LLN Minimal Fragment Forwarding
draft-watteyne-6lo-minimal-fragment-00

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6lo                                                     T. Watteyne, Ed.
Internet-Draft                                            Analog Devices
Intended status: Informational                                C. Bormann
Expires: August 20, 2018                         Universitaet Bremen TZI
                                                              P. Thubert
                                                                   Cisco
                                                       February 16, 2018

                    LLN Minimal Fragment Forwarding
                 draft-watteyne-6lo-minimal-fragment-00

Abstract

   This document gives an overview of LLN Minimal Fragment Forwarding.
   When employing adaptation layer fragmentation in 6LoWPAN, it may be
   beneficial for a forwarder not to have to reassemble each packet in
   its entirety before forwarding it.  This has been always possible
   with the original fragmentation design of RFC4944.  This document
   details the Virtual Reassembly Buffer (VRB) implementation technique
   which reduces the latency and increases end-to-end reliability in
   route-over forwarding, and discusses its limits.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 20, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of

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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   described in the Simplified BSD License.

Table of Contents

   1.  Overview of 6LoWPAN Fragmentation . . . . . . . . . . . . . .   2
   2.  Limits of Per-Hop Fragmentation and Reassembly  . . . . . . .   3
     2.1.  Latency . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Memory Management and Reliability . . . . . . . . . . . .   4
   3.  Virtual Reassembly Buffer (VRB) Implementation  . . . . . . .   4
   4.  Critique of VRB . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Overview of 6LoWPAN Fragmentation

   6LoWPAN fragmentation is defined in [RFC4944].  Although [RFC6282]
   updates [RFC4944], it does not redefine 6LoWPAN fragmentation.

   We use Figure 1 to illustrate 6LoWPAN fragmentation.  We assume node
   A forwards a packet to node B, possibly as part of a multi-hop route
   between IPv6 source and destination nodes which are neither A nor B.

                  +---+                     +---+
           ... ---| A |-------------------->| B |--- ...
                  +---+                     +---+
                                 # (frag. 5)

                123456789                 123456789
               +---------+               +---------+
               |   #  ###|               |###  #   |
               +---------+               +---------+
                  outgoing                incoming
             fragmentation                reassembly
                    buffer                buffer

         Figure 1: Fragmentation at node A, reassembly at node B.

   Node A starts by compacting the IPv6 packet using header compression
   defined in [RFC6282].  If the resulting 6LoWPAN packet does not fit
   into a single link-layer frame, node A's 6LoWPAN sublayer cuts it

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