Table Of Contents
Cisco Unified SIP SRST Feature Overview
Cisco Unified SIP SRST Description
Support for Cisco Unified IP Phones and Platforms
Finding Cisco IOS Software Releases That Support Cisco Unified SRST
Cisco Unified IP Phone Support
Prerequisites for Configuring Cisco Unified SIP SRST
Restrictions for Configuring Cisco Unified SIP SRST
Cisco Unified SIP SRST Feature Overview
Note
Prior to version 4.0, the name of this product was Cisco SIP SRST.
This chapter includes information about supported Cisco IP phones and platforms. It also includes information on Cisco Unified Session Initiation Protocol (SIP) Survivable Remote Site Telephony (SRST) specifications, features, prerequisites, restrictions, and where to find additional reference documents.
For the most up-to-date information about Cisco Unified IP Phone support, the maximum number of Cisco Unified IP phones, the maximum number of DNs or virtual voice ports, and memory requirements for Cisco Unified SRST and Cisco Unified SIP SRST, see the Cisco Unified SRST 4.0 Supported Firmware, Platforms, Memory, and Voice Products at http://www.cisco.com/en/US/customer/products/sw/voicesw/ps2169/prod_installation_guide09186a00805f6f1b.html.
Contents
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Cisco Unified SIP SRST Description
This book describes Survivable Remote Site Telephony (SRST) functionality for Session Initiation Protocol (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.
Figure 1 shows that when the WAN is up, dual registration occurs. The phone registers with the SIP proxy server and the SIP registrar (B2BUA router). But any calls from the SIP phone go to the SIP proxy server through the WAN and out to the PSTN.
Figure 1 Dual Registration When WAN Is Up
Figure 2 shows that when the WAN or SIP proxy server goes down, the call from the SIP phone cannot get to the SIP proxy server and instead goes through the B2BUA router out to the PSTN.
Figure 2 Call Proceeds with Cisco Unified SIP SRST, When WAN Is Down
Support for Cisco Unified IP Phones and Platforms
The following sections provide information about Cisco Feature Navigator and the histories of Cisco Unified IP Phone and platform support from Cisco SRST 3.0 to the present version.
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Finding Cisco IOS Software Releases That Support Cisco Unified SRST
The tables in this chapter list only the Cisco IOS software releases that first introduce new features to Cisco Unified SRST. Other Cisco IOS software releases may subsequently inherit versions of Cisco Unified SRST. To get a list of Cisco IOS software releases that support a particular version of Cisco Unified SRST, use Cisco Feature Navigator.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:
http://tools.cisco.com/RPF/register/register.do
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Cisco Unified IP Phone Support
For the most up-to-date information about Cisco Unified IP Phone support, see Cisco Unified SRST 4.0 Supported Firmware, Platforms, Memory, and Voice Products at http://www.cisco.com/en/US/customer/products/sw/voicesw/ps2169/prod_installation_guide09186a00805f6f1b.html
Cisco UnifiedIP Phone 7940G and Cisco Unified IP Phone 7960G are fully supported if dual registration is enabled. Dual registration means that the SIP phone is capable of registering with the main SIP proxy and the Cisco Unified SIP SRST device (redirect server or back-to-back user agent) at the same time. If this requirement is not met, the Cisco Unified SIP SRST device may not be capable of routing incoming calls to the SIP phone until the SIP phone registers with the Cisco Unified SIP SRST device. Cisco Unified IP Phone 7940G and Cisco Unified IP Phone 7960G,l beginning with phone load POS3-04-2-00.bin, are capable of dual registration of the phone's primary phone line. Additional lines are not registered by the phone for Cisco Unified SIP SRST. To enable dual registration for the primary line, you must set backup proxy information such as proxy_backup and proxy_backup_port in the SIP phone's configuration file. For configuration instructions, see the Cisco SIP IP Phone 7960 Administrator Guide, Version 5.1.
Cisco Unified IP Phone 7905G, Cisco Unified IP Phone 7912G, and Cisco Analog Telephone Adaptor (ATA) 186 are not capable of dual registration; thus they are not supported and have limited functionality with Cisco Unified SIP SRST.
Platform and Memory Support
For the most up-to-date information about platform and memory support, see the Cisco Unified SRST 4.0 Supported Firmware, Platforms, Memory, and Voice Products at http://www.cisco.com/en/US/customer/products/sw/voicesw/ps2169/prod_installation_guide09186a00805f6f1b.html.
Prerequisites for Configuring Cisco Unified SIP SRST
Before configuring Cisco Unified SIP SRST, you must do the following:
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Dual registration is not supported on the Cisco Unified IP Phone 7905G, Cisco Unified IP Phone 7912G, or Cisco Analog Telephone Adaptor (ATA) series with a SIP image. Therefore auto registration to the SIP SRST router is not available.
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Restrictions for Configuring Cisco Unified SIP SRST
Table 3 provides a history of restrictions from Cisco SIP SRST 3.0 to the present version.
Where to Go Next
The next chapters of this book describe how to configure Cisco Unified SIP SRST. As shown in Table 4, each chapter takes you through tasks in the order in which they need to be performed. The first task for configuring Cisco Unified SRST is to ensure that the basic software and hardware in your system are configured correctly for Cisco Unified SRST. For instructions, see the "Prerequisites for Configuring Cisco Unified SIP SRST" section.
Table 4 Cisco Unified SRST Configuration Sequence
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"Upgrading from Cisco SIP SRST 3.0 to Cisco Unified SIP SRST 4.0" chapter
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"Configuring the SIP Registrar" chapter
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"Configuring Cisco Unified SIP SRST Features Using Redirect Mode" chapter
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"Configuring Cisco Unified SIP SRST Features Using Back-to-Back User Agent Mode" chapter
Additional References
The following sections provide additional references related to Cisco Unified SIP SRST:
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Related Documents
Cisco Unified SRST commands and specifications
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Cisco Unified SRST administration
Cisco Unified IP Phones
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Cisco SIP functionality
Command reference information for voice and telephony commands
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Standard preface
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Standard glossary
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Standards
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
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MIBs
RFCs
Technical Assistance
