Alcatel 1660SM Technical Handbook page 361

An example of 2F MS–SPRING is reported in Figure 214. on page 360.
In the example a ring of four nodes is protected with 2F MS–SPRING
AU4–1 carries the traffic of the span : C–B, B–A, A–D, D–C
AU4–2 carries the traffic of the span D–B (pass–through in C)
AU4–9 protects AU4–1.
AU4–10 protects AU4–2.
After a failure in the section C–B, the following actions are performed on :
– node B : Streams access 1 and 2, previously drop–inserted on AU4–1 and AU4–2
– node C: Stream access 1, previously drop–inserted on AU4.1 "side B", is switched on
– nodes A and D do not switch
We can obtain from the example that is possible bandwidth re–used for some traffic patterns (AU4–9
protects four connection on AU4–1) having the same protection for some several connections (shared
protection).
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"side A", are switched respectively on AU4–9 and AU4– 10 "side B" .
In this way, C is reached through nodes A and D.
AU4–9 "side A".
In this way, B is reached through nodes D and A.
Rx AU4–2 "side A", previously in pass–through on Tx AU4–2 "side B", is looped
on Tx AU4–10 "side A". In this way, B is reached through nodes D–A (signal
transmitted D to B).
Rx AU4–2 "side B" is no more received.
So, Rx AU4–10 "side A" is looped on the Tx AU4–2 "side A".
In this way, the signal transmitted by node B follows the path :
A–D– C and here is looped to reaches node D again.
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