Re: SRST Remote site

huntl · ‎02-22-2012

Dear NetPro gurus,

I have a customer where they have a remote site that needs SRST feature. During normal operation, all the site phones will registered with the CUCM 7.x over WAN. However, when the WAN is down, the customer wants the remote site to utilize the local PSTN.

Q1) However, the problem is that the remote site is sharing the same DN range as the primary site. The remote site range is not in a contiguous block range so can't be seperated out on the PSTN E1 trunks. So with the setup of primary PSTN trunk at HQ and secondary backup PSTN trunk at remote site, even during WAN outages, all PSTN calls will still be routed in via the HQ from the PSTN carrier, and because the WAN link is down, the remote site phones will never be able to get the calls.

Is there any way to overcome this?

Q2) For outbound calls at remote site, can all the remote site phones "remember / memorise the DN" such that during SRST, they can all dial out via its local PSTN E1 trunk?

Any ideas would be greatly appreciated.

NB:- I have attached a drawing of the network diagram.

boris.kudr · ‎02-22-2012

Hi Hunt,

I hope I understood your requirements.

You can setup the branch phones with Call Forward Unregistered Numbers (CFUR) matching the branch site secondary DID range. The CFUR destinations can be set under CUCM DN configuration. Don't forget to set proper CSS there.

When WAN link is down the phones will not be seen by CUCM as registered and it will redirect calls to the CFUR numbers.

Translate DNIS on incoming calls to the branch PSTN to match phones DNs.

When branch phones in SRST mode dial out, they will use your secondary PSTN connection. You could restrict Calling Number presentation on such calls to avoid confusion for PSTN users.

Cheers,

Boris

huntl · ‎02-23-2012

Hi Boris,

Let me see if I have understand you correctly too.

On all the branch phones sitting at the remote site SRST Gateway, each phone will have 2 sets of extensions:-

i) 1xxx (original PSTN range at HQ)

ii) 2xxx (new range for branch office)

Point 1) Then at all the 1xxx branch phones, i setup a Call Forward Unregistered Numbers and point them to the relevant 2xxx on each phone. This will take care of all the inbound calls for 1xxx range during WAN failure for branch phones when the PSTN call comes in via HQ.

One Q though, when you said CFUR, do i need to put Call Forward No Coverage as well?

2nd Q, where would i do the "Translate DNIS on incoming calls to the branch PSTN to match Phone DN?? Since the 1xxx range that the remote site phone has is NOT a contiguous block, i can't easily setup a translation to translate them. Also, when you mean to match phone DN, you mean to match it to 1xxx or 2xxx?

Point 2) As for the outbound calls, Caller ID would be blocked and they would go out via the remote SRST Gateways's own PSTN trunk with the DID range of 2xxx.

Did i missed anything?

Thanks so much for your help again.

boris.kudr · ‎02-23-2012

Hi Hunt,

Call Forward No Coverage numbers are used in conjunction with hunt groups only. You don't need to worry this field if you don't have funky hunt-group overflow routing in CUCM.

You don't have to assign 2xxx extensions to the branch phones.

Let's say, your HQ range is 101-101-1xxx and the backup range is 201-201-22xx

First of all you need to allocate one 201-201-22xx number for each 1xxx extension used in the branch (as they are not in cont. block and you can't use masks).

For example, BR phone 1 has extension 1111 and BR phone 2 has extension 1222.

Let's decide to use 201-201-2211 number as CFUR for the first phone and 201-201-2222 for the second phone.

In the BR SRST gateway configure translation to route inbound calls to 201-201-22xx numbers into 1xxx extensions.

It's not very scalable unless you can have one-to-one translation via mask, like if you can allocate

201-201-2111 number as CFUR for the first phone and 201-201-2222 for the second phone.

In this case all CFUR numbers can look like 2012012XXX and translation on the SRST gateway is very simple.

Cheers,

Boris

huntl · ‎02-23-2012

Hi Boris,

Oh i see!!! So you are saying the PSTN range for branch site is 201-201-2XXX. And inside the CFUR fields are asking the centralized HQ Voice Gateway to route the call back out to PSTN (201-201-2XXX), the branch SRST VG would get the call, then somehow translate 201-201-2XXX back to 1XXX.

And i would have to block "Outbound Caller ID" on the remote site since 1XXX doesn't belong to the remote site.

Did i missed anything?

Thanks so much for your help again.

boris.kudr · ‎02-23-2012

Yep, that's correct.