The Signaling Layer
When the caller initiates a call, the call is governed through the intra-LATA layer or inter-LATA layer, depending on the receiver's LATA. Then the call is established through physical circuit using switches. As the call is routed via physical or IP (internet protocol) pathways, the switch identifies the called number, with signaling switches serving the call receivers and notifying them of an incoming call. Earlier, distant calls used to take a minute or so to establish because of the involved hand-offs among different carriers. Recently with the advent of "out of band signaling," distant calls can be made in a fraction of a second. This telecommunications layer plays a key role in making call processing easier.
Crucial information like the telephone number of the caller, PIC (carrier identification code), and mode of delivery is exchanged between the switches during signaling. Advanced features like caller identification, call tracing, repeat dial, etc., provided by different telephone companies, have been made possible by signaling. Throughout the signaling process, information concerning the call is moved between two switches which streamline the phone call process.
Technology has brought drastic changes from wire-dependent communication to wireless communication. With this winning more favor among the public, the signaling layers work in the same ways as wire signaling layers, but they can be modified to accommodate wireless systems.