local Subscribers vs. remote Subscribers for Large Sites

Unanswered Question

Hi Team,

in a centralized CUCM Cluster significant bandwidth is needed for connection of large sites (> 2000 users) to the central applications.

I try to find out, if its better in type of WAN bandwidth and stability

1) to design a Cluster over WAN with local Subscribers and reduce the traffic between phones and Call-Processors but having the Cluster over WAN requirements on the WAN

2) centralize all subscribers

The SRND bandwidth calculations do not

finally judge me.

My feeling says that the Cluster-over-WAN is more batch-traffic and can revover after a WAN failure without large user impact where as the Phone-to-Subscriber traffic is more

real-time and a problem on the WAN

may lead to SRST toggeling, so local Subscribers might be more reliable.

Any comment or better experience is highly welcome...

best regards,


I have this problem too.
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rob.huffman Sun, 10/25/2009 - 08:26

Hi Alfred,

For large sites, like you nicely noted, I would use "local" Subscribers as a Best Practice :)

These guides should be followed when planning;

Multisite with Distributed Call Processing


And this is really your best bet!

Local Failover Deployment Model


Hope this helps!


Hi Rob,

thx for your comment.

To be a little more precise from my side. As long as this would be possible I would like to stay on one Cluster or Supercluster. Having 6 of these large sites with a local subscriber and remote failover the Cluster over WAN would consume 7 Mbps from Publisher to each site, means > 42 Mbps, assuming the Calculation from the the SRND Example 2-1.


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