Call by Call Service allows multiple services to share a PRI line. When a call is originated or terminated, an Information Element (IE) called the Network Specified Facility (NSF) is added to the SETUP message to identify the service associated with the call. The number of Simulated Facility Groups (SFGs) that can be simultaneously used for each service must be restricted. The total number of SFGs must be less than the number of PRI channels. The SFGs are determined when contracting with the network. The network determines whether calls that exceed the restriction are rejected or diverted. For outgoing calls, the KTS counts the number of calls in progress per group, and rejects excess calls. For Call by Call to operate, the number of B channels used for PRI must be specified using Memory Block 1-13-00 (PRT Channel Assignment), and Call by Call service must be assigned to each PRT using Memory Block 1-13-03 (Call by Call Service Selection).