SRST call routing to PSTN

[TrickTrick]

Hi,

In a new deployment for one company of our group we have a publisher CUCM in the HQ, and multiple SRSTs for remote sites, and i'm wondering how routing occurs at the remote sites towards the PSTN, 

let's say the WAN link is up between SRSTs and CUCM, if somebody in a remote site places a call towards the PSTN which voice gateway will route the call, the SRST router ? or the VG in the main site ?

Here is my logic:

All the phones are registred with the CUCM, obviously there's a route pattern to the PSTN using the VG of the main site, following that logic, since the WAN link is UP, every single call towards the PSTN will be routed to that VG, once the link is down, the SRST become an H323 gateway and starts acting like a CME, registers phones and routs calls to the PSTN

in that scenario, after declaring the remote router as SRST, should I add it anyway as an H323 gateway also in CUCM? 

any helpful document on how to accomplish this kind of configuration is appreciated

Thank you

[Shalid Kurunnan Chalil]

Hi,

During the WAN down, you will be losing all the connectivity with Call manager. so whatever configuration available in UCM will not be available to remote site during the downtime. 

you should be having outbound dial peers on your local SRST gateway to route the call to PSTN during the downtime.

--Just wondering If you have your PSTN connectivity at your local gateway, why dont you route your PSTN Calls through this gateway even when the WAN is up. you may be able to use SRG to route the call locally for any PSTN Call made from the remote site. ---

Regards,

Shalid 

[TrickTrick]

Hi Shalid,

Thank you for your answer, yes I was thinking about how to route calls towards PSTN in the remote site, when the wan is up, since all the phones will be registered with CUCM ( in the route pattern I will have maybe just one gateway which is the GW of the central site ?)
you talked about SGR, what it is? can you suggest to me any document so I can learn about it more ? Thanks

[HARIS_HUSSAIN · Accepted solution]

Go Through below document

https://asadraza.wordpress.com/2011/09/26/standard-local-route-groups-explained/
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/8_5_1/ccmfeat/fsgd-851-cm/fslrg.pdf

[TrickTrick]

+5 ..Very helpful explanation. So in my situation i need SLRGs configured in cucm.. so each site can reach the pstn through its local VG instead of the central one

9ne more question if you don't mind... in srst mode.. the remote phones will use the same numbers as when the wan is up or it will give them random numbers .. or maybe i should configure it like CME .. create each phone and fix the number manually ?
Thank you again

[HARIS_HUSSAIN]

1) In srst Mode Phone will use the same number as it has in CUCM. So you will configure the DNs in CUCM and enable SRST configuration in Router. you don't need to configure the DNs, When phone losses connectivity with CUCM it will contact SRST Route rand it will dynamically learn the DN from Phone and dynamically configure same.

THanks,
Haris

[HARIS_HUSSAIN]

Read more about SRST

http://www.ciscopress.com/articles/article.asp?p=2492950&seqNum=6
https://voicetalks.wordpress.com/2013/10/23/cme-as-srst/
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/admin/configuration/manual/cmeadm/cmesrst.html

[Dennis Mink]

If your WAN link goes down, your remote site becomes isolated and SRST will kick in, the phones will register on the SRST router and the SRST router will do the PSTN Calls.

you could use the remote VG/SRST router to route calls to PSTN is a normal scenario as well (i.e. WAN link being up). if that is what you mean

[TrickTrick]

Hi Dennis

Yes. This is what i need.. is there any document on how to do it?

I believe in cucm i will have route patterns pointing to pstn through the central VG...how can i make every remote srst route  local pstn call instead of the central VG?

THANK YOU

[HARIS_HUSSAIN]

You have to use Local Route Group Feature.

[HARIS_HUSSAIN]

1) For SRST Router we should have Local PSTN Lines terminating on each site. So that whether WAN is UP or Down we will always route call using the Local PSTN line terminating on the SRST router.

2) You need to add SRST Router as H323 Gateway/SIP trunk in CUCM to route PSTN Calls.

3) If you have many sites you can use Standard Local Route Group feature. which allows to Create fewer route pattern which says to use the Local PSTN Line for Each Site where phone is located.

*** Please rate helpful post ; Mark "Accept as a Solution" if applicable

Thanks,
Haris