H.323 VoIP Call Preservation for WAN Link Failures

Posted: August 12, 2011 in CUCME

H.323 VoIP call preservation enhancements for WAN link failures sustains connectivity for H.323 topologies where signaling is handled by an entity that is different from the other endpoint, such as a gatekeeper that provides routed signaling or a call agent, such as the Cisco BTS 10200 Softswitch, Cisco PGW 2200, or Cisco CallManager, that brokers signaling between the two connected parties.

Call preservation is useful when a gateway and the other endpoint (typically an Cisco Unified IP phone) are collocated at the same site and the call agent is remote and therefore more likely to experience connectivity failures.

Failure Types

•WAN failures that include WAN links flapping or degraded WAN links
•Cisco Unified CallManager software failure, such as when the ccm.exe service crashes on a Cisco Unified CallManager server.
•LAN connectivity failure, except when a failure occurs at the local branch

onnection Types
•Calls between two Cisco Unified CallManager controlled endpoints
–During Cisco Unified CallManager reloads
–When a Transmission Control Protocol (TCP) connection between one or both endpoints and Cisco Unified CallManager used for signaling H.225.0 or H.245 messages is lost or flapping
–Between endpoints that are registered to different Cisco Unified CallManagers in a cluster and the TCP connection between the two Cisco Unified CallManagers is lost
–Between IP phones and the PSTN at the same site
•Calls between Cisco IOS gateway and an endpoint controlled by a softswitch where the signaling (H.225.0, H.245 or both) flows between the gateway and the softswitch and media flows between the gateway and the endpoint.
–When the softswitch reloads.
–When the H.225.0 or H.245 TCP connection between the gateway and the softswitch is lost, and the softswitch does not clear the call on the endpoint
–When the H.225.0 or H.245 TCP connection between softswitch and the endpoint is lost, and the soft-switch does not clear the call on the gateway
•Call flows that involve a Cisco IP in IP (IPIP) gateway running in media flow-around mode that reload or lose connection with the rest of the network

Example :

voice service voip
h323
call preserve

The following configuration example enables H.323 VoIP call preservation and limits RTP and RTCP inactivity detection and bidirectional silence detection (if configured) to preserved calls only:

voice service voip
h323
call preserve limit-media-detection

Examples

The following configuration example enables H.323 VoIP call preservation for dial peer 1.

voice-class h323 4
call preserve
dial-peer voice 1 voip
voice-class h323 4

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