Importance

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Abstract

In a connection-oriented communications network, a source node selects one of first and second routing mode flags and a first route to a destination node in response to a connection request, and establishes a connection to a first intermediate node located along the first route. The first intermediate node is responsive to the first flag for extending the connection along the first route if there is an acceptable link in the first route. If there is no acceptable link, it finds a first route section therefrom to the destination node and extends the connection along the first route section if a total cost of links from the source node to the destination node using the first route section is less than a cost threshold, or cranks the connection back to an upstream node if there is none of such route sections. The upstream node then finds a second route section if a total cost of links from the source node to the destination node using the second route section is less than the cost threshold and extends the connection from the upstream node to a second intermediate node along the second route section, or clears the connection if there is none of the such route sections. On clearing the connection, the source node may or may not select the other flag. In either case, it selects a second, alternate route to the destination node and establishes a connection to a third intermediate node along the second route. If the flag is set to the first mode, the third intermediate node operates in the same manner as the first intermediate node does, and if the flag is set to the second mode, it extends the connection along the second route if there is an acceptable link. Otherwise, it clears the connection if there is no acceptable link and communicates this fact to the source node.

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First Claim