These diagrams are from this .pdf file, The Speech Transcoding Frame 2000 for GSM Cellular Systems by Victoria Riggs, Robert C. Fairfield, and John Segura. (Copyright 2000 by Lucent Technologies, all rights reserved.)
http://www.lucent.com
This file will mention the TRAU, also known as a TransCoding Unit or TCU. It 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.
Pages: Table of Contents (1) (2) (3) (3A) (4) (5) (5A) (6) (7) (8) (9) (10) (11) (12) (13) (14)
