AS5350 Controller 3/2 Slips

Unanswered Question
May 10th, 2007

Hi, Guys,

Have a problem with increasing slips on controller E1 with a rate of 13-14 slips per 15 (fifteen) minutes.

*** Details:

There is a AS 5350 server with 3 (three) E1 PRI (primary-net5) circuits.

For details, see the picture I've attached.

*** Notes (what has been already done):

1. I've replaced copper circuit between 3/2 and Nortel #2. No effect.

2. I've replaced loop card on Nortel #2. Still no effect.

3. If I change clock source for Nortel #2 from PSTN CO #2, slips occurs on controller 3/2.

4. If I change clock source for Nortel #2 from controller 3/2, slips occurs on circuit/trunk with PSTN CO #2.

5. Unfortunately Nortel #2 can only be q931 user side due to the lack of license.

*** Configuration (AS 5350):

tdm clock priority 1 3/0

tdm clock priority 2 3/1

*** Show (AS 5350):



#sh tdm clocks

Primary Clock:


System primary is slot 3 port 0 of priority 1

TDM Bus Master Clock Generator State = NORMAL

Backup clocks for primary:

Source Slot Port DS3-Port Priority Status State


Trunk 3 1 NO 2 Good Configured

Trunk cards controllers clock health information


Slot Type 3 2 1 0

3 E1 G G G G


#sh contr e1 3/0 | i Source

Framing is NO-CRC4, Line Code is HDB3, Clock Source is Line.

#sh contr e1 3/1 | i Source

Framing is NO-CRC4, Line Code is HDB3, Clock Source is Line.

#sh contr e1 3/2 | i Source

Framing is NO-CRC4, Line Code is HDB3, Clock Source is Line.


Any help will be greatly appreciated.


I have this problem too.
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Paolo Bevilacqua Thu, 05/10/2007 - 12:05

Hi Tobivan,

Nice slide. Do you know if PSTN #1 and 2 are synchronous? If so, you could try getting clock from one and use for all your device.

For this you should make sure that clock on nortel, on trunks going to router, are all internal with the source from pots.

The other nortel would be source from router trunks and internal to PSTN.

I think this is key, how your clock is set on the nortel, that should have nothing to do with the fact you are licensed or not for network side.

Tobivan_Helden_2 Thu, 05/10/2007 - 22:53

Hi, Paolo,

It seems to me, that PSTN #1 and #2 aren't synchronized absolutely.

I mean, we are working with 2 (two) unsync clock sources, thus,

as I suppose, we've got slips on one of the controller.

I'm not deeply informed about nuances in clock sources.

I want to ask you a few question due to we have more than 1 (one) source:

*** 1. As we can see, there is no problem with clocking for the bunch

[ (CONTR 3/0 + CONTR 3/1) <-> NORTEL #1 <-> CO #1 ]

* Nortel #1 is synchronized from CO #1

* AS 5350 3/0 & 3/1 (backup clock) are synced from Nortel #1

All seems to be fine here.

*** 2. We add new E1 PRI. We didn't say anything on AS 5350 about

clocking for controller 3/2. We've only configured 3/2 as netside.

As I remember, NetSide must provide clock for user side (correct me if I wrong).

We have situation, when Nortel #2 is double synced, am I right ?

Might it be better not to provide clock from 3/2 to Nortel #2 ?

By the way, am I wrong thinking that Nortel #2 get synced from 3/2 ?


#sh contr e1 3/2 | i Source

Framing is NO-CRC4, Line Code is HDB3, Clock Source is Line.


Does it mean that 3/2's clock source is Nortel #2 and not vice versa ?

*** 3. Looking through a new attachment: would it be ok, if we use

'tdm clock priority (external | freerun)' ?

*** 4. How much clock sources are active for one server at a time ?

What is the lowers granularity: controller or the whole access server ?

Thank you for explanation.

Hope all my questions have a sense a little.

Paolo Bevilacqua Fri, 05/11/2007 - 03:34

Hi Tobivan,

I will try to answer to your questions, the you make all the test to see if you can make some sense out of them..

2. Clock and user/network side are absolutely independent things. That is, any combination is allowed.

This is true for the router, it may not true for the PBX, but I think it should be.

The idea is that you take clock from 3/0 or 3/1, and use it for 3/2. This is not happening when you see "clock source is line". Again, you must check again how clock (not user/network side) is set on the PBX.

3. Not useful, unless you come up with a solution in which you use clock free running. That is unlikely.

4. As many sources as E1 you have, plus the internal oscillator. Then you defines the priorities, and that's all about it.

Hope this helps, please rate post if it does!

Tobivan_Helden_2 Fri, 05/11/2007 - 07:36

Hi, Paolo,


Ok. I've got the idea, thanks. But the question is still the same: how to implement configuration that allow to avoid slips :)

I've talked with Nortel engineer. He said, that Nortel #2 has the single clock reference towards to CO #2. And that's all.

Do you know what must I say to AS 5350 to redefine clock source for 3/2 ? I mean, to change "clock source is line" to "clock source is internal" or something (like it was in earlier IOS versions).


I've tried to transfer primary clock source to 3/2 and carry out all clock configuration for 3/0 & 3/1: the result is the opposite - slips are become incresing on 3/0 and 3/1 while 3/2 is clear. Hmmm... I even don't know.


Paolo Bevilacqua Fri, 05/11/2007 - 07:48

Ok, to confirm:

PBX (both) has clock from PSTN, and gives it to router, further question to Nortel: can this be changed ?

The goal is to have one PBX to take clock from router. But since the PSTNs does not seem to be synchronous, that would probably just carry the slips to PBX (are these visible on the PBX ?) or to the telco switch (where for sure you cannot see them).

Even If you was to change the router to clock internal that would not benefit. I'm not sure what is the command on the 5400.

Seems like the 5400 has problems with asynchronous sources on the same controller. I know it would be an expensive solution, but perhaps adding another controller would let the circuits to be clear.

Can you send fax on these circuits ? Are D-channels clear? No voice quality issues? If all yes to the above you can probably live with the slips.

Hope this helps, please rate post if it does!

Tobivan_Helden_2 Mon, 05/14/2007 - 05:51

Paolo, hi there,

Today we've found the root cause of the problem. It was the first Telco #1 CO switch #1 that has provided clock for Nortel #1. This CO has lost recently a link with its neigbour CO #2 switch inside Telco #1 which provides clock for CO switch #1.

* ROUTER <> NORTEL #1 <> CO sw #1 CO sw #2

Thus Nortel #1 has been working based on CO sw #1's internal (!) clock for several days. I think, that you've already understand all the situation ... :)

The solution was resync for CO sw #2 from Telco #2 cloud (there was the link).

Thank you so much for your cooperation.

Paolo Bevilacqua Mon, 05/14/2007 - 05:57

Yes, I did understood.. typical case of unsynchronized clocks.

You can be proud of having found a problem not only in your network but in telco too.

Good luck!


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