Abis Optim Dimensioning Rules Ed1

7/28/2019 Abis Optim Dimensioning Rules Ed1

1/10

Dimensioning rules for Abis optimiser in release B10

Alcatel-Lucent Date Edition Page07/07/2008 01 1

All rights reserved. Passing on and copying of this document, use and communication of its contents not permitted without written authorization.

Dimensioning rules for Abis optimiser

In Release B10


2/10




Contents

1. GLOSSARY .......................................................................................................3

2. REFERENCE......................................................................................................3

3. SCOPE............................................................................................................ 4

Notice of proprietary information...................................................................4

4. INTRODUCTION .................................................................................................5

5. APPLICATION CASES AND END-TO-END ARCHITECTURE .................................................. 6

6. BANDWIDTH AFTER OPTIMIZATION ..........................................................................8 6.1 Bandwidth gain brought by Abis optimisation.....................................................8

6.2 Overheads ............................................................................................... 9

6.3 Ultimate configuration per BTS site ................................................................9

Figures

Figure 1 : Abis optimization : application cases ..................................................................... 7

Figure 2 : Cell Site Optimiser for E1 optimisation ................................................................... 9

Figure 3: E1 optimisation: site configuration example 1 ......................................................... 10




3/10




1. GLOSSARY

2. REFERENCE

[REF 1] 3DC 21144 0063 TQZZA: Functional Feature Description Packet Transmission features inrelease B9

Abis nibble 16K timeslot (4 nibbles per 64K TDM timeslot)

CS

DSCP

Circuit Switched

DiffServ Code Point

GboIP Gb interface over IP

GE Gigabit Ethernet

GPRS General Packet Radio Service

GSM Global System for Mobile communications

MFS Multi-BSS Fast packet Server

PSQoS

Packet SwitchedQuality of Service

SGSN Service GPRS Support Node

TS Time Slot (64K TDM TS)


4/10




3. SCOPE

The present dimensioning guidelines gives detailed information about how to dimension theoptimized bandwidth on Abis interface.

These solutions are available as an option in the Alcatel-Lucent BSS B10 MR2, on top of any legacyBSS hardware.

Preliminary notice

The information contained in this document is subject to change without notice.

Notice of proprietary information

This document contains proprietary technical information belonging to Alcatel-Lucent. Byaccepting this material, the recipient agrees that this material will not be reproduced or used inwhole or part except as otherwise agreed between Alcatel-Lucent and the recipient.


5/10




4. INTRODUCTION

On the Abis interface, the reserved bandwidth (i.e. the number of TDM Timeslots) for the voicetraffic is over-dimensioned compared to the actual BTS traffic. This results in an additionalpossibility for the optimization of the Abis traffic, also called compression: only the real trafficis sent over the Abis. Idle radio timeslots do not consume transmission resources, and silences aresuppressed from the voice calls.

Chapter 5 describes the end-to-end architecture.

Chapter 6 provides bandwidth estimation on Abis with optimization over E1.

Thanks to optimization, the number of TDM timeslots required to backhaul Abis traffic isreduced: thus, the maximum number of TRX supported per site to fill up 1 E1 or 2 E1s(referred here as ultimate configuration) is increased. Ultimate configurations arereported in 6.3.


6/10




5. APPLICATION CASES AND END-TO-END ARCHITECTURE

Optimization in the BSS aims at reducing the transmission capacity needs for the backhauling of Mobile traffic, without any impact on legacy transport networks. It is nothing else but atransmission optimization, which is also completely transparent to the BSS.

Despite Alcatel-Lucent provides optimized usage of TDM Timeslots thanks to the Dynamic Abisfeature (see [REF 1]), the reserved bandwidth (i.e. the number of TDM Timeslots) for the Abistraffic is over-dimensioned compared to the actual BTS traffic:

- the statistical usage of the radio Timeslots (and as a consequence the one of TDMtimeslots) is not achieved for the voice traffic.

- the voice activity factor (i.e. the periods during which there is speech activitywithin a call) of the voice traffic is not handled.

This results in an additional possibility for the optimization of the Abis traffic, also calledcompression: only the real traffic is sent over the Abis. Idle radio timeslots do not consumetransmission resources, and silences are suppressed from the voice calls. The optimizationdepends on many factors, as detailed in Chapter 6, but an average value of 30% bandwidth savingsmay be retained.

As a consequence, the required number of TDM timeslots required to backhaul Abis traffic isreduced, allowing for several cases of network optimization, as described in figure below.


7/10




TDMTDM Aggregation AggregationMicroWaveMicroWave /LL)/LL)

BSCBSC

3- More sellable services

Add TRx without need of 2 nd E1

3- More sellable services

Add TRx without need of 2 nd E1

E1E1

2- Reduce Number of E1 at radio site

30% bandwidth reductionBTS 2E1 backhauling with single E1

2- Reduce Number of E1 at radio site

30% bandwidth reductionBTS 2E1 backhauling with single E1

1- Improved chainingcapabilities1- Improved chainingcapabilities

E1E1

(*) leased lines

Cell site optimizer

Aggregation gateway

Figure 1 : Abis optimization : application cases

The following typical application cases are :

1. optimization shall allow to chain 3 BTS instead of 2.

2. The optimization shall allow to reduce the number of E1 at base station site, from 2 E1 to1 E1. This provides significant transmission savings, especially in the case where chainingis not possible.

3. Optimization shall allow for a densification of the coverage (i.e. more TRx at a given radiosite) without the need to reinforce the transmission capacity needs.

End-to-End Architecture

The overall BSS architecture remains unchanged: the Abis flow are backhauled through a TDMnetwork, typically E1 Microwave or E1 leased lines.

Whatever the application case, the architecture relies on two equipments:

A Cell site optimizer, located at radio site,

An aggregation gateway, located in central sites (BSC, TC, MFS).

Both perform the same functions, but are made of a different hardware since they do not addressthe same traffic capacity. Optimization is fully transparent to the legacy BSS.


8/10




6. BANDWIDTH AFTER OPTIMIZATION

This chapter describes the principles of bandwidth dimensioning for Abis interface whenoptimization is activated.

Section 6.1 gives the principles used to derive the optimization gains.

Section 6.2 recalls the overheads that need to be taken into account in the finalbandwidth estimation

Section 6.3 summarizes the ultimate configurations per BTS site to come up with 1 E1.

6.1 Bandwidth gain brought by Abis optimisation

On the Abis interface, the bandwidth gain brought by the optimization is mainly accounted for bythe statistical usage for voice calls of Abis timeslots and the voice activity factor. Contrary tostatic mapping, this approach introduces a Grade of Service on Abis for voice. This GoScorresponds to an overflow once the call is established, mirroring the capability of the vocoder todeliver a good voice quality despite the lost packets. It does not introduce blocking. The overflowprobability is computed by a binomial law taking into account the maximum number of activetimeslots on the air interface and the voice activity factor. A maximum value of 2% for theoverflow is considered in the following.

The expected compression rate is highly sensitive to:

The Voice activity factor is linked to the number of simultaneous active calls at cell site.The denser the cell site activity, the lower the voice activity factor (better statisticaleffect).

Silence rate: ratio of silences during the call. This parameter depends among others onthe speech rhythm (which varies with the language of the speaker), the siteenvironmental noise (background noise reduces the probability to have silences in thecall).A value of 60%, accounting for both silence and activity factor is assumed here.

Data traffic ratio: compression applies to voice traffic, not data traffic. The compressionrate is all the more significant since the voice traffic ratio is high.

Note that the BTS load is supposed to be 100% in the optimization gains computed below. Forlower loads, the gain is expected to be higher.

The bandwidth gain is computed on the number of 64 kbps TS. It ranges from 20 to over 30% depending on the number of TRX on the site: the more TRX, the higher the optimization gain.


9/10




6.2 Overheads

The overall bandwidth must take into account overheads coming from

Signaling and unit management between the optimisation boxes.

E1 framing after optimisation

6.3 Ultimate configuration per BTS site

In case of E1 optimisation, the interest of the solution lies in a configuration where 2 outgoing E1are reduced to 1 (see Figure 2).

E1E1

InputNi 64K TS OutputNo 64K TS

Expected compression rate =f (voice activity factor, silence ratio, % data traffic,..)

E1E1

Figure 2 : Cell Site Optimiser for E1 optimisation

Computations based on the principles explained in 6.1 and 6.2 show that No is less than 31 TS if Niis less than 44 TS. Figures below give 3 examples of site configuration where 2 outgoing E1s arereduced to a single outgoing E1 thanks to the Abis optimizer.

Thanks to the optimisation solution, one site can host up to 18TRX and consume 1 E1bandwidth for Abis.


10/10




E1S222, 1 HR per cell, 3extra TS for EDGE

E1

900MHz

1800MHz

S222, 1 HR per cell, 3extra TS for EDGE

Figure 3: E1 optimisation: site configuration example 1

E1 E1

900MHz

1800MHz

S333, no HR, no EDGE

S333, no HR, no EDGE


S666, 1HR per cell, 2 extra TS

E1

E1


End of Document

Documents

Abis Optim Dimensioning Rules Ed1