2. Signage models

The differences between communication networks lead to two signaling models: the first, developed for telephone networks where signaling must take a different path from that of the content, uses the path-decoupled or push model; the second, used in IP networks, sends all information on the same medium, and uses the path-coupled or pull model.

• In the path-coupled model, signaling and data use the same destination IP address in the downstream path and, sometimes, return messages are sent via the same, reverse path; this implies that the router remembers the address of the previous router for a given flow, which can lead to an explosion in the number of contexts.

• In the decoupled path model, signaling messages are directed to other devices that are not in the communication path of a flow....