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New Member

SRST and DID

How would I go about setting up DID for an SRST site in failover? The issues are:

1) The PSTN user will be dialing a DDI that comes in the central CM site via a PRI.

2) The SRST site has 2 BRI PSTN lines.

3) Normally when the call manager receives a call for an internal extentsion it just looks up the phone IP in the internal directory (i.e no call routing). How would I make this go out/in over PSTN when the phone IP is unreachable?

thanks.

Mark.

9 REPLIES
Cisco Employee

Re: SRST and DID

If the users at the remote site all have an easily definable range of DNs -- say 4050 through 4059 -- and assuming that the BRI telephone number(s) doesn't correspond to this at all, then you could create a route pattern called 405X. and discard PreDot, and prefix whatever telephone number you wanted, like the BRI telephone number, which the SRST router would presumably route to the local receptionist at the remote site.

There are a couple issues... one is that if for any reason one of the DNs in the route pattern range you define is not registered to the CM at that time, or if it doesn't exist, then the call will be routed to the remote site through the route pattern. Also, you can only define ranges for the route pattern(s) because you can't have a DN 4050 and a route pattern 4050.

Also, note that if the DN called is not registered because the WAN link is down, then the default behavior is the call will be routed to the Call Forward Busy destination, which presumably is voicemail. Depending on the customer needs, this might be a better solution.

New Member

Re: SRST and DID

Dave,

Thats useful info, I didn't think of doing it that way.

When the call gets routed to the SRS router over the PSTN, how would the DDI number called then be picked up by the router and directed to a local extension.

I'm thinking along the lines that the PSTN presents a full DDI number (not just the last 4 digits) and that the BRI DDI had no similarities to the local ext number scheme.

Also bearing in mind that the SRS router has VIC-2BRI-S/T-TE cards installed.

thanks.

Cisco Employee

Re: SRST and DID

That is one of the "problems" is that the PSTN has no idea that your WAN link is down, so they can't automatically know to re-route your DDI numbers to the BRI circuit.

So when CallManager re-routes the call across the PSTN because the WAN link is down, you will have to translate the called party number field from the range of DDI numbers for that site to a "main" PSTN number for that site, which presumably the SRST router would route to a receptionist or whomever the lucky person would be.

New Member

Re: SRST and DID

Just to clarify.

Are you saying that the only way to achieve this is by using the "default destination" facility to route all calls to a single IP phone, or is it possible to create "translations" on the SRS router (assuming the BRIs had multiple DDIs available).

Thanks again.

Cisco Employee

Re: SRST and DID

I think normal call routing should work on the SRST router, as long as you have direct-inward-dial enabled on the pots dial-peers. The router can look at the called number in the ISDN SETUP message it gets from the PSTN and route the call to the called number specified by the PSTN... OR you could use translations to change it to all the same IP phone, or different ones at your discretion.

New Member

Re: SRST and DID

Dave,

I finally got round to testing the SRST DID failover.

Unfortunately when a fail happens, CM just gives a busy tone for the remote extension.

This is even with a next best route pattern (i.e 300X, the remote extension is 3005).

If I ring an extension that doesn't exist, but is within the wildcard range, that diverts ok.

It appears CM is always aware that the DN should be contactable via IP even though its not currently registered.

Any other ideas?

Our customer sees this as a big limitation, and may not go for the solution. Whats the chance of getting a later version of CM to resolve this in the future?

thanks, mark.

Cisco Employee

Re: SRST and DID

Mark,

In your example, does the remote extension 3005 have a CFB destination entered in CallManager?

New Member

Re: SRST and DID

No CFB configured. Actually no CF options at all.

This is running 3.0(11).

Is that part of the problem?

If CFB is required, that could be kind of limiting if the user required a normal CFB, for instance, to a colleague.

I was surprised CM didn't go for a nearest Route Pattern match when it didn't find the phone registered.

Any ideas, thanks, Mark.

New Member

Re: SRST and DID

I've tried a TAC case for this, and they are a bit puzzled how to achieve this. Have you any other ideas?

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