Video services via 140 Mbit over SDH

As the new SDH standard becomes widely deployed, increasing numbers of optical transport services at 140 Mbit will be carried entirely or in part over 155 Mbit synchronous optical links. The mechanism of justifying frequency offsets within the SDH network introduces phase quanta at the point of exit for the 140 Mbit signal. Where this 140 Mbit line is carrying video services, excessive phase disturbance during justification events have been found to compromise colour sub carrier jitter standards, resulting in unacceptable video performance. This paper examines the origin of the phase quanta in the synchronous network and shows how this can give rise to phase disturbance in a video service. Desynchronisers are examined and results of a BNR desynchroniser control system are presented