[VoiceOps] Timing slips on subrate DS1s on CT3

[Mark R Lindsey]

T1 is the physical transport, delivered on 4 wires, 2 send and 2 receive, and capable of delivering 1.544 Mbps. T1 defines the voltage states.

DS1 is a service that is readily built on top of a T1 transport. The DS1 delivers 1.536 Mbps. With a framing and coding applied to a T1, you can interpret the voltage transitions as bits. You can also deliver a DS1 via DS3 service.

O'Reilly's book "T1 Survival Guide" goes into this a good bit.

>>> mark at ecg.co +1-229-316-0013 http://ecg.co/lindsey

On Mar 8, 2014, at 11:38 , Frank Bulk <frnkblk at iname.com> wrote:

> Mark,
> 
> Can you expand what you mean by "... the DS1 ... is a layer above the T1
> where the clock ticks happen"?  I'm not familiar with that concept.
> 
> Frank
> 
> -----Original Message-----
> From: Mark Lindsey [mailto:lindsey at e-c-group.com] 
> Sent: Saturday, March 08, 2014 10:34 AM
> To: Alex Balashov
> Cc: Frank Bulk; voiceops at voiceops.org
> Subject: Re: [VoiceOps] Timing slips on subrate DS1s on CT3
> 
> 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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> 
>