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T1 network-clock-select

glenn.martindell
Beginner
Beginner

Hello,

I need some help understanding a problem I just encountered and while I feel like I should know the answer to this, apparently I do not.   Can someone help me understand the difference and appropriate use of the "network-clock-select" command and the "clock source line" command on the T1 controller?

If I have a router with 8 T1s installed, why do I want/need to set the network-clock-select command?   I should want to derive my clocking for each T1 from the provider from the line rather than selecting a single T1 to provide clocking .   It is my understanding that if I do not set network-clock-select command, I'll get timing slips.   What is the advantage to providing clocking for all of my T1s from a single T1?

Thanks,

Glenn

8 Replies 8

Its very simple.. Network clock select select the clock priority and clock source selects the source of clocking.

network-clock-select priority {E1 | T1} slot —Where slot is the card or slot of the interface.

This command needs to be added to configure the clocking priority for the system in order to ensure that the router uses the correct interface as the primary (highest priority) clock source. This same command needs to be repeated with a different priority for each interface in order to establish the clocking hierarchy (in case the primary source goes down):

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

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paolo bevilacqua
Hall of Fame Master Hall of Fame Master
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First of all, normally on a voice circuit you will only receive clock and cannot provide it. So, the default of 'clock soruce line' is the only right option under controller.

Then, 'network-clock-select' is needed to keep the DSP in synch with the circuit(s). And if circuits are no synched among them, as often happens when using different carriers, you will experience slips on these that are not the 'select'.

Thanks to both of you for your replies.   I'm still a little confused.   If I have the following:

network-clock-participate wic 0

network-clock-select 1 T1 0/0/0

controller T1 0/0/0

Framing is ESF, Line Code is B8ZS, Clock Source is Line

controller t1 0/0/1

Framing is ESF, Line Code is B8ZS, Clock Source is Line

Where does 0/0/1 derive it's clocking?

Thanks,

Glenn

Glenn,

Both controllers will derive their clock from the line, however the controller t1 0/0/0 will provide clocking for the system. You need to add the clock priority for controller t1 0/0/1 so that when controller one fails this will take over as the primary clock interface for the system.

network-clock-select 2 t1 0/0/1

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

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Thanks and understood about the controller priority.   What does the "system" need clocking for?

This is actually what started me second guessing what I thought I understood about clocking.   We had 8 T1s and each controller was configured as a priority in the network-clock-select:

network-clock-select 1 T1 0/0/0

network-clock-select 2 T1 0/0/1

.

.

network-clock-select 8 T1 0/1/3

I was seeing massive slips on all of my T1s until I removed all but one of the T1s from network-clock-celect

Thanks,

Glenn

Glenn,

I think you should read this documentation a bit. It will provide the answer to why the system needs clocking... As Paolo explained, in simple terms its required to syncronise data between the gateway and the connected TDM switch.

http://www.cisco.com/en/US/products/hw/routers/ps259/products_tech_note09186a008031a072.shtml

I also doubt that your clock slips are due to the command. If you have clock slips, then I will check the interface that is providing the clock for all other interface. If there is a slip on the primary interface then there will be slips on the others

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"'Nature is too thin a screen, the glory of the omnipresent God bursts through it everywhere"-Ralph Waldo Emerson

Please rate all useful posts

Hi Guys,

I  have the Slip sec issue, it's a 28XX gateway and is experiencing Slips,

I  would like to know if configuring the "network-clock-select 1 T1 x/x/x" -  would it disrupt the services on outbound and inbound calls, if it  does i would need to inform the client in prior.

Please advice.

Thank you in advance.!!

Bijoy Jesse

Bijoy,

You should be able to add this without impact to your T1

Glenn

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