Normally select the value PROGress, with which the public network can cut through the B-channel. The caller can then hear tones provided over the non-ISDN trunk, such as ringback or busy tone .
Selecting the value ALERTing causes the public network in many countries to play ringback tone to the caller. Select this value only if the DS1 is connected to the public network, and it is determined that callers hear silence rather than ringback or busy tone when a call incoming over the DS1 is routed to a non-ISDN trunk.