Telecommunications network including a channel switching protection arrangement

A telecommunications network of a type operating using Synchronous Digital Hierarchy (SDH) which includes a plurality of interconnected nodes in which working channels are defined between respective pairs of the nodes, and one common protection channel is provided to serve a plurality of the working channels, said network comprising:

• means for detecting a fault at a first node on a working channel passing traffic signals from a first node to a second node;
• and means for switching that working channel on to the protection channel, the first node being operative to transmit a channel trace signal along with the traffic signals which serves to identify the respective channel, the second node being operative to monitor for the presence of a channel trace signal on the protection channel for which it is the terminating node, and upon detection thereof, to switch traffic signals associated with that trace signal on the protection channel into the second node for connection to an onward destination, the protection channel being in the shape of a bi-directional channel ring, the first node being operative, in the event of a fault, to initially transmit traffic signals in both directions around the ring, the second node being operative to monitor each direction of the channel and to select traffic signals from one of the directions corresponding to the direction of the working channel.