SRST and MGCP Gateway Fallback

One of the primary benefits of a centralized call processing model is the ability to provide remote sites with all the advanced calling features that were previously available only on large campuses. Survivable Remote Site Telephony (SRST) allows a Cisco voice gateway to handle call processing if the connection between the remote site and the central site is severed.

H.323 and Session Initiation Protocol (SIP) gateways are intrinsically resilient to network connectivity failures because the dial plan and call control are in the gateway, and the gateway is always in control of call-routing decisions. Multiple Gateway Control Protocol (MGCP) gateways are under the control of the call agent, and only the call agent can make dial-plan and call-routing decisions. Therefore, when the call agent and the MGCP gateway have a connectivity failure, you must use a fallback method to return call control to the gateway for the period of the failure. The MGCP Gateway Fallback feature allows the gateway to assume call control for MGCP-controlled voice ports. The gateway uses this feature in conjunction with SRST to allow the router to take care of IP phone and public switched telephone network (PSTN) gateway call routing during network failures.

This chapter helps you to do the following:

• Understand how SRST operates
   
• Understand the difference between SRST and MGCP Gateway Fallback
   
• Configure SRST and MGCP Gateway Fallback
   
• Implement your dial plan
   
• Configure SRST features
   
• Verify and troubleshoot SRST and MGCP Gateway Fallback