SRST - Using multiple Gateways

[davearnold4011]

Hi

I have a site that needs to be configured for SRST.

Due to the hardware the phones will register across 4 different gateways as their are 4000+ extn numbers

This means that  extn numbers will be registered randomly to the different gateways, the DDI range is all 9999 numbers.

If a phone on router A dials a phone that is on router B how would I route the call ?, if the call hits Router C how would router C know what to do with it.

Also DDI Calls appear on all 4 gateways, via ISDN, if a call comes in router A for an extn on router C how would this route ?

My concern is around any possible loops forming if the gateway receives a call for a DN it is not aware of

I hope this makes sense, thanks, for your help

David

[Jaime Valencia]

Well, there is no easy way to do this, you'll need to build all the necessary dial peers to route calls between all the ISRs as you have no control of where the call might land.

Depending on how many digits you get from telco and how many you have for the DNs, you might require separate dial peers to adjust your dialing habits.

Think of this as just CMEs, you want to call a DN on the other CME, you need dial-peers to do that.

[davearnold4011]

Hi

firstly many thanks for all your responses, they are much appreciated.

I am now wondering if I could use COR lists for this.

For example if a call comes into Router A for a phone registered to Router A phone rings, no problem.

If a call comes into router A for a phone on router B, router A would have  dial peers pointing at the IP address of each of the other routers with preference 1, 2 and 3.

The call would, therefore,  be forwarded to Router B and the phone would ring.

If a call came into router A for router C it would try router B first, router B wouldnt recognise the number so would match one of its dial peers to send the call to the next router ( this is where I think  loops could come from) however the  COR list would stop it sending the call out.

This is where I am not sure what would happen, as the call fails would Router A then try the next router , router C, as it would have a preference of 2 ?

i dont really know how the failed call set up to Router B would be handled by Router A ?

I have never used COR list before so not entirely sure if this could work ?

Ps With regard to the ealier responses our incomming calls hunt around all 8 ISDN's.

Once again your comments would be greatly appreciated

David

[Murali Gunnam]

Hi David,

Since the extensions are going to register randomly to the GWs we cannot determine the call routing using COR.

Regards,

Krish

[Murali Gunnam]

Hi David,

As Jaime mentioned, you would have to create the dial-peers to route the calls to other GWs. You need to make sure that internal dial-peer hunt gets finished before the ISDN setup timer expires.

However if you have each ISDN circuit is associated with certain DID range, as in calling a particular number always lands on one specific ISDN circuit, you may think of below solution -

1. Make sure all the corresponding extensions of one particular DID range are configured with same device pool.

2. Configure the SRST reference to this device pool with the IP address of the router which has that ISDN circuit terminated.

This way we can force the phones to register with the GW where their PSTN DIDs are registered with.

Hope this information helps...

Regards,

Krish

[Ayodeji Okanlawon]

This is just my 2 cents. For such a large site you should be using a dedicated cucm subscriber as your SRST gateway. This server will be located locally to the site, that will be a much more efficient solution than having four gateways. It will be messy at best..

[davearnold4011]

Ayodeji,

If only !

That has been my suggestion all along however I am over ruled every time.

All the Servers HAVE to be in the centralised data Centre not on the user sites.

Thanks, David