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Time taken for IP phones to go into SRST mode - Need clarification

This is what I think is true and I request someone to confirm this and if possible point me to a document that confirms this.

Say we have a WAN outage and hence the Voice Gateway and the IP Phones at Site A and Site B loose CCM keepalives across the WAN cloud.

Say Voice Gateway A at site A has the following config:

sccp ccm identifier 1



sccp ccm group 1

bind interface GigabitEthernet0/0

associate ccm 1 priority 1

associate profile 2 register MTPGW1

associate profile 1 register mtp001d46c49870


the Voice Gateway at Site B has the following configuration:

sccp local Loopback0

sccp ccm identifier 1

sccp ccm identifier 2

sccp ccm identifier 3



sccp ccm group 1

bind interface Loopback0

associate ccm 3 priority 1

associate ccm 2 priority 2

associate ccm 1 priority 3

associate profile 2 register CONF_PEK_VG01

associate profile 1 register MTP_PEK_VG0

Question 1:


Is it right to say that Voice Gateway "A" and all IP Phonses at Site "A" will go to SRST mode in about 90 seconds because it has only one CCM in it's config and Voice Gateway "B" and all IP phones at site "B" will go to SRST mode after 3 x 90 = 270 secs. because it has 3 x CCMs in it's config.

Question 2:


What timeers can be tweaked to reduce the above times.


Re: Time taken for IP phones to go into SRST mode - Need clarifi


Q1. Your phone will go through call manager list list from device pool not configured on gateway - you can check it from phone settings or CM_group. CM_group contains up to 3 CM servers.

Default keepalive time is 30s and as you said 3 missing keepalives will go to next server in list - up to 270sec when 3 servers configured. (Source says 3 missing keepalives then go to next server but there is another parameter to configure and not 100% sure if has any impact - Station and Backup Server KeepAlive Interval)

Q2. You can tweak keepalive parameter between phones and CM: 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

: Reset affected IP phone(s) for the parameter change to take effect.

Unit: sec

rate if this help

Hall of Fame Super Red

Re: Time taken for IP phones to go into SRST mode - Need clarifi

Hi Alphonse,

Just to add a note to the great info from Konrad (+5 points here Konrad :)

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 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.

Hope this helps!