[cisco-voip] T1 Clock source question

[Andrew Dorsett]

Rob is correct in that you can use NMs that support DSPs on the NM to have
separate clocking domains.  On the new ISR4k line, we have the option of
placing DSPs on the T1 module (NIM) which will allow us to support multiple
clocking domains.  Some people are placing DSPs on the NIM for the T1
interface and then DSPs on the on-board slots for DSP farm applications.

Typically with different providers you would encounter different clocking
domains and therefore you will see slips.  If you're using on-board DSPs
it's not recommended that you bring multiple providers into the same box.

Sometimes you'll get lucky and a CLEC is clocking off the ILEC and
therefore they are in sync and you can clock off one and not see slips with
the other.  Another lucky situation is when the ILEC is really providing
the service/circuit (thus clocking) and you're just being billed by a
CLEC.  So it pays to know exactly how things are provisioned.  Usually your
ILEC guy can give you the low-down if you ask nicely when he shows up to
install the circuit.

Andrew


On Wed, Apr 22, 2015 at 3:50 PM, Rob Dawson <rdawson at force3.com> wrote:

>  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:cisco-voip-bounces at puck.nether.net] *On Behalf
> Of *Ryan Huff
> *Sent:* Wednesday, April 22, 2015 3:38 PM
> *To:* Matthew Loraditch; cisco-voip at puck.nether.net
> *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: MLoraditch at heliontechnologies.com
> To: ryanhuff at outlook.com; cisco-voip at puck.nether.net
> 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:cisco-voip-bounces at puck.nether.net
> <cisco-voip-bounces at puck.nether.net>] *On Behalf Of *Ryan Huff
> *Sent:* Wednesday, April 22, 2015 3:27 PM
> *To:* cisco-voip at puck.nether.net
> *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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