ROLL P. Thubert, Ed.
Internet-Draft J. Hui
Intended status: Standards Track Cisco
Expires: August 29, 2013 February 25, 2013
LLN Fragment Forwarding and Recovery
draft-thubert-roll-forwarding-frags-01
Abstract
In order to be routed, a fragmented packet must be reassembled at
every hop of a multihop link where lower layer fragmentation occurs.
Considering that the IPv6 minimum MTU is 1280 bytes and that an an
802.15.4 frame can have a payload limited to 74 bytes in the worst
case, a packet might end up fragmented into as many as 18 fragments
at the 6LoWPAN shim layer. If a single one of those fragments is
lost in transmission, all fragments must be resent, further
contributing to the congestion that might have caused the initial
packet loss. This draft introduces a simple protocol to forward and
recover individual fragments that might be lost over multiple hops
between 6LoWPAN endpoints.
Status of this Memo
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This Internet-Draft will expire on August 29, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. New Dispatch types and headers . . . . . . . . . . . . . . . . 8
6.1. Recoverable Fragment Dispatch type and Header . . . . . . 8
6.2. Fragment Acknowledgement Dispatch type and Header . . . . 9
7. Fragments Recovery . . . . . . . . . . . . . . . . . . . . . . 10
8. Forwarding Fragments . . . . . . . . . . . . . . . . . . . . . 12
8.1. Upon the first fragment . . . . . . . . . . . . . . . . . 12
8.2. Upon the next fragments . . . . . . . . . . . . . . . . . 13
8.3. Upon the fragment acknowledgements . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
In most Low Power and Lossy Network (LLN) applications, the bulk of
the traffic consists of small chunks of data (in the order few bytes
to a few tens of bytes) at a time. Given that an 802.15.4 frame can
carry 74 bytes or more in all cases, fragmentation is usually not
required. However, and though this happens only occasionally, a
number of mission critical applications do require the capability to
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