Hi Rya,
Be a little careful with these settings, if you get too fine you might find
the phones "flapping" between SRST and CUCM
For Fallback to CUCM via Device Pool;
Connection Monitor Duration:
This parameter specifies the a common link qualifying time period for all the devices using a specific SRST reference.
This is a required field.
Default: 120
Minimum: 0
Maximum: 2592000
: Restart all services for the parameter change to take effect.
For failover to SRST;
A key part of this config is built with the relationship between the Ip Phones - Device Pool- Callmanager Group. If you have three CCM's in the Callmanager Group (which is the recommended design) then the time to failover to the SRST Router is increased as shown below;
When Cisco IP phones lose contact with primary, secondary, and tertiary Cisco Unified CallManagers, they must establish a connection to a local Cisco Unified SRST router to sustain the call-processing capability necessary to place and receive calls. The Cisco IP phone retains the IP address of the local Cisco Unified SRST router as a default router in the Network Configuration area of the Settings menu. The Settings menu supports a maximum of five default router entries; however, Cisco Unified CallManager accommodates a maximum of three entries. When a secondary Cisco Unified CallManager is not available on the network, the local Cisco Unified SRST router's IP address is retained as the standby connection for Cisco Unified CallManager during normal operation.
Typically, it takes three times the keepalive period for a phone to discover that its connection to Cisco Unified CallManager has failed. The default keepalive period is 30 seconds. If the phone has an active standby connection established with a Cisco Unified SRST router, the fallback process takes 10 to 20 seconds after connection with Cisco Unified CallManager is lost. An active standby connection to a Cisco Unified SRST router exists only if the phone has the location of a single Cisco Unified CallManager in its Unified CallManager list. Otherwise, the phone activates a standby connection to its secondary Cisco Unified CallManager.
If you wanted to change the keepalive timer;
Go to Service Parameter Configuration > Service Cisco CM > Clusterwide Parameters (Device - General) > Station KeepAlive Interval - default is 30s
Station KeepAlive Interval: Required Field This parameter designates the interval between KeepAlive messages sent from Cisco IP Phones to the primary Cisco CallManager.
This is a required field.
Default: 30
Minimum: 10
Maximum: 1000
If a Cisco IP phone has multiple Cisco Unified CallManagers in its CallManager list, it progresses through its list of secondary and tertiary Cisco Unified CallManagers before attempting to connect with its local Cisco Unified SRST router. Therefore, the time that passes before the Cisco IP phone eventually establishes a connection with the Cisco Unified SRST router increases with each attempt to contact to a Cisco Unified CallManager. Assuming that each attempt to connect to a Cisco Unified CallManager takes about one minute, the Cisco IP phone in question could remain offline for three minutes or more following a WAN link failure.
http://www.cisco.com/en/US/products/sw/voicesw/ps2169/products_configuration_guide_chapter09186a00806674d2.html#wp1048437
Cheers!
Rob
