Flex Abis

Flex Abis Feature Parameter Description

Copyright Huawei Technologies Co., Ltd. 2010. All rights reserved.

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The information in this document is subject to change without notice. Every effort has been made in the preparation of this document to ensure accuracy of the contents, but all statements, information, and recommendations in this document do not constitute the warranty of any kind, express or implied.

Huawei Proprietary and Confidential Copyright Huawei Technologies Co., Ltd

BSS Flex Abis Contents

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Contents 1 Introduction ................................................................................................................................1-1

1.1 Scope ............................................................................................................................................ 1-1 1.2 Intended Audience ........................................................................................................................ 1-1 1.3 Change History.............................................................................................................................. 1-1

2 Overview of Flex Abis ..............................................................................................................2-1

3 Technical Description ..............................................................................................................3-1 3.1 About This Chapter........................................................................................................................ 3-1 3.1 Networking Configuration.............................................................................................................. 3-2 3.2 Establishment of Transmission Link.............................................................................................. 3-2 3.3 Algorithm for Half-Rate Channel Allocation Triggered by Abis Overload ...................................... 3-3

3.3.1 Abis Timeslot Allocation for the TCH .................................................................................... 3-3 3.3.2 Abis Timeslot Allocation for the PDCH ................................................................................. 3-4 3.3.3 Abis Resources of the PS Service Preempted by the CS Service....................................... 3-4

4 Engineering Guidelines...........................................................................................................4-1 4.1 Configuration of the Cascaded BTSs............................................................................................ 4-1 4.2 Configuration of BTS combined cabinets and cabinet groups ...................................................... 4-1 4.3 Other Suggestions on the Configuration....................................................................................... 4-1

5 Parameters .................................................................................................................................5-1

6 Counters......................................................................................................................................6-1

7 Glossary ......................................................................................................................................7-1

8 Reference Documents .............................................................................................................8-1

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1 Introduction 1.1 Scope This document describes the Flex Abis networking, establishment of Abis transmission links, and algorithm for half-rate channel allocation triggered by Abis overload.

1.2 Intended Audience This document is intended for:

z Personnel who need to understand Flex Abis z Personnel who work with Huawei products

1.3 Change History This section provides information on the changes in different document versions.

There are two types of changes, which are defined as follows:

z Feature change: refers to the change in the Flex Abis feature of a specific product version. z Editorial change: refers to the change in wording or the addition of the information that was not

described in the earlier version.

Document Issues The document issues are as follows:

z 02(2009-09-30) z 01(2009-06-30)

02 (2009-09-30) This is the second commercial release of GBSS9.0.

Compared with issue 01 (2009-06-30) of GBSS9.0, the following changes are incorporated:

Change Type Change Description Parameter Change

Feature change

None. None.

Editorial change

The structure of the document isoptimized.

None.

01 (2009-06-30) This is the first commercial release of GBSS9.0.

Compared with issue 01 (2009-04-30) of GBSS8.1, issue 01 (2009-06-30) of GBSS9.0, the following changes are incorporated:

1 Introduction BSS

Flex Abis

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Change Type Change Description Parameter Change

Feature change

3.3 Algorithm for Half-Rate Channel Allocation Triggered by Abis Overload is optimized.

The added parameters are listed as follows: z LDR First z LDR Second z LDR Third z LDR Fourth

Editorial change

The structure of the document isoptimized.

None.

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2 Overview of Flex Abis In an actual network, not all the BTSs or cells are busy and not both the PS and CS services have a high traffic volume at a specific time. Generally, if the load of one BTS is heavy, the load of other BTSs is light; if the traffic volume of the PS service is high, that of the CS service is low, and vice versa. Flex Abis (Flexible Abis) enables the sharing of the Abis interface transmission resources among different BTSs, cells, and services, and thus improves the resource utilization. Flex Abis is a mode of allocating the Abis interface transmission resources. That is, the Abis interface transmission resources form a resource pool that is shared by the CS service and PS service (including idle timeslots) among different cells and BTSs.

The Abis interface transmission resources can be used more effectively when Flex Abis applies to the following cases:

z Multi-cell large-capacity BTSs z Cascaded BTSs z EGPRS capable cells

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3 Technical Description 3.1 About This Chapter The transmission resources over the Abis interface can be allocated either fixedly or dynamically.

z Fixed allocation mode In fixed allocation mode, the channels over the Um interface (including the TCH and static PDCH) are always mapped with the Abis interface transmission resources. That is, the Abis interface transmission resources are occupied even when the Um interface channels are idle.

z Dynamic allocation mode In dynamic allocation mode, the Abis interface transmission resources form a pool. The Abis interface transmission resources are allocated to the Um interface channels only when the channels are occupied. Thus, the Um interface channel resources can be much more abundant than the Abis interface transmission resources, and the Abis interface transmission resources can be fully utilized in different time slices. Flex Abis features the dynamic allocation of Abis interface transmission resources, which improves the utilization of the resources, as shown in Figure 3-1.

Figure 3-1 Working principle of Flex Abis

The Flex Abis resource pool consists of all the Abis interface transmission resources, excluding the static PDCH, semipermanent connection timeslots, monitoring timeslots, signaling link timeslots, Abis transmission timeslots in fixed allocation mode, and idle timeslots. The Flex Abis resource pool is shared by the CS service and PS service (including the idle timeslots) among different cells and BTSs.

The timeslots in the Flex Abis resource pool are allocated to the TCH and PDCH. The full-rate TCH and PDCH are allocated 16 kbit/s timeslots; whereas the half-rate TCH is allocated the 8 kbit/s timeslot. For details, see Channel Management Parameter Description and GPRS/EGPRS Channel Management

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Parameter Description. When the transmission resources are insufficient, the CS service can preempt the timeslots of the PS service.

You are advised to enable Flex Abis in the following scenarios to make better use of the Abis interface transmission resources.

z Transmission resources are limited, and the rent for them is very high, for example, in satellite transmission mode.

z The traffic volume in actual situation is far lower than that in the channel resource planning. z The cells that share Abis interface transmission resources have different traffic peak hours. z The proportion of PS service users in the cell is high.

3.1 Networking Configuration The BSC supports the networking mode of multi-level Flex Abis resource pools among cascaded BTSs.

As shown in Figure 3-2, Link1, Link2, and Link3 correspond to the Abis interface transmission links between the BSC and BTS0, between BTS0 and BTS1, and between BTS1 and BTS2 respectively. The transmission over the Abis interface is realized through satellite or one or more E1/T1 cables.

The transmission resources on each Abis interface transmission link form a resource pool for the CS service and PS service to share.

z The transmission resources on Link1 form Pool0. The resources in Pool0 can be shared by the CS service and PS service on BTS0, BTS1, and BTS2.

z The transmission resources on Link2 form Pool1. The resources in Pool1 can be shared by the CS service and PS service on BTS1 and BTS2.

z The transmission resources on Link3 form Pool2. The resources in Pool2 can be shared by the CS service and PS service on BTS2.

Figure 3-2 Flex Abis network topology

3.2 Establishment of Transmission Link If Flex Abis is enabled, the BSC must allocate the Abis interface transmission resources and establish a transmission link between the BSC and the BTS.

When a channel on BTS2 is allocated, the BSC must dynamically allocate the Abis interface transmission resources to Link1, Link2, and Link3 for the channel, and instruct BTS0, BTS1, and BTS2 to establish transmission links for the channel, as shown in Figure 3-3. Therefore, the Extended Signaling Link (ESL) must be configured for each Flex Abis capable BTS to carry the signaling. In 64



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kbit/s multiplexing mode, the ESL and Operation and Maintenance Link (OML) must be physically multiplexed on the same 64 kbit/s E1 timeslot. To increase the number of ESLs, you are advised to reduce the number of Radio Signaling Links (RSLs) multiplexed with the OML to two by setting the parameter Multiplexing Mode.

Figure 3-3 Working principle of Flex Abis

The configuration principles of Multiplexing Mode are as follows:

z Generally, the parameter Multiplexing Mode is set to 4:1. When Flex Abis is enabled, the parameter Multiplexing Mode can be set to 5:1 or 6:1 to multiplex five or six RSLs onto one 64 kbit/s timeslot without occupying another 64 kbit/s timeslot.

z During the initial configuration of a BTS, set Flex Abis Mode to FLEX_ABIS(Flex Abis) or SEMI_ABIS(Semisolid Abis) to enable Flex Abis.

After the BTS configuration is complete, set Flex Abis Mode to FLEX_ABIS(Flex Abis) or SEMI_ABIS(Semisolid Abis) to enable Flex Abis, if required.

3.3 Algorithm for Half-Rate Channel Allocation Triggered by Abis Overload 3.3.1 Abis Timeslot Allocation for the TCH Generally, the resources in the Flex Abis resource pool are allocated to the TCH according to its type. The allocation principles are as follows:

z For a full-rate TCH, the 16 kbit/s Abis timeslot is allocated. z For a half-rate TCH, the 8 kbit/s Abis timeslot is allocated.

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After Flex Abis is enabled, the Abis interface may experience insufficiency in transmission resources prior to the Um interface. In such a case, the half-rate channel allocation is triggered according to the load of the Abis interface transmission resources to increase the success rate of access.

When the proportion of the remaining Abis resources to the total Abis resources is smaller than Congestion remain ratio, the system allocates half-rate channels to newly-accessed MSs if PSDOWN(PS Downspeeding) load control is applied. If CSFHHO(CS TCHF-TCHH HO) load control is applied, the system hands the MSs on the full-rate channels over onto the half-rate channels. In this manner, more MSs can gain access to the network, thus increasing usage efficiency of transmission resources.

When the Abis resource usage drops below the congestion threshold, the system stops PSDOWN(PS Downspeeding) and CSFHHO(CS TCHF-TCHH HO) load control.

Congestion threshold is set for controlling usage of the transmission bandwidth. When the threshold is reached, the following methods of load control can be applied. z PSDOWN(PS Downspeeding): PS service rate decrease z CSPH(CS Preference TCHH): Allocation of half-rate channels to newly-accessed MSs requesting CS services z AMRC(AMRC): Limited AMR rate for MSs in CS services z CSFHHO(CS TCHF-TCHH HO): Handover of MSs in CS services from the full-rate channel to the half-rate channel The execution sequence of PSDOWN(PS Downspeeding), AMRC(AMRC), CSPH(CS Preference TCHH), and CSFHHO(CS TCHF-TCHH HO) is specified by the parameters LDR First, LDR Second, LDR Third, and LDR Fourth.

When all the Abis interface transmission resources are occupied, the new CS service can preempt the Abis interface transmission resources of the PS service. For details, see Abis Resources of the PS Service Preempted by the CS Service.

3.3.2 Abis Timeslot Allocation for the PDCH After Flex Abis is enabled, the transmission resources of the PS service are allocated in the following ways to improve the utilization of transmission resources:

z The BSC allocates a primary link on a per 16 kbit/s sub-timeslot basis. z The BSC dynamically allocates secondary links in steps of 16 kbit/s according to the required coding

rate of the Um interface.

After Flex Abis is enabled, the Abis interface transmission resources can be dynamically allocated without configuring the static PDTCH and Idle TS Count if the actual traffic volume is far lower than the estimated value in network planning. That is, the primary link and secondary link are dynamically allocated to the PS service.

If the traffic volume of the PS service remains low, the configuration of static PDTCH and Idle TS Count is not required. When the CS traffic is heavy, all Abis interface transmission resources may be occupied. In this case, no Abis resource is available for the subsequent PS service. Therefore, when the CS traffic is heavy, some static PDTCHs should be reserved. In addition, the parameter Idle TS Count should be configured to preserve dedicated timeslots for the PS service so that the GPRS or EGPRS service can still be normally processed.

3.3.3 Abis Resources of the PS Service Preempted by the CS Service The CS service and PS service share the Abis interface transmission resources. The CS service can preempt the resources of PS service on the secondary link (or even the primary link when necessary) in the same-level and lower-level BTSs.



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In built-in PCU configuration mode, you are advised to set Sublink Resources Preemption Switch and Low-level Sublink Resource Preempt Switch to Yes to allow the CS service to preempt the transmission resources of the PS service on the secondary link in the same-level or lower-level BTSs.

In external PCU configuration mode, you are advised to set PCU Support PREEMPT_ABIS_LINK Message to Support to allow the CS service to preempt the transmission resources of the PS service if the PCU supports the processing of the PREEMPT_ABIS_LINK message.

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4 Engineering Guidelines 4.1 Configuration of the Cascaded BTSs z If a cascaded BTS is expected to support Flex Abis, the parameter Flex Abis Mode of the upper-level

BTS must be set to Flex Abis. z If the parameter Flex Abis Mode of a cascaded BTS is set to SemiSolid, Flex Abis Mode of all the

lower-level BTSs must be set to SemiSolid. z The master cabinet group of the level 1 BTS is connected to the EIUa only through the E1 port of the

master cabinet group. The slave cabinet group of the level 1 BTS is cascaded to the EIUa through the internal connections of the master cabinet group or is directly connected to the EIUa through the E1 port of the slave cabinet group.

z The BTSs are cascaded only through the E1 ports of the master cabinet group. The slave cabinet group is cascaded with the upper-level BTS only through the master cabinet group. The slave cabinet groups in the same BTS cannot be cascaded.

z Each BTS is cascaded with only one upper-level BTS. One BTS cannot be connected to an upper-level BTS and a EIUa at the same time.

4.2 Configuration of BTS combined cabinets and cabinet groups For the combined cabinets or cabinet groups of the double-transceiver BTS and the BTS that does not support Flex Abis, the suggestions on the configuration are as follows:

z The parameter Flex Abis Mode of the Abis interface between the double-transceiver BTS and the BTS that does not support Flex Abis or between the two BTSs that do not support Flex Abis should be set to Fix Abis.

z The parameter Flex Abis Mode of the Abis interface between the double-transceiver BTS and the BSC or between the double-transceiver BTSs should be set to Flex Abis or SemiSolid.

4.3 Other Suggestions on the Configuration For a Flex Abis enabled BTS, certain timeslots except the permanently allocated timeslots (such as signaling timeslots and monitoring timeslots) on E1 links can be disabled. These disabled timeslots can be used in other transmission modes (such as satellite transmission) or in scenarios where only a few timeslots on an E1 link can be used.

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5 Parameters This chapter describes the parameters related to Flex Abis.

For the meaning of each parameter, see Table 5-1. For the default value, value ranges, and MML commands of each parameter, see Table 5-2.

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Table 5-1 Parameter description (1)

Parameter Description

Multiplexing Mode

Timeslot multiplexing mode at the Abis interface of the BTS. The BTS supports two multiplexing modes: statistical multiplexing on a 64 kbit/s timeslot and physical multiplexing on a 16 kbit/s timeslot. The first mode is further classified into the following six types: 1:1, 2:1, 3:1, 4:1, 5:1, and 6:1. A BTS supports the following six types of timeslot objects: OML: operation and maintenance link of the BTS. Each BTS has only one OML. In the case of statistical multiplexing on a 64 kbit/s timeslot, the OML works at 64 kbit/s. In this case, the OML can be multiplexed only with the signaling links in the same cabinet group of the BTS. In the case of physical multiplexing on a 16 kbit/s timeslot, the OML works at 16 kbit/s. In this case, the OML uses a 16 kbit/s timeslot. ESL: extended signaling link of the BTS. If the BTS supports Flex Abis, in the case of statistical multiplexing on a 64 kbit/s timeslot, a 64 kbit/s timeslot needs to be assigned to the ESL. In this case, the ESL is always multiplexed with the OML in the 64 kbit/s timeslot. In the case of physical multiplexing on a 16 kbit/s timeslot, no timeslot is assigned to the ESL. In this case, the ESL shares the same timeslot with the OML. RSL: radio signaling layer link in each TRX. Each TRX has one RSL link. In the case of statistical multiplexing on a 64 kbit/s timeslot, the RSL link works at 64kbit/s. In this case, the RSL link can be multiplexed only with the signaling links in the same cabinet group of the BTS. In the case of physical multiplexing on a 16 kbit/s timeslot, the RSL link works at 16 kbit/s. In this case, the RSL link uses a 16 kbit/s timeslot exclusively. TCH: traffic channels in each TRX. The TCH works at 16 kbit/s. Idle: idle timeslots of the BTS. An idle timeslot works at 16 kbit/s. In the case of statistical multiplexing on a 64 kibt/s timeslot, the idle timeslots can be multiplexed only with the TCHs in the same cabinet group onto one 64 kbit/s timeslot. A 2048 Mbit/s E1 contains thirty-two 64 kbit/s timeslots. Timeslot 0 is reserved for synchronization and cannot be assigned. Statistical multiplexing means that signaling timeslots are time-division multiplexed in an E1 timeslot, such as the OML and RSL timeslots or the RSL timeslots. For example, in the case of 4:1 multiplexing, one 64 kbit/s timeslot multiplexes one OML and three RSL links or four RSL links of the BTS. The 64 kbit/s timeslot that multiplexes the OML has a multiplexing ratio of up to 4:1 even if the multiplexing ratio exceeds 4:1. HDLC and IP BTS is not support this parameter.



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Parameter Description

Flex Abis Mode

Service timeslot assignment mode for the BTS. If this parameter is set to FIX_16K_ABIS, the BSC assigns a fixed Abis transmission timeslot to a TCH. If this parameter is set to FLEX_ABIS, the BSC assigns an Abis transmission timeslot dynamically to a TCH (except the static PDCH) to increase the resource utilization. If this parameter is set to SEMI_ABIS, the BTS to which a TCH belongs assigns a fixed Abis transmission timeslot to the TCH while the upper-level BTS set to FLEX_ABIS assigns an Abis transmission timeslot dynamically to the TCH. This mode applies where old and new BTSs are cascaded. HDLC and IP BTS is not support this parameter.

LDR First First action taken for load control

LDR Second Second action taken for load control

LDR Third Third action taken for load control

LDR Fourth Fourth action taken for load control

Idle Ts Count

Number of idle timeslots. You can configure up to 128 idle timeslots for the BTS at a time. A BTS can be configured with up to 512 idle timeslots.

Sublink Resources Preemption Switch

This parameter specifies whether the CS services preempt the sublink resources of PS services.

Low-level Sublink Resource Preempt Switch

Whether to permit the preemption of lower-level sublink resources. If the value of this parameter is YES, a CS domain service can preempt the sublink resources of the PS domain services on the lower-level BTS of the cascaded BTSs when the CS domain service fails to preempt the sublink of the corresponding level.

PCU Support PREEMPT_ABIS_LINK message

Whether the PCU supports the PREEMPT_ABIS_LINK message. If the BTS supports the FLEXABIS function, the CS service can preempt the timeslots on the Abis interface used by the PS service. After the preemption occurs, the BSC sends a PREEMPT_ABIS_LINK message to the PCU if the PCU can process the message.

Congestion remain ratio Congestion remain ratio.


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Table 5-2 Parameter description (2)

Parameter Default Value GUI Value Range

Actual Value Range

Unit MML Command Impact

Multiplexing Mode MODE4_1

MODE1_1, MODE2_1, MODE3_1, MODE4_1, MODE5_1, MODE6_1, MODE16K

MODE1_1, MODE2_1, MODE3_1, MODE4_1, MODE5_1, MODE6_1, MODE16K None

ADD BTS(Optional) BTS

Flex Abis Mode

FIX_16K_ABIS

FIX_16K_ABIS(Fix Abis), FLEX_ABIS(Flex Abis), SEMI_ABIS(Semisolid Abis)

FIX_16K_ABIS, FLEX_ABIS, SEMI_ABISNone

ADD BTS(Optional) BTS

LDR First PSDOWN

CLOSE(Close), PSDOWN(PS Downspeeding), AMRC(AMRC), CSPH(CS Preference TCHH), CSFHHO(CS TCHF-TCHH HO)

CLOSE, PSDOWN, AMRC, CSPH, CSFHHO None

SET LDR(Optional) BSC

LDR Second AMRC






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Actual Default GUI Value MML Parameter Value Range Value Unit Impact CommandRange

LDR Third CSPH




LDR Fourth CSFHHO




Idle TS Count None 0~512 0~512 None

SET BTSIDLETS(Mandatory) BTS

Sublink Resources Preemption Switch NO

NO(No), YES(Yes) NO, YES None

SET GCELLSOFT(Optional) Cell

Low-level Sublink Resource Preempt Switch NO

NO(No), YES(Yes) NO, YES None

SET GCELLSOFT(Optional) Cell


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Actual Default GUI Value MML Parameter Value Range Value Unit Impact CommandRange

PCU Support PREEMPT_ABIS_LINK Message NO

NO(NO), YES(YES) NO, YES None

SET BTSFLEXABISPARA(Optional) BTS

Congestion remain ratio 15 0~100 0~100 per cent

ADD TRMLOADTH(Optional) BSC6900

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6 Counters For the counters, see the BSC6900 GSM Performance Counter Reference.

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7 Glossary For the acronyms, abbreviations, terms, and definitions, see the Glossary.

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8 Reference Documents z BSC6900 Feature List z BSC6900 Optional Feature Description z GBSS Reconfiguration Guide z BSC6900 GSM Parameter Reference z BSC6900 GSM MML Command Reference z BSC6900 GSM Performance Counter Reference

1 Introduction 1.1 Scope 1.2 Intended Audience 1.3 Change History 2 Overview of Flex Abis 3 Technical Description 3.1 About This Chapter 3.1 Networking Configuration 3.2 Establishment of Transmission Link 3.3 Algorithm for Half-Rate Channel Allocation Triggered by Abis Overload 3.3.1 Abis Timeslot Allocation for the TCH 3.3.2 Abis Timeslot Allocation for the PDCH 3.3.3 Abis Resources of the PS Service Preempted by the CS Service

4 Engineering Guidelines 4.1 Configuration of the Cascaded BTSs 4.2 Configuration of BTS combined cabinets and cabinet groups 4.3 Other Suggestions on the Configuration

5 Parameters 6 Counters 7 Glossary 8 Reference Documents