Channel-Associated versus Common-Channel

Channel-Associated versus Common-Channel
Channel-Associated signalling employs a signalling channel which is dedicated to a specific bearer channel.
Common-Channel signalling is so-called, because it employs a signalling channel which conveys signalling information relating to multiple bearer channels. These bearer channels therefore have Compelled Signalling
The term Compelled signalling refers to the case where receipt of each signal needs to be explicitly acknowledged before the next signal is able to be sent.
Most forms of R2 register signalling are compelled (see R2 signalling), while R1 multi-frequency is not.
The term is only relevant in the case of signalling systems that use discrete signals (e.g. a combination of tones to denote one digit), as opposed to signalling systems which are message-oriented (such as SS7 and ISDN Q.931) where each message is able to convey multiple items of information (e.g. multiple digits of the called telephone number).