Experimental observation of RPL: routing protocol overhead and asymmetric links
draft-audeoudh-rpl-asymmetric-links-00

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Network Working Group                                         H. Audeoud
Internet-Draft                                                 M. Heusse
Intended status: Informational                                       LIG
Expires: September 12, 2019                               March 11, 2019

     Experimental observation of RPL: routing protocol overhead and
                            asymmetric links
                 draft-audeoudh-rpl-asymmetric-links-00

Abstract

   This document summarizes our observations of the behavior of RPL on a
   testbed composed of tens of IEEE 802.15.4 nodes.  Our first
   observation is that the continuous task of estimating the link metric
   to all candidate neighbors causes a significant background load.
   This traffic is persistent, even in a stable network where DIO
   transmissions are eventually widely spaced.  Next, this document
   focuses on the case of the presence of an asymmetric link, due to
   either a muted or a deaf node.  In these circumstances, the standard
   RPL mechanisms may well generate hundreds of routing messages per
   node and per hour.

Status of This Memo

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   Copyright (c) 2019 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of

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Internet-DraExperimental observation of RPL: routing protoco  March 2019

   publication of this document.  Please review these documents
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1.  Introduction

   We present three cases in which the RPL protocol [RFC6550] incurs a
   large number of routing message transmissions even though they
   correspond to expected situations in LLNs.  This memo summarizes our
   observations on RPL that are part of a broader set of experiments
   [EXPE].

1.1.  Convergence and background traffic

   The maintenance traffic in RPL converges to a low rate of DIO
   generation when the topology is stable.  Nevertheless, the proactive
   approach of RPL imposes that the nodes permanently gauge potential
   new alternative neighbors.  This mechanism is not standardized, but
   it is necessary.  Users need to be aware of its existence and its
   footprint.

1.2.  Asymmetric links

   The quality of radio transmissions depends on the environment and on
   the radio hardware.  In particular, interferences do not have the
   same impact on all nodes.  Also, the transmission conditions are
   different between devices due to the variability of the amplifier
   gain and sensitivity.

   So a link between two nodes may be asymmetric, and not present the
   same packet delivery ratios (PDR) in both directions.  In extreme
   cases, a node N may be "deaf" (i.e. other nodes receive N's packets,
   but N does not receive anything back) or "muted" (i.e.  N receives
   properly, but is not heard).

1.3.  Experimental setup

   Table 1 presents the parameters used in the experiments.  The trickle
   settings match the recommended practice, with Imin more than one
   order of magnitude greater than the broadcast duration (125
   milliseconds in ContikiMAC).  We found that this setting effectively
   avoids DIO collisions in our experiments.

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Internet-DraExperimental observation of RPL: routing protoco  March 2019

   +-----------------------------+-------------------------------------+
   | Parameter                   | Value                               |
   +-----------------------------+-------------------------------------+
   | Platform                    | IoT-lab                             |
   |                             |                                     |
   | Sensors                     | IoT-lab's M3 motes (ARM Cortex M3   |
   |                             | STM32F103REY)                       |
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