Avaya 9608 Administration page 160

System failover and survivability
The deskphone initiates a search for a new Active Controller whenever one of the following
triggers is encountered:
Fast Response Timer Expiry,
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TCP keep-alive failure (or other socket error),
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The deskphone receives an administrative failback trigger,
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An incoming INVITE is received from a non-Active controller,
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A re-registration with the Active Controller times out, or
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Whenever one of these triggers is encountered and a user is logged in, the deskphone initiates
parallel REGISTER transactions with every controller in its configured list, including the
currently active controller.
Simultaneous Registration
The deskphone behavior for simultaneous registration during failover is based on one of four
triggers:
Trigger 1: The TCP socket closes.
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Trigger 2: A TCP Keep-alive timeout occurs.
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Trigger 3: The deskphone receives an administrative failback trigger from a Configured
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Controller.
Trigger 4: "Fast Response Timer"
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Simultaneous registration functions in response to a trigger are:
1. Controller search (maintenance check) - The deskphone tries to establish a connection (if
needed) and then register (or refresh registration) with each of the controllers. If the
deskphone gets a successful response to the REGISTER, the deskphone marks the
controller as "available." If the deskphone cannot establish the connection or if the
deskphone does not receive a successful response, the deskphone marks the controller as
"unavailable".
2. Controller Subscription Refresh - The deskphone sends a refresh SUBSCRIBE to the
current controller for all the subscriptions that the deskphone has. If the deskphone gets any
failure response for any of the refresh SUBSCRIBE messages, the deskphone removes
that particular subscription and re-establishes a subscription for that event package.
3. Controller Failover - The deskphone removes all the existing subscriptions and establishes
subscriptions with the highest priority controller that is available.
4. Controller Failback - If the failback policy is "auto" or if the failback policy is "admin" and the
trigger is a message, the deskphone unsubscribes from the current controller and
subscribes with the highest priority controller available. Otherwise (for example, the failback
policy is "admin" and the trigger is Trigger 1 or Trigger 2), the deskphone executes a
"controller subscription refresh."
When one of the triggers occurs, the deskphone follows this algorithm:
1. If there is no active call, the controller search is performed immediately.
156 Administering Avaya 9601/9608/9608G/9611G/9621G/9641G IP Deskphones SIP
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