What is a Span (for SRP)?

This post briefly defines and describes the term: Span within a Shared-Ring Protection-Switching system.


What is a Span within a Shared-Ring Protection-Switching System?

In short, a Span is the set of fiber-optic connections between two adjacent nodes within a Shared-Ring Protection-Switching system.

In another post, we defined a Shared-Ring Protection-Switching system as a protection-switching system that contains at least three (3) nodes.

We further stated that each node (within this Shared-Ring Protection-Switching system) is connected to two neighboring nodes.

A span is a set of fiber-optic media that exists between and connects any two neighboring nodes.

I illustrate a Shared-Ring Protection-Switching system, with the Span (between Nodes B and C) highlighted below in Figure 1.

Span between Nodes B and C

Figure 1, Illustration of a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system, with the Span (between Nodes B and C) highlighted.  

What kind of Signals does a Span Transport?

In most Shared-Ring Protection-Switching systems, a span will consist of two or four fibers transporting the following optical signals.

  • Clockwise Direction – Working Transport Entity
  • Clockwise Direction – Protection Transport Entity
  • Counter-Clockwise Direction – Working Transport Entity
  • Counter-Clockwise Direction – Protection Transport Entity

Can a System-Designer implement any sort of Protection-Switching across a Span?

Yes, with a 4-Fibre/4-Lambda Shared-Ring Protection-Switching system, the user can implement Span-Switching as a form of Protection-Switching.

Please see the post on Span-Switching for more information on this topic.

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