RFC 3386 (rfc3386) - Page 3 of 27

Network Hierarchy and Multilayer Survivability

RFC 3386          Hierarchy & Multilayer Survivability     November 2002


   proximity to the network fault.  They operate primarily at a single
   network layer.  For hierarchy, there did not appear to be a driving
   near-term need for work on "vertical hierarchy," defined as
   communication between network layers such as Time Division
   Multiplexed (TDM)/optical and Multi-Protocol Label Switching (MPLS).
   In particular, instead of direct exchange of signaling and routing
   between vertical layers, some looser form of coordination and
   communication, such as the specification of hold-off timers, is a
   nearer term need.  For "horizontal hierarchy" in data networks, there
   are several pressing needs.  The requirement is to be able to set up
   many Label Switched Paths (LSPs) in a service provider network with
   hierarchical Interior Gateway Protocol (IGP).  This is necessary to
   support layer 2 and layer 3 Virtual Private Network (VPN) services
   that require edge-to-edge signaling across a core network.

   This document presents a proposal of the near-term and practical
   requirements for network survivability and hierarchy in current
   service provider environments.  With feedback from the working group
   solicited, the objective is to help focus the work that is being
   addressed in the TEWG (Traffic Engineering Working Group), CCAMP
   (Common Control and Measurement Plane Working Group), and other
   working groups.  A main goal of this work is to provide some
   expedience for required functionality in multi-vendor service
   provider networks.  The initial focus is primarily on intra-domain
   operations.  However, to maintain consistency in the provision of
   end-to-end service in a multi-provider environment, rules governing
   the operations of survivability mechanisms at domain boundaries must
   also be specified.  While such issues are raised and discussed, where
   appropriate, they will not be treated in depth in the initial release
   of this document.

   The document first develops a set of definitions to be used later in
   this document and potentially in other documents as well.  It then
   addresses the requirements and issues associated with service
   restoration, hierarchy, and finally a short discussion of
   survivability in hierarchical context.

   Here is a summary of the findings:

   A. Survivability Requirements

   o  need to define a small set of interoperable survivability
      approaches in packet and non-packet networks
   o  suggested survivability mechanisms include
      -  1:1 path protection with pre-established backup capacity (non-
         shared)
      -  1:1 path protection with pre-planned backup capacity (shared)




Lai, et. al.                 Informational