Signalling protocols
What is a protocol?
In order for information to be correctly and efficiently routed from source to
destination within a network, it is necessary for the path through the network (that is,
the switch settings) to be set appropriately.
The signalling between source, switching centres and destination used to set up the
route must be understood by all parties if it is to operate successfully. In other words,
it must conform to a pre-established protocol. This protocol
usually takes the form at the lowest level of sending information, (data words, or perhaps
tones (DTMF) alongside the message signal which could convey information about the
destination address, the type of message, the message length, the occurrence of
transmission errors, and so on, to be picked up by the switching centres or terminal
equipment as appropriate.
There are many different protocols used within large communications networks, each
hopefully optimized for a given control task. For example, the protocol used to control
information flow over a wireless portion of a network often needs to be more robust at
detecting and correcting errors than a protocol employed on a good quality wired link. A
well-known protocol for computer interconnection is the RS232
(see ) protocol. A commonly used packet switch protocol, is the X.25 standard.