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voip7372
Enthusiast

QUESTION: ISDN PRI / T1 Config Example for USA

I'm working on my first real Cisco router as a gateway for voice calls.  Based on advice I received from a Cisco reseller and other info I've seen online, this is how my config ended up.  The router has a 4 port T1/E1 card.  We have 4 live ISDN PRI circuits in use.  The router is setup as a SIP Trunk on CUCM (10.5.2).  

One thing I noticed with my initial config is that the calls were scratchy and rather poor quality.  I had the encapsulation set to PPP at that point.  So I changed it to HDLC and the quality of the calls was excellent.  No noise and overall good quality.  Is there any ryhme or reason as to why you'd use PPP vs. HLDC and vice versa in the US when connecting to common telcos like AT&T and Verizon?  (assuming ISDN PRI with National ISDN 2 (NI2) as the protocol).  

Can you see anything I'm missing in my basic config for this type of setup?  I didn't paste in the dial-peers below because I'm mainly just interested in the config of the T1 itself (controller) and the D channel (serial interface).

The reason for the isdn map address ^011 plan unknown type unknown entry is so that I can mark 011 calls as unknown and send 011 to the telco for international calls.

I appreciate your input!  Thanks...

card type t1 0 0

network-clock-participate wic 0

network-clock-select 1 T1 0/0/0
network-clock-select 2 T1 0/0/1
network-clock-select 3 T1 0/0/2
network-clock-select 4 T1 0/0/3

isdn switch-type primary-ni

controller T1 0/0/0
 description ATT-ISDN-PRI-1
 framing ESF
 linecode B8ZS
pri-group timeslots 1-24

controller T1 0/0/1
description ATT-ISDN-PRI-2
 framing ESF
 linecode B8ZS
pri-group timeslots 1-24

controller T1 0/0/2
description ATT-ISDN-PRI-3
 framing ESF
 linecode B8ZS
pri-group timeslots 1-24

controller T1 0/0/3
description ATT-ISDN-PRI-4
 framing ESF
 linecode B8ZS
pri-group timeslots 1-24

interface Serial0/0/0:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-ni
 isdn incoming-voice voice
 isdn map address ^011 plan unknown type unknown
 isdn supp-service name calling
 no cdp

interface Serial0/0/1:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-ni
 isdn incoming-voice voice
 isdn map address ^011 plan unknown type unknown
 isdn supp-service name calling
 no cdp

interface Serial0/0/2:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-ni
 isdn incoming-voice voice
 isdn map address ^011 plan unknown type unknown
 isdn supp-service name calling
 no cdp

interface Serial0/0/3:23
 no ip address
 encapsulation hdlc
 isdn switch-type primary-ni
 isdn incoming-voice voice
 isdn map address ^011 plan unknown type unknown
 isdn supp-service name calling
 no cdp

trunk group ATT-LOCAL-ISDN-PRI

controller t1 0/0/0
 trunk-group ATT-LOCAL-ISDN-PRI timeslots 1-24 preference 1

controller t1 0/0/1
 trunk-group ATT-LOCAL-ISDN-PRI timeslots 1-24 preference 2

controller t1 0/0/2
 trunk-group ATT-LOCAL-ISDN-PRI timeslots 1-24 preference 3

controller t1 0/0/3
 trunk-group ATT-LOCAL-ISDN-PRI timeslots 1-24 preference 4

1 ACCEPTED SOLUTION

Accepted Solutions

Just wondering what model of the VWICs you are using, the VWIC3s are very very sensitive in my experience, changing them to VWIC2s should help.

HTH

View solution in original post

15 REPLIES 15
Mohammed al Baqari
VIP Advisor

Hi,

 

You can configure ppp if your telco is using it as well. The only reason I think of hdlc over ppp is simplicity. Other than this ppp is preferred over hdlc.

 

Your config looks good and you can verify this using the commands show isdn status (L3 status should be multiple frame established ) and show controller t1 x/x/x br (you shldnt see errors or slips)

Thanks.  The 4 circuits are up and working.  By the way, all 4 of these were previously used in an Avaya system, so they have been installed and working with Avaya for a few years before we moved them to Cisco.  

So far my only problem is the 4th circuit has a scratchy / static type of sound.  Scratchy is the best way I'd describe it.  It's very noticeable.  I tried changing that one to encapsulation ppp but it's still got the noise (so I set it back to hdlc to match the other 3).  

Here's the history.  During the testing before we moved all 4 T1's to the router, I only had the 4th circuit plugged in (the one that has the noise now).  It was plugged into port 0/0/3 and it sounded good at that point.  It was connected for about a week before we did the final cut-over and moved the other 3 circuits over to the router and during that time, it sounded fine and I didn't notice any problems.  Now that all 4 circuits are moved to the router, the first 3 circuits sound good and are extremely clean (all 0's for line code violations and everything else).  But NOW the 4th circuit (the one that was working fine before the other 3 were connected) has the scratchy/static sound and it's taking lots of line code violations, path code violations and errored seconds.   Those errors fluctuate, but they're always there.  Occasionally it'll drop to 0 for a few minutes but if I keep refreshing the show controller command, I eventually see the errors begin to increase again.  

Do you have any idea why it would work fine in 0/0/3 on that card when it was the only circuit connected but then when we plug in the other 3 circuits (into 0/0/0, 0/0/1 and 0/0/2) the 4th circuit in 0/0/3 has that scratchy sound and the errors on the controller?  Just so you know, this module was replaced once already.   We couldn't get the circuit to come up at all with the original module (which was new also).

 

Hi,

 

Check the following:

 

1. Confirm with your telco that the fourth line is using the same line coding which you configured (no line coding mismatch)

2. Change the line build-out using the cablelength long or cablelength short command.

3. If didn't work, try to change the cable

4. If didn't work, try to reset the modem

 

Let us know how this goes

Thanks.   I have a ticket open with the phone company to verify their circuit is ok and to confirm the configuration is the same as the other 3 that are clean.  

The Smartjack from the phone company is only 10 feet away from the router (the actual smartjack, not extended circuit from smartjack on another floor) and we're using a 30' CAT6 cable.   We've replaced the cable already and get the same errors.  

Reset modem?  You mean a CSU?   We don't have a CSU connected because my understand is that the 4 port T1/E1 module has a built-in CSU?  

This is usually a clocking issue.  You can try changing the clocking order to have the 4th T1 be the first priority to see if that fixes the issue:

 

network-clock-select 1 T1 0/0/0
network-clock-select 2 T1 0/0/1
network-clock-select 3 T1 0/0/2
network-clock-select 4 T1 0/0/3 <------ Change to 1 instead of 4

I'll give that a try after we do another test we already have in progress.  I discovered that if I shutdown the troubled circuit in 0/0/3, the static on the circuit most used (0/0/0) goes away.  At least that's the report so far.  had someone call me with 0/0/3 enabled and the user reported there was static on that call.  Then I shutdown 0/0/3 and told the user to call me again and the next two calls were in the user's words 'crystal clear'.   So, we'll leave it shutdown for awhile and see if all the complaints of static are gone.  For now, since this circuit is rarely used in a normal situation, I moved it back over to the Avaya system since it's still online.  I'll monitor the Avaya server and see if that circuit stays super clean on the Avaya and that calls from the Avaya using that circuit are good quality.  If it's good on the Avaya, then we know for sure there's something going on with the Cisco config or some other mystery problem.  

Ok, I rearranged the clocking and the 4th circuit (port 0/0/3) continues with the line code violations immediately after enabling it.   The show network-clock shows all 4 with good status for the clocking.  

At this point, I think we'll install a VWIC2 2MFT T1/E1 module we have on hand and put the 4th circuit in that module and see if it's clean and all static issues gone.  If THAT doesn't work, I think I'll scream ;-)

This circuit was perfectly clean overnight when we put it back in the Avaya system we're retiring.  There's no problem with the circuit.  It has to be something with the router or module, whether it be some weird bug or something.  I don't know.  I just know I can't have this office with that static which is introduced as soon as we reconnect the 4th circuit and enable it, so for now...we'll remove it from that module.  

Just wondering what model of the VWICs you are using, the VWIC3s are very very sensitive in my experience, changing them to VWIC2s should help.

HTH

View solution in original post

It is indeed a VWIC3:  

Show Inventory:  VWIC3-4MFT-T1/E1 - 4-Port RJ-48 Multiflex Trunk - T1/E1

Show Controller T1:  Version info FPGA Rev: 08121917, FPGA Type: PRK

We have a VWIC2 2 port card available, so I'm going to leave the 3 working circuits in the 4 port VWIC3 module and install the 2 port VWIC2 module in an open slot and put the 4th circuit in that VWIC2 2 port module and see how it goes.  

what was your issue in the end?

was it faulty wic hardware?

i am experiencing the same problem

i moved my port 0/0/1 is taking a lot of line code violations

i swapped the circuit from 0/1/0 to the "faulty" port and the errors stayed with the ports.

rebooted equipment and change clock settings did not help

 

Cisco sent us a replacement 4 port T1 module but I still couldn't get one of the circuits to work, so I bought a 2 port module and installed that in a different slot and moved the one of the circuits to the 2 port module and everything was fine.

Here's an update on this situation for anyone reading this in the future...

First, let me recap.  The VWIC3 4 port T1/E1 module we started out with was new.  It had stability problems since the day we installed it.  We could not get the circuits to be in service and clean on that first module we tried.  Cisco sent a replacement.  On the day of the cut-over, we moved all 4 T1 circuits from the old Avaya system to the router and once that was done, we noticed the errors on the forth circuit (in port 0/0/3).  Whenever that circuit was plugged into the 4th port, it was causing static on the other circuits on that model.  When we unplugged the 4th circuit so only the first 3 were still connected, everything was clean and perfect.  Finally, we installed a VIWC2 2 port T1/E1 module and moved the 4th circuit to the first port on that newly inserted module (the other 3 circuits remain in the VWIC3 4 port T1 module).  Now all 4 controllers are perfectly clean.  All 0's for errors and so far, no static.  If there's static later on today I'll update this discussion and let you know, but I believe this has solved the problem.   VWIC3-4MFT T1/E1 for the first 3 circuits and a VWIC2-2MFT T1/E1 module for the 4th circuit.

Hi,

 

It can be a faulty hardware on port 4 of the VWIC3 module. Please let us know how will it go with VWIC2 module.

Nathan Compton
Enthusiast

Encapsulation HDLC is the default setting, and I have never had to change it for a voice PRI in the US.  The only time I change it is for a Frame-relay or Point-to-point data T1.

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