IP phone keepalive and SRST

[annayuzhao]

Scenario: cluster with 2 CCMs. Remote router is enabled SRST.

Question: If WAN lost, how long does it take for IP phones in remote site go into SRST Mode?

Assuming keepalive message is 10seconds, will it take 30s first to determine lost the active CCM, then another 30s to determin lost the backup CCM. Or because IP phone always has tcp connection to the backup CCM, will take less time?Thanks

[Ginger Dillon]

Hi -

This Cisco link discusses the information I believe you are looking for:

"The time taken to reestablish connection to a remote Cisco CallManager depends in part on the keepalive period set by Cisco CallManager itself. Typically, it takes three times the keepalive period for a phone to discover that its connection to Cisco CallManager has failed. The default keepalive period is 30 seconds. If the phone has an active standby connection established with a Cisco SRST router, the fallback process takes 10 to 20 seconds after connection with Cisco CallManager is lost. An active standby connection to a Cisco SRST router exists only if the phone has the location of a single Cisco CallManager in its CallManager list. Otherwise, the phone activates a standby connection to its secondary Cisco CallManager."

http://www.cisco.com/en/US/customer/products/sw/iosswrel/ps5207/products_configuration_guide_chapter09186a00801f3ac7.html

Regards,

Ginger