Article written by John Scourias, with comments in maroon by Tom Farley
Pages: Table of Contents (1) (2) (3) (3A) (4) (5) (5A) (6) (7) (8) (9) (10) (11) (12) (13) (14)
Generic GSM architecture by Scourias / Lucent GSM architecture / Ericsson GSM architecture / Nokia architecture / Siemen's GSM architecture
Siemens' GSM Architecture
"The Global System for Mobile Communication (GSM) network is a cellular telecommunication network with a versatile architecture complying with the ETSI (European Telecommunication Standard Institute) GSM 900/GSM1800 standard. Siemens implementation is the digital cellular mobile communication system D900/1800/1900 that uses the very latest technology to meet every requirement of the standard."
"The Base Station Subsystem consists of the Base Transceiver Station (BTS), the Base Station Controller (BSC), the Transcoding and Rate Adaptation Unit (TRAU) and the Operation and Maintenance Center (OMC-B)."
"TRAU: Transcoding and Rate Adaptation Unit. The TRAU adapts the transmission speed of the digital voice and data traffic on the radio path to the standard speed of 64 kbit/s into the network. Complete redundancy of all boards ensures highest reliability. Furthermore, no hardware upgrades are necessary when features such as new speech codices are introduced."
The TRAU, also known as a TransCoding Unit or TCU, is a compressor and converter. It first compresses traffic coming from the mobiles through the base station controllers. That's quite an achievement because voice and data have already been compressed by the voice coders in the handset. Anyway, it crunches that data down even further. It then puts the traffic into a format the Mobile Switch can understand. This is the transcoding part of its name, where code in one format is converted to another. The TRAU is not required but apparently it saves quite a bit of money to install one. Here's how Nortel Networks sells their unit:
Reduce transmission resources and realize up to 75% transmission cost savings with the TCU.
The TransCoding Unit (TCU), inserted between the BSC and MSC, enables speech compression and data rate adaptation within the radio cellular network. The TCU is designed to reduce transmission costs by minimizing transmission resources between the BSC and MSC. This is achieved by reducing the number of PCM links going to the BSC, since four traffic channels (data or speech) can be handled by one PCM time slot. Additionally, the modular architecture of the TCU supports all three GSM vocoders (Full Rate, Enhanced Full Rate, and Half Rate) in the same cabinet, providing you with a complete range of deployment options.
The voice coders or vocoders are built into the handsets a cellular carrier distributes. The carrier specifies which rate they want traffic compressed, either a great deal or just a little. The cellular system is designed this way, with handset vocoders working in league with the equipment of the base station subsystem. To read more about PCM click here.
"SSS: Switching sub-system."
"SSP: Service Switching Point. The SSP comprises the switch related Intelligent Network functions (IN). Together with the IN SCP operator services like Prepaid, VPN and Personal Number Service are implemented."
http://www.siemens.com
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