Synchronization requirements & modes of timing in SDH transmission networks

 For synchronization of a transmission network, Frequency variation of bits transmitted should be inside the limits determined by the next hop’s ability to transmit these bits further.  Stuffing allows for some limited tolerance. In order to guarantee a low level of BER Frequencies should be synchronized all over the network.  Usually  Synchronization is done by recovering the embedded clock signal from the input signal . Synchronization source should have a very precise clock (reference clock). Reference clock might be reached only by multiple hops, but number of hops should be minimized.

Synchronization modes for transmission networks:

In a transmission network, Each network element has to be configured for time synchronization. Time reference distribution should minimize delay.

Various timing alternatives available are:

–        External

–        Line

–        Loop

–        Through.

Let us see the details .

External timing:

In this mode, all signals transmitted from a node are synchronized to an external source received by that node; i.e. BITS timing source.

Line Timing : 

In this mode,  All transmitted signals from a node are synchronized to one received signal.

Loop timing:

In this mode, the transmit signal in a optical link, east or west, is synchronized to the received signal from the same optical link.

Through timing : 

In this mode, the transmit signal in one direction of transmission around the ring is synchronized to the received signal from that same direction of transmission.