Transmission protection and interfacing in the synchronous local network

A description is given of methods for the practical and secure attachment of switching equipment to subscriber termination equipment using local synchronous distribution systems. The arrangement will include the use of counterrotating optical ring transmission systems with add and drop multiplexers at each node and the use of an intermediate interface. While the authors deal with the design aspects of the intermediate interface, the importance of an agreed higher bit rate standard interface within the exchange is stressed. It is shown that synchronous transmission techniques can be used to give very reliable, economical and flexible systems with integrated switching and transmission using a relatively small amount of equipment. This is provided that rigorous attention is given to protection, practical synchronization and the use of a suitable intermediate interface. The synchronous digital hierarchy virtual tributary mechanisms are very suitable for practical synchronous transmission. The use of an intermediate interface will allow the cost-effective connection of transmission and switching equipment of different manufacture