T1 slip on 6608 and PBX

[ciscoforum]

6608 connects to Nortel 81C PBX. Customer has seen slip increasing on PBX side, how ever I didn't see any slip on 6608 using dick tracy utility. Now PBX is configured as netwrok side and external clocking, mine is user side and internal clocking. Any thought? Thanks

This is the link I am reading through. http://www.cisco.com/en/US/tech/tk713/tk628/technologies_tech_note09186a00800a5cdc.shtml.

Slip Indicates the replication or deletion of the payload bits of a domestic trunk interface (DS1) frame. A slip might happen when there is a difference between the timing of a synchronous receiving terminal and the received signal.

But how this apply on my case? Thanks. Actually I have suggested customer changing their PBX using internal and mine to be external. But apparently they don't think this is the case because there is another T1 is working fine with the same config.

[rboyce]

I don't know if the 6608 has these commands but they worked for me with a 2651 router to an Avaya Definity. These commands are for Wics so I don't know if it will work for you.

network-clock-participate wic 0

network-clock-select 1 T1 0/0

[justincohen]

Make sure that the 6608 is set to slave/span the clock from the port that is your CO so if port 1 is your CO and port 2 is your PBX then make port 2 clock set to slave/span port 1 not Internal Oscc

The PBX should be set to USER side but that's not important for clocking.

[maharris]

We have seen all kinds of problems on controllers when we try to use line/external on two ports that connect to different providers, because while the controller lets you set both to line, it really picks the line Primary port (by default port 0) to take clock from, and feeds it over to the second port - the call that loop, which to me would be another way to say line, but they mean something like their internal PLL - so, you get slips on the port that has the wrong timing imposed. I think PBXs have similar weird timing options, and if they have a PSTN ckt on one, and are taking clock on that, they may not be able to actually take clock from another source - if it was a second ckt from the same source, it would be fine, because timing would be the same on both. I bet if they set that for internal, and let you go to line, it would probably feed through the clock from the other port, and might clear up. For clocking issues on Cisco in general, I just ran across this doc today, has some good discussion - there is also a separate doc for the 17xx platform, because it is so weird.

http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/vvfax_c/int_c/vpcg/ch3_dgtl.htm#wp1009603

http://www.cisco.com/en/US/partner/products/hw/routers/ps221/prod_configuration_guide09186a008007cf5f.html

Mary Beth

[justincohen]

TDM systems almost always have a single clock source, Meridian 1's are no exception, if you clock off an internal source, and then connect to your pstn on another source you will see slips on your PSTN source (unless your internal source is forwarding clock from the same pstn source connected elsewhere)

Bottom line is, your system has to have the same clock redistributed everywhere.

Makre sure they are all clocking off of the same provider.

[ciscoforum]

Thanks guys for your excellent input. Actually 6608 only connects PBX. PBX connects to PSTN.I think PSTN provides clock. Currently there is T1 between 6608 and PBX already, but what weird is both use external as clock and it's been running for couple years and there is no any slip on that. Now we are adding couple more T1 between PBX and T1, I insist my side should use different clock from PBX though the current one is working with the same clock(which doesn't make sense to me).

So since there is slip on PBX side, not my side I think it's the problem on PBX.It most likely as you said it got two source clock( pstn and 6608). As you guys suggested I will ask them to change the clock to internal, maybe including the first one. As far as 6608 side, as soon as the PBX becomes internal, mine can be external for all of them or port1 uses external the rest using SPAN 1.

Make sense?

[justincohen]

Makes sense.

Ok the 6608 should be taking it's clock from the M1, because your M1 is getting it from the CO and passing it towards you. the 6608 can't be set to internal.

[maharris]

On the subject of timing, I just ran across this web site, it looks like it might be very useful and interesting, I have only read this one Q/A page so far, but seems like a great idea!

http://www.syncuniversity.org/drsync/q30.php

Mary Beth

[maharris]

One other thing, you might run into some terminology issues here with the PBX person. You are trying to get them to pass the clock they are getting from their PSTN link over to your interface and pass it on to you - in the case of some Cisco controllers, the way you do that is by setting the port to internal, and it passes on the clock it is receiving from the other port, and if there is no clock there, it uses the internal PLL clock. The PBX will have their own way of describing this, so you can try their internal, but it might be that that will try to pass an internally generated clock, which will still be bad. Their ability to pass you clock might depend on what kind of card they have, or maybe it already is passing clock through, and that might be why your other link works with ext/ext. I think they might also call this 'slaving' the clock to other ports. So, be ready to have a discussion if it doesn't work right away.

Mary Beth

[ciscoforum]

HI Guys

I talked to the PBX guy, apparently he says that there is no way to change the clock to internal on his side. It only support ext. I doubt this. But I don't know how to prove this.Any thought?

The other thing regarding the clock is that I noticed if I click the IP address of the 6608 to see the 6608 infomation, I see the current T1 has the following clock:Transmit Clock Source Slaved to Span 1 Rx Clock, which doesn't have any slip.The new T1: Transmit Clock Source Internal Osc, which has slip.But they both are set with network clock. why shows different? The only difference is the current T1 is PRI and new one is QSIG. We eventually want to convert the current one to QSIG. But since there is slip on PBX side we can't cutover.

Thanks

on the

[maharris]

Well, I don't think it is impossible that he can't set his side to internal, I think those clocking arrangements can get very complicated, and I remember a customer way back who said something about having to buy a clocking card to do something. I think there is a 50% chance he is actually passing his clock through, so I would try setting the 6608 side to line. You will probably have to reset it to take, but if your good conn to the same PBX is slaving to a span, you want the new one to look the same, it would seem to be an acceptible source. It might be that the 6608 blade has the constraints as the other controllers, where you only really get one source and are forced to distribute it.

Mary Beth

[maharris]

I was looking at the available options on a 6608 we have in our lab, and it looks like you should be able to pick a span to grab your timing from. If you have one good link to that PBX, you should try picking that span as your timing source on your new problem link, and see how that looks.

Mary Beth

[maharris]

Looking at the stats a little, it looks like what you normally see, if you set the clock to Network, is that it will report 'slaved to span x', x being it's own port number, unless you have specifically picked a different span to sync it to, in which case you will see that span in the stats. We have a few connections to one PBX in the lab, and we have slaved them all to the first span in the group of connections. I think that your port that still shows internal for his timing was just never reset, it should pick up the change, and show slaved to his own port until you set him specifically for your other, good span.

Mary Beth

[ciscoforum]

Mary :Excellent. I resetted instead of restarting I did before, it shows "Slaved to Span 2 Rx Clock" now. I'll ask PBX guy look at their side. Will keep you posted. Thanks again

[ciscoforum]

FYI. since reset these T1 , slip are gone.Thanks very much. So the result is Nortel 81C has to use external, I think their external has different meaning from Cisco's external.