abis optimization

Feature Description

Abis Optimization

New Feature in BSS 06A

11/22104-FGC 101 917 Rev B Ericsson AB 2005 2 Commercial in Confidence

FAJ 121 997, Abis Optimization

Feature identity: FAJ 121 997, R1, Rev. B

This feature is: OPTIONAL

Summary

Abis Optimization reduces the effective bitrate on the Abis interface between the BSC and the RBS, thus reducing bandwidth requirements and saving transmission costs. To achieve this bitrate reduction optimisation functions are used and a packet protocol is used over the traditional E1 or T1 circuits.

Benefits

The bitrate required on links between BSC and RBS is reduced.

Operator Value

Total Cost of Ownership

The feature offers the values of:

Reducing the leasing costs for Abis transmission

Avoiding re-dimensioning of transmission network at EDGE introduction and growth

Reducing investments in transmission network at traffic growth

The operator can reduce the amount of transmission used for an existing network, thereby saving leasing costs for existing sites:

Alternatively, the traffic volume can grow in the network without a need for additional transmission to the RBS sites. It would for example be feasible to increase the EGPRS traffic without touching the transmission network, or to create transmission capacity for a 3G deployment/growth.

Technical Description

This feature introduces functions to only transfer bits holding information, but no stuffing bits normally used to achieve a constant bitrate on the Abis interface.


The BSS solution for Abis Optimization is based on that traffic and signaling on the Abis interface are sent on common Super Channels, using a packet protocol, instead of using dedicated timeslots on the TDM transmission. A Super Channel is built of one E1 or T1 link, or a fraction of one E1 or T1, where 64 kbit/s consecutive Abis timeslots are used.

Savings are made by taking advantage of for instance:

silent periods (DTX)

idle channels

low MCSs for EGPRS channels

low CSs for GPRS channels

low voice codec rate for voice channels

statistical multiplexing between cells

The bitrate saving achieved is dependent on traffic mix, voice activity factor, amount of halfrate voice channels and RBS configuration. The exact saving has to be estimated per particular network. As an indication of the saving, for a 3*3 site with 60% halfrate, with AMR, 4 EPDCHs per cell and 40% silent frames the saving can be expected to be 25-30% compared to a system running BSS R12. The saving compared to BSS R10 would be around twice as much.

The features FAJ 122 287 Discontinuous Transmission (DTX) Downlink and FAJ 122 256 Discontinuous Transmission (DTX) Uplink should be used in order to take advantage of silent periods in ongoing calls. The silent periods are in many cases contributes a major part of the potential saving.

The transport network is not affected. The same leased E1/T1 or microwave links can be used as today, with the same network architecture, but with narrower links. Abis Optimization assumes that time slot integrity is provided by the transport network

TR

G

TR

ETBS

GP

n*E1/T1

RBS

DXU-21

dTRU dTRU

SW HW & SW

TRH

GS

TRA

ETBSC

GPH Ethernet backplane

PGW

The solution is based on an optimization function in the BSC and corresponding functionality in the RBS. The functionality is implemented in the packet gateway (PGW) in the BSC, whereas the functionality on the RBS side is running on the DXU/IXU and TRU.

The PGW is one or more devices in the BSC. The PGW handles speech, GPRS/EGPRS and signaling. The number of boards depends on the number of connected TRXs and the traffic mix. The same PGW can be used both for optimized Abis and Abis over IP.


The dimensioning of the Super Channels shall be done based on the actual traffic to be supported by an RBS (not the number of TRXs configured to carry traffic). A Super Channel serves one Transceiver Group (TG), and a TG can be served by up to four Super Channels. Optimization is done per TG.

When the load on a Super Channel has increased above an operator specified threshold the optional features FAJ 121 827 Full Rate AMR on 8 kbps Abis and FAJ 121 846 Abis Triggered HR Allocation can be triggered to reduce the payload on the Abis Super Channel. If an overload situation still occurs, Abis Optimization throws away speech and CS&PS data as a first choice. Signaling frames are prioritized. In case transmission on a Super Channel is suffering from continuous overload, the BSC reduces the load by reducing the number of new connections. During the overload, no new allocation of PDCH channels, channels for DTM or channels for HSCSD is made.

The operator is informed about an Abis overload situation via an alarm. This alarm is triggered when the BSC or BTS has started to discard frames due to buffer overflow. The Super Channel is considered overloaded as long as new connections are rejected for the TG.

For dimensioning purposes, it is possible to print the load level per Super Channel. The load level is in percent of total available bandwidth and shows the load level in 5 second intervals the last minute. The operator can also use STS counters to monitor the utilization of the Abis links to each base station in order to determine when new Abis resources need to be added, or when resources can be removed.

Network Impact

BSC HW Impact

Packet Gateway (PGW) boards are required in the BSC. The AXE 810 GEM magazine is required. NNRP4/NNRP5 can be used for expansion of BYB501/AXE10.

BTS HW Impact

dTRU based base stations are required for Abis Optimization.

BSS Characteristics

The functionality introduces a delay on Abis of up to 20 ms one way for voice paths. The delay is dependent on the size of the RBS and the traffic mix (number of EGPRS channels), and is in most common configurations below 15 ms.

The delay for GPRS and EGPRS channels is not affected.


Dependencies to other BSS features

The features FAJ 122 89 LAPD multiplexing and FAJ 122 067 LAPD concentration can not be used on RBSs that are using Abis Optimization, however the same task is performed by Abis Optimization.

FAJ 122 450 Flexible Abis can not be used on RBSs that are using Abis Optimization, however similar task is performed by Abis Optimization.

FAJ 121 618 Remote OMT with IP is supported, but not FAJ 122 345 Remote Operation and Maintenance Terminal

Dependencies to other network elements

None

Terminals

None

FAJ 121 997, Abis OptimizationSummaryBenefitsOperator ValueTotal Cost of Ownership

Technical DescriptionNetwork ImpactBSC HW ImpactBTS HW ImpactBSS CharacteristicsDependencies to other BSS featuresDependencies to other network elementsTerminals

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abis optimization

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