Let us consider a ring network. Normal synchronization works around a ring. In this case, Nodes B-F are line timed. Node A is timed to an external reference. When a sync source is failed, new time source should be selected in a reasonable amount of time
If synchronization is not restored , BER will be increasing through time.
SPS Timing Loops (SPS = Synchronization Protection Switching):
During a ring failure, simple reference switching would result in timing loops as shown below.
Operations – Normal Flow :
Let us read about the operation. Following diagram shows the normal flow of operation. Synchronization messaging in normal operation.
S1 = Stratum 1 Traceable
DU = Don’t UseHO = Holdover
Operations – Fiber Cut:In the ring, if fiber cuts between B & C, Node C goes into short term holdover as shown below.
Then, Node F switches to timing from Node A as shown below.
Finally ring is reconfigured and all nodes are again synchronized to BITS as shown below.
Please let me know if any clarification required :)