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Community Member

Re-route internal calls to PSTN if T1 is down??

-Office A has (2) Call Managers

-Office B has Catalyst 4224 with IP phones

-4 digit dialing setup between offices

If the T1 connection between office A and B is dropped and a user in Office B places a 4 digit call is it possible to re-route the 4 digit call to the PSTN and place the long distance call automatically? We do have an ISDN backup and when that kicks in would it still be possible to re-route the calls until the T1 is re-established?

Thanks!

5 REPLIES
Community Member

Re: Re-route internal calls to PSTN if T1 is down??

Chris,

If the T1 between A and B goes down you can route the four digit calls to the PSTN. You need to have SRST set up on the 4224, appropriate dial peers, and you can use num-exp to make the four digits into what you need for the LD call. Like this:

num-exp 2... 918648552...

The expanded number will then match on the dial peers.

If you have ISDN backup working, IP calls and the CM connection will continue across it, though the limited bandwidth and QoS may be an issue.

Mike

Silver

Re: Re-route internal calls to PSTN if T1 is down??

Thats correct, and an alternate to num-exp would be to use translation rules.

translation-rule 1

rule 1 2 918648552

call-manager-fallback

translate called 1

Community Member

Re: Re-route internal calls to PSTN if T1 is down??

Thanks for the information! We do have SRST setup on the 4224 and it is working, but I was hoping that there is a way to detect and/or route calls to the PSTN if the ISDN kicks in (to avoid calls going over a slow connection). The only real use for the ISDN is for the UNity server to be in contact with the CM.

Any other thoughts as to a better backup method when the T1 goes down? Does anyone use a decentralized model with your call managers?

Community Member

Re: Re-route internal calls to PSTN if T1 is down??

Hi -

To block VoIP traffic from going over your ISDN line use ACLs under your BRI interface. You do not want VoIP traffic on your ISDN line. It is way too slow and should be reserved for non-voice data only when your primary T1 is down.

The below example will force your phones and gateway to go into fallback mode.

Ex:

interface BRI0/0

ip access-group 101 out

ip access-group 102 in

access-list 101 remark The following line blocks SCCP

access-list 101 deny tcp any any range 2000 2002

access-list 101 remark The following lines block MGCP

access-list 101 deny udp any any eq 2427

access-list 101 deny tcp any any eq 2428

access-list 101 permit ip any any

access-list 102 remark The following line blocks SCCP

access-list 102 deny tcp any range 2000 2002 any

access-list 102 remark The following lines block MGCP

access-list 102 deny tcp any eq 2428 any

access-list 102 deny udp any eq 2427 any

access-list 102 permit ip any any

-Jaret

Community Member

Re: Re-route internal calls to PSTN if T1 is down??

Thanks Jaret! I will give it a try.

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