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Ericsson Internal 2010-04-161

Abis Optimisation – Concept & Implementation

This ppt. consists of the following :-

1) Concept of Abis Opt.

2) Working of Abis Opt. ( B/W Savings )

3) Dimensioning tool used

4) Configuration DT and parameters .

5) Implementation in Idea Mumbai

- Scenarios tried .

- Problems faced and solutions .

- Counters to be activated .


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CONCEPT & PURPOSE OF ABIS OPTIMISATION :-

Abis optimization gives bandwidth utilization on the Abis interface. The BSS solution for Abis Optimization is based on that traffic and signalling on the Abis interface are sent as LAPD frames on SUPER CHANNELS instead of using dedicated timeslots.

Abis optimization feature achieves bandwidth savings by introducing the super channel concept. A super channel is one E1 link, or a fraction of one E1, where 64 kbit/s consecutive A bis timeslots can be used as a wideband connection for sending signaling and payload as LAPD frames between BSC and BTS. As all traffic and signaling share the same wideband connection, statistical multiplexing gains are achieved.

Optimization takes benefit of statistical multiplexing and removes redundant information on the Abis interface to optimize the bandwidth usage. This is achieved by, for example, removal of TRAU frames during silence speech periods and removal of spare bits in CS and PS frames.


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HOW ABIS OPTIMISATION WORKS ?

New Additions :- New concept of Super Channel as described in the previous slide . On the H/W end , there is addition of PGW ( Packet Gateway ) in BSC No new H/W addition on the BTS end .

What is a Super Channel ?

A SuperChannel (SC) can be perceived as a set of contiguous timeslots on a PCM link that terminate in one BTS port. The timeslots are used to create a single highspeed link using the HDLC protocol.

Similarly to the ordinary Digital Paths, there will be up to four SC’s possible to use per TG. The SCs going to one TG will be grouped in a Super Channel Group (SCGR).

Each TG MO can be connected to one SCGR and each TRXC MO can be connected to one SC (there can be several TRX’s connected to the same SC).

One of the SCs belonging to the TG will always be used by CF link (regardless if there’s TRXC connected to this SC or not). If the SC with CF link turns out to be faulty, the CF link will be moved to another SC.

SCGRs are numbered from 0-511 and the SCs from 0-3, thus to find the certain SC, its SCGR number must be also known.


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Super Channel :-

A SuperChannel (SC) can be perceived as a set of contiguous timeslots on a PCM link that terminate in one BTS port. The timeslots are used to create a single highspeed link using the HDLC protocol.SCs belonging to the TG will always be used by CF link hence isolatation or localization of CF/TRX signaling TS is not possible in this case.Bandwidth allocation is completely dynamic among mapped devices (RBLT & PGW devices).


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Dimensioning tool to be used :-Following are the inputs :-1) TRX count for the sectors , numreqegprsbpc , FPDCH and Control Channels ( SD + BCCH )2) VAF ( Voice Activity Factor ) , Pure HR and FR , AMR HR and FR for the site .3) Full rate AMR on 8 kbps Abis to be check-marked depending on whether the feature is enabled

or not .4) GPRS Bandwidth is decided on the following inputs :-

a) Taking the trend for the site’s data busy hour for some days b) FPDCH for the complete site multiplied by 64

Preferred input is the first one .for GPRS Bandwidth .While doing so , pls remember that for BSS07B there is no reservation of 64k on Abis . So correctSetting of this value is very important .

5) Abis Threshold Parameters :- SDAMRREDABISTHR , SDHRAABISTHR and SDFRMAABISTHR .

Dimensioning Tool for Abis Opt


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What is the Output for Dimensioning tool ?

How devices ( RBLT2 & RTPGD )are calculated .?

In abis opt , we are dealing with two device types – RTPGD ( from PGW ) and RBLT2 ( Abis )

RBLT2 Devices :-

From the dimensioning tool , we get the number of RBLT2 devices on which SEBU MBL

( Semi – Permanent ) connections are made .

Super channel ( RBLT2 devices ) is defined with the help of command :-

RRSCI:SCGR=TG no , SC=0 , DEV1=RBLT2 NUMBER , DCP=dcp number , NUMDEV = no of devices ;

RTPGD Devices :-

It is actually the RTPGD devices that reflect towards the RBS .

Signalling on radio with RTPGD devices is UNCONC , so devices need to be planned

accordingly .

RTPGD devices are allocated with the help of command :-

RXAPI : MO = RXOTG - ….., NUMDEV = no of devices ;


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ETC

PGw

GS

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

RTPGD

Superchannel definitionRRSCI:SCGR=.... ;Uses one set of PGw devices

RBLT

RBLT

RBLT

RBLT

RBS

Concen-trator

TRA

TRH

PGW device definitionRXAPI:MO=xxx,DEV=.... ;Uses another set of PGw devices.Devices used for 64k EDGE must be defined.(Only Logical, the actual data will be sent over the Ethernet backplane)

Ethernet backplane

GPH/

PCU

TG to Superchannel connectionRXMOC:MO=xxx,SCGR=.... ;

RTPGD

RTPGD

3 key definitions- RXAPI- RRSCI- RXMOC

PGw Device Connections for Abis Opt


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DT for Configuration :-Attached is the DT for Abis Opt done on one of the sites in Idea – Mumbai .

Important parameters on Abis Opt :- PACKALG – Package Algorithm to be kept 1 . SDHRAABISTHR - This parameter defines a threshold value for starting and stopping the allocation of AMR

HR and HR channels, in case of high transmission load on a TG. The allocation is stopped when the threshold value is set to 100%.

SDAMRREDABISTHR - This parameter defines a threshold value for starting and stopping the allocation of AMR FR channels with reduced codec set, in case of high transmission load on a TG. The allocation is stopped when the threshold value is set to 100%. The parameter is set per TG.

SDFRMAABISTHR -This parameter defines a threshold value for starting and stopping of move from FR to HR channels, including AMR, in case of high transmission load on a TG. The moving of channels is stopped when the threshold value is set to 100%. The parameter is set per TG.

ATHABIS & DAMRCRABIS to be kept ON in RLDAP command .

Microsoft Excel Worksheet


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Implementation in Idea – Mumbai :-

Following are the scenarios :-

There has been very exhaustive implementation for Idea – Mumbai of Abis Opt :-

1. High Traffic ( voice and data ) site with two E1’s

2. 2111 expanded site ( B sector split ) with single E1 in cascading .

3. 2111 expanded site ( B sector split ) with two E1’s ( on different TG’s )

4. Two different sites in cascading ( single E1 )

5. Abis Opt on site with two E1’s ( creating two super channels on same TG )

All these have been successfully implemented with huge B/W reduction seen .

In some cases with two E1’s , there has been saving of a complete E1 also .

5th case that has been mentioned was two super channels created on same

TG . For its implementaion , total TRX’s were divided in two sets and subsequent super channels

created .


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Problems faced and solutions :-

Implementation of 5th case i.e creation of second super channel on same TG gave the following

Fault code :-

RRSCI:SCGR=15,SC=1,DEV1=RBLT2-3777,DCP=287,NUMDEV=23;

NOT ACCEPTED

FAULT CODE 172

NO MORE SCS ALLOWED FOR THE TG DUE TO HARDWARE LIMIT

Solution :-

All RTPGD devices in PGW have to be in Idle state ( i.e properly in-service and de-blocked )

All the other cases were implemented with relatively greater ease .


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How Abis – Opt is monitored ( KPI’s and counters ) ?

Voice KPI’s :-

TCH & SD Drop

TCH & SD Blocking

TASR , TCH Congestion , HOSR , SQI

All have to be within the decided & agreed limits .

Data KPI’S :-

DL EDGE Throughput

DL GPRS Throughput

Total GPRS Data

Total EDGE Data

Total Data Transfer

Others :-

Super Channel Utilisation ( has to be always less than 70% ) . In case it case exceeds

re-dimensioning would be required .

Overloadrejcon - counts number of rejected new CS connections due to Abis overload per cell.

This counter is stepped when an attempt to allocate an idle TCH fails and Abis overload is indicated in the

cell. Object name is CLTCH .


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