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/ _______________________________________________ VoiceOps mailing list VoiceOps at voiceops.org https://puck.nether.net/mailman/listinfo/voiceops