a logical connection between two routers or between a router and a telephony device
a segment of a call path, for instance, between a telephone and a router, a router and a network, a router and a PBX, or a router and the PSTN
A unidirectional or bi-directional part of a call between two telephony devices endpoints (as defined by SGCP) on the same IP, DS0, Frame Relay, or ATM network.