VWIC-2MFT-T1-DI to PBX problem

[jonathan_hays]

I would appreciate ideas from anyone who has successfully gotten Drop-and-Insert (aka TDM Cross Connect) to work on the VWIC-2MFT-T1-DI card. An ASCII diagram of our current configuration is shown below. The circuit of interest is a T1 between the Branch Office Router and the Small Office router. Routers are as follows:

Branch office router:

3640

c3640-ik8o3s-mz.122-1.bin

Small Office router:

2611

c2600-ik8o3s-mz.122-23.bin.

Branch Office

Router

WIC-1DSU-T1

|

| [9-24]

|

Branch Office

Adtran TSU 120--[1-8]--PBX

|

T1

|

Small Office

Adtran TSU 120--[1-8]--PBX

|

| [9-24]

|

WIC-1DSU-T1

Small Office

Router

T1 channels 1-8 are for PBX communication and the Drop-and-Inset is performed on the Adtran CSU/DSU devices at each end of the T1 circuit. Last week we installed VWIC-2MFT-T1 cards in each router (2611 and 3640), leaving the WIC-1DSU-T1 cards in place. We configured each end for Drop-and-Insert and swapped cables from the Adtran to the VWIC-2MFT-T1-DI card.

The T1 port came up with a green CD LED and the data connection worked fine. But the PBX line would not come up, with a yellow Alarm LED. We had the same problem at both ends. So we swapped everything back into the Adtrans. Here's the ASCII diagram for the VWIC architecture:

Branch Office

Router

VWIC-2MFT-T1-DI----[1-8]--PBX

|

T1

|

VWIC-2MFT-T1-DI----[1-8]--PBX

Small Office

Router

The PBX's are Nortel Meridian 1.

The configuration is basically the same on each end (interface designators are slightly different) and is shown below:

controller T1 0/1

framing esf

clock source line primary

linecode b8zs

channel-group 0 timeslots 9-24 speed 64

tdm-group 1 timeslots 1-8 type e&m

!

controller T1 0/2

framing esf

clock source internal

linecode b8zs

tdm-group 2 timeslots 1-8 type e&m

!

connect xconnect T1 0/1 1 T1 0/2 2

!

interface Serial0/1:0

ip address 10.151.16.253 255.255.255.0

We played around with the clock and the tdm-group 'type' but nothing worked. The PBX won't talk to us. There is no special configuration on the Adtrans - they just have a Map to drop and insert channels 1-8 to the PBX.

Any ideas?

[maharris]

Are the VWIC-2MFT-T1-DIs installed on NM-HDVs with PVDMs to provide DSPs for the voice connections? After that, you want to think through your clocking, since right now the PBX on one side is probably providing the clock, and the other side is receiving it - so on your routers, you will have the port facing the 'master' PBX set to pick up clock from the attached PBX, and then pass it through to the WAN side, then on the other side, pick up clock from the WAN link, and feed it through to the attached PBX port there. I think there is some kind of TDM Clock command you might need to use to pass clock through. You definitely don't want either router trying to use the internal PLL clocking for the PBX attachment.

Mary Beth

[maharris]

Thinking about this some more, using the DI feature you are not terminating the voice trunk, so you don't need the dsps, but we have had a few people try this every now and then. We have seen issues where the cable from the PBX to the CSU was different than what we needed for the Cisco T1 interface, you could check that with vendor doc for pinouts. Once you have the connection right, then clocking becomes your issue. The 1751/1760 config guide has a chapter just for timing http://www.cisco.com/en/US/partner/products/hw/routers/ps221/prod_configuration_guide09186a008007cf5f.html

We had one going, with the PBX on one side providing clock, passing it out the WAN link(I think we had a 26xx on that side), picking it up on the other side,and passing that timing from the WAN to the second PBX port, with a 1751 on that side. It was fine until the WAN link would drop, causing the 1751 to switch to its internal clock for backup to time the PBX port. The PBX port did not like this, and it did not recover when the WAN link came back until the port (or router) was reset, and then it was fine again. I don't think they kept that in place long. There may be people who have had better luck with this, but the timing issue is a bear, and hard to tell what is really going on.

Mary Beth

[jonathan_hays]

Hi Mary Beth,

Thanks for taking the time to reply.

I agree that timing may be part of the problem. AT&T is saying the same thing.

I also think CAS (robbed-bit signaling) may be a key. One engineer who was involved with the original installation says he remembers for sure that the PBX link used CAS and was not a PRI link. Given the fact that we did not have 'mode cas' configured on either router (which CCO docs indicate is a requirement) perhaps that was our problem.

Thanks again,

Jonathan

[maharris]

Well, good luck, if you get it going maybe you could post the details here. One other thing to think of, the old TSU might have been putting out hotter levels than the MFT1 port, you can use the cablelength commands on the controller to adjust that, tell it the cable is longer to make it increase its output. I am sure it will be frustrating to get the timing thing right, since it seems to vary a lot across platforms. I would simulate a bunch of different points of failure and graceful recovery, too, before calling it good.

Mary Beth

[jonathan_hays]

No, neither WIC is installed in a voice card, and I don't see that this is necesary unless I were doing VOIP. I do not want to terminate voice calls on either router and encapsulate them in IP, Frame or ATM packets. I simply want to pass T1 channels 1-8 from the PBX over the WAN to the other PBX.

http://www.cisco.com/en/US/tech/tk652/tk653/technologies_configuration_example09186a008010f05d.shtml

The white paper "Integrating PBXs into VoIP Networks Using the TDM Cross Connect Feature" referenced by the link above, shows approximately what I want to do, except I don't want to terminate the call on the router. I just want drop-and-insert the raw data from one T1 port to another. This is what the Adtran TSU 120 has been doing for over a year.

Thanks for your reply. - Jonathan