The routing of a call or message over a substitute route when a primary route is unavailable for immediate use. 2. In signaling, the process of allocating substitute routes for a given signaling traffic stream in case of failure (s) affecting the signaling links or routes involved in the normal routing of that signaling traffic stream. 3. In signaling, the routing of a given signaling traffic flow in case of failures affecting the signaling link (s,) or route (s,) involved in the normal routing of that signaling traffic flow. Synonym alternative routing.