(19)

(11)

EP 0 524 237 A1

(12)

(43) Date of publication: 27.01.1993 Bulletin 1993/04 (21) Application number: 91907680.0 (22) Date of filing: 10.04.1991

(51) International Patent Classification (IPC):  H03M 9/ 00( . ) H04B 14/ 04( . ) H04N 7/ 32( . ) H03M 13/ 00( . ) H04L 7/ 04( . ) H04N 7/ 62( . ) (86) International application number: PCT/GB1991/000569 (87) International publication number: WO 1991/015926 (17.10.1991 Gazette 1991/24)

(84) Designated Contracting States: AT BE CH DE DK ES FR GB GR IT LI LU NL SE (30) Priority: 10.04.1990 GB 19900008161 (71) Applicant: BRITISH TELECOMMUNICATIONS public limited company London EC1A 7AJ (GB)	(72) Inventors: COOK, Andrew Robert, John Clacton-on-Sea, Essex CO16 9AA (GB) FAULKNER, David Wynford Ipswich, Suffolk IP5 7RE (GB) (74) Representative: Semos, Robert Ernest Vickers, et al  BRITISH TELECOM PLC. Intellectual Property Unit 13th Floor 151 Gower Street London WC1E 6BA London WC1E 6BA (GB)