WTF is OOD Refer ?

Posted by Andy on May 6, 2009

According go SIP System Administration Guide:

Out-of-dialog REFER (OOD-R) enables remote applications to establish calls by sending a REFER message to Cisco Unified SRST without an initial INVITE. After the REFER is sent, the remainder of the call setup is independent of the application and the media stream does not flow through the application. The application using OOD-R triggers a call setup request that specifies the Referee address in the Request-URI and the Refer-Target in the Refer-To header. The SIP messaging used to communicate with Cisco Unified SRST is independent of the end-user device protocol, which can be H.323, POTS, SCCP, or SIP. Click-to-dial is an example of an application that can be created using OOD-R.

A click-to-dial application enables users to combine multiple steps into one click for a call setup. For example, a user can click a web-based directory application from his or her PC to look up a telephone number, off-hook the desktop phone, and dial the called number. The application initiates the call setup without the user having to out-dial from his or her own phone. The directory application sends a REFER message to Cisco Unified SRST, which sets up the call between both parties based on this REFER.

Figure 3 shows an example of OOD-R being used by a click-to-dial application. In this scenario, the following events occur (refer to the event numbers in the illustration):

1. Remote user clicks to dial.

2. Application sends out-of-dialog REFER to Cisco Unified SRST.

3. Cisco Unified SRST 1 connects to SIP phone 1 (Referee).

4. Cisco Unified SRST 1 sends INVITE to SRST 2.

5. Cisco Unified SRST 2 sends INVITE to SIP phone 2 (Refer-Target) and the call is accepted.

6. Voice path is created between the two SIP phones.

Note The connectivity to Cisco Unified Communications Manager has been lost and, therefore, IP phone 1 and IP phone 2 have registered to SRST routers.

Figure 3 Click-to-Dial Application using Out-of-Dialog REFER

via Cisco Unified SIP SRST System Administrator Guide – 4.1 Features  [Cisco Unified Survivable Remote Site Telephony] – Cisco Systems.


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