Automatic Route Selection (ARS)

All station user calls, direct distance dialed and private network, are routed to trunk groups that have access to exchange carrier facilities terminating in a central office. The many types of port circuit interfaces and trunk facilities were described in Chapter 6 (Traditional PBX Common Equipment). The software feature controlling access to the trunk groups is ARS. PBX ARS features and functions support control and routing of calls over public network carrier facilities and across private networks. ARS is used to select among various types of trunks:

1. Local CO, analog or digital

2. Foreign exchange (FX)

3. Wide area telecommunications service (WATS)

4. Tie line (private line); analog and/or digital

5. ISDN PRI service circuits

When the ARS software program routes calls to public network carrier facilities, it is referred to as off-net routing; when calls are routed to private network carrier facilities, it is referred to as on-net routing. Off-net calls are based on the public network dialing format and terminate in the public network. On-net calls are based on a private network dialing format and usually terminate within the private network, although some calls may be routed off the private network and onto public network facilities, if the called station is not configured as part of the network. The private networking feature used to describe the latter routing option is known as tail end hop off (TEHO). On-net routing programs support tie-trunk protocols, proprietary private network protocols,...