SRST Failover Time for 3945 with 1200 Phones

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Dec 5th, 2009
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Is there any reference material that indicates how long it would take for 1200 phones to failover to SRST on a 3945 ISR router?  I understand the keepalive issues but curious about the load on the router when a large number of phones failover at the same time.

- Dennis

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Ajay Singh Thu, 12/10/2009 - 04:45
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Once there is a wan link failure, phones wait for three consecutive keepalive miss and then only register to SRST enabled router.Default value for this keepalive is 30 sec and can be reduced to 10sec

In case Wan link is restored, it looks for the Connection Monitor duration under device pool on GUI page of CUCM.Default vlaue is 120 sec and can be reduced to 0 as well, from Connection monitor duration enterprise parameter..

For more information you can refer SRST System admin guide at

I could not find any document where you can calulate total overhead or time taken for phones to re register from SRST to CUCM. I think it can not be calculated, rather it depends on network performance.



dvaggalis Thu, 12/10/2009 - 06:33
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I'm not referring to the time it takes to restore back to CUCM but rather what the performance hit is on the 3945 router when 1200 phones try to fail-over to SRST,  at the same time, and how long it would take for the 1200 phone to failover.


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