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Design and implementation of the operation and maintenance software for a new GSM transcoder - page 6 / 26

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© NOKIA6 paavo.markkola@nokia.com18.10.2005

Transcoders in GSM networks (1)

The GSM system features several codecs that are used in order to reduce the number of bits transferred over the radio interface

On the network side these codecs are implemented in Transcoding and Rate Adaptation Unit (TRAU)

The purpose of the TRAU is to

Transcode speech between the standard 64 kb/s PCM format and the encoded formats used on the GSM radio interface

Perform rate adaptation for data calls between 64 kb/s and limited bit rates on the radio interface

Speech codecs

Full Rate (FR) 16 kb/s

Half Rate (HR) 8 kb/s

Enhanced Full Rate (EFR) 16 kb/s

Adaptive Multirate (AMR) 16 kb/s

Bits rates for data calls

GSM data 9.6 kb/s

GSM data 14.4 kb/s

High Speed Circuit Switched Data (HSCSD) allows more than one channel to be used for the same connection, max 40 – 50 kb/s

Every call in a GSM network must eventually go through TRAU

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