Avaya ESS User Manual page 57

ESS failover examples
In an ESS environment, a no service timer activates when the IPSI can no longer communicate
with the Main server or controlling ESS server. The no service timer is administrable and can be
set from 3 to 15 minutes.
The media gateway recovery variable timer design incorporates three separate timers that
monitor the period of time that the server or gateway spends in specific Link Recovery
processes. If the timers expires before the ESS no service timer, the G350 Media Gateway and
IP telephones will automatically attempt to connect with an alternate CLAN circuit pack within
the original server's configuration, or to a LSP.
Because of a catastrophic Main server failure, Port Networks 1 through 8 can no longer
communicate with the Main server. The no service timer activates. After the no service time out
interval expires, the IPSIs in Port Networks 1 through 8 request service of the S8700 ESS
server.
In Figure 23 the Link Recovery was able to re-establish the link through the CLAN board in Port
Network 1 to the S8700 ESS server before the Link Recovery timers expired. For more
information on Link Recovery see, Link Recovery on page 84.
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