Browse Prior Art Database

A MINIMUM DELAY CEPT INTERFACE

IP.com Disclosure Number: IPCOM000008020D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-13
Document File: 2 page(s) / 90K

Publishing Venue

Motorola

Related People

Kevan Hobbis: AUTHOR

Abstract

GSM Cellular systems utilize a number of net- work topologies to allow more than one BTS Lo be controlled from a BSC via a single 2.048Mbs CEPT line. This includes a daisy chain (shown in Figure 1) where a CEPT link is passed from one BTS to another. Each BTS extracts only the data that is nec- essary for itself and passes the rest onwards. The CEPT links are full duplex.

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MOTOROLA Technical Developments

A MINIMUM DELAY CEPT INTERFACE

by Kevan Hobbis

BACKGROND

  GSM Cellular systems utilize a number of net- work topologies to allow more than one BTS Lo be controlled from a BSC via a single 2.048Mbs CEPT line. This includes a daisy chain (shown in Figure
1) where a CEPT link is passed from one BTS to another. Each BTS extracts only the data that is nec- essary for itself and passes the rest onwards. The CEPT links are full duplex.

  The limit to the length of such a daisy chain is partly due to the delay through the CEPT relay stage of each BTS. The overall GSM delay budget for each speech channel must still be met even at the end of the chain. The addition of a second CEPT link so that there is one at both ends of the chain allows for redundancy and longer chains.

  Reduction in the delay through the CEPT switch would allow the chains to be lengthened fur- ther. The delay through the CEPT switch is limited by the converting of the data to binary from HDB3 and detecting frame alignment, passing the data through a switch etc. and is generally of the order of a number of CEPT frames.

DETAILED DESCRIPTION

  The block diagram in Figure 2 on next page shows the proposed implementation. The circuit transparently switches data from one CEPT line to another with a minimum of delay, but allowing insertion of timeslot data as required by the local equipment.

  Two CEPT lines are needed to support a daisy chain, A and B. Both have Data and Clock in and Data and Clock Out. The circuit shown would be duplicated twice to cross-over the two CEPT inter- faces when in daisy chain mode, but if d...