Browse Prior Art Database

BANDWIDTH SAVINGS IN INTER-MSC LINKS VIA STATISTICAL MULTIPLEXING

IP.com Disclosure Number: IPCOM000009161D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-12
Document File: 2 page(s) / 125K

Publishing Venue

Motorola

Related People

Steve Aftelak: AUTHOR [+3]

Abstract

Currently, the European Telecommunications Standards Institute (ETSI) is working on creating a standard for Tandem Free Operation (TFO) for the European 2nd Generation Public Cellular mobile Communications system, GSM. This will signifi- cantly improve the quality of calls placed between 2 GSM mobiles by avoiding transcoding of speech in the network. This contrasts with the current practice where the network decodes encoded speech received from a mobile, only to re-encode it before sending it to the 2nd mobile. The implementation of TFO means that encoded speech is transported within the fixed part (core) of the GSM network, and it is this fact which facilitates the invention which is described. Initially the state of the art is described, in the context of TFO.

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Developments Technical 0 M MO-LA

BANDWIDTH SAVINGS IN INTER-MSC LINKS

VIA STATISTICAL MULTIPLEXING

by Steve Aftelak, Rob Davies and Graham Johnson

INTRODUCTION

  Currently, the European Telecommunications Standards Institute (ETSI) is working on creating a standard for Tandem Free Operation (TFO) for the European 2nd Generation Public Cellular mobile Communications system, GSM. This will signifi- cantly improve the quality of calls placed between 2 GSM mobiles by avoiding transcoding of speech in the network. This contrasts with the current practice where the network decodes encoded speech received from a mobile, only to re-encode it before sending it to the 2nd mobile. The implementation of TFO means that encoded speech is transported within the fixed part (core) of the GSM network, and it is this fact which facilitates the invention which is described. Initially the state of the art is described, in the context of TFO.

EFFICIENT UTILIZATION OF BANDWIDTH IN THE CORE NETWORK

  Cellular operators are beginning to include speech compression equipment in their core net- works to reduce the cost of leased lines between switching elements (MSCs). This involves the insertion of equipment between the MSCs (i.e. one at each MSC site in the simplest example of opera- tion) which encode speech and sub-multiplex the resulting low bit rate speech between the MSCs such that, for example, four speech channels can be accommodated in one 64kbps timeslot. The situa- tion is depicted in Figure 1. In this specific example it is possible to reduce the number of transmission links between the MSCs by as much as 75%. Clearly, the greater the speech compression, the greater the potential savings.

  In the context of TFO, it is feasible that in all cases (that is both mobile to mobile and mobile to/from PSTN calls), only coded speech would be transferred between the MSCs. Furthermore, only one transcoding (encode/decode) of the speech

should take place between the endpoints of commu- nication. In an ideal application of the technique, transcoding would only occur at the interface between the mobile network and an external net- work. In this context, external does not include a 2nd mobile network of the same type as the 1st. (For example it is assumed that two GSM networks transfer coded low bit rate speech between them which do not undergo any transcoding). The tech- nique to be described in the following extends this idea so that the bandwith savings can be extended even further.

NOVEL BANDWIDTH SAVING TECHNIQUE

  It is assumed that speech is transported in encoded low bit rate form throughout the mobile network, as noted above. This means that encoded speech is transferred between the Base Station Sub- system (BSS) and MSC in some framed format. In GSM, so-called TRAU frames are used. These frames contain, in addition to the coded speech, side information that includes synch...