Video door intercom systems connected to the Gigaset T300/T500 can be made visible on the display of the Gigaset DE900/700. Here we describe the protocol used to make this possible.
When a door intercom is pressed, it initiates a call to a user phone through the PBX. The PBX appends additional proprietary SIP headers "X-GC-Doorline" and "X-GC-Doorline-DTMF" in the SIP INVITE.
The header X-GC-Doorline contains an URL address to images made by IP camera of door intercom
This header can only be used upon call setup, not in Re-INVITE or UPDATE Transactions. The phone must identify itself with a suitable User Agent Header (Model Type, MAC Adress, Firmware version… ) when requesting the file.
PBX shall process the images coming from the door intercom to display properly on the separate phones (resize, rescale).
The header X-GC-Doorline-DTMF contains the DTMF sequence for action “open door”.
Remark: Various door intercoms can provide various action interfaces, e.g. via DTMF, SIP INFO, etc…
When the user phone receives such kind of INVITE, it recognizes that the call is triggered by a door intercom. Then it can present user interface different than in usual Voip call. The Phone shows the scene catched by the camera of the doorline (URL is carried by "X-GC-Doorline") and provides the “Open door” key. When the user presses the “Open door” key, the phone sends the DTMF sequence (carried by "X-GC-Doorline-DTMF") to the door intercom for opening the door.
The phone may play this sequence when the user presses the “Open Door” key.