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New Member

VoIP clocking synchronization

I have a question about VoIP sync.

We have two PBX connected to routers via an IP network.

These two PBX, have a connection to the PSTN to sync the clocking with an external clocking

Assuming that only the Headquarters have a connection to the PSTN, the sync between the 2 PBX for Faxing and Taxing how can be achieved ???

If I set the NTP on both the routers to sync to a stratum 1 clocking and forcing the ISDN interface on the router to use on the E1 connection the internal router interface clock....this could help me to syncing both the PBX ???

Thanks for any help


These Snyc can be achieved also if the tow Router

How can I be sure that the Sync on VoIP between the 2 PBXes is effectively working ???

Cisco Employee

Re: VoIP clocking synchronization

If you are doing pure VoIP between the PBXs, then no TDM timing is passed.

Faxes should be fine as long as the T1 at each PBX is running clean.

ntp and clocking of ISDN ant T1 interfaces are two completely different things...

New Member

Re: VoIP clocking synchronization

What do you mean exactly with pure VoIP ??? CAS or CCS signalling ???

Is TDM timing passed with T-CCS solution ???

Cisco Employee

Re: VoIP clocking synchronization

Well, there are only packets that leave the router, there is no TDM so the timing is independent on each end.

All we do is encapsulate the date stream from the T1 send it across and play it out the other side. As long as the data is placed back the in the T1exactly as it was taken out, this works.

So you can have different clocks at each end.

Effectively, you are passing the TDM clock, but not physically.

This has absolutly nothing to do with NTP, BTW.

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