[cisco-voip] network-clock-participate???

[Derick Winkworth]

In telco-land, there is the idea that all network switches are synchronized to the same clock.  This is achieved by planning how a clock is distributed through your network.  The idea is that there is one clock device in a network switch, called a PLL (phase-lock loop).  The PLL will receive/recover the master clock on one of its bearer ports, or on a dedicated clock port called a BITS port.
All other ports on that switch/device will be timed using this master clock.
Cisco's ISRs were built using this model.  There is one PLL on the motherboard, called the network-clock.  Modules on your router may participate in this clocking scheme or not.  Some have to, because they don't have their own PLLs/clocks on-board.  When you need/want a module to participate in the network clock, you use the network-clock-select command.  You select the master clock with the network-clock-select command.  You can choose multiple master clocks and order them by priority.  Only one is active at a time.
The implication here is that if you connect to multiple carriers (and thus multiple clock domains), you may/will end up with clock slips on one of the ports.  Otherwise, you would set the telco port as the master clock and then time the rest of your private ports off of this.  You may need to do this if you want the ISR to do TDM switching, for instance.



----- Original Message ----
From: "Carter, Bill" <bcarter at sentinel.com>
To: john edwards <voicenerd at googlemail.com>; cisco-voip at puck.nether.net
Sent: Sunday, August 24, 2008 7:45:32 PM
Subject: Re: [cisco-voip] network-clock-participate???

http://www.cisco.com/en/US/docs/ios/voice/voiceport/configuration/guide/
vp_cfg_digital_vps_ps6441_TSD_Products_Configuration_Guide_Chapter.html#
wp1009559

"The network-clock-participate command allows the router to use the
clock from the line via the specified slot/WIC/AIM and synchronize the
onboard clock to the same reference."




-----Original Message-----
From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of john edwards
Sent: Sunday, August 24, 2008 5:53 PM
To: cisco-voip at puck.nether.net
Subject: [cisco-voip] network-clock-participate???

Hi everyone,

I wonder if anyone knows where I can find a thorough explanation of
the 'network-clock-participate' and 'network-clock-select' commands?

I have trawled through multiple references, but I am still confused :-(

Thanks very much in advance.

Voicenerd
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