If SDH is based on node and signal synchronization, why do fluctuations occur?Very general question for a Optics beginner.
The answer lies in the practical limitations of synchronization. SDH networks use high-quality clocks feeding network el- ements. However, we must consider the following:
- A number of SDH islands use their own reference clocks, which may be nominally identical, but never exactly the same.
- Cross services carried by two or more operators always generate offset and clock fluctuations whenever a common reference clock is not used.
- Inside an SDH network, different types of breakdown may occur and cause a temporary loss of synchronization. When a node switches over to a secondary clock reference, it may be different from the original, and it could even be the internal clock of the node.
- Jitter and wander effects