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2006NOKIA 1 [email protected] 1.12.2006

3G Media Gateway Softwarefor GSM Transcoder

Author: Mikko Mkinen

Supervisor: Professor Raimo KantolaInstructor: Lic.Sc. (Tech) Jyri Suvanen

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Contents of the presentation

Objectives of the thesis

Speech transcoding in mobile networks

Role of TRAU (Transcoder and Rate Adaptation Unit) and MGW (MediaGateway) in GSM and 3G networks

Digital Signal Processing (DSP) Hardware and Software (HW/SW)

Comparing TRAU and MGW software

Applying MGW software for TRAU environment

Performance of the new software

Conclusions

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Objectives of the thesis

Problem:

Two separate network elements (TRAU and MGW) are handlingbasically the same task i.e. transcoding speech. However, theirdevelopment has been relatively independent in Nokia up to this date.

Methods: Study the roles of the TRAU and the MGW unit in current and future

network architectures Comparison of the MGW and the TRAU software Apply the MGW software in the TRAU hardware environment and

implement needed software parts Feasibility & performance study of the new software

Thesis was carried out in Nokia Networks Signal Processing System unit

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Speech transcoding in mobile networks

Radio frequencies are scarce and expensive resource

Speech encoding saves radio channels remarkably Traditional PCM (64kbit/s) versus HR (5.6kbit/s), FR (13kbit/s),

EFR(12.2kbit/s) and AMR-NR(4.75-12.2kbit/s)

Exploitation of the statistical characteristics of the human speech Short term correlation linear prediction

Long term correlation fundamental period of voiced sounds

Hybrid coders combination of waveform coders and vocoders

Compatible interconnections towards other wireless and wireline networks

usually implemented with PCM

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Role of TRAU and MGW (1/3)

MS Mobile Station

BTS Base Transceiver StationBSC Base Station Controller

TRAU Transcoding and RateAdaptation Unit

MSC Mobile Switching Station

GMSC Gateway MSC

VLR Visitor Location Register

HLR Home Location Register

AuC Authentication Centre

EIR Equipment Identity Register

PSTN Public Switched TelephoneNetwork

PLMN Public Land Mobile Network

TRAU is a part of the GSM access network

Handling FR/HR/EFR/AMR-NB to PCM conversion

Most of its new markets in developing countries (plus capacity updates indeveloped countries)

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MGW is a part of the 3G core network (Release4)

MGW handles only user plane traffic

Placed behind TRAU if co-operated with the GSM/EDGE access network Handling data type conversion (IP/ATM/PCM) in addition to the media format

conversion

Under active product development (new features + capacity updates)

RAN Radio Access Network

GERAN GSM/EDGE RAN

UTRAN UMTS Terrestrial RAN

CS Circuit Switched

PS Packet Switched

RNC Radio Network Controller

SGSN Serving GPRS Support Node

GGSN Gateway GPRS SupportNode

MGW Media Gateway

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Problem: Duplicate transcoders in 3G core/ GSM access network situation Expensive for the operator and multiple lossy transcodings decrease

the speech quality

Solution 1: Avoid tandem transcoding with end-to-end codec negotiation Tandem Free Operation (TFO) pack encoded bits inside 64kbit/s PCM

stream, no bandwidth savings Transcoder Free Operation (TrFO) send encoded bits directly over an

IP/ATM network, saves also bandwidth compared to 64kbit/s PCM Does not solve the problem of duplicate hardware units

Solution 2: Remove separate TRAU-unit, implement Ater-interface in MGW Cost efficient Dynamic allocation of 2G/3G transcoding capabilities Unfortunately Ater-interface is proprietary and thus this solution works

only in limited situations (access and core network from the samemanufacturer)

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DSP HW/SW (1/2)

Why to use specialized DSP hardware with processor specific Assemblycode when commercial off-the shelf processors have higher clock rates,

wider range of third party compilers/development tools/software/etc. andsupport for higher (more abstracted) programming languages(C/C++/Java..) that are easily ported for new hardware environments?

DSP processors are superior in certain application fields (price competitiveand computationally demanding functions) due to their special

characteristics Separate multiply-accumulate unit (e.g. for vector products) Multiple memory fetches within single clock cycle Fixed point arithmetic Special instruction sets Minimal and power consumption effective design

Skilled Assembly programmer can beat modern C-compilers anytime insmall, algorithm intensive tasks

Tenfold margin is not extraordinary

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DSP HW/SW (2/2)

However, modern transcoding units have new requirements for DSP SW

Size of the software has explode Dynamic functionality, lots of control oriented tasks

Shorter time-to-market cycles

Rapid hardware updates to increase capacity

It is not possible to design each new hardware from scratch and reprogramthe whole software for the new hardware

Use of common and modular hardware units

Separation of the hardware dependent software from others

Separation of the control oriented and the algorithm intensive pieces of

softwareUse of higher languages (mostly C) whenever its possible

Use of Assembly only when really needed!

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TRAU and MGW software comparison

The development of these units have been relatively independent due totheir distinct functions and different historical background

However, today the functionality set of TRAU is almost an inclusive subsetof the corresponding MGW functionality set. Moreover, the MGW softwareoffers several additional services such as the wideband AMR codec.

The whole TRAU software was originally written in Assembly although in

later releases some C-code was added -> simple and effective butnowadays unmanageable, error prone and stretched to its limits

Not too optimized anymore, as the current version is only translatedversion of the previous release (optimized for a different processor)

The MGW software has a more modern layered architecture (operatingsystem, drivers, platform, application) making it flexible, modular and

portable Even more detailed separation in application part, making it possible to

for example outsource the development of standard speech codecs

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Applying MGW software for TRAU environment(1/2)

Two similar products but both have distinct markets and hardwareenvironments, although both units use the same DSP currently (TexasInstruments TNETV3010)

However, Nokia could enhance its software development and maintenanceprocesses by reusing the more modern MGW software in TRAU unit. Thisis possible, as also the Assembly code is portable between units due to thesame processors.

Minimum target: same functionality and similar capacity

Possible problems in external interfaces: MGW SW has no support for direct serial port traffic that TRAU uses for

all user traffic

Operation & Maintenance (O&M) interface technically very different MGWs dynamic resource control vs. TRAUs static speech coding

channels

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Applying MGW software for TRAU environment(2/2)

Only few new modules

However, lots of little changesand adjusting -> fiddly andtime consuming project

Only basic call throughfunctionality, O&M interfaceignored at this stage

Simplified picture of the newSoftware

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Performance of the new Software

Clear performanceadvantage compared tothe old TRAU SW

Greatest difference inactual speech codecs(translated versus native

code)

Possibility to evendouble the capacity!

Average MIPS consumption of an EFR speech coding channel

0

10

20

30

40

50

60

70

Platform Serial Port

Forwarder

Others Speech codec Total

Module

MIPS

First channel (with

fixed structures)

Additional channel

Old TRAU SW

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Conclusions

Separate GSM transcoder unit have markets for years, although largerinvestments should be reconsidered thoroughly

The MGW software has clear performance advantage -> more handledchannels per unit or less needed DSP hardware capacity

Only minor changes needed for the new software -> possible to develop inparallel with the main MGW software -> only one software to maintain

More flexible software for new features or other updates. AMR-WB is apossible newcomer for GSM networks in the future.

Final product decisions not made yet, but used approach seems to be verypromising

Further study: Implementation of the O&M interface if green light shown

Future of the AMR-WB codec (in GSM networks)

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Thank You!

Questions/Comments?

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