Cisco Cisco IOS Software Release 12.2(11)YT

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releases occur. For the most current information, go to the Cisco Feature Navigator home page at the 
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Platform support for particular Cisco IOS software releases is dependent on the availability of the 
software images for those platforms. Software images for some platforms may be deferred, delayed, or 
changed without prior notice. For updated information about platform support and availability of 
software images for each Cisco IOS software release, refer to the online release notes or, if supported, 
Cisco Feature Navigator.

The following are general prerequisites for SIP deployment:

Ensure that your Cisco router has the minimum memory requirements.

Ensure that the gateway has voice functionality that is configurable for SIP. 

As with all SIP call transfer methods, the dial peers must be configured for correct functioning of 
the Refer method. See the 

 for the complete configuration steps.

Load Cisco IOS Release 12.2(11)YT or a later release.

Configure hookflash signaling.