3G Media Gateway Software
for GSM Transcoder
© 2006 NOKIA
Author:
Mikko Mäkinen
Supervisor:
Professor Raimo Kantola
Instructor:
Lic.Sc. (Tech) Jyri Suvanen
1
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1.12.2006
Contents of the presentation
•
Objectives of the thesis
•
Speech transcoding in mobile networks
•
Role of TRAU (Transcoder and Rate Adaptation Unit) and MGW (Media
Gateway) 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 handling
basically the same task i.e. transcoding speech. However, their
development 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 Network’s 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 Station
BSC – Base Station Controller
TRAU – Transcoding and Rate
Adaptation 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 Telephone
Network
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 in
developed countries)
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Role of TRAU and MGW (2/3)
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 Support
Node
MGW – Media Gateway
•
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)
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Role of TRAU and MGW (3/3)
•
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 same
manufacturer)
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DSP HW/SW (1/2)
•
“Why to use specialized DSP hardware with processor specific Assembly
code when commercial off-the shelf processors have higher clock rates,
wider range of third party compilers/development tools/software/etc. and
support 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 competitive
and 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 in
small, 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 reprogram
the 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
software
►Use 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 to
their distinct functions and different historical background
However, today the functionality set of TRAU is almost an inclusive subset
of the corresponding MGW functionality set. Moreover, the MGW software
offers 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 but
nowadays unmanageable, error prone and stretched to its limits
• Not too optimized anymore, as the current version is only translated
version of the previous release (optimized for a different processor)
•
The MGW software has a more modern layered architecture (operating
system, 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 hardware
environments, although both units use the same DSP currently (Texas
Instruments’ TNETV3010)
•
However, Nokia could enhance its software development and maintenance
processes by reusing the more modern MGW software in TRAU unit. This
is possible, as also the Assembly code is portable between units due to the
same 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
• MGW’s dynamic resource control vs. TRAU’s static speech coding
channels
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Applying MGW software for TRAU environment
(2/2)
•
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•
Only few new modules
•
However, lots of little changes
and adjusting -> fiddly and
time consuming project
•
Only basic call through
functionality, O&M interface
ignored at this stage
Simplified picture of the new
Software
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Performance of the new Software
Average MIPS consumption of an EFR speech coding channel
70
•
Clear performance
advantage compared to
the old TRAU SW
•
Greatest difference in
actual speech codecs
(translated versus native
code)
•
Possibility to even
double the capacity!
60
First channel (with
fixed structures)
Additional channel
MIPS
50
40
Old TRAU SW
30
20
10
0
Platform
Serial Port
Forwarder
Others
Speech codec
Total
Module
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Conclusions
•
Separate GSM transcoder unit have markets for years, although larger
investments should be reconsidered thoroughly
•
The MGW software has clear performance advantage -> more handled
channels per unit or less needed DSP hardware capacity
•
Only minor changes needed for the new software -> possible to develop in
parallel with the main MGW software -> only one software to maintain
•
More flexible software for new features or other updates. AMR-WB is a
possible newcomer for GSM networks in the future.
•
Final product decisions not made yet, but used approach seems to be very
promising
•
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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•
•
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Thank You!
Questions/Comments?
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1.12.2006
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3G Media Gateway Software for GSM transcoder