Ring networks - G.841 - Interview notes for UPSR

       Further to Linear protection, let us read about ring protection. ITU-T recommendation covers several types of ring network architectures. Ring protection switching can be implemented at path level or at line level. Rings can  be uni-directional or bi-directional. & they may utilise 2-fiber or 4-fibers.

UPSR : Uni-directional Path Switched Ring : 

 In a uni-directional ring, service traffic flows in one direction. ( clockwise in below diagram). Protection traffic flows in opposite direction  (counter clockwise)

In this example, traffic from C to B travels in clockwise direction via A. Traffic from B to C travels directly in clockwise direction. This configuration is also known as multiplex section dedicated protection ring.  This is because, one fiber carries service traffic, while the other is dedicated to protect the main path.All traffic is added in both directions. Decision as to which to use at drop point (no signaling). Normally non-revertive, so effectively two diversity paths

Main advantage of this configurations are :

 single ended switching, simple to implement and does not require any protocol. Single ended switching is always faster while compared to dual ended switching. Chances of restoring traffic under multiple fail conditions is high. Also, implementation of this architecture is least expensive.

However this arcitecture is Inefficient for core networks. There is no spatial reuse. Node needs to continuously monitor every tributary to be dropped.

In next post let us read about BLSR - Bi-directional line switched ring