• Provide gateway functionality to IP Phones in SRST mode
• Might be used as a standalone feature to provide analog phones locally attached to a Cisco IOS router with survivability
• Most often used with SRST
• MGCP fallback to its default call-control application (H.323 or SIP)
• PSTN Call Preservation
  • Preserve for Analog or CAS call
  • No call preservation for ISDN PRI or BRI because of q.932 backhaul
  • Preserve in fall back to MGCP
• This is really SRST (a Cisco term) but the industrial term is MGCP Fallback

Fallback

• Immediate - after a preconfigured time
• Graceful - after all the open connections are closed

• Under System > SRST
• Create SRST reference

• Under System > Device Pool
• Assign SRST reference to device pool of phone

• Configure Router SRST

• Enable MGCP fallback

ccm-manager fallback-mgcp

• Specifies that the voice application named Default takes over if the MGCP call agent is not available; this allows a fallback to H.323 ro SIP

call application alternate default

• Or

application
  global 
    service alternate Default