I can’t understand the difference between trunk and line. Is right to suppose # of lines = # of calls? and if I have a different codec (e.g. 22 kb/s and not 64 kb/s) the number of trunk will change?
Your question is about PBX! It has some trunks and some extensions (ex. : 4/16 or 8/120..)
The line is PSTN connection to this PBX. Is’s must be connected to Trunk. If we talk about analog lines – for 4 trunks possible connect only 4 PSTN lines.
In case digital – 1 T1 connection(trunk in PBX) is connect 24 PSTN lines.
For the VoIP GWs are same way – numbers of line = max # concurrent calls.
Use different codec will give you more or less used bandwidth… for the same number of calls…
Trunks are commonly used by PBX switches to communicate with each other. Among the many types of trunks, the most widely used types are Central Office (CO) trunks, which provide connection to the public network through a Central Office and tie trunks which provide connections between switches in a private network.