The call forwarding feature is an important feature for VoIP providers. It is implemented using forking or redirection. When you use forking, a new call leg is created, sending a new INVITE to the new destination after the first destination fails (busy or timeout). Using redirection, the proxy sends an answer to the call originator and gives it the address where it should redirect the call.
By the end of this chapter you will be able to:
Describe concepts such as forking and redirection
Implement call forwarding
Implement call forward on busy
Use the AVP resource to store call forward data
Use the failure route to forward unanswered and busy calls
We will use just forking on this material, because it is safer than redirect and will allow us to bill the calls. The redirection method is almost useless for VoIP providers, because the proxy stays out of the signaling path and billing in this situation is not possible.
Let's verify our progress. The VoIP provider...