEST (HANDOVER COMMAND) <---------------------- <---------------------------------------------------------- start T3103 (4) HANDOVER ACCESS 1--------------------------------------------------> HO DETECTION 2--------------------------------------------------> --------------------------> 3--------------------------------------------------> start T3106 4--------------------------------------------------> (5) SABM ----------------------------------------------------> ESTABLISH

INDICATION

UA --------------------------> <---------------------------------------------------- stop T3106 note A start T_CFI_TR (6) I (HANDOVER COMPLETE) DATA IND (HO CMP) ----------------------------------------------------> --------------------------> stop T3103 Handover case (7) HO PERFORMED ----------------------> ICC send success to HOM


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Directed Retry case (8) stop T11 or

stop T11_FORCED

ASSIGNMENT COMPLETE ----------------------> ICC send success to HOM

Note B

CHANNEL MODE MODIFY <------------------------------------------------------------------------------------------ CHANNEL MODE MODIFY ACK ------------------------------------------------------------------------------------------> (End of the scenario) (9) RF CHANNEL RELEASE start <---------------------------------------------------------- T_RCR_ACK RF CHANNEL RELEASE ACK stop ----------------------------------------------------------> T_RCR_ACK

Figure 3-2 : Successful inter-cell synchronous internal channel change

Note A: T3106 may be stopped earlier upon the reception of any correct layer 2 frame, depending on the O&M parameter STOP_HO_ACC_FAIL.

Note B: The release of the old channel is started at this point and is performed independently of the channel mode modification procedure.

(1) The BSC ICC entity: Triggers the physical context procedure towards the old channel, on the serving BTS, and starts T9108.

(2) The BSC ICC entity: Requests a new channel on the target cell to the RAM entity. When the RAM entity has selected the target channel, starts the

channel activation procedure (see section 3.2.5.2 “CHANNEL ACTIVATION message construction”), starts T9103 and starts ignoring CONNECTION FAILURE INDICATION cause “Remote transcoder failure” from the BTS.

The target BTS: For the new channel: - starts ciphering immediately, - starts transmitting on the SACCH, using the power and timing

advance indicated in the CHANNEL ACTIVATION message, dedicated system information messages.




(2a) The BSC ICC entity: In case of speech TCH handover, if TFO is enabled (EN_TFO = 1) in the serving cell and TFO is disabled (EN_TFO = 0) in the target cell, the BSC sends a TFO MODIFICATION REQUEST with EN_TFO=0 to the serving BTS, to stop TFO in the TRAU before performing the handover. Indeed, in the case where the target BTS does not support TFO (BTS FUMO), the only possibility to stop TFO in the TRAU and avoid inconsistencies in the exchanges with the distant TRAU in TFO, is to stop TFO in the TRAU before performing the handover. As the BSC does not know if the BTS supports TFO or no, the mechanism is extended to all cells where TFO is disabled. This has no system impact.

(3) The BSC ICC entity: Sends the HANDOVER COMMAND to the MS and starts T3103 to supervise the procedure.


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The serving BTS: Passes the HANDOVER COMMAND message transparently.

(4) The MS: Moves to the new channel and sends 4 consecutive HANDOVER ACCESS bursts on the DCCH of the new channel with a timing advance of 0.

The target BTS: Adjusts the timing advance depending on value calculated from the reception of HANDOVER ACCESS.

Starts deciphering. Sends the HANDOVER DETECTION message to the BSC. Starts T3106. In this release, the HANDOVER DETECTION is sent on the reception

of a correct access burst on the target channel. The alternative method described in ref.[23] (where HANDOVER DETECTION is sent on the reception of correctly decoded and eventually deciphered frame on the target channel) is not implemented.

The BSC ICC entity: Switches (TCH only) the uplink direction of the internal path set up in (2) on a per call basis, depending on the full rate / half rate requirements of the connection.

(5) The MS: Establishes the SAPI 0 connection on the new channel via the exchange of SABM and UA.

The target BTS: On the reception of either a SABM SAPI 0 or any correctly received layer 2 frame, (depending on an O&M parameter), stops T3106 and resynchronises system information messages on the new channel (restarts at SYSTEM INFORMATION TYPE 5 message).

On reception of the SABM SAPI 0, the target BTS: sends the ESTABLISH INDICATION SAPI 0 to the serving BSC, starts T_CFI_TR, starts the reporting of the measurements to the BSC, starts TA computation, starts radiolink failure detection. The BSC ICC entity: On reception of the ESTABLISH INDICATION, starts MS and BS power

control (if appropriate). (6) The MS: Sends the HANDOVER COMPLETE to the target BTS. The target BTS: Forwards the message transparently to the serving BSC. The BSC ICC entity: Stops the timer T3103, (7) The BSC ICC entity: If the channel change is a handover: sends HANDOVER PERFORMED to the MSC and sends a success

indication to the HOM entity (8) The BSC ICC entity: If the channel change is a directed retry : Sends ASSIGNMENT COMPLETE to the MSC. Sends a success indication to the HOM entity, which asks the RAM

entity to stop T11 or T11_FORCED (the choice of the timer, T11 or T11_FORCED, is described in ref.[2]) and to dequeue the request..

Starts the release of the old channel (see below). If the channel change is a directed retry, and if MS is a phase 1 MS and

if a full rate TCH has been allocated for speech version 1 in (1), then at this point in time the BSC sends a CHANNEL MODE MODIFY message to the MS on the new main channel. The CHANNEL MODE MODIFY ACK message that may be sent by the MS is discarded unless received during In-call modification procedure, see section 3.3.5 ”Internal directed retry & In-call modification”.

(9) The BSC: Performs an RF channel release procedure towards the old serving cell - ref.[4] IH0700.

Note: In case of TCH to TCH channel change, the BSC performs a “Y” connection in the downlink direction.


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3.1.3 Successful inter-cell asynchronous internal channel change

The following message sequence chart shows the scenario of a successful inter-cell asynchronous internal channel change for a BSS. The HOM entity requests either a handover, either a directed retry. Serving Target MS BTS BTS BSC MSC

ICC (inter-cell) request from HOM

- Asynchronous ICC -

(1) CHANNEL ACTIVATION <-------------------------- start T9103 CHAN ACTIV ACK --------------------------> stop T9103

(1a) (opt) TFO MODIFICATION REQUEST <-------------------------- <----------------------------------------------------------

(2) I (HO CMD) DATA REQUEST (HANDOVER COMMAND) <-------------------------- <---------------------------------------------------------- start T3103

(3) start T3124 HANDOVER ACCESS ----------------------------------------------------------> ----------------------------------------------------------> HO DETECTION PHYSICAL INFORMATION --------------------------> <---------------------------------------------------------- start T3105

(4) stop T3124 start T200 SABM ----------------------------------------------------------> stop T3105 note A ESTABLISH

INDICATION

UA --------------------------> <---------------------------------------------------------- stop T200 start T_CFI_TR

(5) I (HANDOVER COMPLETE) DATA IND (HO CMP) ----------------------------------------------------------> --------------------------> stop T3103 Handover case

(6) HO PERFORMED ----------------------> ICC send success to HOM Directed Retry case

(7) stop T11 or stop T11_FORCED

ASSIGNMENT COMPLETE ----------------------> ICC send success to HOM

Note B

CHANNEL MODE MODIFY <------------------------------------------------------------------------------------------ CHANNEL MODE MODIFY ACK ------------------------------------------------------------------------------------------> (End of the scenario)

(8) PHYSICAL CONTEXT REQUEST (old main channel)

<---------------------------------------------------------- start T9108 PHYSICAL CONTEXT CONFIRM

(old main channel)

----------------------------------------------------------> stop T9108 RF CHANNEL RELEASE start <---------------------------------------------------------- T_RCR_ACK RF CHANNEL RELEASE ACK stop ----------------------------------------------------------> stop T_RCR_ACK


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Figure 3-3 : Successful inter-cell asynchronous channel change

Note A: T3105 may be stopped earlier upon the reception of any correct layer 2 frame, depending on the O&M parameter STOP_HO_ACC_FAIL

Note B: The release of the old channel is started at this point and is performed independently of the channel mode modification procedure.

(1) The BSC ICC entity: Requests a new channel on the target cell to the RAM entity. When the RAM entity has selected the target channel, starts the

channel activation procedure (see section 3.2.5.2 “CHANNEL ACTIVATION message construction”), starts T9103 and starts ignoring CONNECTION FAILURE INDICATION cause “Remote transcoder failure” from the BTS.

The target BTS: For the new channel: - starts ciphering immediately, - starts transmitting on the SACCH, using the power indicated in the

CHANNEL ACTIVATION message, dedicated system information messages. The TA contained in the layer 1 header of SACCH messages contains the default TA.




(1a) The BSC ICC entity: In case of speech TCH handover, if TFO is enabled (EN_TFO = 1) in the serving cell and TFO is disabled (EN_TFO = 0) in the target cell, the BSC sends a TFO MODIFICATION REQUEST with EN_TFO=0 to the serving BTS, to stop TFO in the TRAU before performing the handover. Indeed, in the case where the target BTS does not support TFO (BTS FUMO), the only possibility to stop TFO in the TRAU and avoid inconsistencies in the exchanges with the distant TRAU in TFO, is to stop TFO in the TRAU before performing the handover. As the BSC does not know if the BTS supports TFO or no, the mechanism is extended to all cells where TFO is disabled. This has no system impact.

(2) The BSC ICC entity: Sends the HANDOVER COMMAND to the MS and starts T3103 to supervise the procedure.

The serving BTS: Passes the HANDOVER COMMAND message transparently. (3) The MS: Moves to the target BTS and sends continuously HANDOVER ACCESS

messages on the DCCH of the new channel with a timing advance of 0. The target BTS: Calculates the timing advance and updates that value sent in the layer

1 header on SACCH, sends the PHYSICAL INFORMATION message to the MS containing the calculated timing advance

Starts deciphering, starts T3105 and sends the HANDOVER DETECTION to the serving BSC.

The BSC ICC entity: Switches (TCH only) the uplink direction of the internal path set up in (1) on a per call basis, depending on the full rate / half rate requirements of the connection and awaits the completion of the procedure.

(4) The MS: Having received the timing advance information, adjusts its timing advance and establishes the SAPI 0 connection on the new channel via the exchange of SABM and UA.


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The target BTS: After having received either a SABM SAPI 0 or any correct layer 2

frame (depending on an O&M parameter), stops T3105 and resynchronises system information messages on the new channel (restarts at SYSTEM INFORMATION TYPE 5 message).

On reception of the SABM SAPI 0, the target BTS: starts T_CFI_TR, sends the ESTABLISH INDICATION SAPI 0 to the serving BSC, starts reporting of the measurements to the BSC, starts TA computation, starts radiolink failure detection. The BSC ICC entity: On reception of the ESTABLISH INDICATION, starts MS and BS power

control if appropriate and continues to await for the end of the procedure.

(5), (6) & (7) See section 3.1.2 “Successful inter-cell synchronous internal channel change

(8) The BSC: Performs an RF channel release procedure towards the old serving cell - ref.[4] IH0700. A physical context procedure is triggered on the old channel before releasing it.

Note: In case of TCH to TCH channel change, the BSC performs a “Y” connection in the downlink direction.

3.1.4 Unsuccessful internal channel changes This section presents the unsuccessful cases where the MS is unable to perform the internal channel change for one of the following reasons: • Inability to find or synchronise to the new cell (inter-cell asynchronous channel change only). • T3124 expiry due to non reception of the PHYSICAL INFORMATION message after sending the HANDOVER ACCESS (inter-cell asynchronous channel change only).

• Failure to receive the UA when attempting to establish the channel, or any layer 2 or layer 1 failure (any internal channel change).

• Severe MS failure or disconnection of MS by the user. In the first three cases, the MS returns to the old channel, re-establishes the layer 2 connection and sends the HANDOVER FAILURE (inter-cell) or ASSIGNMENT FAILURE (intra-cell). In the last case where the MS has been either switched off or has failed, the connection will be eventually released when timers in the BSC expire (T3107 for intra-cell, T3103 for inter-cell). The following message sequence charts show the scenario for unsuccessful channel changes when the MS successfully returns to the old channel.


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3.1.4.1 Unsuccessful intra-cell internal handover

MS BTS BSC MSC I (ASSIGNMENT CMD)

DATA REQUEST (ASSIGNMENT COMMAND) (old channel)

(1) <----------------------------- <------------------------------------------------------------ start T3107 (2) start T200 SABM (new channel) -----------------------------> ESTABLISH INDICATION (new channel) ------------------------------------------------------------> UA (new channel) start T_CFI_TR (new channel) (3) X- - - - - -------------------- : (4) T200 expiry start T200 SABM (new channel) -----------------------------> UA (new channel) X- - - - - -------------------- : T200 expiry start T200 SABM (new channel) T_SYNC expiry (old channel)

CONNECTION FAILURE INDICATION

-----------------------------> “Remote transcoder failure” - (old channel) UA (new channel) ------------------------------------------------------------> X- - - - - -------------------- : (5) T200 expiry (note A) SABM (old channel) -----------------------------> ESTABLISH INDICATION (old channel) UA (old channel) ------------------------------------------------------------> <----------------------------- start T_CFI_TR (old channel) (6)

I (ASSIGNMENT FAIL) DATA INDICATION (ASSIGNMENT FAILURE)

(old main channel)

-----------------------------> ------------------------------------------------------------> stop T3107 (7) PHYSICAL CONTEXT REQUEST

(new channel)

<------------------------------------------------------------ start T9108 PHYSICAL CONTEXT CONFIRM

(new channel)

------------------------------------------------------------> stop T9108 RF CHANNEL RELEASE (new channel) start <------------------------------------------------------------ T_RCR_ACK RF CHANNEL RELEASE ACK

(new channel) stop

------------------------------------------------------------> T_RCR_ACK

Figure 3-4 : Unsuccessful intra-cell internal handover Note A: MS detects a problem with the new cell or RF channel.

(1) The BSC ICC entity: Initiates the intra-cell handover by sending the ASSIGNMENT COMMAND after having performed the physical context procedure on the old channel and the channel activation procedure on the new channel.

The BTS: (old channel) passes it to the MS transparently. The MS: Switches to the new channel.


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(2) The MS: Attempts to establish the new channel by the sending of SABM.

The BTS: (new channel), responds with a UA, sends the ESTABLISH INDICATION to the serving BSC and starts T_CFI_TR.

The BSC ICC entity: Switches (TCH only) the uplink direction of the internal path previously set up upon reception of the CHANNEL ACTIVATION ACK message on a per call basis, depending on the full rate / half rate requirements of the connection and starts MS and BS power control.

The BTS: (old channel) will start to detect remote transcoder alarms, as the transcoder is now switched to the new channel, and will consequently send a CONNECTION FAILURE INDICATION cause “Remote transcoder failure” every T_SYNC expiry.

The BSC ICC entity: Ignores these CONNECTION FAILURE INDICATION. (3) In this example the UA is lost on the Radio interface. (4) In the MS: T200 expires continuously and the SABM is resent. (5) The MS: After it has sent the SABM N200 times, decides to return to the old

channel. Sends SABM SAPI 0 on the old channel. The BTS: (old channel) responds with UA SAPI 0, sends an ESTABLISH

INDICATION to the serving BSC, starts T_CFI_TR and resynchronises system information messages on the old channel (restarts at SYSTEM INFORMATION TYPE 5 message)..

The BSC ICC entity: Accepts ESTABLISH INDICATION (no external action is triggered). (6) The MS: Sends the ASSIGNMENT FAILURE on the old channel. The BTS: (old channel) relays the message transparently to the BSC. The BSC ICC entity: Stops T3107, and switches the uplink direction of the internal path back

to the old channel depending on the full rate / half rate requirements of the connection Sends a MS failure indication to the HOM entity.

(7) The BSC: Releases the new channel: see ref.[4] IH0300.


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3.1.4.2 Unsuccessful inter-cell asynchronous internal channel change

Serving Target MS BTS BTS BSC MSC I (HO CMD) DATA REQUEST (HANDOVER COMMAND) (1) <----------------------- <---------------------------------------------------------- start T3103 (2) start T3124 HANDOVER ACCESS ----------------------------------------------------------> ----------------------------------------------------------> HO DETECTION PHYSICAL INFORMATION --------------------------> (3) <---------------------------------------------------------- start T3105 stop T3124 Note B (4) start T200 SABM ----------------------------------------------------------> ESTABLISH

INDICATION

UA --------------------------> <---------------------------------------------------------- stop T3105 stop T200 start T_CFI_TR (5) I (HANDOVER COMPLETE) -------------------------------------------------- - - - -X Note A start T200 SABM -----------------------> ESTABLISH INDICATION UA ----------------------------------------------------------> <----------------------- start T_CFI_TR stop T200 (6) I (HO FAILURE) --------------------------> DATA INDICATION (HANDOVER FAILURE) ----------------------------------------------------------> stop T3103 (7) PHYSICAL CONTEXT REQUEST (new channel) <------------------------- start T9108 PHYSICAL CONTEXT CONFIRM (new channel) -------------------------> stop T9108 RF CHANNEL

RELEASE

start

<-------------------------- T_RCR_ACK RF CHAN REL ACK

stop

--------------------------> T_RCR_ACK

Figure 3-5 : Unsuccessful inter-cell asynchronous internal channel change Note A: MS detects a Radio link failure condition (I frame is sent N200 times without LapDm

acknowledgement). Note B: For TCH calls, the timing in this scenario is so quick that the serving BTS may not be able to

detect the transcoder failure event, before the MS can return and complete the failure scenario on the old channel.

However in the cases where the events take a longer time to detect on the new channel (e.g. permanent loss of UA or other layer 2 errors) the serving BTS may be able to detect the transcoder failure and send a CONNECTION FAILURE INDICATION (cause "remote


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transcoder failure") before the MS can complete the failure scenario. In these cases the BSC

will ignore the CONNECTION FAILURE INDICATION message. (1) The BSC ICC entity: (after having performed the channel activation procedure with the target

BTS), starts the inter-cell channel change by sending the HANDOVER COMMAND to the serving BTS and starting T3103.

The serving BTS: Passes the message transparently. The MS: Changes to the new channel. (2) The MS: Starts to send continuously the HANDOVER ACCESS message to the

target BTS on the DCCH of the new channel with a timing advance of 0 and starts T3124.

The target BTS: Sends the HANDOVER DETECTION to the BSC. The BSC ICC entity: Switches (TCH only) the uplink direction of the internal path previously

set up upon reception of the CHANNEL ACTIVATION ACK message on a per call basis, depending on the full rate / half rate requirements of the connection to the new channels.

The serving BTS: Starts detecting the loss of remote transcoder frames (TCH only) - see note B.

(3) The target BTS: Calculates the timing advance, sends it to the MS in the PHYSICAL INFORMATION message and starts T3105.

The MS: After receiving the PHYSICAL INFORMATION message, adjusts its timing to the value sent and stops T3124.

(4) The MS: Establishes the new channel by sending SABM. The target BTS: Sends the UA to the MS, stops T3105, sends an ESTABLISH

INDICATION to the serving BSC and starts T_CFI_TR. The BSC ICC entity: Starts MS and BS power control as appropriate and awaits the

HANDOVER COMPLETE message. (5) The MS: Whilst sending the HANDOVER COMPLETE, detects the failure in the

handover, returns to the old channel and re-establishes the old main channel.

The serving BTS: Sends UA to the MS, sends ESTABLISH INDICATION to the serving BSC and starts T_CFI_TR.

The BSC ICC entity: Ignores the reception of the ESTABLISH INDICATION on the old main channel.

(6) The MS: Sends the HANDOVER FAILURE message to the serving BTS. The serving BTS: Passes it transparently. The BSC ICC entity: Switches the uplink direction of the internal path back to the old channel

depending on the full rate / half rate requirements of the connection and stops T3103.

Sends a MS failure indication to the HOM entity, with the indication of the target cell attempted.

(7) The BSC ICC entity: Releases the new channel - see ref.[4] IH0100.


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3.1.5 BSC protocol failures

In this section, the possible failures are sorted in the order they can appear during the channel change protocol, from the first step of protocol to the last one. 3.1.5.1 Unavailability of a channel on the selected cell When the Internal Channel Change entity requests a new channel on the target cell to the RAM entity, it can occur that the RAM entity rejects the request (due to congestion or to no suitable channels, see ref.[14]). The answer from RAM will be handled as follows.

Intra-cell ICC Inter-cell ICC

Channelselected

by RAM ?

Channelselected

by RAM ?

"Internal Failureon all cells"

to HOM

Performintra-cell

ICCYes

No

Performinter-cell

ICCYes

No

Other cellsin the list ?

"Internal Failureon all cells"

to HOMNo

No Next cellis external ?

Yes

Yes

"Next cell is external"

to HOM

"Select channel"(on this next cell)

to RAM

Figure 3-6 : Processing of the answer from RAM

3.1.5.2 T9108 expiry T9108 expiry means that the physical context procedure has failed. The following reasons for the failure are possible: 1) The PHYSICAL CONTEXT REQUEST was lost on the Abis interface. 2) The PHYSICAL CONTEXT CONFIRM was lost on the Abis interface. 3) The BTS is under load and can not respond in time. 4) The BTS is performing a reset or re-configuration caused by O&M actions and the messages

are awaiting transmission in the BSC.


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If the timer expires in the BSC at the beginning of a channel change, the protocol will go on with the

following changes in behaviour: The CHANNEL ACTIVATION message will not contain any timing advance information. For

intra-cell handover, the MS Power will be calculated using MIN(P, MS_pwr_max) and the BS Power will be the maximum allowable in the cell (BS_pwr_max).

The expiry of T9108 at the end of the channel change protocol, during the release of the main channel, is described in ref.[4]. 3.1.5.3 CHANNEL ACTIVATION NACK The reception of the CHANNEL ACTIVATION NACK from the BTS during the internal channel change indicates that the handover can not occur towards this channel. For all supported cause values, a local release is performed in the target BTS as specified in ref.[4] ICC0100, and an O&M error report is generated. The Internal Channel Change entity will try to reattempt a channel change: see section 3.1.5.1 “Unavailability of a channel on the selected cell”. 3.1.5.4 T9103 expiry T9103 expiry means that the channel activation or modification procedure has failed. The following reasons for the failure are possible: 1) A CHANNEL ACTIVATION was lost on the Abis interface. 2) A CHANNEL ACTIVATION ACK or NACK was lost on the Abis interface. 3) The BTS is under load and can not respond in time. 4) The BTS is performing a reset or re-configuration caused by O&M actions and the

messages are awaiting transmission in the BSC. The new channel(s) is (are) released, see ref.[4] ICC0100. The Internal Channel Change entity will try to reattempt a channel change: see section 3.1.5.1 “Unavailability of a channel on the selected cell”. 3.1.5.5 T3107 expiry (Intra-cell channel change) When the assignment procedure is in operation, the timer T3107 is used to supervise the events from the MS, that is the ASSIGNMENT COMPLETE or ASSIGNMENT FAILURE. The expiry of this timer indicates the intra-cell channel change failed. The MS is assumed to be lost on the Radio interface and the appropriate call release scenario is initiated: see ref.[4] IH0400. The Internal Channel Change entity sends an “exit and clear” indication to the HOM entity to indicate that the call has been cleared. 3.1.5.6 T3103 expiry (Inter-cell internal channel change) When the handover procedure is in operation, the timer T3103 is used to supervise the responses from the MS, that is the HANDOVER COMPLETE and the HANDOVER FAILURE. The expiry of this timer indicates the inter-cell handover has failed. The MS is assumed to be lost on the Radio interface and the appropriate call release scenario is initiated:

• if the channel change is a handover, see ref.[4] IH0400, • if the channel change is a directed retry, see ref.[4] DR0600.

The Internal Channel Change entity sends an “exit and clear” indication to the HOM entity to indicate that the call has been cleared.


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3.1.5.7 CONNECTION FAILURE INDICATION cause "Handover access failure"

This message is sent from the target BTS to the BSC during an inter-cell internal channel change. The reception of this message is an indication that the target BTS received a correct HANDOVER ACCESS but did not receive an SABM SAPI 0 or correct layer 2 frame within either the periods (NY1+1)*T3105 (for asynchronous channel change) or T3106 (for synchronous channel change). The connection is released on the new channel, see section 3.1.4.2 “Unsuccessful inter-cell asynchronous internal channel change“ & see ref.[4] IH0200. The MS is assumed to come back on the old channel. The stopping of either T3105 or T3106 on reception of SABM SAPI 0 or any layer 2 frame is controlled by an O&M flag (STOP_HO_ACC_FAIL). When the flag is set to ANY FRAME, any correct Layer 2 frame (including SABM SAPI 0) will stop the timer (i.e. T3105 or T3106) which is guarding the procedure. When the flag is set to SABM SAPI 0 ONLY, only the reception of an SABM SAPI 0 will stop the timer (i.e. T3105 or T3106) which is guarding the procedure. Message sequence charts are in ref.[16]. 3.1.5.8 CONNECTION FAILURE INDICATION cause "Remote transcoder failure" The handling of this message is described in ref.[2]. 3.1.5.9 ASSIGNMENT FAILURE from the MS This message is sent by the MS during an intra-cell internal channel change. When received on the old main channel, this message means that the MS was unable to seize the new main channel. The Internal Channel Change entity will send a “HO fail from MS” indication to the HOM entity and the BSC will release the new channel(s) : see ref.[4] IH0300. 3.1.5.10 HANDOVER FAILURE from the MS This message is sent by the MS during an inter-cell internal channel change. When received on the old main channel, this message means that the MS was unable to seize the new channel on the target cell. The Internal Channel Change entity will send a “HO fail from MS” indication to the HOM entity, with the indication of the cell attempted. The BSC releases the new channel(s) : see ref.[4] IH0100. 3.1.6 Target BTS protocol failures The following protocol failures are detected by the target BTS for internal channel change:

• T3105 expiry NY1+1 times (asynchronous inter-cell channel change). • T3106 expiry (synchronous inter-cell channel change).

These failures are described in ref.[16].


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3.2 DETAILED INTERNAL CHANNEL CHANGE PROTOCOL BEHAVIOUR

3.2.1 BTS internal channel change protocol The role of the serving BTS (for all internal channel changes) controlling the old channel is described in ref.[16]. The essential aspect is that the BTS controlling the old channel plays a passive part in the internal channel change (as it does in the external channel change). The serving BTS is unaware of the channel change taking place, as the HANDOVER COMMAND or ASSIGNMENT COMMAND is passed transparently. The protocol for the target BTS is described in ref.[16]. 3.2.2 BSC intra-cell internal channel change When the need for an internal intra-cell handover is detected by the HOP entity (see ref.[9]) or RAM (see ref.[14]), the HOM entity receives from HOP this alarm and decides to trigger an intra-cell handover (see ref.[15]). In case of codec mismatch or codec optimisation detected by RAM, when TFO is enabled, RAM requests to HOP to trigger a intracell TFO alarm towards HOM (i.e. HO cause #29) with a new codec type. In case a TCH remains allocated in the non pre-emptable PS zone (see ref[14]), RAM requests to HOP to trigger an intracell alarm towards HOM with HO cause#30. The HOM entity sends to the Internal Channel Change entity a “Request for IHO” with the list of target cells, the handover cause and the new codec type in case of HO cause #29. In the case of an intra-cell handover, the target cell list will only contain the current serving cell. On reception of this “Request for IHO”, the Internal Channel Change entity starts to queue (if it is the first handover attempt) or goes on queuing (if a previous handover attempt has been triggered by the HOM entity and has failed, see [15]) some BSSMAP messages. The detailed description of BSSMAP messages queuing is given in section 3.3.1 “Internal channel change interaction with assignment, ciphering, classmark request, classmark update & DTAP”.


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3.2.2.1 States and major events description

A list of logical BSC states (Internal Channel Change entity) is presented in the following table.

STATE DESCRIPTION ABBREVIATION The ICC entity has sent “Select channel” to RAM with the type of channel and the indication that queuing is not allowed.

ICC INTRA INIT

The ICC has started the intra-cell handover protocol by performing the physical context procedure. T9108 is running to supervise the reception of the PHYSICAL CONTEXT CONFIRM message.

ICC INTRA AWAIT PHY CTXT

The BSC has sent the CHANNEL ACTIVATION message to the new channel. T9103 is running to supervise the reception of the CHANNEL ACTIVATION ACKNOWLEDGE message.

ICC INTRA AWAIT CHN ACT ACK

The BSC having completed the channel activation procedure has sent the ASSIGNMENT COMMAND to the MS. T3107 is running to supervise the procedure. The next expected message is the ESTABLISH INDICATION on the new channel.

ICC INTRA IN PROG

The BSC has received an ESTABLISH INDICATION on the new channel. ICC AWAIT ASSGN CMPLT

This state is added as the exit point for Intra cell handovers NULL Table 3-1 : Logical BSC states for intra-cell handover


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The figure below shows the major events that can occur in each state. This figure does not give an

exhaustive view of the events. Refer to the tables following the figure to have the exhaustive list of events.

ICC AWAITASSGN CMPLT

ICC (Intracell)Request from HOM

"Channel Selected"from RAM

CHN ACT ACK

ESTABIND

ASSGNCOMPLETE

ICC INTRA AWAITCHN ACT ACK

ICC INTRAIN PROG

PHY CNTCNF

T9108expiry

T9103 expiry orCHN ACT NACK

T3107expiry

T3107expiry

Stop T9103Send ASSGN CMD

Start T3107

Send CHN ACTStart T9103

Stop T9108Send CHN ACTStart T9103

Send "Select aChannel" to RAM

ICC INTRA AWAITPHY CTXT

ICC INTRAINIT

Send PHY CNT REQStart T9108

"Exit and clear"to HOM

"Internal failure onall cells" to HOM

Stop T3107"Exit and clear" to HOMSend HO PERFORMED

NULL

"Select channel reject"

Figure 3-7 : BSC intra-cell channel change state diagram & major events

The events appearing in the tables below are to be considered as not applicable or ignored if received in any other states other than those indicated by the table.


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3.2.2.2 Normal events during intra-cell channel change

State / event table: Normal events during internal channel selection

STATE EVENT

ICC INTRA INIT

“Channel Selected” from RAM Send PHYSICAL CONTEXT REQUEST to the old channel, Start T9108, Next state (ICC INTRA AWAIT PHY CTXT).

“Select Channel Reject” from RAM

“Internal Failure on all cells” sent to HOM, Next state (NULL).

Table 3-2 : Normal events during internal channel selection. (intra-cell channel change)

State / event table: Normal events during physical context procedure.

STATE EVENT


PHYSICAL CONTEXT CONFIRM (old channel)

Stop T9108, Send CHANNEL ACTIVATION to the new channel, Start T9103, Next state (ICC INTRA AWAIT CHN ACT ACK).

T9108 expiry (old channel)

See Note 1, Send CHANNEL ACTIVATION to the new channel, Start T9103, Next state (ICC INTRA AWAIT CHN ACT ACK).

Table 3-3 : Normal events during physical context procedure. Note 1: Default values are taken for the channel activation (MS power is set to MIN(P,

MS_pwr_max), BS power is set to BS_pwr_max ), the Timing Advance is not included.


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State / event table: Normal event during channel activation procedure.

STATE EVENT


CHANNEL ACTIVATION ACKNOWLEDGE

Stop T9103, Set up the internal path across the switch (TCH only) and switch the downlink direction (see Note 2) taking into account the full rate / half rate requirements of the new channel,

Go on queuing BSSMAP procedures, Send ASSIGNMENT COMMAND, Start queuing (or continue to queue) DTAP messages, Start T3107, Next state (ICC INTRA IN PROG).

CHANNEL ACTIVATION NEGATIVE ACKNOWLEDGE

Stop T9103, NC ref.[4] ICC0100, “Internal failure on all cells” sent to HOM Next state (NULL).

T9103 expiry NC ref.[4] ICC0100, “Internal failure on all cells” sent to HOM Next state (NULL).

Table 3-4 : Normal events during channel activation procedure (intra-cell channel change)

Note 2: In case of TCH to TCH channel change, the BSC performs a “Y” connection in the downlink direction.

State / event table: Normal event whilst MS is not fully connected.

STATE EVENT

ICC INTRA IN PROG ICC AWAIT ASSGN CMPLT

ESTABLISH INDICATION (new channel)

Switch the uplink direction (if TCH) on a per call basis, depending on the full rate / half rate requirements of the connection,

Start power control, Next state (ICC AWAIT ASSGN CMPLT).

Don't care.

ESTABLISH INDICATION (old channel)

Accepted - Note 3. Don't care.


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ASSIGNMENT COMPLETE (new channel)

Stop T3107, Switch the uplink direction (if TCH) on a per call basis, depending on the full rate / half rate requirements of the connection,

Start power control,

Stop T3107,

Send HANDOVER PERFORMED, OC ref.[4] IH0700,

Send queued DTAP messages, Start queued procedures (Note 2), “Exit and clear” sent to HOM

Next state (NULL). If an LCS response is awaited by the MSC

Send to the MSC an 08.08 PERFORM LOCATION RESPONSE (cause “Intra-BSC Handover Complete”)

Else If an LCS procedure is on-going for this call, and needs to be reset (see Note 4)

Send BSCLP COI RESET (cause “Intra-BSS handover”) to the SMLC. See ref.[20] for more details.

ASSIGNMENT FAILURE (old channel) Note 1

Stop T3107, NC ref.[4] IH0300,

Stop T3107, NC ref.[4] IH0300, Switch back the uplink direction (if TCH) on a per call basis, depending on the full rate / half rate requirements of the connection,

“HO FAIL from MS” sent to HOM, Next state (NULL).

If an LCS response is awaited by the MSC Send to the MSC an 08.08 PERFORM LOCATION RESPONSE (cause “Intra-BSC Handover Complete”)

Else If an LCS procedure is on-going for this call, and needs to be reset (see Note 4)

Send BSCLP COI RESET (cause “Intra-BSS handover”) to the SMLC. See ref.[20] for more details.


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T3107 expiry If an LCS response is awaited by the MSC Send an 08.08 PERFORM LOCATION RESPONSE (cause “Intra-BSC Handover Complete”) to the MSC

If an LCS procedure is on-going for this call Send BSCLP PERFORM LOCATION ABORT (cause “Intra-BSS handover”) to the SMLC.

See also ref.[20] for more details. OC & NC – Release call, ref.[4] IH0400,

“Exit and clear” sent to HOM Next state (NULL).

Table 3-5 : Normal events whilst MS is not fully connected (intra-cell channel change)

Note 1: The MS can send an ASSIGNMENT FAILURE message in response to an ASSIGNMENT COMMAND without the need to establish the old channel or even move to the new channel.

Note 2: The procedures which were deferred whilst the internal handover was in progress are now triggered in the order in which they were received.

Note 3: There are no external actions taken by the BSC at this point, however on reception of this message the BSC performs some internal actions.

Note 4: As it is an intra-cell internal channel change, the LCS characteristics of the cell remain identical after the channel change. The MS position is assumed to be the same (or almost the same) after this channel change, or in case of failure, the MS stays on the current channel. So the BSCLP COI RESET message, usually sent to the SMLC to restart the on-going LCS procedure, is not systematically sent at the outcome of the intra-cell internal channel change procedure. It is only sent if the LCS procedure has been disturbed by the intra-cell internal channel change procedure (see further, in Table "Unexpected event handling from BSCLP interface").

3.2.2.3 Unexpected events during intra-cell channel change State / event table: Unexpected event handling on A interface & DTAP events.

STATE EVENT

ICC INTRA INIT ICC INTRA AWAIT

PHY CTXT

ICC INTRA AWAIT

CHN ACT ACK

ICC INTRA IN PROG

ICC AWAIT ASSGN CMPLT

DTAP message Forward to old channel. Queue message. CIPHER MODE COMMAND

Queue procedure (only one CIPHER MODE COMMAND is queued, the first one).

HANDOVER COMMAND

Send HANDOVER FAILURE The external handover is refused by sending a HANDOVER FAILURE ("Radio

interface message failure - Reversion to old channel"). This cause value is used in GSM to indicate that the MS has failed the handover and is still connected.

In this case the Alcatel BSS returns this value so as to cancel any pending external handover that the MSC may be processing. This condition is specified in ref.[16].

ASSIGNMENT REQUEST

SDCCH->TCH TCH->SDCCH & in call mod.

Queue procedure (Only one ASSIGNMENT REQUEST is queued, the first one).


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CLEAR COMMAND

OC ref.[4] N0600. OC & NC : see Note 1.


OC ref.[4] N0600. NC : deferred, Note 2.

OC & NC deferred : see Note 3.

OC & NC deferred : see Note 3.

“Exit and clear” to HOM, Next state (NULL)

SCCP N DISC OC ref.[4] N0500, Note 4. OC & NC : see Note 1.

OC ref.[4] N0500, Note 4. OC & NC : see Note 1.

OC ref.[4] N0500. NC : deferred, Notes 2 & 4.

OC & NC ref.[4] IH0900, Notes 4 & 6.

OC & NC ref.[4] IH0900, Notes 4.

“Exit and clear” to HOM, Next state (NULL).

RESET CIRCUIT (TCH Only)



OC ref.[4] N1000. NC deferred, Note 2.

OC & NC deferred, Notes 3 & 5.

OC & NC deferred, Notes 3 & 5.


RESET OC ref.[4] N0900. OC & NC : see Note 1.


OC ref.[4] N0900. NC Deferred, Note 2.

OC & NC ref.[4] N0900.

OC & NC ref.[4] N0900.


CLASSMARK UPDATE

Processed as specified in ref.[6].

CLASSMARK REQUEST

Classmark enquiry procedure is initiated. Queued.

PERFORM LOCATION

REQUEST from the MSC

See Note 7. If EN_LCS = FALSE

Send back to the MSC an 08.08 PERFORM LOCATION RESPONSE (cause “Facility not supported”)

If EN_LCS = TRUE Store in the LCS context that a response is awaited by the MSC (response sent at the outcome of the internal channel change i.e. when ASSIGNMENT COMPLETE or ASSIGNMENT FAILURE is received, or when timer expires).

For more details, see ref.[20].


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PERFORM LOCATION

ABORT from the MSC

When an LCS context exists in the BSC (LCS procedure has been started before the intra-cell channel change procedure) Store the abort cause value received on A interface Send a BSCLP PERFORM LOCATION ABORT to the SMLC Stop T_Location Start T_Loc_Abort

When no LCS context exists in the BSC Sends back to the MSC an 08.08 PERFORM LOCATION RESPONSE (cause copied from the Abort message)

For more details, see ref.[20]. Table 3-6 : Unexpected event handling on A interface & DTAP events

(intra-cell channel change) Note 1: The physical context procedure starts (if it has not already started) and goes on irrespective

of the release on the A interface. After the physical context procedure terminates (successfully or unsuccessfully), the release of the old channel is started and the channel activation of the new channel will be initiated.

At the end of the channel activation procedure, the resource will be released: see ref.[4] events NC0200 & NC0202.

Note 2: At this point the resource release of the new channel is deferred until the result of the channel activation procedure(s) is known. Afterwards, the correct scenario will be chosen for the release of each new channel: see ref.[4] events NC0200, NC0202 & NC0203.

Note 3: The outcome of the channel change is awaited before an attempt is made to perform the call release. The type of release will depend on the result of the channel change procedure (i.e. where the MS is, on the old channel, new channel or lost).

For the handling of DTAP messages see section 3.3.4 “Internal channel change & call release”.

Note 4: For TCH handovers, if the SCCP-N-DISC contains the cause "SCCP inactivity timer expiry" then once the A interface has been released the reset circuit procedure may be initiated - see ref.[10].

Note 5: For TCH connections the A interface Circuit (CIC) is not released immediately until the internal handover procedure terminates, i.e. either the MS is on the old or new channel or the timer guarding the procedure expires.

Note 6: If the SCCP-N-DISC-IND contains a DTAP message and for this specific state, the BSC does not forward the DTAP message to the MS as usually done, but discards it, because the MS may not be on the new channel yet.

Note 7: The MSC is not aware that an internal channel change is ongoing in the BSS. It may, unfortunately, trigger an LCS procedure for the target MS at the same moment.


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State / event table: Handling of errors and events on the old main channel.

STATE EVENT

ICC INTRA INIT &



ICC INTRA IN PROG &




OC ref.[4] N0700. NC : Note 2.

Don't care.

(Radio link failure) “Exit and clear” to HOM Next state (NULL)




Don't care.

(Remote transcoder failure) TCH only

“Exit and clear” to HOM Next state (NULL)

ERROR REPORT (O&M intervention)



OC ref.[1] OC0100. NC : await MS. Note 6.


ERROR REPORT SAPI 0 (Message



Don't care.

sequence error) “Exit and clear” to HOM Next state (NULL)

ERROR INDICATION SAPI 0 (Note 3)



Don't care.



Don't care.

RELEASE INDICATION SAPI 0



Don't care Note 5.


CLASSMARK CHANGE Process as specified in ref.[6].


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APPLICATION INFORMATION

When an LCS context exists in the BSC (LCS procedure has been started before the intra-cell channel change procedure)

Check the RRLP reference number If it is still a valid one for the ongoing LCS procedure Then

Send a BSCLP COI MS POSITION RESPONSE to the SMLC, encapsulating the RRLP message See Note 7

Else Discard the message

When no LCS context exists in the BSC Discard the message

For more details, see ref.[20]. Table 3-7 : Handling of errors and events on the old channel

(intra-cell channel change) Note 1: The physical context procedure starts (if it has not already started) and goes on irrespective



Note 2: The old channel and A interface are released immediately. The new channel(s) that has just been activated is released after the channel activation

procedure(s) has finished by using one of the following channel release procedures: see ref.[4] NC0200, NC0202 & NC0203.

Note 3: Causes: "Timer T200 expired (N200+1) times", "Unsolicited DM response: Multiple frame established state" and "Sequence error".

Note 4: All other causes other than those mentioned in Note 3 above. Note 5: For simplicity the RELEASE INDICATION is ignored, although the message is a promise

that the MS is no longer there. Note 6: The old channel is released locally (see ref.[4] OC0100) and the procedure awaits the MS

on the new channel side. Note 7: When an RRLP message is received on the old channel from the MS during an internal

channel change, it is forwarded towards the SMLC, as much as possible, as it may contain the final location estimate calculated by the MS.


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State / event table: Handling of errors & events on the new main channel.

STATE

EVENT


PHY CTXT

ICC INTRA AWAIT

CHN ACT ACK

ICC INTRA IN PROG


CONNECTION FAILURE

INDICATION (Radio link failure)

NA NA NA Don't care. Don't care.

CONNECTION FAILURE

INDICATION (Remote transcoder failure)

TCH Only

NA NA Don’t care. Don't care. Don't care.

ERROR Stop T9108, Stop T9103, REPORT (O&M intervention)

Abort ICC. NC : Note 4.


OC : Note 5. NC ref.[4] NC0300.



sequence error)

Don't care. Don't care. Don't care. Don't care. Don't care.

ERROR INDICATION

SAPI 0 (Note 1) NA NA NA Don't care. Don't care.

ERROR INDICATION

SAPI 0 (Note 2) NA NA NA Don't care. Don't care.

RELEASE INDICATION

SAPI 0 NA NA NA Don't care,

Note 3. Don't care.


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STATE EVENT


PHY CTXT

ICC INTRA AWAIT

CHN ACT ACK

ICC INTRA IN PROG


CLASSMARK CHANGE

NA NA NA

Process as specified in ref.[6]. APPLICATION INFORMATION

When an LCS context exists in the BSC (LCS procedure has been started before the channel change procedure)


Send a BSCLP COI MS POSITION RESPONSE to the SMLC, encapsulating the RRLP message See Note 6



For more details, see ref.[20].

Table 3-8 : Handling of errors & events on the new channel (intra-cell handover)

Note 1: Causes: "Timer T200 expired (N200+1) times", "Unsolicited DM response : Multiple frame established state" and "Sequence error".

Note 2: All other causes other than those mentioned in Note 1 above. Note 3: For simplicity the RELEASE INDICATION is ignored, although the message is a promise

that the MS is no longer there. Note 4: The new channel is released locally (see ref.[4] NC0300) and the internal channel change is

abandoned until the next handover alarm. Note 5: The ASSIGNMENT FAILURE is awaited from the old channel side. Note 6: When an RRLP message is received on the new channel from the MS during an internal



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State / event table: Unexpected event handling from BSCLP interface

STATE EVENT

ICC INTRA INIT

ICC INTRA AWAIT

PHY CTXT


ICC INTRA IN PROG


BSCLP PERFORM LOCATION RESPONSE

from the SMLC

When an LCS context exists in the BSC (LCS procedure has been started before the intra-cell channel change)

Send the 08.08 PERFORM LOCATION RESPONSE to the MSC Stop T_Location or T_Location_Longer or T_Loc_Abort Clear LCS context

When no LCS context exists in the BSC Discard message.

For more details, see ref.[20]. BSCLP COI MS

POSITION COMMAND

from the SMLC

See Note 1. Store in the LCS context that the LCS procedure shall be reset towards the SMLC at the end of the intra-cell internal channel change procedure. Discard message. For more details, see ref.[20]. Table 3-9 : Unexpected event handling from BSCLP interface

Note 1: As the BSC is performing an intra-cell internal channel change, no LCS message is sent on Radio interface towards the MS. So the on-going LCS procedure shall be reset in the BSS at the end of the channel change procedure.

3.2.3 BSC inter-cell internal channel change When the need for an inter-cell channel change (handover or directed retry) is detected by the HOP entity (see ref.[9]), the HOM entity receives this alarm and decides to trigger an inter-cell channel change (see ref.[15]). If an internal channel change is needed, the HOM entity sends to the Internal Channel Change entity a “Request for IHO” or “Request for IDR”, depending on the channel change type, with the list of possible target cells in the preferred order (the “filtered cell list”) and the handover cause. On reception of this “Request for IHO” or “Request for IDR”, the Internal Channel Change entity starts to queue (if it is the first channel change attempt) or goes on queuing (if a previous channel change attempt has been triggered by the HOM entity and has failed, see ref.[15]) some BSSMAP messages. The detailed description of BSSMAP messages queuing is given in section 3.3.1 “Internal channel change interaction with assignment, ciphering, classmark request, classmark update & DTAP”. 3.2.3.1 Internal Channel Change type decision Each time a target cell is chosen, the Internal Channel Change must determine the channel change type : synchronous or asynchronous. The parameters used for this computation are: • Physical synchronisation of the serving cell and the target cell, • O&M flags to authorise synchronous channel change (EN_SYNCHRONISED_HO, on a cell level)


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The following diagram describes this decision process.

Cells aresynchronised ? No

Yes

FALSE

TRUE

EN_SYNCHRONISED_

HO (servingcell)

EN_SYNCHRONISED_

HO (targetcell)

TRUE

ASYNCHRONOUSHANDOVER

SYNCHRONOUSHANDOVER

FALSE

Figure 3-8 : Decision for channel change type

In the following sections, this procedure will be called each time a new target cell is chosen by Internal Channel Change entity to make a channel change attempt.


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3.2.3.2 States and major events description

A list of logical BSC states (Internal Channel Change entity) is presented in the following table.

STATE DESCRIPTION ABBREVIATION The ICC entity has sent “Select channel” to RAM with the type of channel and the indication that queuing is not allowed.

ICC INTER INIT

The ICC has received “Channel Selected” from RAM (see ref.[14]) and the channel change type is synchronous (see section 3.2.3.1 “Internal Channel Change type decision”). The ICC starts the protocol by performing the physical context procedure. T9108 is running to supervise the reception of the PHYSICAL CONTEXT CONFIRM message.

ICC INTER AWAIT PHY CTXT

The BSC has completed the physical context procedure and is activating the new channel.

or The ICC has received “Channel Selected” from RAM (see ref.[14]) and the channel change type is asynchronous (see section 3.2.3.1 “Internal Channel Change type decision”).

The ICC starts the protocol by performing the channel activation procedure.

T9103 is running to supervise the reception of the CHANNEL ACTIVATION ACKNOWLEDGE message.

ICC INTER AWAIT CHN ACT ACK

The BSC has completed the channel activation procedure and has sent the HANDOVER COMMAND to the MS. T3103 is running to supervise the procedure. The BSC is now awaiting the HANDOVER DETECTION from the target BTS.

ICC AWAIT HO DETECT

The BSC is now awaiting the ESTABLISH INDICATION from the target BTS

ICC AWAIT HO ESTAB

The BSC is now awaiting the HANDOVER COMPLETE from the target BTS.

ICC AWAIT HO CMPLT

The BSC has released the new channel side due to reception of a CONNECTION FAILURE INDICATION (cause "Handover access failure") received on the new channel side, and is awaiting for the MS to return to the old channel and send the HANDOVER FAILURE message.

ICC AWAIT HO FAIL

This state is added as the exit point for inter-cell channel changes. NULL Table 3-10 : Logical BSC states for inter-cell internal channel change


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The figure below shows the major events that can occur in each state. This figure does not give an

exhaustive view of the events. Refer to the tables following the figure to have the exhaustive list of events.

ICC INTERINIT

IHO (Intercell) or IDRRequest from HOM

Channel selected from RAMICC is sycnhronousChannel selected from RAM

ICC is asycnhronous

NULL

ICC AWAITCHN ACT ACK

ICC AWAITHO DETECT

ICC AWAITHO ESTAB

CHNACT ACK

HO DETECT

ESTAB IND

HO COMPLETE

PHY CNT CNFT9108 expiry

"Select Channel reject"No retries possible

T3103expiry

T3103expiry

T3103expiry


"Select Channel reject"Retries possible


Send PHY CNT REQStart T9108

ICC INTER AWAITPHY CTXT

ICC AWAITHO CMPLT


Stop T9103Send HO CMDStart T3103


Stop T9108Send CHN ACTStart T9103

"Exit and clear"to HOM

Stop T3103"Exit and clear" to HOM

Send :HO PERF (if IHO)

orASSGN CMPLT (if IDR)

Figure 3-9 : BSC inter-cell channel change state diagram & major events


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The events appearing in the tables below are to be considered as not applicable or ignored if received

in any other states other than those indicated by the table. 3.2.3.3 Normal events during inter-cell channel changes State / event table: Normal events during target channel selection.

STATE EVENT

ICC INTER INIT

“Channel Selected” from RAM ICC is synchronous (see section 3.2.3.1 “Internal Channel Change type decision”): send PHYSICAL CONTEXT REQUEST to old channel, Start T9108, Next state (ICC INTER AWAIT PHY CTXT). ICC is asynchronous (see section 3.2.3.1 “Internal Channel Change type decision”): Send CHANNEL ACTIVATION to the new channel, Start T9103, Next state (ICC AWAIT CHN ACT ACK).

“Select Channel Reject” from RAM

Next cell in the preferred cell list is internal : Send “Select channel” (on this next cell) to RAM, Next state (ICC INTER INIT). Next cell in the preferred cell list is external : Send “Next cell is external” to HOM, Next state (NULL). No cells left in the preferred cell list : Send “Internal Failure on all cells” to HOM, Next state (NULL).

Table 3-11 : Normal events during target channel selection (Inter-cell channel change)

State / event table: Normal events during physical context procedure.

STATE EVENT

ICC INTER AWAIT PHY CTXT

PHYSICAL CONTEXT CONFIRM (old channel)

Stop T9108, Send CHANNEL ACTIVATION to the new channel, Start T9103, Next state (ICC AWAIT CHN ACT ACK).

T9108 EXPIRY Send CHANNEL ACTIVATION to the new channel (see Note 1), Start T9103, Next state (ICC AWAIT CHN ACT ACK).

Table 3-12 : Normal events during physical context procedure. (Inter-cell channel change)


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Note 1: The handover goes on regardless of the non reaction of the serving BTS.

State / event table: Normal events during channel activation procedure.

STATE EVENT

ICC AWAIT CHN ACT ACK

CHANNEL ACTIVATION ACKNOWLEDGE (new channel)

Stop T9103, Set up the internal path across the switch (TCH only) and switch the downlink direction (see Note 1) taking into account the full rate / half rate requirements of the new channel,

In case of speech TCH handover, if TFO is enabled (EN_TFO=1) in serving cell and EN_TFO=0 in target cell: Send TFO MODIFCATION REQUEST to serving BTS (see Note 2)

Send HANDOVER COMMAND to MS via serving BTS, Start queuing (or continue to queue) DTAP messages, Start T3103, Next state (ICC AWAIT HO DETECT).

CHANNEL ACTIVATION NEGATIVE ACKNOWLEDGE

(new channel)

Stop T9103, NC ref.[4] ICC0100. Next cell in the preferred cell list is internal: Send “Select channel” (on this next cell) to RAM, Next state (ICC INTER INIT). Next cell in the preferred cell list is external : Send “Next cell is external” to HOM, Next state (NULL). No cells left in the preferred cell list : Send “Internal Failure on all cells” to HOM, Next state (NULL).

T9103 EXPIRY NC ref.[4] ICC0100. Next cell in the preferred cell list is internal : Send “Select channel” (on this next cell) to RAM, Next state (ICC INTER INIT). Next cell in the preferred cell list is external : Send “Next cell is external” to HOM, Next state (NULL). No cells left in the preferred cell list : Send “Internal Failure on all cells” to HOM, Next state (NULL).

Table 3-13 : Normal events during channel activation procedure (Inter-cell channel change)

Note 1: In case of TCH to TCH channel change, the BSC performs a “Y” connection in the downlink direction.


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Note 2: This message is not acknowledged. The BSC sends the HANDOVER COMMAND to the MS

without checking that the serving BTS has received the TFO MODIFICATION REQUEST and that the TC has stopped TFO. If the handover fails, the TFO MODIFICATION REQUEST is not sent to the serving BTS to re-start TFO. It is considered that in this case, another handover will be tempted, and if supported, TFO will be restarted in the new cell.

State / event table: Normal events whilst MS is not connected

STATE EVENT

ICC AWAIT HO DETECT ICC AWAIT HO ESTAB ICC AWAIT HO CMPLT

HANDOVER DETECTION

(new channel)

Switch the uplink direction (if target is TCH) on a per call basis, depending on the full rate / half rate requirements of the connection,

Next state (ICC AWAIT HO ESTAB).

NA NA

CONNECT. FAILURE INDICATION (HO acc fail)

(new channel)

Note 1. Note 4. Ref.[4] IH0200, Next state (ICC AWAIT HO FAIL).

Switch back the uplink direction (if serving is TCH) depending on the full rate / half rate requirements of the call,

Ref.[4] IH0200, Next state (ICC AWAIT HO FAIL).

NA

ESTABLISH INDICATION

(new channel)

Note 1. Switch the uplink direction (if target is TCH) on a per call basis, depending on the full rate / half rate requirements of the connection,

Don't care.

Enable MS & BS power control, Next state (ICC AWAIT HO CMPLT).

ESTABLISH INDICATION (old channel)

Accepted - see Note 6. Accepted - see Note 6. Accepted - see Note 6.


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STATE EVENT


HANDOVER COMPLETE (new

channel)

Note 3. Switch the uplink direction (if target is TCH) on a per call basis, depending on the full rate / half rate requirements of the connection,

Enable MS & BS power control,

Note 2. Enable MS & BS power control,

Stop T3103, Send queued DTAP messages to target BTS,

Start queued procedures (Note 5), If the ICC is an IHO :

Send HANDOVER PERFORMED to the MSC. If the ICC is an IDR :

Send ASSIGNMENT COMPLETE to the MSC, Note 7.

OC ref.[4] IH0700, Send “Exit and clear” to HOM,



Else If an LCS procedure is on-going for this call Send BSCLP COI RESET (cause “Intra-BSS handover”) to the SMLC.

See ref.[20] for more details. HANDOVER FAILURE (Serving BTS)

Stop T3103, NC ref.[4] IH0100, Note 4,

Stop T3103, NC ref.[4] IH0100, Switch back the uplink direction (if serving is TCH) depending on the full rate / half rate requirements of the call,

Send “HO FAIL from MS” to HOM,



Else If an LCS procedure is on-going for this call, and needs to be reset (see Note 8) Send BSCLP COI RESET (cause “Intra-BSS handover”) to the SMLC.

See ref.[20] for more details.


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STATE EVENT


T3103 EXPIRY

If an LCS response is awaited by the MSC Send an 08.08 PERFORM LOCATION RESPONSE (cause “Intra-BSC Handover

Complete”) to the MSC If an LCS procedure is on-going for this call

Send BSCLP PERFORM LOCATION ABORT (cause “Intra-BSS handover”) to the SMLC.

See ref.[20] for more details. If the ICC is an IHO : OC & NC ref.[4] IH0400, If the ICC is an IDR : OC & NC ref.[4] DR0600,

Send “Exit and clear” to HOM, Next state (NULL).

Table 3-14 : Normal events whilst MS is not connected (Inter-cell channel change)

Note 1: HANDOVER DETECTION lost on Abis. Note 2: ESTABLISH INDICATION lost on Abis. Note 3: HANDOVER DETECTION and ESTABLISH INDICATION lost on Abis. Note 4: No switch back of the uplink direction of the internal path is performed as the switching of the

uplink direction has not been initiated. Note 5: The procedures (assignment and ciphering) which where deferred whilst the internal channel

change procedure was in process are initiated in the order in which they were received. Note 6: No external actions are taken by the BSC. Note 7: If the ICC is an IDR and the MS is a phase 1 MS and the target channel is a TCH FR for

speech version 1, then the BSC will send a CHANNEL MODE MODIFY message to the MS (see section 3.3.5 “Internal directed retry & In-call modification”).

Note 8: In case of failure of the inter-cell channel change, the MS stays on the old channel. So the BSCLP COI RESET message, usually sent to the SMLC to restart the on-going LCS procedure, is not systematically sent at the outcome of the inter-cell internal channel change procedure in case of failure. It is only sent if the LCS procedure has been disturbed by the inter-cell internal channel change procedure (see further, in Table "Unexpected event handling from BSCLP interface").


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State / event table: Normal events whilst MS is going back to old channel.

In this state, the BSC has received the CONNECTION FAILURE INDICATION (cause "Handover access failure"), has released the new channel and is awaiting the return of the MS to the old channel. The switch of the uplink direction of the internal path was either not performed yet (ICC AWAIT HO DETECT) or is already switched back to the old channel (ICC AWAIT HO ESTAB).

STATE EVENT

ICC AWAIT HO FAIL

HANDOVER FAILURE Stop T3103, Send “HO FAIL from MS” to HOM, Next state (NULL).

T3103 EXPIRY If the ICC is an IHO : OC ref.[4] IH0800, If the ICC is an IDR : OC ref.[4] DR0601, Send “Exit and clear” to HOM, Next state (NULL).

ESTABLISH INDICATION (SAPI 0)

See Note 1, Next state (ICC AWAIT HO FAIL).

Table 3-15 : Normal events whilst MS is going back to old channel (Inter-cell channel change)

Note 1: There are no external actions taken by the BSC at this point, however on reception of this message the BSC performs some internal actions.

3.2.3.4 Unexpected events during inter-cell channel change State / event table: Unexpected event handling on A interface & DTAP events.

STATE EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT

& ICC AWAIT HO FAIL (Note 8)

DTAP message

Forward to Serving BTS, see (*) Queue message.

CIPHER MODE

COMMAND Queue procedure (only one CIPHER MODE COMMAND is queued, the first one).

HANDOVER COMMAND

Send HANDOVER FAILURE. In this case the MSC has already reserved an RF channel to which an external handover is to take place. The BSC sends a HANDOVER FAILURE (cause value "Radio interface failure - Reversion to old channel"). This allows the MSC to release the reserved channel, and ensures that the MSC knows where the MS is.


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STATE EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT


ASSIGNMENT REQUEST

SDCCH->TCH TCH->SDCCH & in-call mod.

Queue procedure (Only one ASSIGNMENT REQUEST is queued, the first one). If the ICC is an IDR, the original ASSIGNMENT REQUEST is in the queue, so no

more ASSIGNMENT REQUESTs can be queued

CLEAR COMMAND

OC ref.[4], N0600. OC & NC : see Note 1.

OC ref.[4], N0600. NC : deferred, see Note 2.

OC & NC deferred, see Note 3.




SCCP N DISC OC ref.[4], N0500, Note 4. OC & NC : see Note 1.

OC ref.[4], N0500, Note 4. NC : Note 2.

OC & NC deferred, see Notes 3 & 4.

OC & NC ref.[4] IH0900, see Notes 4 & 7.

OC & NC ref.[4] IH0900, see Note 4.


RESET CIRCUIT (TCH only)


OC ref.[4], N1000. NC : Note 2.





RESET OC ref.[4], N0900. OC & NC : see Note 1.

OC ref.[4], N0900. NC : Note 2.

OC & NC ref.[4], N0900.

OC & NC ref.[4], N0900.

OC & NC ref.[4], N0900.


CLASSMARK UPDATE

Processed as specified in ref.[6].


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STATE EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT


CLASSMARK REQUEST

Classmark enquiry procedure is initiated.

Queue procedure.

PERFORM LOCATION REQUEST from the MSC

See Note 8. If EN_LCS = FALSE

Send back to the MSC an 08.08 PERFORM LOCATION RESPONSE (cause “Facility not supported”)

If EN_LCS = TRUE Store in the LCS context that a response is awaited by the MSC (response sent at the outcome of the internal channel change i.e. when HANDOVER COMPLETE or HANDOVER FAILURE is received or when timer expires).

For more details, see ref.[20]. PERFORM LOCATION ABORT from the MSC

When an LCS context exists in the BSC (LCS procedure has been started before the inter-cell channel change procedure) Store the abort cause value received on A interface Send a BSCLP PERFORM LOCATION ABORT to the SMLC Stop T_Location Start T_Loc_Abort

When no LCS context exists in the BSC Sends back to the MSC an 08.08 PERFORM LOCATION RESPONSE (cause copied from the Abort message)

For more details, see ref.[20]. Table 3-16 : Unexpected event handling on A interface & DTAP events

(Inter-cell channel change) (*) : forward only before the first HANDOVER COMMAND message related to the cell list handled by the dedicated radio resource entity, otherwise queue message. Note 1: The physical context procedure starts (if it has not already started) and goes on irrespective




procedure(s) has finished by using one of the following channel release procedures : see ref.[4] NC0200, NC0202 & NC0203.

Note 3: The outcome of the handover is awaited before an attempt is made to perform the call release with the MS.

For the handling of DTAP messages see section 3.3.4 “Internal channel change & call release".


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Note 4: For TCH handovers, if the SCCP-N-DISC contains the cause "SCCP inactivity timer expiry"

then once the A interface has been released the reset circuit procedure may be initiated - see ref.[10].

Note 5: There is no new channel associated to the state INTER AWAIT HO FAIL. As a result all the channel release scenarios indicating NC should be ignored.

Note 6: For TCH connections the A interface Circuit (CIC) is not released immediately until the internal handover procedure terminates, i.e. either the MS is on the old or new channel or the timer guarding the procedure expires.

Note 7: If the SCCP-N-DISC-IND contains a DTAP message and for this specific state, the BSC does not forward the DTAP message to the MS as usually done, but discards it, because the MS may not be on the new channel yet.

Note 8: The MSC is not aware that an internal channel change is ongoing in the BSS. It may, unfortunately, trigger an LCS procedure for the target MS at the same moment.

State / event table: Handling of errors & events from Serving BTS

STATE

EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT

& ICC AWAIT HO FAIL

CONNECTION FAILURE INDICATION (Radio link


OC ref.[4], N0700 OC & NC : see Note 2.

Don't care. Don't care. Don't care.

failure) “Exit and clear” to HOM Next state (NULL)

CONNECTION FAILURE INDICATION (Remote




transcoder failure) TCH only





OC Release locally - Note 4. NC Note 7.





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STATE

EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT

& ICC AWAIT HO FAIL





sequence error) “Exit and clear” to HOM Next state (NULL)







Don't care. Don't care. Don't care. Don't care. Don't care.

RELEASE INDICATION SAPI 0 (Note 2)

OC ref.[4], N0200. OC & NC : see Note 1


Don't care, Note 3.

Don't care, Note 3.

Don't care Note 3.



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STATE

EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT

& ICC AWAIT HO FAIL

CLASSMARKCHANGE

Process as specified in ref.[6].

APPLICATION INFORMATION

When an LCS context exists in the BSC (LCS procedure has been started before the inter-cell channel change procedure)


Send a BSCLP COI MS POSITION RESPONSE to the SMLC See Note 8



For more details, see ref.[20]. Table 3-17 : Handling of errors & events from serving BTS (inter-cell handover)

(Inter-cell channel change) Note 1: The physical context procedure starts (if it has not already started) and goes on irrespective




procedure has finished by using one of the following channel release procedures: see ref.[4] NC0200, NC0202 & NC0203.

Note 3: For simplicity the RELEASE INDICATION is ignored, although the message is a promise that the MS is no longer there.

Note 4: The old channel is released immediately for use. This behaviour can be accepted as the BTS has been carrying out a full release of the MS - see ref.[4].


Note 6: All other causes other than those mentioned in Note 6 above. Note 7: The MS is awaited on the new channel side. Note 8: When an RRLP message is received on the old channel from the MS during an internal



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State / event table: Handling of errors from Target BTS

STATE EVENT

ICC INTER INIT

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT & ICC AWAIT HO ESTAB

& ICC AWAIT HO CMPLT


(Radio link failure)

NA NA NA Don't care.


(Remote transcoder failure) TCH only

NA NA Don’t care. Don't care.


Stop T9108. NC ref.[4], NC0300.

Stop T9103. NC ref.[4], NC0300.

Ref.[4] N0400 - Note 4.

Next cell in the preferred cell list is internal : Send “Select channel” (on this next cell) to RAM,

Next state (ICC INTER INIT). Next cell in the preferred cell list is external : Send “Next cell is external” to HOM, Next state (NULL).

No cells left in the preferred cell list : Send “Internal Failure on all cells” to HOM,

Next state (NULL).

ERROR REPORT SAPI 0 (Message sequence error)

Don’t care Don't care. Don't care. Don't care.





RELEASE INDICATION SAPI 0

NA NA NA Don't care Note 3

Table 3-18 : Handling of errors from Target BTS (Inter-cell channel change)



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Note 2: All other causes other than those mentioned in Note 1 above.

Note 3: For simplicity the RELEASE INDICATION is ignored, although the message is a promise that the MS is no longer there.

Note 4: The references to ref.[4] are only valid for the new channel release which will apply immediately on the new RF channel. There will be NO CALL RELEASE on the A interface or on the old RF channel.

The serving BSC will await the failure case (i.e. HANDOVER FAILURE on the old channel from the MS).

State / event table: Unexpected event handling from BSCLP interface

STATE EVENT

ICC INTER INIT &

ICC INTER AWAIT

PHY CTXT


ICC AWAIT HO DETECT

ICC AWAIT HO ESTAB

ICC AWAIT HO CMPLT

& ICC AWAIT HO FAIL

BSCLP PERFORM LOCATION RESPONSE from the SMLC

When an LCS context exists in the BSC (LCS procedure has been started before the inter-cell channel change)

Send the 08.08 PERFORM LOCATION RESPONSE to the MSC Stop T_Location or T_Location_Longer or T_Loc_Abort Clear LCS context

When no LCS context exists in the BSC Discard message.

For more details, see ref.[20]. BSCLP COI MS POSITION COMMAND from the SMLC

See Note 1. Store in the LCS context that the LCS procedure shall be reset towards the SMLC at the end of the inter-cell channel change procedure. Discard message. For more details, see ref.[20]. Table 3-19 : Unexpected event handling from BSCLP interface

Note 1: As the BSC is performing an internal channel change, no LCS message is sent on Radio interface to the MS. So the on-going LCS procedure shall be reset in the BSS at the end of the channel change procedure.

3.2.4 PHYSICAL CONTEXT procedure The physical context procedure provides the following information: 1) MS Timing Advance, 2) MS Power, 3) BS Power, 4) LapDm O&M performance counters. The tables below show, for the intra-cell internal channel change and inter-cell synchronous channel change procedures, how the MS timing advance, MS power & BS power information are used in the


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construction of the CHANNEL ACTIVATION, ASSIGNMENT COMMAND and HANDOVER

COMMAND messages. CHANNEL ACTIVATION ASSIGNMENT COMMAND MS Timing Advance Used in the OIE Timing Advance,

Note 1 Not used.

MS Power Used in the OIE MS Power Note 2.

Used in the MIE Power Command Note 2.

BS Power Used in the OIE BS Power Note 3.

Not used.

Table 3-20 : intra-cell channel change CHANNEL ACTIVATION HANDOVER COMMAND MS Timing Advance Used in the OIE Timing Advance,

Note 1. Not used.

MS Power Not used. Not used. BS Power Not used. Not used.

Table 3-21 : inter-cell synchronous channel change No physical context procedure is performed before inter-cell asynchronous channel change. Note 1: If the physical context procedure failed (expiry of T9108), there will be no timing advance in

the CHANNEL ACTIVATION message. Note 2: In the case of inter-zone handover : - In a single band cell, Min (MS Power, MS_TXPWR_MAX_INNER) is used. - In a multiband cell,, min(Pband outer, MS_TXPWR_MAX) is used for an inner to outer zone

handover and min(Pband inner, MS_TXPWR_MAX_INNER) is used for an outer to inner zone handover.

If the physical context procedure failed (expiry of T9108) the MS Power is set to MIN (P, MS_pwr_max), where P is the maximum power of the MS and MS_pwr_max is the maximum MS power allowed in the cell (MS_TXPWR_MAX in a normal cell or in the outer-zone of a concentric cell, MS_TXPWR_MAX_INNER in the inner-zone of a concentric cell).

Note 3: When the new channel is a channel completely supported by the BCCH frequency, the maximum BS transmit power (BS_TXPWR_MAX) is used.

In the case of inter-zone handover : - In a single band cell, when the new channel is not completely supported by the BCCH

frequency, Min (BS Power, BS_TWPWR_MAX_INNER) is used. - In a multiband cell, BS_TXPWR_MAX is used for an inner to outer zone handover and

BS_TXPWR_MAX_INNER is used for an outer to inner zone handover. If the physical context procedure failed (expiry of T9108) the BS Power is set to

BS_pwr_max, the maximum allowable BS power in the cell (BS_TXPWR_MAX in a normal cell or in the outer-zone of a concentric cell, BS_TXPWR_MAX_INNER in the inner-zone of a concentric cell).

The LapDm O&M performance counters are sent to the O&M Performance Management entity.


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3.2.5 CHANNEL ACTIVATION message construction

This message is sent by the BSC to the target BTS to activate the new channel. In case of intra-cell handover, this message is sent to the serving BTS. The following tables give the methods by which the CHANNEL ACTIVATION message is constructed for each procedure. 3.2.5.1 CHANNEL ACTIVATION message construction for intra-cell handover

Setting or Algorithm Information Element Info field Main channel MIE Activation Type R Set to “Initial activation”

A3, A2 Set to “Activation related to intra-cell channel change”

A1 Set to “Related to normal assignment procedure”

MIE Channel Mode DTXd If FORBID_DTXD_NH_BCCH_F is set to TRUE and the allocated TCH is non-hopping and belongs to the BCCH TRX, DTXd shall be set to 0 (i.e. DTXd is not applied)

Otherwise see ref.[7]. DTXu See ref.[7]. Speech or

data indicator Set equal to octet 3 of the Channel Type MIE extracted from the last ASSIGNMENT / HANDOVER REQUEST successfully performed, or equal to "signalling" after immediate assignment procedure.

Channel rate and type

If “speech or data indicator” indicates "signalling" : set to “SDCCH” Else set to "Full rate TCH channel Bm" or "Half rate TCH channel Lm", depending on the radio resource allocation procedure (see ref.[14]).


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Setting or Algorithm Information Element Info field Main channel

Speech coding algo / data rate + transp. ind.

If “speech or data indicator” indicates "signalling": set to "no resource required", If “speech or data indicator” indicates "speech": set to "GSM speech coding algorithm version 1", "GSM speech coding version 2" or “GSM speech coding version 3” according to the choice made by dedicated radio resource allocation procedure see ref.[14], If octet 4 indicates "data" :

set equal to octet 5 of the Channel Type MIE extracted from the last ASSIGNMENT / HANDOVER REQUEST successfully performed, except if this one indicates "non transparent service”-”6 kbit/s". In this last case, octet 6 is set equal to "non transparent service"-"12 kbit/s".

MIE Channel Identification

The Channel Identification IE contains the 44.018 Channel Description & 44.018 Mobile Allocation for the activated channel. Only the training sequence code (TSC) of the Channel Description field is computed by the BTS. The BTS does not use the Mobile Allocation field. See Note 7. The Channel Description field used in this message is also used in the building of the ASSIGNMENT COMMAND message. See also ref.[16].

OIE Encryption Information

Always sent. Set to "No Encryption" if ciphering is not applied, otherwise it is set as specified in ref.[3].

CIE Handover Reference

Not present (Not applicable to the assignment procedure).

OIE BS Power In a single band cell or for an intrazone handover : Set to the value of the BS Power received in the PHYSICAL CONTEXT CONFIRM message - Notes 1 & 2. For an interzone handover in a multiband cell : Set to BS_TXPWR_MAX for an inner to outer zone HO. Set to BS_TXPWR_MAX_INNER for an outer to inner zone HO.


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Setting or Algorithm Information Element Info field Main channel OIE MS Power In a single band cell or for an intrazone handover :

Set to the value of the MS Power received in the PHYSICAL CONTEXT CONFIRM message - Note 3. For an interzone handover in a multiband cell : Set to min(Pband outer, MS_TXPWR_MAX) for an inner to outer zone HO. Set to min(Pband inner, MS_TXPWR_MAX_INNER) for an outer to inner zone HO.

CIE Timing Advance Set to the value of the Timing Advance received in the PHYSICAL CONTEXT CONFIRM message - Note 4 & 5.

OIE BS Power Parameters

Not used.

OIE MS Power Parameters

Not used.

OIE Physical Context Not applicable. OIE SACCH Information

Contains the setting of system information filling on SACCH for this channel. If present, it updates the system information previously intended to be transmitted, see ref.[13]. “Extended measurement order” msg is included for a TCH channel activation • if MAFA is supported (EN_EXT_MEAS_REP)

• and if the MS is GSM phase2

• and if a RMS job is running (see ref[18]).

OIE main channel reference

Not used.

OIE MultiRate configuration

Included in case of the target channel type selected by RAM is AMR. Contains the initial codec mode, the codec subset and, if more than one codec is defined, thresholds and hysteresis used by the BTS for the uplink codec adaptation. It contains also the indication to allow or forbid use of AMR Noise Suppressor. See section 4.4 “Parameter list”.


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Setting or Algorithm Information Element Info field Main channel OIE MultiRate Control

Not used.

OIE TFO Command Alcatel proprietary IE. Included for speech intra-cell handover when EN_TFO flag=”Enabled”. • Field “EN_TFO” is either set to EN_TFO flag when the

active codec type (i.e. chosen channel rate and speech version in “Channel selected” message received from RAM) is HR, FR, EFR, or set to FORCE_TFO_VS_AMR flag when the active codec type is AMR, or set to 0 if the codec list is empty (see Note 6).

• Field “TFO_MATCH” is set to EN_TFO_MATCH flag. • Field “TFO_OPT” is set to EN_TFO_OPT flag. • Field “T_TFO” contains the value of the timer T_TFO. • Field “TFO Codec” contains the TFO codec type received in “Channel selected” message from RAM. It is set to ‘0xFF’ when EN_TFO field is set to FALSE.

For the coding of this IE see ref.[19]. OIE Supported Codec Types

Included for speech calls, and when the field EN_TFO in OIE TFO COMMAND is set to TRUE. • Field “Codec List” indicates, as received from RAM in “Channel Selected” message, a list of codecs :

- supported by the cell and - allowed by the operator (via O&M) and - allowed by the MSC (in the last ASSIGNMENT / HANDOVER REQUEST) • Field “Preferred Codec” is not used (set to ‘0xFF’).

OIE Uplink Identity Code

Not used

Table 3-22 : CHANNEL ACTIVATION message construction for intra-cell internal handover Note 1: If the new channel is supported only on the BCCH frequency then the power used is

BS_TXPWR_MAX - see ref.[8]. Note 2: In the case of inter-zone handover, when the new channel is not completely supported by

the BCCH frequency, Min (BS Power, BS_TWPWR_MAX_INNER) is used. If the physical context procedure failed, the BS Power is set to BS_pwr_max - see section

3.2.4 “PHYSICAL CONTEXT procedure”. Note 3: In the case of inter-zone handover, Min (MS Power, MS_TXPWR_MAX_INNER) is used. If the physical context procedure failed, the MS Power is set to MIN (P, MS_pwr_max ) - see

section 3.2.4 “PHYSICAL CONTEXT procedure”. Note 4: If the physical context procedure failed, there will be no Timing Advance.


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Note 5: If there is no CIE Timing advance, the BTS will not consider this CIE as mandatory and will

transmit a timing advance in the Layer 1 header on SACCH with the default value of "7FH". Note 6: In some rare cases, the codec list may be empty (e.g. request DR_P_NCA, AMR FR, AMR

HR, FR as possible codecs, FORCE_TFO_VS_AMR = 1, chosen codec is AMR HR). Note 7: In the case of allocation in the inner zone of a multiband cell or in the EGSM band, the

Mobile Allocation field is not correctly filled by the BSC.

3.2.5.2 CHANNEL ACTIVATION message construction for inter-cell channel change


MIE Activation Type R Set to “Initial activation” A3, A2 Set to “Activation related to

inter-cell channel change”

A1 Asynchronous ICC : Set to “Related to asynchronous handover procedure” Synchronous ICC : Set to “Related to synchronous handover procedure”

MIE Channel Mode DTXd If FORBID_DTXD_NH_BCCH_F is set to TRUE and the allocated TCH is non-hopping and belongs to the BCCH TRX, DTXd shall be set to 0 (i.e. DTXd is not applied),

Otherwise see ref.[7]. DTXu See ref.[7]. Speech or

data indicator Set equal to octet 3 of the Channel Type MIE extracted from the last ASSIGNMENT / HANDOVER REQUEST successfully performed, or equal to "signalling" after immediate assignment procedure.

Channel rate and type

If “speech or data indicator” indicates "signalling" : set to “SDCCH” Else set to "Full rate TCH channel Bm" or "Half rate TCH channel Lm", depending on the radio resource allocation procedure (see ref.[14]).


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Speech coding algo / data rate + transp. ind.

If “speech or data indicator” indicates "signalling" : set to "no resource required", If “speech or data indicator” indicates "speech" : set to "GSM speech coding algorithm version 1", "GSM speech coding version 2" or “GSM speech coding version 3” according to the choice made by dedicated radio resource allocation procedure see ref.[14], If octet 4 indicates "data" :

set equal to octet 5 of the Channel Type MIE extracted from the last ASSIGNMENT / HANDOVER REQUEST successfully performed, except if this one indicates "non transparent service”-”6 kbit/s". In this last case, octet 6 is set equal to "non transparent service"-"12 kbit/s".

MIE Channel Identification

The Channel Identification IE contains the 44.018 Channel Description & 44.018 Mobile Allocation for the activated channel. Only the training sequence code (TSC) of the Channel Description field is computed by the BTS. The BTS does not use the Mobile Allocation field. See Note 4. The Channel Description field used in this message is also used in the building of the ASSIGNMENT COMMAND message. See also ref.[16].

OIE Encryption Information

Always sent. Set to "No Encryption" if ciphering is not applied, otherwise it is set as specified in ref.[3].

CIE Handover Reference

Always sent, see ref.[16].

OIE BS Power Set to BS_TXPWR_MAX. OIE MS Power Set to MIN(P, MS_TXPWR_MAX).

CIE Timing Advance Synchronous ICC: Set to the value of the timing advance received in the PHYSICAL CONTEXT CONFIRM message, see Note 1 & 2. Asynchronous ICC: Not used, see Note 2.


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OIE BS Power Parameters

Not used.

OIE MS Power Parameters

Not used.

OIE Physical Context Not used. OIE SACCH Information

Contains the setting of system information filling on SACCH for this channel. If present, it updates the system information previously intended to be transmitted, see ref.[13]. “Extended measurement order” msg is included for a TCH channel activation • if MAFA is supported (EN_EXT_MEAS_REP)

• and if the MS is GSM phase2

• and if a RMS job is running (see ref[18]).

OIE main channel reference

Not used.

OIE MultiRate configuration

Included in case of the target codec type selected by RAM is AMR. Contains the initial codec mode, the codec subset and, if more than one codec is defined, thresholds and hysteresis used by the BTS for the uplink codec adaptation. It contains also the indication to allow or forbid use of AMR Noise Suppressor. See section 4.4 “Parameter list”.

OIE MultiRate Control

Not used.


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OIE TFO Command Alcatel proprietary IE. Included if the target channel is TCH for a speech call when EN_TFO flag=”Enabled”. • Field “EN_TFO” is either set to EN_TFO flag when the active codec type (i.e. chosen channel rate and speech version in “Channel selected” message received from RAM) is HR, FR, EFR, or set to FORCE_TFO_VS_AMR flag when the active codec type is AMR, or set to 0 if the codec list is empty (see Note 3).

• Field “TFO_MATCH” is set to EN_TFO_MATCH flag. • Field “TFO_OPT” is set to EN_TFO_OPT flag. • Field “T_TFO” contains the value of the timer T_TFO. • Field “TFO Codec” contains the TFO codec type received in “Channel selected” message from RAM. It is set to ‘0xFF’ when EN_TFO field is set to FALSE.

For the coding of this IE see ref.[19]. OIE Supported Codec Types

Included for speech calls, and when the field EN_TFO in OIE TFO COMMAND is set to TRUE. The information is provided by RAM in “Channel selected” message. • Field “Codec List” indicates a list of codecs: - supported by the target cell and - allowed by the operator (via O&M) and - allowed by the MSC (in the last ASSIGNMENT / HANDOVER REQUEST) • Field “Preferred Codec” is not used (set to ‘0xFF’).

OIE Uplink Identity Code

Not used

Table 3-23 : CHANNEL ACTIVATION message construction for inter-cell channel change Note 1: If the physical context procedure failed then there will be no Timing Advance available. Note 2: If there is no CIE Timing Advance, the BTS will not consider this CIE as mandatory and will

transmit a timing advance in the Layer 1 header on SACCH with the default value of "7FH". Note 3: In some rare cases, the codec list may be empty (e.g : request DR_P_NCA, AMR FR, AMR

HR, FR as possible codecs, FORCE_TFO_VS_AMR = 1, chosen codec is AMR HR). Note 4: In the case of allocation in the inner zone of a multiband cell or in the EGSM band, the

Mobile Allocation field is not correctly filled by the BSC.


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3.2.6 ASSIGNMENT COMMAND message construction

This message is sent by the BSC to the MS (on the old channel) to trigger the intra-cell handover on the Radio interface. The setting and algorithm to build the ASSIGNMENT COMMAND message depend on which frequency range the target channel belongs to (i.e. EGSM (and not PGSM), P-GSM, GSM850, DCS1800 or DCS1900) when frequency hopping is supported.

Setting or Algorithm Information element Towards a P-GSM channel Towards a EGSM or GSM850 or

DCS1800 or DCS1900 channel MIE Description of the First

Channel, after time (Channel type and TDMA

offset)

Set to the same coding given in the Channel Description field, contained in the Channel Identification MIE of the CHANNEL ACTIVATION

message.

(other subfields) Set to the same coding given in the Channel Description field, contained in the Channel Identification MIE of the CHANNEL ACTIVATION

message. MIE Power Command In a single band cell or for an intrazone handover:

Set to MS Power found in the PHYSICAL CONTEXT CONFIRM message. In the case of inter-zone handover, Min (MS Power,

MS_TXPWR_MAX_INNER) is used. If the physical context procedure failed, MIN (P, MS_pwr_max) is used.

For an interzone handover in a multiband cell: Set to min(Pband outer, MS_TXPWR_MAX) for an inner to outer zone HO. Set to min(Pband inner, MS_TXPWR_MAX_INNER) for an outer to inner

zone HO. CIE Frequency List, after

time Phase 2 biband: Used when target channel is hopping (i.e. more than 1 frequency).

Used when target channel is hopping (i.e. more than 1 frequency).

OIE Cell Channel Description Phase 1 monoband P-GSM MS or Phase 2 monoband P-GSM or E-GSM MS: Used when the target channel is hopping (i.e. more than 1 frequency). The bit map 0 format is used.

Not used

CIE Description of the multislot configuration

Not used.

OIE Mode of the First Channel (Channel Set 1)

Always used. (see note).

Mode of Channel Set 2 Not used Mode of Channel Set 3 Not used Mode of Channel Set 4 Not used


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DCS1800 or DCS1900 channel Mode of Channel Set 5 Not used Mode of Channel Set 6 Not used Mode of Channel Set 7 Not used Mode of Channel Set 8 Not used OIE Description of the

Second Channel, after time Not used - relevant to Lm + Lm only.

OIE Mode of the Second Channel

Not used - relevant to Lm + Lm only.

CIE Mobile Allocation, after time

Phase 1 monoband P-GSM MS or Phase 2 P-GSM or E-GSM MS: Used when the target channel is hopping (i.e. more than 1 frequency).

Not used

OIE Starting Time Not used (valid during frequency redefinition for both Phase 1 & 2 MSs). CIE Frequency List, before

time Not used (valid during frequency redefinition and only for Phase 2 MSs).

OIE Description of the First Channel, before time

Not used (valid during frequency redefinition and only for Phase 2 MSs).

OIE Description of the Second Channel, before time

Not used (valid during frequency redefinition for Lm + Lm only, and only for Phase 2 MSs).

CIE Frequency Channel Sequence, before time


CIE Mobile Allocation, before time


OIE Cipher Mode Setting Never sent. OIE VGCS target mode

Indication Not used

OIE MultiRate configuration Included in case of the target channel type selected by RAM is AMR: - for a TCH assignment - for an intra-cell handover from AMR FR to AMR HR - for an intra-cell handover, when the initial codec mode, the codec

subset, the thresholds or the hysteresis has changed since the last assignment or intra-cell handover.

Contains the initial codec mode, the codec subset and, if more than one codec is defined, thresholds and hysteresis used by the MS for the downlink codec adaptation. It contains also the indication to allow or forbid use of AMR Noise Suppressor. See section 4.4 “Parameter list”.

Table 3-24 : ASSIGNMENT COMMAND message construction


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Note : Although according to 3GPP, OIE Mode of the First Channel (Channel Set 1) is mandatory only

when the channel mode is changed, it is always sent by the Alcatel BSS, because some MSs do not behave correctly when it is missing (in particular during handovers from AMR FR to AMR HR and vice-versa).

3.2.7 HANDOVER COMMAND message construction This message is sent by the BSC to the MS (on the old channel) to trigger the inter-cell internal channel change on the Radio interface. The setting and algorithm to build the HANDOVER COMMAND message depend on which frequency range the target channel belongs to (i.e. EGSM (and not PGSM), P-GSM, GSM850, DCS1800 or DCS1900) when frequency hopping is supported.


DCS1800 or DCS1900 channel MIE Cell Description Set NCC, BCC & BCCH ARFCN (High & Low part) to the values allocated

to the target BTS. MIE Description of the First

Channel, after time (Channel type and TDMA

offset)

Set to the same coding given in the Channel Description field, contained in the Channel Identification MIE of the CHANNEL ACTIVATION message.

(other subfields) Set to the same coding given in the Channel Description field, contained in the Channel Identification MIE of the CHANNEL ACTIVATION message.

MIE Handover Reference See ref.[16]. MIE Power Command and

access type Set to MIN (P, MS_TXPWR_MAX target cell).

Field Access type is set to "sending of HANDOVER ACCESS is mandatory"

OIE Synchronisation Indication

Phase 1 MS : this IE is always included as required in ref.[24]. Phase 2 MS : this IE is only included for synchronous channel changes. GSM phase 2 format is always used : SI field is set according to the channel change type : asynchronous (00) or synchronous (01).

ROT bit is set depending on O&M parameter, NCI bit is set depending on O&M parameter.

CIE Frequency Short List, after time

Phase 2 bibandMS: Used when the target channel is hopping (i.e. more than 1 frequency), and if it is the shortest way of coding the frequencies: see Note 1.

Used when the target channel is hopping (i.e. more than 1 frequency), and if it is the shortest way of coding the frequencies: see Note 1.


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DCS1800 or DCS1900 channel CIE Frequency List, after

time Phase 2 biband MS: Used when the target channel is hopping (i.e. more than 1 frequency), and if it is the shortest way of coding the frequencies: see Note 1.

Used when the target channel is hopping (i.e. more than 1 frequency), and if it is the shortest way of coding the frequencies: see Note 1.

CIE Cell Channel Description Phase 1 monoband P-GSM MS or Phase 2 monoband P-GSM or E-GSM MS: Used when CIE “Frequency Channel Sequence, after time” can not code all the frequencies used. Used with CIE “Mobile Allocation, after time” to describe frequency hopping sequence.

Not used

CIE Description of the multislot configuration

Not used.

OIE Mode of the First Channel (Channel Set 1)

Always used (see note 2)

OIE Mode of channel set 2 Not used OIE Mode of channel set 3 Not used OIE Mode of channel set 4 Not used OIE Mode of channel set 5 Not used OIE Mode of channel set 6 Not used OIE Mode of channel set 7 Not used OIE Mode of channel set 8 Not used OIE Description of the

Second Channel, after time Not used - relevant to Lm + Lm.

OIE Mode of the Second Channel

Not used - relevant to Lm + Lm.

CIE Frequency Channel Sequence, after time

Phase 1 monoband P-GSM MS or Phase 2 P-GSM or E-GSM MS: Used when the target channel is hopping (i.e. more than 1 frequency) and if this IE can code all the frequencies. Phase 2 biband MS: Used when the target channel is a P-GSM channel and is hopping (i.e. on more than 1 frequency), and if it is the shortest way of coding the frequencies: see Note 1.

Not used.


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DCS1800 or DCS1900 channel CIE Mobile Allocation, after

time Phase 1 monoband P-GSM MS or Phase 2 monoband P-GSM or E-GSM MS: Used only if CIE “Cell Channel Description” is used.

Not used.

OIE Starting Time Not used (used during frequency redefinition). CIE Real Time Difference Not used (used for pseudo synchronous handover) CIE Timing Advance Not used (used for pre-synchronous handover)

CIE Frequency Short List, before time

Not used (used during frequency redefinition and only sent to Phase 2 MSs).

CIE Frequency List, before time


OIE Description of the First Channel, before time


OIE Description of the Second Channel, before time

Not used (used during frequency redefinition, for Lm + Lm, and only sent to Phase 2 MSs).

CIE Frequency Channel Sequence, before time


CIE Mobile Allocation, before time


OIE Cipher Mode Setting Phase 1 MS : never sent. Phase 2 MS : only sent if the ciphering algorithm chosen is different from the one on use on the old channel, see ref.[14].

OIE VGCS target mode Indication

Not used

OIE MultiRate configuration Included in case of the codec type selected by RAM is AMR and when: - the inter-cell handover is performed from AMR FR to AMR HR, or - the initial codec mode, the codec subset, the thresholds or the

hysteresis are different on the serving cell and on the target cell. Contains the initial codec mode, the codec subset and, if more than one codec is defined, thresholds and hysteresis used by the MS for the downlink codec adaptation on the target cell. It contains also the indication to allow or forbid use of AMR Noise Suppressor. See section 4.4 “Parameter list”.

Table 3-25 : HANDOVER COMMAND message construction


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Note 1: For phase 2 biband (supporting GSM900 or GSM850 band) or GSM850 monoband MSs,

and when the target channel is hopping (i.e. on more than 1 frequency), the shortest frequency encoding IE will always be used. See ref.[11] for the frequency encoding algorithms.

When the target channel is in the P-GSM band, the choice will be made between the following CIEs:

- “Frequency Channel Sequence, after time”, - "Frequency Short List, after time" - "Frequency List, after time". When the target channel is in the EGSM band (and not in the PGSM band), the GSM850

band, the DCS1800 band or the DCS1900 band, the choice will be made between the following CIEs:

- "Frequency Short List, after time" - "Frequency List, after time". Note 2 : Although according to 3GPP, OIE Mode of the First Channel (Channel Set 1) is mandatory

only when the channel mode is changed, it is always sent by the Alcatel BSS, because some MSs do not behave correctly when it is missing (in particular during handovers from AMR FR to AMR HR and vice-versa).

Remarks:

• In the building of the HANDOVER COMMAND message, the “Synchronisation Indication” tells the mobile which type of protocol is to be performed on the Radio interface. In the case of synchronous channel change, the MS knows that the timing advance that it is currently using will be used in the target cell, this matches the setting given in the CHANNEL ACTIVATION message given to the target BTS.

• The power used by the MS is set to the maximum capable (or allowable if smaller) for the MS on the new channel: this ensures a high probability of success. The reason for not using the MS power obtained from the PHYSICAL CONTEXT CONFIRM message is due to the fact that there is no relationship between the power used on the serving cell and the reception level of the MS on the target cell.

3.2.8 HANDOVER PERFORMED message construction This message is sent by the BSC to the MSC when an internal handover (intra-cell or inter-cell) has been successfully performed. Information element Setting or Algorithm

MIE Cause A mapping will be done between the alarm detected by the internal handover detection algorithms corresponding to the final target cell (see ref.[9]) and the cause on the A interface : see table below.

MIE Cell Identifier If CGI_REQD = TRUE the coding will use the Cell Global Identifier, else the coding will use Location Area Code & Cell Identity (i.e. LAC + CI). Note 1.

OIE Chosen Channel If GSM_PHASE = PHASE 1: Not sent.

If GSM_PHASE = PHASE 2: Sent only if there has been previously a TCH assignment or an external channel change an if the MIE Channel Type in either ASSIGNMENT REQUEST or HANDOVER REQUEST gives a choice to the BSS.


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OIE Chosen Encryption Algorithm If GSM_PHASE = PHASE 1:

Not sent. If GSM_PHASE = PHASE 2: This IE is only sent after ciphering has taken place and when the MSC allows the BSS a choice of more than one ciphering algorithm, see ref.[3] & Note 2.

OIE Speech Version (chosen)

This IE is included if allowed by the O&M parameter EN_SEND_SPEECH_VER and when the speech version has been changed by the BSS.

OIE LSA Identifier Not included.

Table 3-26 : HANDOVER PERFORMED message construction Note 1: The Cell Identifier will always be included in the message even if the BSS is a single cell

BSS and the channel change was an intra-cell handover. Note 2: After ciphering has been initiated by the MSC the Chosen Encryption Algorithm IE is only

included if more than one permitted algorithm field of the Encryption Information IE is supplied in the CIPHER MODE COMMAND message. After external channel change the Chosen Encryption Algorithm IE is only included if more than one ciphering algorithm is allowed in the permitted algorithm field of the Encryption Information IE supplied in the HANDOVER REQUEST message.

Mapping of handover causes between internal BSS causes and A interface:


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Internal cause raised by HOP A interface GSM cause Decimal Binary

(2) Uplink quality too low Uplink quality (2) (000 0010) (3) Uplink level too low Uplink strength (3) (000 0011) (4) Downlink quality too low Downlink quality (4) (000 0100) (5) Downlink level too low Downlink strength (5) (000 0101) (6) MS-BTS distance too long Distance (6) (000 0110) (7) consecutive bad SACCH frames Uplink quality (2) (000 0010) (10) Inner zone uplink level too low Uplink strength (3) (000 0011) (11) Inner zone downlink level too low Downlink strength (5) (000 0101) (12) Power budget Better cell (12) (000 1100) (13) Outer zone uplink & downlink level

too high Better cell (12) (000 1100)

(14) High level in neighbour lower layer cell for slow mobile

Better cell (12) (000 1100)

(15) High interference on Uplink Uplink quality (2) (000 0010) (16) High interference on Downlink Downlink quality (4) (000 0100) (17) Uplink level Microcell : high threshold Uplink strength (3) (000 0011) (18) Downlink level Microcell : high

threshold Downlink strength (5) (000 0101)

(20) Forced directed retry Directed retry (13) (000 1101) (21) High level in neighbour cell in the

preferred band Better cell (12) (000 1100)

(22) Too short MS-BTS distance Distance (6) (000 0110) (23) Traffic Handover Traffic (15) (000 1111) (24) General capture HO Traffic (15) (000 1111) (26) HR to FR channel adaptation due to

bad radio quality Uplink quality (2) (000 0010)

(27) FR to HR channel adaptation due to good radio quality

Better cell (12) (000 1100)

(28) Fast Traffic Handover Traffic (15) (000 1111) (29) Intracell TFO alarm Traffic (15) (000 1111) (30) Move from PS to CS zone Traffic (15) (000 1111) (31) 2G-3G Handover Ec/No Better cell (12) (000 1100)

Table 3-27 : Mapping of handover causes on A interface


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3.2.9 ASSIGNMENT COMPLETE message construction

This message is sent by the BSC to the MSC when an internal directed retry has been successfully performed. Information element Setting or Algorithm OIE RR cause This is copied from the HANDOVER COMPLETE message received from

the MS, if it is present in this message. OIE Cell identifier If CGI_REQD == TRUE the coding will use the Cell Global Identifier

else the coding will use Location Area Code & Cell Identity (i.e. LAC + CI). OIE Chosen channel This IE is only sent if the MIE Channel Type in the ASSIGNMENT

REQUEST gives a choice to the BSS. OIE Chosen encryption

algorithm This IE is only sent after ciphering has taken place and when the MSC allows the BSS to choose more than one ciphering algorithm, see ref.[3].

OIE Circuit pool Not used. OIE Speech version

(chosen) This IE is only sent if the MIE Channel Type in the ASSIGNMENT REQUEST gives a choice to the BSS.

OIE LSA Identifier Not included. Table 3-28 : ASSIGNMENT COMPLETE message construction

3.2.10 CHANNEL MODE MODIFY message construction This message is sent by the BSC to the MS after a successful directed retry, if the MS is phase 1 and if the target channel is a FR TCH with speech algorithm version 1. For the message construction, see ref.[16]. 3.2.11 TFO MODIFICATION REQUEST message construction This message is sent by the BSC to the serving BTS in the case where TFO has to be disabled in the TRAU before performing the handover (TFO not supported in the target BTS). Information element Setting or Algorithm MIE Channel Number In the direction BSC to BTS, the Channel Number parameter is used to

indicate on which physical channel/subchannel the message is to be sent. OIE MultiRate Control Not used. MIE TFO Command Alcatel proprietary IE.

• Field “TFO_PREF” is set to 0. • Field “TFO_OPT” is set to 0. • Field “TFO_MATCH” is set to 0. • Field “EN_TFO” is set to 0. • Field “TFO Codec” is set to ‘0xFF’. • Field “T_TFO” contains the value of the timer T_TFO in the serving cell.

OIE Supported Codec Types

Not included.

Table 3-29 : TFO MODIFICATION REQUEST message construction


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3.2.12 HANDOVER COMPLETE, HANDOVER FAILURE, ASSIGNMENT COMPLETE,

ASSIGNMENT FAILURE messages checking The HANDOVER COMPLETE, HANDOVER FAILURE, ASSIGNMENT COMPLETE, ASSIGNMENT FAILURE messages received by the BSC from the MS are checked as follows: If message length is greater or equal to 2 octets, then the message is accepted. If message length is greater or equal to 3 octets, then octet 3 is considered as the RR cause IE. 3.2.13 BTS CHANNEL ACTIVATION message checking See ref.[2], for all checks, with the following added: For inter-cell channel change (i.e. MIE Activation Type is 0 1 1 or 0 1 0), if CIE Handover reference is missing then:

- Send CHANNEL ACTIVATION NACK with cause "Optional Information Element error" - Discard CHANNEL ACTIVATION message

If the requested SDCCH or TCH channel in CHANNEL ACTIVATION message is already activated in the BTS, the BTS shall first release this busy channel (resource state mismatch between BTS and BSC - see ref.[4] N1500). In conflict situations within the BTS (i.e. CHANNEL ACTIVATION messages indicating SDCCH for timeslots configured as TCH, or vice versa), the request from the BSC will be followed. 3.2.14 MS behaviour Both phase 1 and phase 2 MSs can perform inter-cell channel changes from SDCCH or TCH to SDCCH or TCH (any combination possible). The HANDOVER COMMAND message contains the OIE Channel Mode to indicate that the channel mode to be used on the new channel is different than the one used on the old channel. (for example Signalling -> Speech or Signalling -> Data). For compliance with ref.[24], the MS may receive CHANNEL MODE MODIFY message at the end of a directed retry procedure, and may reply with CHANNEL MODE MODIFY ACK. For an intra-cell handover or an inter-cell handover using AMR (EN_AMR_FR or EN_AMR_HR = TRUE on the serving cell and on the target cell), the MS may get AMR parameters in the ASSIGNMENT COMMAND or HANDOVER COMMAND messages, but surely does in case of handover from AMR FR to AMR HR (see ref.[22]). If these parameters are not present, then the MS goes on using the old AMR parameters (received in the last ASSIGNMENT COMMAND or HANDOVER COMMAND message) once on the target channel. On the target channel, the MS uses the indicated start mode until the BTS starts codec mode adaptation, see ref.[18]. 3.2.15 MSC behaviour The MSC is unaware that the BSS is performing a handover until it receives HANDOVER PERFORMED message. The MSC is unaware that the BSS is performing a directed retry until it receives ASSIGNMENT COMPLETE message with a new cell identity. Upon reception of these messages, the MSC keeps the call connected and in addition updates the MS’s position in the network. In case of VGC, the MSC may release the dedicated TCH allocated to the talker.


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3.3 INTERACTION WITH OTHER PROCEDURES

3.3.1 Internal channel change interaction with assignment, ciphering, classmark request, classmark update & DTAP

Assignment: In the case where the BSC receives more than one ASSIGNMENT REQUEST message, only the first ASSIGNMENT REQUEST message will be queued. If the channel change is a directed retry, there is already the initial ASSIGNMENT REQUEST in the queue, so no other ASSIGNMENT REQUEST message will be queued during the procedure. Ciphering: In the case where the BSC receives more than one CIPHER MODE COMMAND message, only the first CIPHER MODE COMMAND message will be queued. If ciphering has already been commanded (by the MSC through a ciphering procedure or an external channel change procedure) the internal channel change is able to change the ciphering algorithm for Phase 2 MSs, depending on the MS ciphering capabilities, the BTS ciphering capabilities and MSC ciphering requirements. The MS ciphering capabilities are obtained from the following procedures: Immediate assignment (see ref.[1]); External channel change (see ref.[16]); Classmark change, Classmark update and Classmark enquiry (see ref.[6]). The BTS capabilities are obtained from O&M data, and maintained by O&M procedures when the ciphering capabilities of the TRX changes. The MSC ciphering requirements are obtained from the following procedures: ciphering procedure (see ref.[3]) and external channel change procedure (see ref.[16]). Classmark: Only the first CLASSMARK REQUEST is queued after the sending of the HANDOVER COMMAND or ASSIGNMENT COMMAND to the MS, subsequent CLASSMARK REQUEST are discarded. CLASSMARK UPDATE is immediately handled when received on the A interface - see ref.[6]. DTAP: Whilst an internal channel change is in progress, up to five DTAP messages are queued. These procedures will be re-enabled once the connection with the MS is re-established. There are two queues implemented : - one for the DTAP messages, - one for the BSSMAP procedures. At the end of the successful internal channel change, the DTAP messages will be sent to the MS (via the BTS) before any BSSMAP procedure (Assignment or ciphering or Classmark request) is initiated. This behaviour will lead to a reordering of messages and procedures which have been received from the MSC. The failure case, when the MS goes back to the old channel, is described in ref.[15]. 3.3.1.1 Ciphering & DTAP With respect to reordering of the ciphering procedure and DTAP messages, any mis-operation (i.e. the sending of signalling information on the Radio interface unciphered, and therefore a breach of the security aspects of GSM) will be the responsibility of the MSC as 3GPP TS 44.018 specifies that if ciphering is applied, it will be applied after the authentication procedure and before the transaction phase. This implies that the MSC must await the CIPHER MODE COMPLETE message before the sending of DTAP messages to the MS.


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The MSC should not assume that the ordering is maintained by the BSS and due to the inherent

security aspects of the ciphering (as defined by 3GPP), that it is impossible to send a message unciphered on Radio interface after having initiated the ciphering procedure. Messages and procedures which could be sent unciphered are as follows: LOCATION UPDATING ACCEPT message (as part of the TMSI Re-allocation procedure) this message contains the TMSI for the MS; SETUP message (as part of the Mobile terminating call establishment). The message sequence chart below shows an incorrect behaviour sequence where the MSC does not await the CIPHER MODE COMPLETE message. Note: Correct setting of the variable SDCCH COUNT may help to cure the problem, as it will hold off the possible starting of an internal SDCCH handover, allowing the procedures to be performed uninterrupted. Serving Target MS BTS BTS BSC MSC HO CMD HANDOVER COMMAND <-------------------------- <---------------------------------------------------------- (1) CIPHER MODE

COMMAND

<-------------------------- DTAP

(LOC UPDT ACC)

<-------------------------- HANDOVER COMPLETE HO CMP ----------------------------------------------------------> --------------------------> LOC UPDT ACC (unciphered) LOC UPDT ACC (2) <---------------------------------------------------------- <-------------------------- (3) ENCRYPTION

COMMAND

CIPHERING MODE COMMAND <-------------------------- <----------------------------------------------------------

Figure 3-10 : Incorrect behaviour sequence (1) During internal handover CIPHER MODE COMMAND & LOCATION UPDATING ACCEPT

are received. (2) LOCATION UPDATING ACCEPT is sent unciphered. (3) The ciphering procedure is then performed.

3.3.1.2 Assignment & DTAP With respect to the reordering of the assignment procedure and the DTAP messages, any mis-operation (i.e. the sending of signalling messages on the Radio interface before a TCH is assigned) will be the responsibility of the MSC as the procedure may fail (ASSIGNMENT FAILURE on old channel) and the sending of signalling before the successful completion of the procedure is the MSC responsibility. For call control and SMS this may cause a problem, this may not cause a problem with Supplementary Services.


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3.3.2 Internal handover & power control

The power control algorithm is enabled on the new channel when the ESTABLISH INDICATION is received. The power control on the old channel is not disabled during internal channel change. 3.3.3 Internal handover & SMS PP It is possible that an SMS message is lost during internal channel change if there are two SMS messages pending for transmission after the internal channel change has finished. The behaviour of the BSC and BTS is as shown below. Target MS BTS BSC MSC (1) DTAP (SAPI 3') <-------------------------- (1) DTAP (SAPI 3") SABM <-------------------------- (2) --------------------------> ESTABLISH INDICATION UA --------------------------------------------------------> <-------------------------- (2) HO CMP HANDOVER COMPLETE --------------------------> --------------------------------------------------------> stop T3103 (3) ESTABLISH REQUEST (SAPI 3) <-------------------------------------------------------- (SAPI 3 establishment) (3) DTAP (SAPI 3’) <--------------------------------------------------------

Figure 3-11 : Internal handover & SMS PP (1) Two SAPI 3 DTAP messages are received and queued during an internal channel change.

Up to 5 DTAP messages can be queued during the procedure. (2) The channel change completes. (3) The BSC sets up the SAPI 3 connection and sends the first queued SAPI 3' message, the

second queued SAPI 3'' message is discarded.


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3.3.4 Internal channel change & call release

If a release occurs on A interface during an internal channel change, the channel change procedure goes on until its completion (except in case of SCCP disconnection on A interface). DTAP messages are added in the queue (if there is free space). If the A interface release is triggered by a SCCP RELEASED message the Abis and Radio resources are released immediately. The optional DTAP message contained in the SCCP RELEASED message is sent to the MS on the current channel, except when the BSC is awaiting the HANDOVER DETECTION or the ESTABLISH INDICATION message In these latter cases, the DTAP message is discarded. Once the channel change has completed: • If the MS is still connected (i.e. either HANDOVER / ASSIGNMENT COMPLETE on the new

channel or HANDOVER / ASSIGNMENT FAILURE on the old channel), then the DTAP messages are dequeued and sent to the MS, except in the case of a SAPI 3 DTAP message: - if a SAPI 3 connection has been previously established towards the BTS, the oldest SAPI 3 message of the queue is sent to the MS. Subsequent SAPI 3 messages in the queue are discarded.

- if no SAPI 3 connection is established towards the BTS, all SAPI 3 messages of the queue are discarded.

Then, the call release procedure will be initiated towards the MS. All queued procedures will be discarded.

• If the MS is lost (i.e. expiry of T3103 or T3107) all DTAP messages (SAPI 0 & 3) & any queued procedures will be discarded.

3.3.5 Internal directed retry & In-call modification Due to compliance with ref.[24], CHANNEL MODE MODIFY message is sent to the MS after a directed retry if the MS is a phase 1 MS and if the target channel is a FR TCH with speech algorithm version 1. When the MS replies with CHANNEL MODE MODIFY ACK, this message is discarded except if an In-call modification procedure is on-going (another CHANNEL MODE MODIFY message has been sent). In this case, the first CHANNEL MODE MODIFY ACK message received will be interpreted as a failure of the In-Call modification procedure (because the Channel Mode IE will be "speech version 1"), and the second one will be ignored. Following figure gives an example of scenario: MS BSS (1) CHANNEL MODE MODIFY (mode : FR Speech version 1, for DR) <---------------------------------------------------------------------------------------- (2) CHANNEL MODE MODIFY (mode : any, for in-call modification) Start T9112 <---------------------------------------------------------------------------------------- (3) CHANNEL MODE MODIFY ACK (full rate speech version 1) ----------------------------------------------------------------------------------------> Stop T9112 (4) CHANNEL MODE MODIFY ACK (any) ---------------------------------------------------------------------------------------->

Figure 3-12 : Directed retry & In-call modification


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(1) The BSS sends a CHANNEL MODE MODIFY message.

(2) An In-call modification procedure is started, and another CHANNEL MODE MODIFY message is sent.

(3) The BSS receives the first CHANNEL MODE MODIFY ACK, with a mode set to "FR speech version 1", which is interpreted as a failure of the In-call modification procedure (the mode asked in the CHANNEL MODE MODIFY for In-call modification was not FR speech version 1, since the MS already uses this mode).

(4) The second CHANNEL MODE MODIFY ACK is discarded. 3.3.6 Internal channel change & timer T3103 T3103 is a guard timer for the internal inter-cell channel change procedure (handover or directed retry). Due to the possible inclusion of optional IEs (see section 3.2.7 “HANDOVER COMMAND message construction”), the HANDOVER COMMAND message can be too long to be passed in one frame on the Radio interface. The HANDOVER COMMAND message will be segmented and passed in two consecutive frames on the Radio interface (see ref.[12] for details on transmission on Radio interface). The timer T3103 must take into account this possible delay. 3.3.7 Internal handover & concentric cells The Interzone handover is performed by the initiation of an intra-cell handover procedure, see ref.[9]. 3.3.8 Internal channel change & handover algorithms The interaction between the internal channel change protocol and the handover algorithms such as new handover alarms or different target cell list is described in ref.[15]. 3.3.9 Internal handover & eMLPP During the internal handover, the BSC shall not change the A-interface priority information (pvi, pci…) of an on going call.


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4 INTERFACE DESCRIPTIONS

4.1 GSM interfaces / Physical interfaces The following interfaces are defined for this procedure. 4.1.1 Radio interface ASSIGNMENT COMMAND

BSC -> Serving BTS (Transparent) -> MS sent on main DCCH, initiates intra-cell change of channel.

ASSIGNMENT COMPLETE MS -> Serving BTS (Transparent) -> BSC sent on main DCCH, initiates completion of the procedure

ASSIGNMENT FAILURE MS -> Serving BTS (Transparent) -> BSC sent on main DCCH and indicates failure to move to new channel.

CHANNEL MODE MODIFY BSC -> Target BTS (Transparent) -> MS Sent on FACCH for compliance with ref.[24].

HANDOVER ACCESS MS -> Target BTS Synchronous channel change: sent four times on the main DCCH of the target cell with a timing advance of zero. Asynchronous channel change: sent continuously on the main DCCH of the target cell with a timing advance of zero.

HANDOVER COMMAND BSC -> Serving BTS (Transparent) -> MS sent on main DCCH, initiates channel change of the MS.

HANDOVER COMPLETE MS -> Target BTS (Transparent) -> BSC sent on main DCCH, initiates completion of the procedure

HANDOVER FAILURE MS -> Serving BTS (Transparent) -> BSC Sent on main DCCH, indicates failure of the channel change.

PHYSICAL INFORMATION Target BTS -> MS sent ciphered (if ciphering is applied) for an asynchronous channel change on the main DCCH.

SABM SAPI 0 Layer 2 LapDm MS -> BTS

UA SAPI 0 Layer 2 LapDm BTS -> MS Confirms reception of SABM

4.1.2 Abis interface CHANNEL ACTIVATION

BSC -> BTS Commands the activation of an RF channel.

CHANNEL ACTIVATION ACK BTS -> BSC Acknowledges successful activation of an RF channel.


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CHANNEL ACTIVATION NACK

BTS -> BSC Acknowledges the unsuccessful activation of an RF channel.

CONNECTION FAILURE INDICATION (cause “Radio link failure”) BTS -> BSC Indicates that there has been a failure at Layer 1, caused by loss of SACCH frames.

CONNECTION FAILURE INDICATION (cause “Remote transcoder failure”) BTS -> BSC Indicates that the BTS has detected either loss of synchronisation or loss of transcoder frames.

ERROR INDICATION SAPI 0 BTS -> BSC Indicates that particular types of errors are being detected by the LapDm entity from the MS.

ERROR REPORT SAPI 0 (cause “Message sequence error”) BTS -> BSC Indicates that the channel concerned is deemed to be inactive in the BTS.

ERROR REPORT (cause “O&M intervention”) BTS -> BSC Indicates that the BTS has lost all associated connections.

ESTABLISH INDICATION BTS -> BSC Sent during this procedure when the MS has established Layer 2 LapDm, there should be no Layer 3 information IE contained in this message.

HANDOVER DETECTION BTS -> BSC Sent when the BTS has received the correct HANDOVER ACCESS message from the MS on the Radio interface.

PHYSICAL CONTEXT REQUEST BSC -> BTS For intra-cell handover and synchronous inter-cell channel change, request from the BSC to obtain the currently used timing advance. The message also carries information for O&M LapDm performance measurement.

PHYSICAL CONTEXT CONFIRM BTS -> BSC Message sent conveying the information.

RELEASE INDICATION SAPI 0 BTS -> BSC Indicates that the BTS LapDm entity has detected that the MS has released the LapDm connection at SAPI 0.

TFO MODIFICATION REQUEST BSC -> BTS For inter cell speech TCH handover, orders from the BSC to stop TFO in the TRAU before performing the handover.

4.1.3 A interface ASSIGNMENT COMPLETE

BSC -> MSC Indicates that an internal directed retry has successfully taken place.

HANDOVER PERFORMED BSC -> MSC Indicates that an internal handover has successfully taken place.

HANDOVER FAILURE BSC -> MSC Cause "Radio interface failure - Reversion to old channel" Sent whilst an internal channel change is in progress


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4.2 Internal interfaces

4.2.1 BSS internal entities

ICC

HOP

HOM RAM

ECC

"IHO request""IDR request"

"Exit and clear""HO FAIL from MS"

"Next cell is external""Internal failure on all cells"

"Select a channel"

"Channel selected""Select channel reject"

BSS

Figure 4-1 : BSS handover internal entities

Entities: HOP: Handover Preparation

This entity is responsible of triggering handover alarms by checking continuously the radio environment of the mobile (radio level, radio quality, possible target cells, traffic load, multi-layer network, etc.). The HOP behaviour is described in ref.[9].

HOM: Handover Management

This entity is responsible of managing the channel changes depending on handover alarms sent by the HOP entity, the O&M configuration of the BSS, the events arriving from the protocol entities, etc. The HOM behaviour is described in ref.[15].

ICC: Internal Channel Changes

This entity is responsible of running the internal channel change protocol when the HOM asks for it. The current document described the ICC behaviour.

ECC: External Channel Changes

This entity is responsible of running the external channel change protocol, either for an outgoing external channel change when the HOM asks for it (serving BSC) or autonomously for an incoming channel change (target BSC). The ECC behaviour is described in ref.[16].

RAM: Resource Allocation and Management

This entity is responsible of managing the radio resources of the BSS. The RAM behaviour is described in ref.[14].


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4.2.2 BSS internal interfaces with Internal Channel Changes

Direction Message Parameter or information HOM -> ICC Request for IHO - Filtered cell list(see Note 1)

- HO cause for each cell - Zone indication in case of concentric cell - new codec type if HO cause=#29 (i.e. intracell TFO alarm when TFO is enabled)

Request for IDR - Filtered cell list - HO cause for each cell - Zone indication in case of concentric cell

ICC -> HOM Exit and clear None HO FAILURE from MS - Index of the cell in the cell list. Next cell is external - Index of the cell in the cell list. Internal failure on all cells None ICC -> RAM Select channel - Reason for Request: intra-cell IHO, inter-cell

IHO, IDR - Channel type (with or without a choice) - Queuing not allowed - Pre-emption not allowed (see Note 3) - HO cause - current channel - current codec - list of speech versions - new codec type in case of HO cause=#29, initially triggered by RAM (i.e. intracell TFO alarm when TFO is enable) - MS band ability: E-GSM or Not_Applicable (see Note 2)

RAM -> ICC Channel Selected - Chosen Channel type - Chosen Speech version If TFO is enabled, in case of speech calls (except if FORCE_TFO_VS_AMR=FALSE and chosen codec type is AMR FR or AMR HR):

- TFO codec type - List of supported codec types

Select channel reject Cause Table 4-1 : BSS internal interfaces with Internal Channel Changes

Note 1: in case of an intra-cell handover, the filtered cell list will be limited to the serving cell. Note 2: If the MS supports the G1 band, then the “MS band ability” is set to the value ‘E-GSM’.

Otherwise the “MS band ability” is set to the value ‘Not_Applicable’.


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Note 3: No pre-emption of on-going calls is implemented during internal channel change procedure

(as it is linked to queuing procedure defined in RAM, which is not used in case of internal channel change neither). However, in case of emergency handover towards congested internal cells for a call allowed to pre-empt other on-going calls, an external channel change is processed instead. See ref.[15] & [16] for details.

4.3 Timer list MS Timers T3124

MS timer. Started when the first HANDOVER ACCESS is sent during asynchronous inter-cell channel change, this timer supervises the reception of PHYSICAL INFORMATION message from the BTS

BTS Timers T200

MS, BTS timer. Supervises the repetition of Layer 2 frames on LapDm. T3105_F_FR, T3105_F_HR & T3105_D

These timers are referred in this document as T3105. Supervise the rate of sending PHYSICAL INFORMATION messages to the MS for FACCH

connections on Full Rate or Half Rate channels and for SDCCH connections respectively. T3106_F & T3106_D

These timers are referred in this document as T3106. Supervise the reception of the establishment by the MS or any Layer 2 frame, after the

reception of the HANDOVER ACCESS during synchronous channel changes for FACCH and SDCCH connections respectively.

T_CFI_TR Used to filter the internally detected transcoder alarm after RL ESTABLISH INDICATION from the LAPDM

T_SYNC Used to supervise the reception of TRAU frames from the transcoder.

T_TFO BTS & Transcoder timer. This timer is used in both entities to control the acknowledgement of TFO messages between BTS and TRAU. Its value is provided by the BSC to the BTS in CHANNEL ACTIVATION message.

BSC Timers T11

Queuing timer for assignment requests when the MSC authorises queuing. T11_FORCED

Queuing timer for assignment requests when the MSC does not authorise queuing and if forced queuing is authorised by O&M.

T3103 Supervises inter-cell internal channel change.

T3107 Supervises intra-cell internal channel change.

T9103 Supervises the channel activation procedure in the BTS.

T9108 Supervises the physical context procedure.

T_RCR_ACK Supervises the RF channel release procedure.


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4.4 Parameter list

BTS PARAMETERS NY1

The maximum number of repetitions for the PHYSICAL INFORMATION message during a channel change.

STOP_HO_ACC_FAIL This is a generic name associated to the flags controlling the behaviour of the BTSs.

Due to testing requirements in the BTS, the BTS has implemented four flags on to which this single name maps.

These flags appear in the BTS CONF DATA message and are named : T3105_D_STOP, T3105_F_STOP, T3106_D_STOP & T3106_F_STOP (see below).

T3105_D_STOP See STOP_HO_ACC_FAIL

T3105_F_STOP See STOP_HO_ACC_FAIL

T3106_D_STOP See STOP_HO_ACC_FAIL

T3106_F_STOP See STOP_HO_ACC_FAIL

BSC VARIABLES BS_pwr_max

Maximum power that the BTS can use to transmit to the MS (either BS_TXPWR_MAX_INNER or BS_TXPWR_MAX).

MS_pwr_max Maximum power that the MS is allowed to use in a cell (either MS_TXPWR_MAX_INNER or MS_TXPWR_MAX).

BSC PARAMETERS AMR_FR_HYST Hysteresis for AMR FR codec mode adaptation. AMR_FR_SUBSET Bitmap of 8 bits defining the codec subset that shall be used for AMR Full Rate (1 to 4

codecs out of 8). AMR_FR_THRi (i=1, 2, 3) Thresholds for AMR FR codec mode adaptation. AMR_HR_HYST Hysteresis for AMR HR codec mode adaptation. AMR_HR_SUBSET Bitmap of 6 bits defining the codec subset for AMR Half Rate (1 to 4 codecs out of 6). AMR_HR_THRi (i=1, 2, 3) Thresholds for AMR HR codec mode adaptation. AMR_START_MODE_FR Indicates the codec used at the beginning of a FR AMR call, until codec mode adaptation is

started by the BTS. AMR_START_MODE_HR Indicates the codec used at the beginning of a HR AMR call, until codec mode adaptation is

started by the BTS. BS_TXPWR_MAX

Maximum power that the BTS can use to transmit to the MS in a non-concentric cell or in the outer zone of a concentric cell.


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BS_TXPWR_MAX_INNER

Maximum power that the BTS can use to transmit to the MS in the inner zone of a concentric cell.

CGI_REQD When set to 'used', dictates that the encoding of cell identifiers will use the CGI encoding rules.

EN_AMR_FR Enable / Disable Adaptive MultiRate speech codec (AMR) Full Rate calls.

EN_AMR_HR Enable / Disable Adaptive MultiRate speech codec (AMR) Half Rate calls.

EN_EXT_MEAS_REP Enable / Disable Extended Measurement Reports (MAFA).EN_SEND_SPEECH_VER

Enable / Disable the sending of OIE “Speech Version (chosen)” in HANDOVER PERFORMED message towards the MSC.

EN_SYNCHRONISED_HO Flag allowing synchronous handover.

EN_TFO When set to true, the basic functions of TFO are possible in the cell for GSM FR, EFR and HR codecs.

EN_TFO_MATCH When set to true, the codec mismatch resolution procedure is possible in the cell. This flag is relevant only if EN_TFO is set to true.

EN_TFO_OPT When set to true, the codec optimisation procedure is possible in the cell. This flag is relevant only if EN_TFO and EN_TFO_MATCH are both set to true.

FORBID_AMR_NS O&M flag to forbid / allow AMR noise suppressor in the MS.

FORBID_DTXD_NH_BCCH_F O&M parameter which forbids or not the downlink DTX on the non-hopping TCH of the BCCH TRX.

FORCE_TFO_VS_AMR When set to true, it forces TFO negociation while AMR is used. This flag is relevant only if EN_TFO and (EN_AMR_FR and/or EN_AMR_HR) are set to true.

GSM_PHASE This flag indicates the mode of operation/behaviour that the BSS needs to adopt on A interface. It is set to either PHASE 1 or PHASE 2.

MS_TXPWR_MAX Maximum power that the MS is allowed to use in a non-concentric cell or in the outer zone of a concentric cell.

MS_TXPWR_MAX_INNER Maximum power that the MS is allowed to use in the inner zone of a concentric cell.

NCI This parameter has no effect on the BSS behaviour. O&M parameter which controls the setting of the NCI (“Normal Cell Indication”) bit field in the Synchronisation indication IE in the HANDOVER COMMAND message.

PLMN_FREQUENCY_BANDS Frequency bands used in the whole PLMN. ROT

This parameter has no effect on the BSS behaviour. O&M parameter which controls the setting of the ROT (“Report Observed Time difference”) bit field in the Synchronisation indication IE in the HANDOVER COMMAND message.


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5 GLOSSARY

3GPP 3rd Generation Partnership Project ACK Acknowledge ACT Activation AMR Adaptative Multi-Rate speech codec BCCH Broadcast Control Channel BSC Base Station Controller BSCLP BSC-MFS LCS Protocol BSS Base Station System BTS Base Transceiver Station CGI Cell Global Identifier CIE Conditional Information Element CMD CoMmanD CMP CoMPlete DCS1800 band Frequency band 1710.2 - 1784.8 MHz + 1805.2 - 1879.8 MHz.

ARFCN 512 to 885. DCS1900 band Frequency band 1850.2 - 1909.8 MHz + 1930.2 - 1989.8 MHz.

ARFCN 512 to 810. DCS This generic term is used to designate either DCS1800 or DCS1900. As

those bands are mutually exclusive, there cannot be any ambiguity. Don't care This is used in State transition tables to indicate that when an event is

received it will be ignored DTX Discontinuous Transmission EFR Enhanced Full Rate E-GSM This refers to the extended frequency band used by GSM (primary P-GSM

range and G1 range) eMLPP Enhanced Multi-Level Precedence and Pre-emption EST IND ESTablish INDication FR Full Rate G1 range This is a frequency range added to the initial P-GSM frequency allocation

(880.2 - 890.0 MHz and 925.2 - 935.0 MHz) ARFCN 975 to 1023 + 0.

GSM Global System for Mobile communications HO HandOver HOM HandOver Management entity HR Half Rate HSCSD High Speed Circuit Switched Data ICC Internal Channel Change IE Information Element IHO Internal HandOver LCS LoCation Services MAFA Mobile Assisted Frequency Allocation main channel The channel that carries the main signalling channel (FACCH). In a non

HSCSD transaction, the only channel is the main channel. MIE Mandatory Information Element MS Mobile Station MSC Mobile Switching Centre NA Not Applicable


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This is used to indicate in State transition tables that an event should not be

received in a specific state. If the event is received then it is ignored NACK Negative Acknowledge NC New Channel NT Non Transparent O&M Operations & Maintenance OIE Optional Information Element OC Old Channel P MS power capability (different for GSM and for DCS) in the frequency band

where the power command will be used Pband inner MS power capability in the frequency band of the inner zone (multiband

cells) Pband outer MS power capability in the frequency band of the outer zone (multiband

cells) P-GSM This refers to the primary frequency band used by GSM (890.2 - 915.0 MHz

/ 935.2 - 960.0 MHz) ARFCN 1 to 124

PHY INFO PHYsical INFOrmation PLMN Public Land Mobile Network RACH Random Access Channel RAM Resource Allocation and Management entity REJ REJect REP REPort REQ REQuest RES RESults RESP RESPonse RF Radio Frequency RMS Radio Measurements Statistics RR Radio Resource RRLP Radio Resource LCS Protocol SABM Set Asynchronous Balanced Mode SACCH Slow Associated Control CHannel SAPI Signalling Access Point Identifier SCCP Signalling Connection Control Part SDCCH Standalone Dedicated Control CHannel Serving BTS The BTS which is currently handling the MS connection SMLC Serving Mobile Location Centre TA Timing Advance Target BTS The BTS which is going to handle the connection TCH Traffic CHannel TDMA Time Division Multiplex Access TFO Tandem Free Operation UA Un-numbered Acknowledge

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