5. Signaling protocols

Signaling is the passage of commands through a network. It is an important, even essential, function in the life of a network. Signaling protocols, like those of the user plane, can be either standardized or proprietary.

In the IT world, signaling has always been integrated into the user plane. For example, in the X.25 protocol, the opening, closing and maintaining of a virtual circuit is carried out by packets circulating in the user plane. In the switched telephone network, signaling also passes through the user circuit. This lack of a specific signaling network means that circuits or virtual circuits are misused.

Improvements began with the advent of the narrowband Integrated Services Digital Network (ISDN) and frame relay, both of which have control planes, conceptually indicating the existence of a network dedicated to control routing....