Signals from line circuits requesting service are transferred to a T1 channel via a Pulse Amplitude Modulated (PAM) bus. The number of line circuits which can be served by a T1 line is not limited by the capacity of the T1 line since the probability of all line circuits requesting service at the same time is extremely low. A processing unit detects requests for service and assigns them a slot in a memory which defines the scanning sequence for insertion of line circuit signals in the T1 channel.