Clustering SRST Routers

Unanswered Question

Hi Team,

if the capacity of 2 SRST Routers per Site

is not sufficient (currently 2 x 1200), what more can I do to still provide SRST

functionality for everybody for larger sites. Would it be possible to build triangles or quaders full meshed with dialpeers or is it possible to use a

gatekeeper ? If gatekeeper, assuming 5000 phones register to it, what sizing will apply ?

thx for comments


I have this problem too.
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James Hawkins Mon, 11/02/2009 - 14:44

Hi Alfred,

Sounds like an interesting project you have there. Before considering SRST I would explore other avenues such as clustering over the WAN or deploying a dedicated cluster for this site - there are some features either roadmapped by Cisco or available through third parties that may make this possible.

If SRST is your only option then I would recommend deploying extensions in as larger blocks as possible to reduce the number of dial peers on the system.

The ideal would be five blocks of 1000 extensions so each SRST router could reach all other extensions on the site using just four VOIP dial peers. This would be straightforward in a green field site but would be difficult in an established site (PABX replacement).

This number of dial peers is pretty straightforward to configure and the SRST routers can be fully meshed. Any more and it can become really complex.

You also need to think about how hunt groups etc. will be handled whilst SRST is active. Each SRST router can have up to 50 alias commands but you can get through that number really quickly if you have lots of hunt group users.

I will be really interested to see what path you follow with this.



kelvin.blair Mon, 11/02/2009 - 16:47

I agree with James. A deployment this size it is best to go down the route of Clustering over the WAN. Of course you will need to ensure 80ms RT between the servers. On a side not by adding multiple gateways to get your user base covered, you would have already bought a 7835 server.


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