csu/dsu ,clocking by telco

Answered Question
Jul 2nd, 2009
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Hi every body!

Acoording to my book and responses to my past posts, telco provides the clocking to csu/dsu at each side.

How about if i have two sides one in newyork the other side is india and both need to be connected by T3 circuit? how will the clocking between two telcos ( one from telco in newyork and other from telco in india) be coordinated?

It is easy to have one telco providing clocking to both sides. But some times as in our case due to geograhpical locations, it is not possible to use same telco. Then the question is how the clocking issue is resolved when two different telcos are being used for Wan connection (T3) ?


Thanks and happy 4th of july to all of you!

Correct Answer by pciaccio about 7 years 11 months ago

Remembering back to my circuit provisioning days with foreign ITMC's.. When a circuit is ordered one long distance carrier owns the circuit and is responsible for the end to end validation of the circuit prior to handing it off to the customer. That carrier should coordinate with all the foreign and intermediate breakout points down the line to asure that the circuit passes all BERT and long traffic stressing tests from end to end. It is at this point that any clocking issues will be weeded out and resolved. However All carriers will provide a high stratum clock to use as a reference. On a T-3 to be safe you should clock from the line. You would use internal and or external if you are running straight copper within your own bldg or you know that the carrier has no active componants on the line and is a straight run (useally within close proximity)... I hope I answered your question and concern....

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Correct Answer
pciaccio Thu, 07/02/2009 - 19:53
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Remembering back to my circuit provisioning days with foreign ITMC's.. When a circuit is ordered one long distance carrier owns the circuit and is responsible for the end to end validation of the circuit prior to handing it off to the customer. That carrier should coordinate with all the foreign and intermediate breakout points down the line to asure that the circuit passes all BERT and long traffic stressing tests from end to end. It is at this point that any clocking issues will be weeded out and resolved. However All carriers will provide a high stratum clock to use as a reference. On a T-3 to be safe you should clock from the line. You would use internal and or external if you are running straight copper within your own bldg or you know that the carrier has no active componants on the line and is a straight run (useally within close proximity)... I hope I answered your question and concern....

viyuan700 Thu, 07/02/2009 - 20:44
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Suppose you and me are in two geographical location and we both set our time to a standard time, will our time will match.Yes so is the case with Telcos.


All SONET/SDH systems are synchronized with a Primary Reference Clock (PRC). It is the highest quality clock can be Cesium atomic clock or coordinated universal time signal transmitted via GPS.


So there are no issue when a telco in one country connects to telco of another country. After connection between two providers the link is tested for errors for long time if both are not synchronized it will not pass the BER test.


In some cases, one country is using SONET and other SDH, even then there are no problems as they follow a standard.



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