not usually pre-installed and pre-connected into the patch panel. Even if the patch
panel is manually cross-connected, no splicing is usually required end-to-end. The
difficulty, as one can observe in Figure 13.5, is that the fiber spans (edges) can
sometimes run together on portions of the route, called a shared-risk-link group
(SRLG) originally defined in Ref. [5]. Thus, the planner must be knowledgeable
about the actual fiber paths of these fiber spans to ensure that restoration objectives
are met for whatever higher-layer network link (or service) is being provisioned.
SRLGs are addressed again later in the discussion about network restoration.
Figure 13.5 illustrates only a simplified picture of the common metro layers. The
dotted lines signif ...