Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Clocking in SDH

Hi Guys.

It is very hard to me to understand how the clocking in SDH works. I understand, when there is one shared clock to several elements, and all the elements are synchronized to this clock and to each other. But how the elements can be synchronized when the clock is passed in the frame of SDH (in E1 byte)? How the clock can pass in some byte in the frame, for my understanding, the clock must me connected directly to all the elements? And the last question, is how can elements use internal clocks if they need to be synchronized with each other.

I will be very thankfull for your answers, this issue is very bothering me.

New Member

Re: Clocking in SDH


E1 is "orderwire Byte" and has nothing to do with Clocking/Synchronization on SDH. If you are talking about Clocking on a SDH Ring, then an Optical Mux can derive it's clock from three different sources.

1) Internal Stratum 3 (Standby normally)

2) Line (Optical Trunk cards - STM-4, STM-16)

3) External,Directly from Timing pins provided on mux, which are connected to GPS enabled Stratum 1 Timing source.

Normally One or Two Mux's in a ring are Timed externally to a Stratum 1 source (highest possible) and rest of mux's on Ring derive their clocking from their Optical Trunk cards.

Check this link as well,

New Member

Re: Clocking in SDH


Can we change in GSR 12k line cards from default stratum 3 to 1.

We have the problem of connecting the DWDM link between two locations, becuase of the clocking because the Nortel gear will work fine if we can use Stratum 1 in Cisco router's interfaces.

Thanks for help in advance.


CreatePlease login to create content