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The ISDN-Protocol

Chapter 4a

This chapter is designed to provide the student with a reference

about the protocols used for ISDN-Primary Rate Access.

OBJECTIVES:Upon completion of this chapter the student will be able to:

describe the ISDN layer model

describe the function of the different layers within this

model

describe the elements a layer3 message consists of

describe the function of timers on layer3

describe simple ISDN traffic cases on layer3 level

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GSM ISDN-E Accesses and Services Operation in MSC/VLR

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4a The ISDN-Protocol

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Table of Contents

Topic Page

SCOPE...............................................................................................133

LAYER 1 ............................................................................................135

LAYER 2 ............................................................................................138

LAYER 3 ............................................................................................141

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EN/LZT 123 1207 R1A 133

SCOPE

This chapter is intended to be used as a reference. It does not

replace the specifications it is extracted from.

Although the signaling and addressing principles for Primary

Rate Access (PRA) and Basic Access (BA) are quite similar,

this chapter covers those aspects with a main focus on PRA. The

S-reference point is not a main issue covered in this chapter.

Conventions

In order to provide help for reading the relevant specifications

and to avoid misunderstandings the important basics areexplained shortly.

ISDN-Reference points

The ISDN-reference model defines functional units and

reference points that divide those units. The functional units and

the reference points are shown in Figure 4a-1.

NT2

LT/ET

NT1

T US

TA

R

NTTE

Figure 4a-1: Functional units and reference points of the ISDNreference model.

In general, signaling is performed between LT/ET and TE. The

NT1 is transparent for signaling and performs only a conversion

of layer1. NT2 provides switching and supervision functions and

serves as an end-point of signaling from the LT/ET point of

view. The logical communication queue can be described as

follows: LT/ET NT2 TE.

The layer model

Communication in ISDN is based on a 3-layer model as shown

in Figure 4a-2.

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134 EN/LZT 123 1207 R1A

In communication between two entities, there can be more than

one instance of each layer. Each instance is communicating with

a peer instance in the other entity. All of these layer instances

are managed by one layer-management instance per entity. Thelayer management instance can also communicate to its peer

instance via layer1 3.

Layer 1 is also called the physical layer and layer 2 is also called

the data link layer.

The layer-to-layer and the layer-to-management communication

within one entity is performed by using so-called primitives.

These primitives are a set of basic commands for usage within

one entity and should not be mixed up with protocol elements in

peer-to-peer communication.

Layermanagement

Layer 1

Layer 2

Layer 3

physical interface

application

processes

Layer 2

Layer2 management

Layer 2 instances

Figure 4a-2: The ISDN Layer-model

Primitives

In the ETSI-specifications there are naming conventions for

these primitives. Some examples are shown in Table 1

Primitive Direction Function

DL-UNIT DATA-REQUEST Layer3 -> Data Link LayerRequest a message unit to be

sent using unacknowledged

information transfer service

MDL-UNIT DATA-REQUEST Management -> Data Link Layer

Request a message unit to be

sent using unacknowledged

information transfer service to

the peer-management instance

PH-ACTIVATE-REQUEST Data Link Layer-> Physical Layer Request activation of thephysical layer (layer1)

Table 1: Examples for primitives

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LAYER 1

This section covers supervision principles on the 2Mbit/s

PCM30 link between LT/ET and NT1/NT2 as specified in ITU-TRec. G.703 and G.704

Frame structure

The PCM30 frame consists of 32 time-slots (TS). Each TS

contains 8 bit and is transferred 8000 times a second. This

results in a data rate of (8bit/TS 32 TS/frame) 8000 frames/s

=2048 kbit/s.

0 15 1716 311 30

D-channel signallingSynchronization and

quality supervision

32 channels x 8 bit = 256 bit

30 traffic channels

Figure 4a-3

TS-0 is used for synchronization and layer1 quality supervision.

Frame synchronization is provided by a synchronization word

transmitted in every even numbered frame (0,2,). The first TS

of odd numbered frame contains information about the remote-

end status (Remote Alarm Indication, RAI ) or even more

detailed information about the location of an error that occurred.

CRC-4

The latter case is available when so called CRC-4 supervision isused. CRC-4 supervision of PCM-frames also allows quality

supervision, by means of countable bit-errors.The CRC-4

checksum is calculated for so called Sub-Multi-Frames (SMF).

1 SMF consists of 8 PCM frames. Each even numbered frame

carries one bit of the 4-bit CRC word (CRC= Cyclic

Redundancy Check). The bit-order in an SMF pair is shown in

Table 2.

1 multi-frame (MF) consists of two SMF. The MF- alignment

word (001011) is carried in bit 1 of the first 6 odd-numbered

frames. This enables the receiving end to locate the MF. If one

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136 EN/LZT 123 1207 R1A

side needs to transmit RAI to the remote side, it sets the A-bits

to binary 1.

SMF-No.

Frame No.TS-0

Bit 1

TS-0

Bit 2

TS-0

Bit 3

TS-0

Bit 4

TS-0

Bit 5

TS-0

Bit 6

TS-0

Bit 7

TS-0

Bit 8

0 C1 0 0 1 1 0 1 1

S 1 0 1 A Sa4 Sa5 Sa6 Sa7 Sa8

M 2 C2 0 0 1 1 0 1 1

F 3 0 1 A Sa4 Sa5 Sa6 Sa7 Sa8

- 4 C3 0 0 1 1 0 1 1

1 5 1 1 A Sa4 Sa5 Sa6 Sa7 Sa8

6 C4 0 0 1 1 0 1 1

7 0 1 A Sa4 Sa5 Sa6 Sa7 Sa88 C1 0 0 1 1 0 1 1

S 9 1 1 A Sa4 Sa5 Sa6 Sa7 Sa8

M 10 C2 0 0 1 1 0 1 1

F 11 1 1 A Sa4 Sa5 Sa6 Sa7 Sa8

- 12 C3 0 0 1 1 0 1 1

2 13 E 1 A Sa4 Sa5 Sa6 Sa7 Sa8

14 C4 0 0 1 1 0 1 1

15 E 1 A Sa4 Sa5 Sa6 Sa7 Sa8

Table 2 : The table shows the bit order in TS-0 when usingCRC-4 supervision.

The CRC-word (C1=MSB) transmitted is always to check the

contents of the last received SMF. If the receiving side finds an

SMF faulty, it has to set the E-bits in the next transmitted MF

according to Table 3. The received E-bits are always evaluated,

even if the frame is found faulty by the CRC-check.

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Sa-bits

The bits Sa4 - Sa8 are used as spare-bits. They can be used to

point out the source of an error in order to make maintenanceactivities more effective

1.

E1 Bit

(Frame13)

E2 Bit

(Frame 13)

CRC-Result

1 1 Last SMF-1 fault free

Last SMF-2 fault free

1 0 Last SMF-1 fault free

Last SMF-2 faulty

0 1 Last SMF-1 faulty

Last SMF-2 fault free

0 0 Last SMF-1 faultyLast SMF-2 faulty

Table 3: Meaning of E-Bits in CRC-4 multi-frame

Using CRC-4 check means to have the number of bit-faults

available. With this input, the following values can easily be

calculated:

Bit Fault Frequency (BFF)

Disturbance Frequency (DF)

Errored Second (ES) (second with faults in parts permillion)

Severely Errored Second (SES)

Degraded Minute (DM)

If the quality of a line reaches a set low-limit value, the operator

can be notified in order to take the line out of service.

1

In the ERICSSON implementation these bits are used for Sectionalized Supervision

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LAYER 2

The ISDN layer2 is also referred as the User-Network Interface-

Data Link Layer. In general terms, the tasks of layer2 are:

Provision of end-to-end addressing

Provision of negotiation mechanisms for the assignment oflogical addresses

Provision of error-free data transmission

Identification of TEs

Layer 2 Addressing

The address of a layer 2 entity consists of two parts:

TEI-value

SAPI-value

On the user side, the TEI-value identifies the TE. With only few

exceptions, it can be considered as a physical address. On the

network side, the TEI identifies a layer 2 process in the ET.

The SAPI-value identifies the service access point (SAP)

towards layer 3 within this layer 2 instance. In ISDN, the layer 3offers several different services. The SAPI value determines the

service wanted. The addressing of two different TEs on different

SAPIs is shown in Figure 4a-4.

Layer 1

Layer 2

Layer 3

Layer 1

Layer 2

Layer 3

D-ChannelTEI=127

SAPI=0

TEI=72

SAPI=16

TEI=68

SAPI=63

Figure 4a-4: The picture shows the addressing of two TEs, onewith TEI 68 and the other with TEI 72 on different SAPIs.

The protocol used on layer2 is called LAPD (Link AccessProcedure for D-channels) and is derived from the HDLC

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protocol. The set of primitives and the communication

mechanisms of the LAPD protocol are not discussed in this

document. For detailed information refer to [3.]or to Q.921. The

structure of a layer2 address field is shown in Figure 4a-5.

Layer2 frame structure

A layer2 frame containing an information field (e.g. layer3

information) looks like the following:

8 7 6 5 4 3 2 1 Octet

Flag

1 0 0 0 0 0 0 11

Address

(high order octet)2

Address(low order octet)

3

Control4

Control5

Information

FCS(first octet)

N-2

FCS(second octet)

N-1

Flag

1 0 0 0 0 0 0 1N

Table 4: A layer2 frame containing an information field

The address field can be found in octet 2 and 3 in the layer2

frame. It contains the SAPI and the TEI value. The TEI field is

able to code an address space of 128.

8 7 6 5 4 3 2 1

SAPI C/R EA=0 Octet 2

TEI EA=1 Octet 3

Figure 4a-5: LAPD address field

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The C/R bit indicates whether the frame contains a command or

a response. The usage of this bit is shown in Table 5.

Command/Response Direction C/R value

Network side user side 1

Command User side network side 0

Network side user side 0

Response User side network side 1

Table 5: Usage of the C/R-bit

The values for the SAPI and for the TEI are not free of choice,

but have to be chosen according to Table 6 and Table 7.

SAPI Value Related layer 3 or management entity

0 Call control procedures

1-15 Reserved for future standardization16 Packet communication conforming to X.25 level 3 procedures

17-31 Reserved for future standardization

63 Layer 2 management procedures

All others Not available for Q.921 procedures

Table 6: SAPI- values for layer 3 services

TEI Value User Type

00-630 Non-automatic TEI assignment user equipment

64-126 Automatic TEI assignment user equipment

Table 7: Assignment rules for TEI-values

For single point-to-point connections (e.g. connection of PABX)

TEI 0 is the recommended value (see [2.]). The administration

and the addressing of TEs in this case is done by the NT2 of the

PABX.

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LAYER 3

This chapter gives examples about different traffic cases seen

from the layer 3 point-of-view as well as an overviewconcerning the structure of layer3 messages.

The layer3 information is carried in the layer2 information field.

The size of this information field depends on the type of

message. For different message types there can be a different

number of additional information elements belonging to this

message. The general format of a layer3 message is shown in

Table 8.

Layer3 message format

8 7 6 5 4 3 2 1

Protocol discriminator 1

0 0 0 0Length of call

reference value (oct).2

Call reference value 3

0 Message type

Other information elements as required

Table 8: Layer3 message format

The protocol discriminator determines the protocol variant that

must be applied to this message. These can either be national

variants or other protocols like QSIG (protocol for inter-PABX

communication). The call reference identifies a call or a service

transaction on layer3. This identification is necessary due to the

fact that there can be several active calls/transactions on one

layer2 connection. The length of the call reference is given in

the second octet and may vary, depending on the network and

type of access. The default minimum length for BA is 1, for

PRA 2 octets. Other values can be used if supported by the

network. After the associated call/service transaction is cleared,

the call reference value may be used to identify another action.

Information elements

The message type describes the kind of message, similar to a

command, and is followed by a various number of information

elements (comparable to command-parameters). These

information elements are either optional or mandatory. Most

information element can have a variable number of octets.Therefore each information element contains a length identifier

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142 EN/LZT 123 1207 R1A

in the first octet of the associated data. An example for a layer3

frame carrying the message type SETUP is given in Figure 4a-6.

According to the ETSI recommendation, there are different

coding sets of information elements in order to allow national orprivate functional extensions. A switch between these coding

sets can be achieved by using a so called "shift operator". This

shift operator ("1001Lxxx") can either be valid for all following

information elements or only for the next information element,

depending on the setting of a "locking bit" (L).

Caution:

When referring the ETSI specification one has to distinguish

carefully between message types and information elements for

packet and for circuit switched data

Figure 4a-6 shows the structure of a layer2 frame carrying a

layer3 SETUP message with all mandatory and some optional

information elements.

8 7 6 5 4 3 2 1

Message type

0 0 0 0 0 1 0 1 -> SETUP

0 0 0 0 0 1 0 0 -> Bearer capability

length of bearer capability contents (= 12

0 0 0 1 1 0 0 0 ->Channel Identification

Length of channel identification

0 1 1 1 0 0 0 0 -> Called party number

Length of called party number

0 1 1 0 1 1 0 0 ->Calling party number

Length of calling party number

8 7 6 5 4 3 2 1 OctetFlag

1 0 0 0 0 0 0 11

Address(high order octet)

2

Address

(low order octet)3

Control4

Control5

Information

FCS

(first octet)

N-2

FCS(second octet)

N-1

Flag

1 0 0 0 0 0 0 1N

8 7 6 5 4 3 2 1

Protocol discriminator 1

0 0 0 0Length of call

reference value (oct).2

Call reference value 3

0 Message type

Other information elements as required

Layer2 Layer3

Figure 4a-6: A layer3 frame with message type SETUPcontained in a layer2 frame.

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Shift operator

The complete set of information elements of code-set 0 (which

is the ETSI default code-set that is active if no shift operator isused) for message type SETUP can be found in Table 9. For

detailed information on the contained information elements

please refer to [3.]

Message type: SETUP

Significance: global

Direction: both

Information elementReference

(subclause)Direction Type Length

Protocol discriminator 4.2 Both M 1

Call reference 4.3 Both M 2-*

Message type 4.4 Both M 1

Sending complete 4.5 Both O (Note 1) 1

Bearer capability 4.5 Both M (Note 2) 6-8

Channel identification 4.5 Both M 3-*

Network specific facility 4.5 Both O (Note 3) 2-*

Display 4.5 n u O (Note 4) (Note 5)

Keypad facility 4.5 u n O (Note 6) 2-34

Calling party number 4.5 Both O (Note 7) 2-*

Calling party subaddress 4.5 Both O (Note 8) 2-23

Called party number 4.5 Both O (Note 9) 2-*

Called party subaddress 4.5 Both O (Note 10) 2-23

Transit network selection 4.5 u n O (Note 11) 2-*

Low layer compatibility 4.5 Both O (Note 12) 2-18

High layer compatibility 4.5 Both O (Note 13) 2-5

Table 9: Information elements for message type SETUP

Timers

In order to avoid deadlock situations, there are timers for nearly

every transaction started either in the ET as well as in the TE. If

a message is issued, the timer is started. If the appropriate

response is not received before the expiry of this timer, action is

taken independently. There are different timers for the network

side (ET) and for the user side (TE/NT2). A summary of these

timers on the network and on the user side is shown in Table 10

to Table 13.

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Timer

number

Time-out

value

State of

call

Cause for start Normal stop At the first

expiry

At the second

expiry

Cross-

reference

T301 Minimum 3

min

Call

received

ALERT

received

CONNECT received Clear call Timer is not

restarted

(Note 2)

T302 10-15 s(Note 5)

Overlapsending

SETUP ACKsent Receipt of

INFO, restarts

T302

With sendingcomplete indication,

or network alert, or

connect requestreceived

Clear if callinformation

determined to be

definitelyincomplete; else

send CALL

PROC

Timer is notrestarted

Mandatory

T303 4 s(Note 1)

Call present SETUP sent ALERT,CONNECT CALL

PROC or SETUP

ACK received, RELCOMPLETE

received if SETUP

sent on point-point

data link

RetransmitSETUP; restart

T303. If REL

COMPLETE hasbeen received,

clear the call

Clear networkconnection. Enter

call abort state

Mandatory

T304 20 s

(provisional

values)

Overlap

receiving

SETUP ACK

received.

Sending ofINFO restarts

T304

Send INFO; receive

CALL PROC,

ALERT orCONNECT

Clear the call Timer is not

restarted

Mandatory

only if

5.2.4implement

ed

T305 30 s Disconnectindication

DISC withoutprogress

indicator No. 8

sent

REL or DISCreceived

Network sendsREL


Mandatory

T306 30 s(Note 6)

Disconnectindication

DISC withprogress

indicator No. 8

sent

REL or DISCreceived

Stop thetone/announceme

nt. Send REL


Mandatorywhen

inband

tones/announcements

are

provided;see 5.4,

5.3.4.1,

andRec. I.300-

Series

T307 3 min Null SUSPENDACK sent

RES ACK sent Cleare thenetwork

connection.

Release call

identity


Mandatory

T308 4 s

(Note 1)

Release

request

REL sent REL COMPLETE

or REL received

Retransmit REL

and restart T308

Place B-channel

in maintenance

condition Releasecall reference

(Note 9)

Mandatory

T309 90 s Any stablestate

Data linkdisconnection.Calls in stable

states are not

lost

Data linkreconnected

Clear networkconnection.Release B-channel

and call reference


Mandatory

T310 10 s

(Note 7)

Incoming

CallProceeding

CALL PROC

received

ALERT,

CONNECT or DISCreceived. If DISC,

retain cause and

continue timing

Clear call in

accordance with5.2.5.3

Timer is not

restarted

Mandatory

Table 10: Timers on the network side (1)

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Timer

number

Defaut

time-out

value

State of

call


expiry

At the second

expiry

Cross-

reference

T312 T303 + 2 s CallPresent,

Call Abort,etc.

SETUP sent orresent on

broadcast datalink

Timeout (Note 4) Timer is notrestarted

Mandatory

T314 4 s Receivingsegmented

message

Messagesegment

received

Last messagesegment received

Discard message Timer is notrestarted

Mandatorysee

Annex H

T316 2 min Restartrequest

RESTART sent RESTART ACKreceived

RESTART maybe retransmitted

several times

RESTART maybe retransmitted

several times

Mandatorywhen 5.5 is

implement

ed

T317 (Note 3) Restart RESTARTreceived

Internal clearing ofcall references

Maintenancenotification


Mandatorywhen 5.5 is

implement

edT320 30 s

(Note 8)

a)

For B-

channelaccess:

active

b)For D-

channel

access: null

a)

For B-channel

access:connection

b)For D-

channel access:DL-ESTAB-

LISHMENT

Confirmation orDL-ESTAB-

LISHMENT

indicationreceived

c)

Last logical

channel, clearedreceived

Call request packet

received; or

incoming call packetdelivered; or DISC

received; or for D-

channel access DL-RELEASE

indication received

a)

For B-channel

access: disconnectlink layer and

initiate clearing

b)For D-channel

access: send DL-

RELEASErequest

Timer is not

restarted

Optional.

See 6.3

T321 30 s Any call

state

D-channel

failure

Response to layer 3

message received

Send DL-ESTAB-

LISHMENTrequest on both D-

channels

Timer is not

restarted

Mandatory

whenAnnex is

implement

ed

T322 4 s Any all

state

STATUS ENQ

sent

STATUS DISC

REL or REL

COMPLETE

received

STATUS ENQ

may be

retransmitted

several times

STATUS ENQ

may beretransmitted

several times

Mandatory

when5.8.10 is

implement

ed

NOTES

1 This default value assumes the use of default values at layer 2 (i.e. N200 + 1] times T200). Whether these values should be modified

when layer 2 default values are modified by an automatic negotiation procedure is for further study.2 The network may already have applied an internal alerting supervision timing function; e.g. incorporated within call control. If such a

function is known to be operating on the call, then timer T301 is not used.

3 The value of this timer is implementation dependent but should be less than the value of T316.4 If in the call abort state, the call reference is released. Otherwise, no action is taken on expiry of timer T312.

5 The value of timer T302 may vary beyond these limits, e.g. as a result of called party number analysis.

6 The value of timer T306 may depend on the length of the announcement.7 The value of timer T310 may be different in order to take into account the characteristics of a private network.

8 This value may vary by network-user agreement.

9 The restart procedures contained in 5.5 may be used on B-channels in the maintenance condition.

Table 11: Timers on the network side (2)

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146 EN/LZT 123 1207 R1A

Timer

number

Defaut

time-out

value

State of

call


expiry

At the second

expiry

Cross-

reference

T301 Minimum 3

min.

Call

Delivered

ALERT

received

CONNECT received Clear call Timer is not

restarted

Mandator

y whenAnnex D

is imple-mented

(Note 3)

T302 15 s Overlapreceiving

SETUP ACKsent Restart

when INFO

received

INFO received withsending complete

indication; or

internal alerting; orinternal connection;

or a determination

that sufficientinformation has

been received

Clear if callinformation

determined to be

incomplete; elsesend CALL

PROC


Mandatory only if

5.2.4 is

imple-mented

T303 4 s

(Note 1)

Call

Initiated

SETUP sent ALERT (Annex D),

CONNECT

(Annex D), SETUPACK, CALL PROC

or RELCOMPLETE

received

Retransmit

SETUP; restart

T303. If RELCOMPLETE was

received, clear thecall (Annex D)

Clear internal

connection. Send

RELCOMPLETE.

Enter Null state

Mandator

y when

Annex Dis imple-

mented;otherwise

optional

T304 30 s Overlap

Sending

INFO sent

Restarted whenINFO sent again

CALL PROC,

ALERT,CONNECT or DISC

received

DISC sent Timer is not

restarted

Optional

T305 30 s DisconnectRequest

DISC sent REL or DISCreceived

REL sent Timer is notrestarted

Mandatory

T308 4 s

(Note 1)

Release

request

REL sent REL COMPLETE

or REL received

Retransmit REL;

and restart T308.

B-channel is

placed in

maintenancecondition. Call

reference released(Note 5)

Mandator

y

T309 90 s Any stablestate

Data linkdisconnection.

Calls in stable

states are notlost

Data linkreconnected

Clear internalconnection. Release

B-channel and call

reference


Optional

T310

(Note 4)

30-120 s Outgoing

CallProceeding

CALL PROC

received

ALERT,

CONNECT,DISC, or

PROGRESS

received

Send DISC Timer is not

restarted

Mandator

y whenAnnex D

is

implemented

T313 4 s

(Note 1)

Connect

request

CONNECT sent CONNECT ACK

received

Send DISC Timer is not

restarted

Mandator

y

T314 4 s Receiving

SegmentedMessage

Message

segmentreceived

Last message

segment received

Discard message Timer is not

restarted

Not

initiallyrequired

T316 2 min Restart

Request

RESTART sent RESTART ACK

received

RESTART may be

retransmitted severaltimes

RESTART may

be retransmittedseveral times

Mandator

y when5.5 is

implement

ed

T317 (Note 2) Restart RESTARTreceived

Internal clearingof call reference

Maintenancenotification


Mandatory when

5.5 is

implemented

T318 4 s Resume

Request

RES sent RES ACK or RES

REJ received

Send RELEASE

message with

cause No. 102

Timer is not

restarted

Mandator

y when

5.6 isimplement

edTable 12: Timers on the user side (1)

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EN/LZT 123 1207 R1A 147

Timer

number

Defaut

time-out

value

State of

call

Cause for start Normal stop At the first expiry At the second

expiry

Cross-

reference

T319 4 s SuspendRequest

SUSPEND sent SUSPEND ACKor SUSP REJ

received

Enter Active state.Notify user

application


Mandatory when

5.6 isimplement

ed

T321 30 s Any call

state

D-channel

failure

Response to layer

3 messagereceived

Send DL-ESTAB-

LISHMENT requeston both D-channels

Timer is not

restarted

Mandator

y whenAnnex F

is

implemented

T322 4 s Any call

state

STATUS ENQ

sent

STATUS, DISC,

REL, REL

COMPLETEreceived

STATUS ENQ may

be retransmitted

several times

STATUS ENQ

may be

retransmittedseveral times

Mandator

y when

5.8.10 isimplement

ed

NOTES

1 This default value assumes the use of default values at layer 2, i.e. [N200 + 1] times T200. Whether these values should be modifiedwhen layer 2 default values are odified by an automatic negotiation procedure is for further study.

2 The value of this timer is implementation dependent, but should be less than the value of T316.2 The user may already have applied an internal alerting supervision timing function, e.g. incorporated within call control. If such a

function is known to be operating on the call, then timer T301 is not used.

3 T310 is not started if progress indicator 1 or 2 has been delivered in the CALL PROCEEDING message or in a previous PROGRESSmessage.

5 The restart procedures contained in 5.5 may be used on B-channels in the maintenance conditions.

Table 13: Timers on the user side (2)

Traffic cases

In order to give some help for the understanding of the

principles of DSS1 signaling some traffic cases are shown in thefollowing figures. To provide a better overview, not all timers

and all possible actions are shown. The timers shown always

belong to the network element to their left.

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148

EN

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1231207R1A

TE AET BET A

Off hook SETUP

SETUPACKdial toneT302

some digits INFO

T302

missing digits INFO SETUP

ALERTALERT

T302

ringing tone (2 )

(1) T304 is started on the TE and is not shown in the following diagrams(2) At this time, the B-Channel is switched through

SETUP

T303

CONNCONN

CONN ACK CONN ACK

FAC AOC

conversation

display of

charging info

T304 1

T304

T304

Successful call attempt

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EN/LZT

1231207R1A

149

TE A ET BET A

Off hook SETUP


some digits INFO

T302

missing digits INFO SETUP

ALERTALERT

T302

ringing tone (2)

(1) T301 expiery before T303 expiery

SETUP

T303

RELDISC

REL REL COM

REL COM

T304 1

T304

T304

Unsuccessful call attempt (B-subscriber not responding

T3031T301 1

T305 T308

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150

EN

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1231207R1A

(1) ETS 300-102 recommends that the call should be cleared on second expiery of timer T303

TE A ET BET A

Off hook SETUP


some digits INFO

T302

missing digits INFO SET

SET

T303

SET

DISC REL

REL ACK

busy tone

T303

RE

T305

REL

Unsuccessful call attempt (B-subscriber busy)

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EN/LZT

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151

TE A ET BET A

CALL PROC

D3-CONNECTrequest

SETUP SETUP

(1) a direct connection without ALERT indication is set up for example between two comp

CONNCONN

T303

Successful call attempt (direct connect 1)

CONN ACK

D3-CONNECTconfirm

CONN A

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EN

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1231207R1A

TE A ET BET A

on hook DISC DISC

REL COM

T305

REL

T308

REL

REL COM

Release

call reference

Normal call release

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EN/LZT 123 1207 R1A 153

References:

[1.]ETS 300 011-1

Integrated Services Digital Network (ISDN)

Primary rate User-Network Interface (UNI)

Part 1: Layer 1 specification

[2.]ETS 300 125


User-network interface data link layer specification

Application of CCITT Recommendations Q.920/I.440 and

Q.921/I.441

[3.]ETS 300 102-1


User-network interface layer 3 Specifications for basic call

control

[4.]ITU-T Recommendation Q. 931

Digital Subscriber Signalling System No. 1 (DSS1)

User-network interface layer 3

Specifications for basic call control

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