The Minimum Rank with Hysteresis Objective Function
RFC 6719

Internet Engineering Task Force (IETF)                        O. Gnawali
Request for Comments: 6719                         University of Houston
Category: Standards Track                                       P. Levis
ISSN: 2070-1721                                      Stanford University
                                                          September 2012

          The Minimum Rank with Hysteresis Objective Function

Abstract

   The Routing Protocol for Low-Power and Lossy Networks (RPL)
   constructs routes by using Objective Functions that optimize or
   constrain the routes it selects and uses.  This specification
   describes the Minimum Rank with Hysteresis Objective Function
   (MRHOF), an Objective Function that selects routes that minimize a
   metric, while using hysteresis to reduce churn in response to small
   metric changes.  MRHOF works with additive metrics along a route, and
   the metrics it uses are determined by the metrics that the RPL
   Destination Information Object (DIO) messages advertise.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6719.

Copyright Notice

   Copyright (c) 2012 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must

Gnawali & Levis              Standards Track                    [Page 1]
RFC 6719                          MRHOF                   September 2012

   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  The Minimum Rank with Hysteresis Objective Function  . . . . .  4
     3.1.  Computing the Path Cost  . . . . . . . . . . . . . . . . .  4
     3.2.  Parent Selection . . . . . . . . . . . . . . . . . . . . .  5
       3.2.1.  When Parent Selection Runs . . . . . . . . . . . . . .  6
       3.2.2.  Parent Selection Algorithm . . . . . . . . . . . . . .  6
     3.3.  Computing Rank . . . . . . . . . . . . . . . . . . . . . .  7
     3.4.  Advertising the Path Cost  . . . . . . . . . . . . . . . .  8
     3.5.  Working without Metric Containers  . . . . . . . . . . . .  8
   4.  Using MRHOF for Metric Maximization  . . . . . . . . . . . . .  9
   5.  MRHOF Variables and Parameters . . . . . . . . . . . . . . . .  9
   6.  Manageability  . . . . . . . . . . . . . . . . . . . . . . . . 10
     6.1.  Device Configuration . . . . . . . . . . . . . . . . . . . 10
     6.2.  Device Monitoring  . . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13

1.  Introduction

   An Objective Function specifies how RPL [RFC6550] selects paths.  For
   example, if an RPL instance uses an Objective Function that minimizes
   hop count, RPL will select paths with a minimum hop count.  RPL
   requires that all nodes in a network use a common Objective Function;
   relaxing this requirement may be a subject of future study.

   The nodes running RPL might use a number of metrics to describe a
   link or a node [RFC6551] and make these metrics available for route
   selection.  RPL advertises metrics in RPL Destination Information
   Object (DIO) messages with a Metric Container suboption.  An
   Objective Function can use these metrics to choose routes.

   To decouple the details of an individual metric or Objective Function
   from forwarding and routing, RPL describes routes through a value