[VoiceOps] Timing slips on subrate DS1s on CT3

Mark Lindsey lindsey at e-c-group.com
Sat Mar 8 11:33:41 EST 2014

Normally in the TDM world, you don't try to time a DS3 off anything on
a DS3, including a DS1. You time a DS3 off a T1 transmitting all 1s,
preferably one generated by a BITS clock.

As I think you alluded, the DS1 -- what you're using to derive timing
-- is a layer above the T1 where the clock ticks happen.

But whatever it takes to discipline the internal 1.544 MHz clock to
sync up with the transmitter will work. It's interesting that Cisco
has this option.

Cisco TDM always seems a little out of step with traditional (and
often overpriced) 1970s-thought-process TDM gear.

>>> mark at ecg.co +12293160013 http://ecg.co/lindsey

> On Mar 8, 2014, at 0:43, Alex Balashov <abalashov at evaristesys.com> wrote:
> The T3's timing is logically independent of the subrate channels. The T3 is configured to take clock from the line. But the timing on the subrate DS1s should be identical, since they're all on the same DS3, right?
>> On 03/08/2014 12:37 AM, Frank Bulk wrote:
>> No, I was just wondering if there is generally one that carries the timing
>> on a T3.
>> Frank
>> -----Original Message-----
>> From: Alex Balashov [mailto:abalashov at evaristesys.com]
>> Sent: Friday, March 07, 2014 11:33 PM
>> To: Frank Bulk; voiceops at voiceops.org
>> Subject: Re: [VoiceOps] Timing slips on subrate DS1s on CT3
>> No particular reason for choosing that one. Should I have chosen another?
>>> On 03/08/2014 12:28 AM, Frank Bulk wrote:
>>> Thanks for sharing.  Why did you choose that T1?
>>> Frank
>>> -----Original Message-----
>>> From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Alex
>>> Balashov
>>> Sent: Friday, March 07, 2014 1:33 PM
>>> To: voiceops at voiceops.org
>>> Subject: Re: [VoiceOps] Timing slips on subrate DS1s on CT3
>>> Someone e-mailed me privately off-list with a link to:
>> http://www.cisco.com/c/en/us/support/docs/routers/2600-series-multiservice-p
>>> latforms/48567-clocking.html
>>> Which clued me into the fact that I can take global TDM clocking off a
>>> particular T1:
>>>      tdm clock priority 1 6/0:1
>>> So far, that seems to have fixed the slips!  I'll see if it holds.
>>> Thanks a lot for the pointer!
> --
> Alex Balashov - Principal
> Evariste Systems LLC
> 235 E Ponce de Leon Ave
> Suite 106
> Decatur, GA 30030
> United States
> Tel: +1-678-954-0670
> Web: http://www.evaristesys.com/, http://www.alexbalashov.com/
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