Whichever interface you select in the ‘network-clock-select’ command provides 
signal to the PLL, which controls the on-board clocking domain. The other 
interface will get clock from the line on the RX buffer, but since the TX 
buffer is using the on-board domain for clock you will get slips on that 
interface. You can only have one clock source for the on-board PLL.

It may not cause issues, but I have certainly seen instances of dropped calls 
and other anomalies where the only abnormal diagnostic was clock slips, and 
correcting the slips resolved the issues.

I think that you can use network modules to split the clock domains since they 
have their own onboard PLLs.

Rob


From: cisco-voip [mailto:[email protected]] On Behalf Of Ryan 
Huff
Sent: Wednesday, April 22, 2015 3:38 PM
To: Matthew Loraditch; [email protected]
Subject: Re: [cisco-voip] T1 Clock source question

That's correct, and that is where I am at. I have different carriers and I am 
wondering if I should/need to use multiple clock sources? I'm in way-back mode 
myself here.

I have a T1 PRI and a T1 CAS (separate providers). Can't I just clock source 
one and it provides that clock on the backplane to everything?

Thanks,

-r
________________________________
From: 
[email protected]<mailto:[email protected]>
To: [email protected]<mailto:[email protected]>; 
[email protected]<mailto:[email protected]>
Subject: RE: [cisco-voip] T1 Clock source question
Date: Wed, 22 Apr 2015 19:33:26 +0000
This is one of my foggier areas, but wouldn’t you use multiple when you have 
T1s from multiple carriers? I could be wrong.. very wrong..  I love Ethernet 
circuits! :P
Matthew G. Loraditch – CCNP-Voice, CCNA-R&S, CCDA
Network Engineer
Direct Voice: 443.541.1518
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From: cisco-voip [mailto:[email protected]] On Behalf Of Ryan 
Huff
Sent: Wednesday, April 22, 2015 3:27 PM
To: [email protected]<mailto:[email protected]>
Subject: [cisco-voip] T1 Clock source question

I have always subscribed to the idea that you should use one clocking source in 
situations where you have multiple T1's. In fact, I've read (not experienced) 
that when you use multiple clocking domains, that in-fact can sometimes cause 
slips.

Can anyone explain the advantages of using multiple clocking sources?

Thanks,

Ryan
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