Call Source is the dedicated line.
The dedicated line is that the voice channel is used separately for one user (such as 7000), and other users cannot use it. If the leased line fails, it can be rerouted to other channels. A dedicated line refers to a voice channel.
The function of the Call Source: The voice channel with circuit number 1 can only be used by user 7000 in call source 1 by call source rerouting.