Cisco Unified Sip Srst; Information About Sip Srst; Prerequisites For Configuring Cisco Unified Sip Srst; Restrictions For Configuring Cisco Unified Sip Srst - Cisco CP-7911G-CH1 System Administrator Manual

Cisco Unified SCCP and SIP SRST Feature Overview

Cisco Unified SIP SRST

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Information About SIP SRST

This guide describes Cisco Unified SRST functionality for SIP networks. Cisco Unified SIP SRST
provides backup to an external SIP proxy server by providing basic registrar and redirect server or
back-to-back user agent (B2BUA) services. These services are used by a SIP IP phone in the event of a
WAN connection outage when the SIP phone is unable to communicate with its primary SIP proxy.
Cisco Unified SIP SRST can support SIP phones with standard RFC 3261 feature support locally and
across SIP WAN networks. With Cisco Unified SIP SRST, SIP phones can place calls across SIP
networks in the same way as SCCP phones.
Cisco Unified SIP SRST supports the following call combinations:
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SIP proxy, registrar, and B2BUA servers are key components of a SIP VoIP network. These servers are
usually located in the core of a VoIP network. If SIP phones located at remote sites at the edge of the
VoIP network lose connectivity to the network core (because of a WAN outage), they may be unable to
make or receive calls. Cisco Unified SIP SRST functionality on a SIP PSTN gateway provides service
reliability for SIP-based IP phones in the event of a WAN outage. Cisco Unified SIP SRST enables the
SIP IP phones to continue to make and receive calls to and from the PSTN and also to make and receive
calls to and from other SIP IP phones.
To see a branch office Cisco Unifed IP Phones connected to a remote central Cisco Unified CM
Operating in SRST mode, see

Prerequisites for Configuring Cisco Unified SIP SRST

Before configuring Cisco Unified SIP SRST, you must do the following:
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Restrictions for Configuring Cisco Unified SIP SRST

Table 2
Cisco Unified SIP SRST.
OL-13143-04
Information About SIP SRST, page 19
Prerequisites for Configuring Cisco Unified SIP SRST, page 19
Restrictions for Configuring Cisco Unified SIP SRST, page 19
SIP phone to SIP phone
SIP phone to PSTN / router voice-port
SIP phone to Skinny Client Control Protocol (SCCP) phone
SIP phone to WAN VoIP using SIP
An SRST feature license is required to enable the Cisco Unified SIP SRST feature. Contact your
account representative if you have further questions.
provides a history of restrictions from Cisco SIP SRST Version 3.0 to the present version of
Figure 1.
Cisco Unified SCCP and SIP SRST System Administrator Guide
Cisco Unified SIP SRST
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