V5 is a set of protocols defined by ETSI by which a multiplexer in the access network of the PSTN can communicate with a telephone exchange. The protocols are designed to handle both POTS and ISDN traffic. They are based on the principle of common channel signalling where message-based signalling for all subscribers uses the same signalling channel(s) rather than separate channels existing for different subscribers.
V5 comes in two forms:
- V5.1 (ETS 300 324) in which there is a 1 to 1 correspondence between subscriber lines and bearer channels in the aggregate link to the exchange. A V5.1 interface relates to a single aggregate E1 (2Mbps) link between a multiplexer and an exchange.
- V5.2 (ETS 300 347) which provides for concentration where there are not enough bearer channels in the aggregate link(s) to accommodate all subscribers at the same time. A single V5.2 interface can control up to 16 E1 links at once and can include protection of the signalling channels.
The protocols
- Control protocol
- PSTN protocol
- BCC protocol
- Link control protocol
- Protection protocol