Shared Risk Link Groups; Figure 46: Srlg Example - Alcatel-Lucent 7450 Manual

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Shared Risk Link Groups

Shared Risk Link Groups (SRLG) are used in the context of a gLSP to ensure that diverse

paths can be taken for different gLSPs through the optical network. For example, consider the

network shown in the following figure:

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link-ID 1500

In this dual-homing scenario, the primary gLSP takes TE-Link 1-A, and C-2, while the

secondary gLSP path takes TE-Links 1-D and F-2. In order to ensure that a failure in the

underlying optical network does not affect both the primary and secondary paths for the gLSP,

the SRLG list used by the optical network for the primary path is shared with the UNI-C (1)

by the UNI-N (A) at the time the gLSP is established along the primary path. When the

secondary path is signaled, the UNI-C (1) will signal the SRLG list to avoid to the UNI-N (D).

Note that a similar procedure is beneficial even if a UNI-C is not dual homed to the optical

network, but diverse primary and secondary paths are required through the optical network.

The 7x50 supports two methods for indicating a set of SRLGs to exclude:

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link-ID 2500

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Explicit configuration of an SRLG list for a gLSP path. These are signaled in the

XRO of the RSVP PATH message towards the optical network

Automatic SRLG collection for a gLSP, using the procedures specified in draft-ietf-

ccamp-rsvp-te-srlg-collect-04.txt, and operate as follows:

→ Retrieving SRLG information from a UNI-N for an existing gLSP Path — When

a dual-homed UNI-C device intends to establish a gLSP path to the same

destination UNI-N device via another UNI-N node, it can request the SRLG

information for an already established gLSP path by setting the SRLG

information flag in the LSP attributes sub-object of the RSVP PATH message

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link-ID 3500

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