Patent ID: 6377542
Filing Date: 2002-04-23
Classification: H04J,H04L,H04Q

Abstract:
A synchronous digital hierarchy (SDH) based communications network, comprising:a) a plurality of data communications channels embedded within the communications network; b) a plurality of intermediate systems (IS) divided between at least one ISâ€”IS area and at least one non-ISâ€”IS area, said at least one ISâ€”IS area being an area within which a routing protocol, that forms a part of a network layer of an open systems interconnection (OSI), is provided for routing messages between the areas; c) a plurality of connections between said at least one ISâ€”IS area and said at least one non-ISâ€”IS area, the plurality of connections including at least one internal reachable address prefix (RAP) route and at least one external RAP route; and d) means for routing a message from an originating ISâ€”IS area to a destination IS within said at least one non-ISâ€”IS area via said at least one internal RAP route when one of the connections to the destination IS is broken within said at least one non-ISâ€”IS area, to cause the message to be returned from said at least one non-ISâ€”IS area to the originating ISâ€”IS area via said at least one internal RAP route, by making another connection to the destination IS by a further one of the plurality of connections between the originating ISâ€”IS area and said at least one non-ISâ€”IS area via said at least one external RAP route.