Signaling Introduction

The transmission of any actual application information between communication devices is always accompanied by the transfer of control information. They operate according to established communication protocols, delivering application information to the destination safely, reliably, and efficiently. In computer networks, this information is called protocol control information, while in telecommunication networks it is called signaling (Signal). English references also frequently use the term "Signalling" (the signaling process), but most Chinese technical documentation uses only the term "signaling," meaning that "signaling" encompasses both "Signal" and "Signalling." Signaling is essentially a type of control signal.
    Signaling is classified by purpose into user signaling and inter-office signaling. The former operates between user terminal equipment (such as telephones) and the exchange at the telephone office, while the latter operates between two exchanges connected by trunk lines.
    Inter-office signaling is mainly classified into channel-associated signaling (CAS) and common-channel signaling (CCS). Channel-associated signaling means that the signaling network is attached to the computer network or telephone network, requiring no new network to be built, whereas common-channel signaling requires the construction of a separate signaling network (mainly between central offices). For example, when making a phone call: as we pick up the telephone, a signal is transmitted to the local central office. After a series of switching operations, the local office first sends signaling over the network. Once the remote end receives the signaling and responds with an acknowledgment to accept the call, the signaling function over the network is complete, and voice signal transmission begins, allowing the conversation to proceed. When the call ends, signaling is likewise required to control the release of the circuit.