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E1 slips errors and line drops

Hello all,

Wondering if anyone has come across this problem before or has any ideas?

We have about 10 sites around the country all showing these symptoms which when occur we lose voice either intermittantly or permanently. We need to get the SP to reset the line, or reboot the router to resolve.

The setup is:

2801 router with the following


relevant config:

network-clock-participate wic 1

network-clock-select 1 E1 0/1/0

isdn switch-type primary-net5


voice-card 0

no local-bypass




voice service pots

fax rate disable


voice service voip

allow-connections h323 to h323

supplementary-service h450.12

fax protocol pass-through g711alaw

modem passthrough nse codec g711alaw

interface Serial0/1/0:15

no ip address

isdn switch-type primary-net5

isdn incoming-voice voice

no cdp enable

What we are seeing is that intermittantly, we are getting E1 controller outputs such as this:

E1 0/1/0 is up.

Applique type is Channelized E1 - balanced

No alarms detected.

alarm-trigger is not set

Version info Firmware: 20040713, FPGA: 15, spm_count = 0

Framing is CRC4, Line Code is HDB3, Clock Source is Line.

CRC Threshold is 320. Reported from firmware is 320.

Data in current interval (698 seconds elapsed):

3250 Line Code Violations, 3310 Path Code Violations

0 Slip Secs, 0 Fr Loss Secs, 682 Line Err Secs, 11 Degraded Mins

674 Errored Secs, 643 Bursty Err Secs, 10 Severely Err Secs, 0 Unavail Secs

Total Data (last 24 hours)

286159 Line Code Violations, 297530 Path Code Violations,

0 Slip Secs, 0 Fr Loss Secs, 52504 Line Err Secs, 868 Degraded Mins,

51673 Errored Secs, 49893 Bursty Err Secs, 883 Severely Err Secs, 0 Unavail

and on the router we are seeing:

Dec 9 14:25:28.076: %MARS_NETCLK-3-CLK_TRANS: Network clock source transitioned from priority 1 to priority 11

Dec 9 14:25:30.072: %LINK-3-UPDOWN: Interface Serial0/1/0:15, changed state to down

The SP has checked (and double checked)the line and cant see any errors at all on the line, but obviously from the output there are problems.

One possibility maybe that the clocking is drifting beyond the limits set by the SP and as such the E1 drops??

Maybe the SP termination equipment??

We have checked cabling, replaced the hardware and in doing this all may be well for a few weeks and then the clock slips return. Obviously when the E1 drops we lose voice.

We have many sites that work with no problems at all which make it all the more strange.

If anyone has any ideas or suggestions, they would be gratefully received.




Re: E1 slips errors and line drops

Hello Andy,

Seems like a clocking issue which is always hard to track. My understanding is that you configure the router to take the E1 0/1/0 as a clock source also used for the backplane of the 2801. This will however compare it with it´s internal clock and in case the deviation is too large, drop it and switch to the next best clock (in fact here its internal one).

So not the SP is dropping the line, but your router does. What you could try is to use the internal clock by removing the network-clock- statements.

Hope this helps! Please rate all posts.

Regards, Martin

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