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Question re clocking on a serial line - G.703 termination • RouterDiscussions.com

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Question re clocking on a serial line - G.703 termination

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Question re clocking on a serial line - G.703 termination

Postby Guest » Thu Jan 06, 2011 12:00 pm

Hi, I have a customer who has a 2Mb Megastream circuit by BT in the UK.

 

One end is terminated using X21 and the other end is terminated using 120ohm G.703.

 

They have an intermittent problem with the circuit whereby it will fine for a few weeks, then they start to see input frame errors at the G.703 end from the output of show int.

show controllers e1 output was showing a large number of Line Code Violations and Frame Loss Seconds – but only a few Slip Seconds.

 

These will continue to increment until the circuit becomes unsuable

This is resolved when either the service provider puts a hard loop on the circuit, or the customer physically disconnects the serial cables at both ends and then reconnects them.

 

The service provider has done extensive tests on the circuit and say there is no fault found.

 

The service provider says that they are not proving a clock at the G.703 end, yet the interface says its getting its clock from the line;

 

E1 0 is up.

  Applique type is Channelized E1 - balanced

  No alarms detected.

  alarm-trigger is not set

  Version info Firmware: 20040108, FPGA: 11

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

  Data in current interval 780 seconds elapsed:

     0 Line Code Violations, 0 Path Code Violations

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

     0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs

  Total Data (last 24 hours)

     0 Line Code Violations, 0 Path Code Violations,

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

     0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs

 

This output was taken when the circuit is running fine.

 

Should we configure the clock as internal?

The config for this is very basic;

 

!

controller E1 0

channel-group 0 timeslots 1-16

!

interface Serial0:0

ip address 10.200.200.1 255.255.255.252

!

 

To me this looks more like a timing issue of some sort rather than a physical problem with the circuit but I don know enough about it to be sure.

 

Any advice greatly appreciated

 

Cheers, Dom

 

Guest
 

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Re:Question re clocking on a serial line - G.703 termination

Postby Guest » Thu Jan 06, 2011 12:40 pm

Hello Dom,

>> Should we configure the clock as internal?

yes because SP is not providing it

 

>> The service provider says that they are not proving a clock at the G.703 end, yet the interface says its getting its clock from the line

 

clock source line is default settings and it is good when SP provides clock

 

the fact that the link starts good and becomes not usable over time is clearly a clock problem

 

Over time a free running clock will cause errors in the sampling rate/time that will make the receiver considers a 1" just to say

 

the act of disconnecting or the remote loop done by SP provides a new clean start, but it does not solve the issue

 

Hope to help

Giuseppe

Guest
 

Re:Question re clocking on a serial line - G.703 termination

Postby Guest » Thu Jan 06, 2011 12:46 pm

Hi Giuseppe,

 

Thanks for your reply,

 

I set the clocking source to line and left it for a hour, however started seeing increasing frame and crc errors again at a rate of 3%+ of total packets on the serial interface and also getting slip errors on the E1 controller.  So I’ve set it back to line source again and in the last hour the crc/frame errors & slip errors stopped....

 

Can you think of anything else we can try?

 

Cheers, Dom

Guest
 

Re:Question re clocking on a serial line - G.703 termination

Postby Guest » Thu Jan 06, 2011 1:25 pm

Guest
 

Re:Question re clocking on a serial line - G.703 termination

Postby Guest » Thu Jan 06, 2011 1:53 pm

Thank you so much for your help Giuseppe,

 

I have asked my customer to request the SP provides a clock. If anything positive comes of it Ill post if here for reference

 

Cheers, Dom

Guest
 



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