CCAMP WG - http://www.ietf.org/internet-drafts/draft-many-inference-srlg-00.txt

[Dimitri Papadimitriou <dimitri.papadimitriou@alcatel.be>]

NAME OF I-D:

http://www.ietf.org/internet-drafts/draft-many-inference-srlg-00.txt

SUMMARY:

The Shared Risk Link Group (SRLG) concept introduced in [IPO-Framework]
is considered as one of the most important criteria involved into
constraint-based path computation for non-packet LSP explicit routing, 
such as Fiber, Lambda and TDM LSP. By applying the SRLG criteria to the
constraint-based path computation, one can select a route taking into 
account physicalresource an logical structure disjointness that implies
a lower probability of simultaneous lightpath failure.

This contribution describes the various physical and logical resoucre
types considered in the SRLG concept. The proposed model focuses on the
inference of SRLG information between the network physical and 
transmission layers as well as logical structures such as geographical
locations. The main applications of the proposed model are the 
Constraint-based Shortest Path First (C-SPF) algorithm for LSP explicit 
route computation and the reduction (or summarization) of the SRLG 
information flooded throughout traffic-engineering extensions of IGP
routing protocols (such as OSPF and IS-IS). 

RELATED DOCUMENTS

http://www.ietf.org/internet-drafts/draft-awduche-mpls-te-optical-03.txt
http://www.ietf.org/internet-drafts/draft-bernstein-optical-bgp-00.txt
http://www.ietf.org/internet-drafts/draft-chiu-strand-unique-olcp-03.txt
http://www.ietf.org/internet-drafts/draft-ietf-isis-gmpls-extensions-01.txt
http://www.ietf.org/internet-drafts/draft-kompella-ospf-gmpls-extensions-01.txt
http://www.ietf.org/internet-drafts/draft-kompella-mpls-bundle-05.txt
http://www.ietf.org/internet-drafts/draft-many-ip-optical-framework-03.txt
http://www.ietf.org/internet-drafts/draft-many-optical-restoration-00.txt
http://www.ietf.org/internet-drafts/draft-rs-optical-bundling-01.txt
http://www.ietf.org/internet-drafts/draft-venkatachalam-ospf-traffic-01.txt

WHERE DOES IT FIT IN THE PICTURE OF THE SUB-IP WORK

CCAMP WG - Control C

WHY IS IT TARGETED AT THIS WG.

Many proposals include the SRLG concept (as IPO framewrok for instance) 
when considering constraint-based path computation of non-packet LSP. 
For instance, in the optical domain, the SRLG concept is used to derive
a path, which is disjoint with respect to the physical resource and 
logical topology from a given set of LSP. However, the definition of 
SRLG in the current format as described in GMPLS Traffic-Engineering 
extensions documents does not provide:
- the relationship between logical structures levels or physical
  resources
- the risk assessment during path computation implying the allocation of
  a conditional failure probability with the SRLGs
- the analysis of the specifications of constraint-based path
  computation and path re-optimization taking SRLG information into 
  account

JUSTIFICATION

The model proposed in this document covers a technique to compute SRLG
with respect to a given risk type. This is achieved by identifying for
a given physical layer the resources belonging to an SRLG. The proposed
model also permits to compute the dependencies of the resources into 
the ones belonging to lower physical layers. The result of the 
computation enables to determine the risk associated to each of the 
SRLGs. 

This document present the hierarchical model of the network resources
and the logical structures as well as the corresponding SRLG encoding. 
A proposed model for risk assessment is described when computing 
explicit routes. The appendix described a method enabling the reduction
of SRLG information which in turn enables intra- and inter-area diverse
routing.