T1 Timing Issue using the 15454

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Sep 4th, 2008
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So, I am supporting a VERY large network for the Government and we have 454s all over the place. These MSPPs are usually connected to an Optical Switch or to a DWDM box via a 192 pipe. At given sites we drop out anything from T1s to 48s. I want to know if the 454 can provide timing to T1s carried in channelized DS3 circuits W/O the use of DS1 cards. We are currently having to dedicate a "re-timing" node at many of our sites where we slot a couple of DS1 cards only to demux each T1, push it over the cable to a patch panel where we cross it back into the SAME card in the MSPP that we just came out of....SO THAT THE T1 GETS ITS TIMING!!! This seems incredibly low tech and I want to know if with the new revisions we will be able to synch the T1s via passing them over the XC card matrix instead of having to break out each T1 physically and push it right back into the box. This is an incredibly low tech and cumbersome way of timing our T1s. Please help by providing some insight and an alternative way of doing T1 timing. [email protected] Tom

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ja_lomonaco1 Fri, 09/05/2008 - 19:15
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I'm confused as to why you need to put timing on the DS1s with a 454. Can't the DS1s be timed at either of the end points(commonly a CSU)?

Merahute28 Mon, 09/08/2008 - 05:49
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Many of our circuits are encrypted and the encryption gear doesn't provide clocking. These circuits have to be timed somewhere in our network. I am wondering if Cisco is planning on moving this timing feature into the box instead of having to come out ports 1-28 of the DS1 card and then back into ports 29-56...hairpinning.

Michael Dooley Thu, 09/11/2008 - 10:33
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I'm having to make an educated guess on part of your setup here.. let's see if this is correct...

This is setup where the encrypted gear sends/receives a DS1 to an M13 which maps it into a DS3. The DS3 connects to the 15454. Somewhere else the DS3 leaves the 15454 and connects to a M13 where the DS1 is extracted and sent to another piece of Encrypted gear.

The encrypted gear requires timing from an external source. This source can either be the receive DS1 or from an external timing source.

If you take the DS3 and extract the DS1s via DS1 cards connected back on themselves the DS1 card provides timing so the signal is stable. Without this the Encrypted gear occasionally takes hits and has to be reset when traffic drops.

Is this correct?

Merahute28 Thu, 09/11/2008 - 11:03
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Precicely the issue; our encrypted gear needs very clean T1 signaling and we're having to do this loopback using the 454s at many sites in our network. Do you have any suggestions?

Michael Dooley Fri, 09/12/2008 - 07:36
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Yes. The encrypted devices need a stable timing source. Most people look at this setup (without the DS1 cards) and think they are being timed from the ONS15454 when the end devices are actually being timed by each other.

Both are relying on the receive signal (line timing) to be a stable timing source. In fact neither is stable. If the oscillator on one drifts (as it will) the other follows. This is OK until the frequency falls outside the limits of the T1 carrying equipment.

My suggestion is this: Look at the encrypted devices and see if the timing source option on them can be changed to either internal, or external (versus line).

If either option is available, set the encrypted device on one end to internal (or external) and the device on the other end to line timed.

Also, if you choose external, the encrypted device will need a source for its external timing input. The ONS15454 has a BITS out that can provide a stable DS1 for timing to this device.


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