Impairments and Other Constraints on Optical Layer Routing
RFC 4054

Document Type RFC - Informational (May 2005; No errata)
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Network Working Group                                     J. Strand, Ed.
Request for Comments: 4054                                  A. Chiu, Ed.
Category: Informational                                             AT&T
                                                                May 2005

      Impairments and Other Constraints on Optical Layer Routing

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   Optical networking poses a number challenges for Generalized Multi-
   Protocol Label Switching (GMPLS).  Fundamentally, optical technology
   is an analog rather than digital technology whereby the optical layer
   is lowest in the transport hierarchy and hence has an intimate
   relationship with the physical geography of the network.  This
   contribution surveys some of the aspects of optical networks that
   impact routing and identifies possible GMPLS responses for each:  (1)
   Constraints arising from the design of new software controllable
   network elements, (2) Constraints in a single all-optical domain
   without wavelength conversion, (3) Complications arising in more
   complex networks incorporating both all-optical and opaque
   architectures, and (4) Impacts of diversity constraints.

Table of Contents

   1.  Introduction .................................................  2
   2.  Sub-IP Area Summary and Justification of Work ................  3
   3.  Reconfigurable Network Elements ..............................  3
       3.1.  Technology Background ..................................  3
       3.2.  Implications for Routing ...............................  6
   4.  Wavelength Routed All-Optical Networks .......................  6
       4.1.  Problem Formulation ....................................  7
       4.2.  Polarization Mode Dispersion (PMD) .....................  8
       4.3.  Amplifier Spontaneous Emission .........................  9
       4.4.  Approximating the Effects of Some Other
             Impairments Constraints ................................ 10
       4.5.  Other Impairment Considerations ........................ 13

Strand & Chiu                Informational                      [Page 1]
RFC 4054                 Optical Layer Routing                  May 2005

       4.6.  An Alternative Approach - Using Maximum
             Distance as the Only Constraint ........................ 13
       4.7.  Other Considerations ................................... 15
       4.8.  Implications for Routing and Control Plane Design ...... 15
   5.  More Complex Networks ........................................ 17
   6.  Diversity .................................................... 19
       6.1.  Background on Diversity ................................ 19
       6.2.  Implications for Routing ............................... 23
   7.  Security Considerations ...................................... 23
   8.  Acknowledgements ............................................. 24
   9.  References ................................................... 25
       9.1.  Normative References ................................... 25
       9.2.  Informative References ................................. 26
   10. Contributing Authors ......................................... 26

1.  Introduction

   Generalized Multi-Protocol Label Switching (GMPLS) [Mannie04] aims to
   extend MPLS to encompass a number of transport architectures,
   including optical networks that incorporate a number of all-optical
   and opto-electronic elements, such as optical cross-connects with
   both optical and electrical fabrics, transponders, and optical add-
   drop multiplexers.  Optical networking poses a number of challenges
   for GMPLS.  Fundamentally, optical technology is an analog rather
   than digital technology whereby the optical layer is lowest in the
   transport hierarchy and hence has an intimate relationship with the
   physical geography of the network.

   GMPLS already has incorporated extensions to deal with some of the
   unique aspects of the optical layer.  This contribution surveys some
   of the aspects of optical networks that impact routing and identifies
   possible GMPLS responses for each.  Routing constraints and/or
   complications arising from the design of network elements, the
   accumulation of signal impairments, and the need to guarantee the
   physical diversity of some circuits are discussed.

   Since the purpose of this document is to further the specification of
   GMPLS, alternative approaches to controlling an optical network are
   not discussed.  For discussions of some broader issues, see
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