Abstract: In a Synchronous Digital Hierarchy (SDH) based communications network comprising a plurality of Intermediate Systems (IS), the IS being divided between at least one IS—IS Area and at least one non-IS—IS Area, an IS—IS Area being an area with which a routeing protocol forming part of the Network Layer (Layer 3) of the Open Systems Interconnection including routeing (OSI), is provided for routeing messages between areas, whereby where a message is routed from an IS—IS Area to a destination IS within a non-IS—IS Area and the connection to the destination IS is broken, and as a result a message is returned from the non-IS—IS Area to the originating IS—IS Area connection to the destination IS is made by a second choice connection.