What is CUCM Group?

--> CUCM Group Provides redundancy of Call Processing Servers.

--> CUCM group Specifies a list of Call Processing servers on which an IP Phone can register.

--> CUCM group contains the maximum of 3 servers. The first one in the CUCM Group is called as the Primary Server, the second one is called as Secondary and the third one is the tertiary Server.

--> The phone first tries to register with Primary Call Processing Server, if the primary Server is unavailable then IP Phone try to register with Secondary CUCM Server.

--> If Secondary CUCM Server is also not available then IP Phone try to register with tertiary CUCM Server.

--> If the Primary CUCM Server comes online then IP Phone reregister to it from other CUCM Servers.

--> KeepAlives are used to know the availability of CUCM Server in CUCM Group.

--> IP Phone tries to send keepalives for every 30 seconds to CUCM Server.

--> KeepAlives are sent between IP Phone and CUCM Server, CUCM Server and CUCM Server.

--> If 3 KeepAlives are missed from Primary CUCM Server then it sends KeepAlives to Secondary CUCM Server or tertiary CUCM Server.

--> We can change the default value of Keep Alive time in CUCM.

--> It is recommended to configure subscribers as primary CUCM Server instead of Publisher.

--> CUCM Group can be associated with IP Phone with the help of Device Pool configuration in CUCM.

--> The number of servers in the CUCM group depends upon the number of IP Phones used in the network.

Ref: Cisco.com

Md.Kareemoddin

CCIE # 54759