Specifications

Getting Started
Configuration and Upgrade Tasks
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Cisco Unified SIP SRST 4.0 System Administrator Guide
Cisco Unified SIP SRST V4.0, Cisco IOS Release 12.4(4)XC
With Cisco Unified SIP SRST 4.0, a SIP redirect server is not necessary. Instead, a back-to-back user
agent (B2BUA) server routes the call as desired. A B2BUA is a separate call agent that has more features
than a redirect server, which can accept and forward calls only. With a B2BUA you can also configure
call blocking and call forwarding. In call forwarding, the B2BUA forwards calls on behalf of the phone,
while maintaining a presence as call middleman in the call path.
Configuration and Upgrade Tasks
The table below lists the high-level steps you need to take to upgrade to Cisco Unified SIP SRST 4.0. It
also lists the high-level steps you need to take in order to run Version 3.0 or Version 4.0.
Cisco Unified SIP SRST Version Instructions and Procedures
If you are interested in Cisco SIP SRST 3.0 (using
a redirect server), complete these procedures.
Cisco SIP SRST Version 3.0 provides a backup to
an external SIP proxy server by providing basic
registrar and redirect services. The following
chapters provide full Version 3.0 information,
including basic voice register pool configurations.
• Configuring the SIP Registrar
• Configuring Backup Registrar Service to SIP
Phones
• Configuring Cisco Unified SIP SRST
Features Using Redirect Mode (for Version
3.0 Only)