Patton electronic SmartNode 4110 Series manual 452

SmartWare Software Configuration Guide 39 • SIP interface configuration

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(b)

(c)

(d)

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Central Office

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REFER

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BYE

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Figure 61. Example SIP network connecting two devices to give a home office access to the CO PBX

The phone in the home office has two active calls to other subscribers of the PBX in the central office. The user wants to connect the other two participants and (a) sends an explicit call-transfer invocation to the device HO. The device HO internally connects the two calls and sends a DISCONNECT message to the phone for both calls. In a second step (b) the firmware on HO detects an internal loop. Both call legs are connected to the same network. In this example, both call legs are handled by the same SIP gateway. The firmware on device HO sends a REFER message to device CO, which connects the two call legs internally and sends a BYE mes- sage to the device HO. (c) Again the firmware of CO detect an internal loop. This time the call legs are han- dled by the same SIP interface, connected to the PBX. Since the ISDN port is a user port it sends an explicit call-transfer invocation to the PBX (d), which connects the call and sends the device CO a DISCONNECT message for both calls. During all these push back operations the datapath of the two participants keeps con- nected.

The push back mechanism over ISDN (using ECT) and SIP (using REFER) works independently of the pro- tocol that invoked the call-transfer. For example, the same scenario also works if the phone in the home office is connected to an FXS port.

SIP interface configuration task list 452