Where are you trunking to? If you are using a CUBE, these do have limits based upon the hardware the amount of concurrent calls it can handle.
You may also want to check the capacity planner.
The Cisco Unified Communications Manager Capacity Tool (Unified CMCT) enables you to calculate the capacity of the Unified CM system for various configurations. The capacity planning tool is currently available to all www.cisco.com users with a login account. If you would like to verify the capacity of your system design but you do not have access to the Cisco Unified CM Capacity Tool, please contact your Cisco Systems Engineer (SE) or the Cisco Technical Assistance Center (TAC).
The Cisco Unified CM Capacity Tool is available at
Its going to be limited by a number of factors. The capacity planner helps you figure that out.
So for example, if your Provider has SIP trunk to a CUBE, the CUBE has a limit as does the PSTN provider. (bandwidth usually) on the CUBE it is hardware/software resources.
You also have to determine the number of devices supported in the cluster. If you have 12k phones, it depends on what type of phones, this then determines the number of servers in the cluster, failover, MGCP, CTI, Media resources, etc.
So there is more pieces to the puzzle then just max call. You cant terminate 12k calls onto one CUCM server.
IntroductionCUCM Routing RulesDial String implementation PolicyCUCM Routing LogicSIP URI Call Routing Analysis+++ Case Study: 1 ++++++ Case Study: 2 +++Conclusion
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