SIP phone: Forward unattended call

The Event Type 33 - Private Ringing Outgoing can be used to forward unattended SIP calls. In order to work, it requires that the SIP phone returns the SIP status "180 Ringing" when the phones starts to ring, and "200 OK" when connecting.

The forwarding function has been verified with X-Lite and Grandstream GXP2000.

Example:

Event programming for SIP phone forwarding

• The SIP phone is 9555, the SIP Registrar node is node number 73.
• Transfer to local dirno 9547, if call not answered.
• When an intercom station calls 9555, the phone will start to ring, the ringing time is controlled by the "Private Ringing Time" timer (30 sec default). If not answered, the call will time out, and the event 33 is triggered. This event sets up a new call to directory number 9547 (which can be an intercom or another SIP phone).
  
• $C is needed to "speed up" the disconnection, so that the $DD command is not lost during the disconnection tone

Note that the initiator of the call (A-subscriber) must be an intercom station, not a SIP phone. The call forwarding will not work if the A-subscriber is a SIP phone.

The event type 33 require AMC 10.30 or later.