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New Member

Distributed Call Processing Design question

Hi all,

I have scenario:

Site A: 1000 users

Site B: 300 users (may increase to 500 users)

Site C: 300 users

Site A,B,C are connected through E1 connectoins.

Obviously, I can use a cluster of CCM in Site A and use SRST in Site B & C. However, I have the following quesitons:

1. What's the BW usage between the Site A and others?? What I am afraid is the overhead on the signaling between the IP Phone and the CCM.

2. Should I use distributed call processing model?? 2 CCM in Site A and 2 CCM in Site B?? Under what condition should I consider to use distributed model?? Just by no. of users or others??? Any design guideline??

3. If I use distributed model, how the extension mobility can be maintained?? As I known, extension mobility only works within the same cluster. If Site A user goes to Site B, how the extension can be carried to Site B??

New Member

Re: Distributed Call Processing Design question


Your questions are good ones and the answers really depend on your requirements. First, I would suggest you check out the latest Cisco IP telephony design guide (callmanager 3.3):

That document specifies all the BW requirements for the various deployment scenarios. SRST with 300+ users can be done but I think you are starting to approach where you may want to think of Distributed Model. Look in the following document to see the requiremetns for SRST (Router platofrms, memory etc..):

You assumptions about Extention Mobility are correct (same cluster). There are many advantages of Single Cluster (Unified Centralized Dial Plan, Extension Mobility etc...). However, be careful about media resources in the remote sites versus central sites....

Hope that helps....D

New Member

Re: Distributed Call Processing Design question

Thanks for your suggestion. BTW can I do that:

Site A:




Site B:



In site B, all phone points to CCM_C for call processing while in site A all phones points to CCM_A.

Logically, within site B calls, only CCM_C will involved and hence it saves the WAN BW. Am I right??

From the design guide, two points are important:

1. Every 10,000 busy hour call attempts (BHCA) in the cluster requires 900 Intra-Cluster Communication Signaling (ICCS). This is a minimum bandwidth is allocated in multiples of 900 kbps.

2. A maximum Round Trip Time (RTT) of 40 ms is allowed between any two servers in the Cisco CallManager cluster. This time equates to a 20 ms maximum one-way delay, or a transmission distance of approximately 1860 miles (3000 km) under ideal conditions.

For point 1, the BW issue, for every second generate 2.7 (10000/3600) calls will introduce 900kbps between two site. Is it still applied even the calls are made within same site?

For point 2, 20ms one-way delay is very harsh! If I just has a T1 or lower FR line, it is not easy to achieve.

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