Abstract: A digital video network comprises a controller and network sites each coupled to the controller via communication paths. The network sites and controller include codecs for converting between encoded signals on the communications paths and video and audio signals in the network sites and in the controller. The controller also includes at least one unit for producing a quad split video signal from four video signals supplied thereto. The coders encode four audio signal channels and audio mixing control signals in each encoded signal. The decoder in each network site decodes the audio signal channels from the encoded signal which it receives, and is responsive to the control signal in the encoded signal to mix the decoded audio signal channels in a predetermined manner to provide a continuous audio presence at the network site, independently of whether or not the video signal in the encoded signal comprises the quad split video signal.

Abstract: A transmission system comprises nodes coupled in a ring via two multiplexed transmission paths having opposite transmission directions. The two paths can be time, space, or wavelength division multiplexed. Bidirectional communications between any two nodes are provided in normal operation using both paths around a first, most direct, part of the ring. In the event of a fault affecting such communications, a protection switch is made to maintain bidirectional communications between the two nodes using both paths around a second, remaining, part of the ring. In this manner, each path can simultaneously carry both normal and protection switched signals. In an embodiment of the invention, only the two nodes adjacent a fault need be aware of the fault, each of these nodes effecting a protection switch for signals terminated at the node and effecting a protective loopback for other signals needing protection. The invention enhances the total capacity of the paths for carrying normal and protection switched signals.