Manage blind call forwarding from a SIP device

The following example shows how to “setup” and “stop” blind call forwarding from a SIP device.

This example assumes that only authorized users are allowed to turn on or turn off blind call forwarding. The example also checks for and rejects recursive blinc call forwarding (attempts to blindly call forward to the same number the caller is using).

This example DOES NOT implement the call forwarding function. It just dynamically sets an AVP called fwd_blind. There must be additional logic placed in the configuration file to actually implement the call forwarding function when an INVITE to the caller's number takes place.

The “xlog” statements are just reminders that you will probably want to send an audio clip to the caller letting him/her know the status of the blind call forwarding operation.

As an exercise, this example can be expanded to offer the end user the ability to just enter *21 and then be presented with a voice prompt to enter the number that calls will be forwarded to.

Another exercise would be to offer the caller the ability to change the “call forward on no answer” and “call forward on busy” settings.

Regards, Norm

  #---------------------------------------------------------------------------
  # Setup BLIND CALL FORWARD BLIND (ACL=fwd_blind) (AVP=fwd_blind)
  # *21 + NPA + NXX + NNNN
  #---------------------------------------------------------------------------
  if (uri=~"^sip:\*21[2-9][0-9]{9}@") {
    if (is_user_in("From", "fwd_blind")) {
      strip(3);
      avp_write("$ruri", "s:fwd_blind");
      # Check for (and reject) attempts to perform recursive blind call forwarding
      if (!avp_check("s:fwd_blind", "eq/$from/i")) {
        avp_db_delete("$from/username","s:fwd_blind");
        avp_db_store("$from/username","s:fwd_blind");
        xlog("L_NOTICE", "blind call forwarding setup audio clip");
      } else {
        xlog("L_NOTICE", "recursive blind call forwarding not allowed audio clip");
      };
    } else {
      xlog("L_NOTICE", "blind call forwarding not authorized audio clip");
    };
    exit;
  };


  #---------------------------------------------------------------------------
  # Stop BLIND CALL FORWARD(ACL=fwd_blind) (AVP=fwd_blind)
  # *22
  #---------------------------------------------------------------------------
  if (uri=~"^sip:\*22@") {
    if (is_user_in("From", "fwd_blind")) {
      avp_db_delete("$from/username","s:fwd_blind");
      xlog("L_NOTICE", "blind call forwarding stopped audio clip");
    } else {
      xlog("L_NOTICE", "blind call forwarding stop not authorized audio clip");
    };
    exit;
  };