A Framework for Defining Network Complexity
draft-behringer-ncrg-complexity-framework-00

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Document Type Active Internet-Draft (individual)
Authors Michael Behringer  , Alvaro Retana  , Russ White  , Geoff Huston 
Last updated 2015-08-21
Replaces draft-irtf-ncrg-complexity-framework, draft-irtf-ncrg-network-design-complexity
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Network Working Group                                       M. Behringer
Internet-Draft                                                 A. Retana
Intended status: Informational                             Cisco Systems
Expires: February 22, 2016                                      R. White
                                                                Ericsson
                                                               G. Huston
                                                                   APNIC
                                                         August 21, 2015

              A Framework for Defining Network Complexity
              draft-behringer-ncrg-complexity-framework-00

Abstract

   Complexity is a widely used parameter in network design, yet there is
   no generally accepted definition of the term.  Complexity metrics
   exist in a wide range of research papers, but most of these address
   only a particular aspect of a network, for example the complexity of
   a graph or software.  There is a desire to define the complexity of a
   network as a whole, as deployed today to provide Internet services.
   This document provides a framework to guide research on the topic of
   network complexity, as well as some practical examples for trade-offs
   in networking.

   This document summarizes the work of the IRTF's Network Complexity
   Research Group (NCRG) at the time of its closure.  It does not
   present final results, but a snapshot of an ongoing activity, as a
   basis for future work.

Status of This Memo

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   This Internet-Draft will expire on February 22, 2016.

Behringer, et al.       Expires February 22, 2016               [Page 1]
Internet-Draft            Complexity Framework               August 2015

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  General Considerations  . . . . . . . . . . . . . . . . . . .   4
     2.1.  The Behavior of a Complex Network . . . . . . . . . . . .   4
     2.2.  Robust Yet Fragile  . . . . . . . . . . . . . . . . . . .   4
     2.3.  The Complexity Cube . . . . . . . . . . . . . . . . . . .   5
     2.4.  Related Concepts  . . . . . . . . . . . . . . . . . . . .   5
     2.5.  Technical Debt  . . . . . . . . . . . . . . . . . . . . .   6
     2.6.  Layering considerations . . . . . . . . . . . . . . . . .   6
   3.  Tradeoffs . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  Control Plane State versus Optimal Forwarding Paths
           (Stretch) . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.2.  Configuration State versus Failure Domain Separation  . .   9
     3.3.  Policy Centralization versus Optimal Policy Application .  10
     3.4.  Configuration State versus Per Hop Forwarding
           Optimization  . . . . . . . . . . . . . . . . . . . . . .  11
     3.5.  Reactivity versus Stability . . . . . . . . . . . . . . .  12
   4.  Parameters  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   5.  Elements of Complexity  . . . . . . . . . . . . . . . . . . .  15
     5.1.  The Physical Network (Hardware) . . . . . . . . . . . . .  15
     5.2.  Algorithms  . . . . . . . . . . . . . . . . . . . . . . .  15
     5.3.  State in the Network  . . . . . . . . . . . . . . . . . .  15
     5.4.  Churn . . . . . . . . . . . . . . . . . . . . . . . . . .  15
     5.5.  Knowledge . . . . . . . . . . . . . . . . . . . . . . . .  15
   6.  Location of Complexity  . . . . . . . . . . . . . . . . . . .  16
     6.1.  Topological Location  . . . . . . . . . . . . . . . . . .  16
     6.2.  Logical Location  . . . . . . . . . . . . . . . . . . . .  16
     6.3.  Layering Considerations . . . . . . . . . . . . . . . . .  16
   7.  Dependencies  . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.1.  Local Dependencies  . . . . . . . . . . . . . . . . . . .  17
     7.2.  Network Wide Dependencies . . . . . . . . . . . . . . . .  17
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