A new feature for Asterisk 1.8 is Call Completion Supplementary Services. This document aims to explain the system and how to use it. In addition, this document examines some potential troublesome points which administrators may come across during their deployment of the feature.
What is CCSS?
Call Completion Supplementary Services (often abbreviated "CCSS" or simply "CC") allow for a caller to let Asterisk automatically alert him when a called party has become available, given that a previous call to that party failed for some reason. The two services offered are Call Completion on Busy Subscriber (CCBS) and Call Completion on No Response (CCNR). To illustrate, let's say that Alice attempts to call Bob. Bob is currently on a phone call with Carol, though, so Alice hears a busy signal. In this situation, assuming that Asterisk has been configured to allow for such activity, Alice would be able to request CCBS. Once Bob has finished his phone call, Alice will be alerted. Alice can then attempt to call Bob again.