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Single CM clustering over the WAN


Would there be any issues for us to have a subscriber in Sydney and the Publisher in the US (as a single cluster) over a DS3 45MB WAN pipe connection between both sites? e.g registration, call processing, singnalling, etc. Basically what i want to achieve is the ip phones in sydney to register to Subscriber in sydney and US phones to register to the Publisher in US or Subscriber. After looking at the design specs for a Callmanager IP Telephony solution maximum round trip time for callmanager servers is 40ms which is around 6000KM distance apart from each server.

For a test I pinged from my Sydney Publisher to the US the Publisher and the RTT averaged around 203ms, is that way too much, right ?

At the moment my current setup is that i have a Publisher in each location and talk via the inter cluster trunk across each site.

Before i do any changes i would like to make sure with Cisco if this is supported way. Let me know if this achievable?

Thank you,

Yavuz Sabuncuoglu

Network and Communications Engineer

Nighthawk Radiology Services


I am no longer with Cisco and still have my CCO login. Please could someone help me answer my query.


Chris Deren
Hall of Fame Master

According to Cisco SRND Intra-Cluster Communication should not exceed 40 ms (we are correct), so 203 ms will probably create too big of a delay.


The maximum one-way delay between any Cisco CallManager server for all priority ICCS traffic

should not exceed 20 ms, or 40 ms round-trip time (RTT). Delay for other ICCS traffic should be

kept reasonable to provide timely database and directory access. Measuring the delay is covered in

Delay Testing, page 2-19. Propagation delay between two sites introduces 6 microseconds per

kilometer without any other network delays being considered. This equates to a theoretical

maximum distance of approximately 3000 km for 20 ms delay or approximately 1860 miles. These

distances are provided only as relative guidelines and in reality will be shorter due to other delay

incurred within the network."

Found in CCM 4.1 SRND:

You are probably better off leaving Distributed Call Processing model.


Don't forget to rate all posts!


From personal experiences, I can tell you that Cisco will not support an IP-over-WAN Cluster model that does not meet the specifications set out in the SRND.

Will it work? Probably. I recently worked on a project that has a cluster split across approximately 2800 miles apart, with an average RTT of 70ms. The subscriber is able to maintain its database connectivity. However, there have been occasional replication issues.

The biggest issues that I think you will see are as follows:

1. ***TAC will not support the design.***

2. Database replication/synchronization issues.

3. Call setup and teardown issues on calls between IP Phones in the US and AUS.

Hi Guys,

Thank you for this information.

I was just waiting to hear that TAC would not of supported this design.

Because we have radiologyst globally and they travel between offices around the US, Zurich, Sydney. I wanted to implement the IP Phones services features e.g Extension mobility as well as be able to search employees/user through corporate directory on there phones which interfaces to our AD LDAP parent and child domaian servers.

Then I dont think that I have the option to achieve the above with distributed call processing solution (ICT trunks),which i have currently.

Please tell me if this is correct? and how would i get around this?



Chris Deren
Hall of Fame Master

Extension Mobility can definitely NOT be used over ICT.

The directory I know some people who were able to implement to over ICT, you need custom service and replace the standard link.


Ok Chris thanks for your help. I am so Cisco's got a forum to address any design related queries :-).

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