T1 CAS with Telco Nightmare Circuit

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Jan 7th, 2009
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I have a CUCM 6.1 install, using a 2811 with MGCP to telco.

The site is in the middle of nowhere, so the only circuit they can provide is a voice T1 off of a "1A" switch. I am not familiar with a 1A switch, but appearantly it is pretty uncommon and old. I ordered the circuit as a wink start e&m circuit. What was delivered is the following:

Channels 1-14 are incoming DID channels, wink start.

Channels 15-24 are, as per the telco, "just like pots lines...dial tone"

Incoming works fine, but outbound is not working properly. When I call out, the call will ring, but when the caller answers, it does not show as a connected call. The voice path is established, but if you view the phone, it still shows "Ring Out" and if you show the voice port in the router, it shows EM_Wait_For_Answer.

Does anyone have any suggestions where to begin? Telco insists that this is the only way this circuit will work.

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Overall Rating: 2.8 (4 ratings)
kgroves42 Wed, 01/07/2009 - 14:52
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Have you tried h323 config. Here is a snippet of a h323 config that I hooked up in a similar situation. The first 14 channels where incoming only and the last 10 channels where outgoing only.

controller T1 0/2/0

framing sf

linecode ami

cablelength long 0db

ds0-group 0 timeslots 1-14 type e&m-wink-start dtmf dnis

ds0-group 1 timeslots 15-24 type e&m-wink-start dtmf dnis

dial-peer voice 5 pots

description voip dial peer to PSTN

preference 1

destination-pattern 9T


port 0/2/0:1


Not really what you are asking for but it might help.


a.gooding Wed, 01/07/2009 - 14:55
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this might seem way out of it

try using H323 and ensure you have the "h323-gateway voip bind srcaddr " command on the interface. see if that works. if it does then we know it isnt the carrier. Dont forget to create your pots and VoIP DPs.

i experienced an issue with similar (NOT EXACTLY LIKE )this already which was a routing/Firewall issue.

Nicholas Matthews Wed, 01/07/2009 - 16:08
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The provider may not be doing immediate start rather than wink-start.

If the other 15-24, you may want something like this:

controller t1 0/0/0

ds0-group 0 time 1-14 type wink-start(or immediate)

ds0-group 1 time 15-24 type fxo-loop-start

That's what I think of when they say pots dial tone.



hauchinango Mon, 01/12/2009 - 07:18
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Thanks for the helpful info guys. I am getting closer, but still having problems. I configured the first channel group for E&M wink start, and configured the outbound channels for FXO-Ground start as requested by telco.

Outbound does not work. I can confirm in debug that I am sending the proper digits and accessing the correct channel, but all I get is a busy signal.

Incoming works to an extent. If I call into an IP phone over the T1, I can answer the call and works fine. When I hang up the IP phone, the remote side does not disconnect for an additional 10 seconds. Minor issue but I would still like to resolve this.

paolo bevilacqua Mon, 01/12/2009 - 07:56
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Hi, output of "debug vpm signal" would help for both issues. Havin msec timestams is key as often these are timing issues.

paolo bevilacqua Mon, 01/12/2009 - 08:18
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For outgoing, seems like you have ground start configured ? It should be loop start in 99% of the cases. Still looking at incoming trace.

paolo bevilacqua Mon, 01/12/2009 - 09:21
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Right, you had specified GS before. I think you also said you're using MGCP and that moves all signalling on the CCM. So I would try an H.323 config where all the signaling is done that the router that rarely is wrong.

jbankstonga Mon, 01/12/2009 - 10:07
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Try creating a RG/RL that only uses the first 14 channels and sidesteps the FXO channels, and see if at least inbound and outbound works.


hauchinango Wed, 01/14/2009 - 06:46
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Well, Still working on this one. Inbound works fine.

Telco is stating that the outbound channels are ground start. Should these be configured on the H323 gateway as FXO-GS or FXS-GS?

I have tried both ways with little success.

When using FXO-GS, I can dial out, the called party phone rings for a split second then drops. The calling party just gets fast busy.

jbankstonga Wed, 01/14/2009 - 07:15
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channels aren't configurable based on inbound or outbound - the T1 layer 2 is set for the circuit. Below is my T1 config for CAS-T1

controller T1 0/0/0

framing esf

linecode b8zs

ds0-group 1 timeslots 1-24 type e&m-wink-start

and in CUCM configure the circuit the same, if that helps.


paolo bevilacqua Thu, 01/15/2009 - 04:28
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Please send output of "show controllers T1", you might have a clock issue. Also note, for an H.323 trunk there are no details about the signaling to be entered in the CM. This because the config you sent about the router does not reflect an MGCP configuration.

hauchinango Thu, 01/15/2009 - 04:55
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Well, after a week and a half, two TAC cases and endless hours on the phone with Telco, a resolution was reached.

For starters, I had followed others suggestions and created two DS0 groups, one E&M Wink for incoming and one FXO_Ground Start.

Secondly, Telco had an issue in translations between their CO's.

Third, On my outgoing dial peer I had a "Forward Digits All". This caused issues with variable lenght dial strings, so I had to delete the dial peer and re-add without the fwd digits command.

Thanks to all who offered assistance.


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