A trunk group is a logical group of physical trunks and channels to the PSTN and/or to connected devices. It consists of one or more BRI, PRI or FXS connections. The physical trunk (BRI, PRI, FXS) must be assigned the numbers which are valid for it. The channels must also be assigned to the trunk.

A BRI trunk typically consists of two channels, a PRI trunk of 30 channels.