





Internet Engineering Task Force (IETF)                   P. Thubert, Ed.
Request for Comments: 8025                                         Cisco
Updates: 4944                                                  R. Cragie
Category: Standards Track                                            ARM
ISSN: 2070-1721                                            November 2016


               IPv6 over Low-Power Wireless Personal Area
                   Network (6LoWPAN) Paging Dispatch

Abstract

   This specification updates RFC 4944 to introduce a new context switch
   mechanism for IPv6 over Low-Power Wireless Personal Area Network
   (6LoWPAN) compression, expressed in terms of Pages and signaled by a
   new Paging Dispatch.

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 7841.

   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/rfc8025.

Copyright Notice

   Copyright (c) 2016 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
   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.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Updating RFC 4944 . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Page 1 Paging Dispatch  . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Page Switch Dispatch Types  . . . . . . . . . . . . . . .   5
     6.2.  New Column in Dispatch Type Registry  . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The design of Low-Power and Lossy Networks (LLNs) is generally
   focused on saving energy, which is often a very constrained resource.
   Other constraints, such as memory capacity and duty cycle
   restrictions on LLN devices, usually derive from that primary
   concern.  Energy is often available only from primary batteries that
   are expected to last for years or is scavenged from the environment
   in very limited amounts.  Any protocol that is intended for use in
   LLNs must be designed with a primary focus on saving energy, which is
   a strict requirement.

   Controlling the amount of data transmission is one possible means of
   saving energy.  In a number of LLN standards, the frame size is
   limited to much smaller values than the IPv6 maximum transmission
   unit (MTU) of 1280 bytes.  In particular, an LLN that relies on the
   classical Physical Layer (PHY) of IEEE 802.15.4 [IEEE.802.15.4] is
   limited to 127 bytes per frame.  The need to compress IPv6 packets
   over IEEE 802.15.4 led to the 6LoWPAN Header Compression (6LoWPAN-HC)
   [RFC6282] work.

   As more and more protocols need to be compressed, the encoding
   capabilities of the original dispatch defined in the 6LowPAN
   adaptation-layer framework ([RFC4944] and [RFC6282]) becomes
   saturated.  This specification introduces a new context switch
   mechanism for 6LoWPAN compression, expressed in terms of Pages and
   signaled by a new Paging Dispatch mechanism.








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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119].

   The terminology used in this document is consistent with and
   incorporates that described in "Terms Used in Routing for Low-Power
   and Lossy Networks" [RFC7102] and "Terminology for Constrained-Node
   Networks" [RFC7228].

3.  Updating RFC 4944

   This document adapts 6LoWPAN while maintaining backward compatibility
   with IPv6 over IEEE 802.15.4 [RFC4944] by introducing the concept of
   a "parsing context" in the 6LoWPAN parser, a context being identified
   by a Page Number.  This specification defines 16 Pages.

   Pages are delimited in a 6LoWPAN packet by a Paging Dispatch value
   that indicates the next current Page.  The Page Number is encoded in
   a Paging Dispatch with the Value Bit Pattern of 11 11xxxx, where xxxx
   is the Page Number, 0 to 15, as described in Figure 1:

                            0
                            0 1 2 3 4 5 6 7
                           +-+-+-+-+-+-+-+-+
                           |1|1|1|1|Page Nb|
                           +-+-+-+-+-+-+-+-+

            Figure 1: Paging Dispatch with Page Number Encoding

   Values of the Dispatch byte defined in [RFC4944] are considered as
   belonging to the Page 0 parsing context, which is the default and
   does not need to be signaled explicitly at the beginning of a 6LoWPAN
   packet.  This ensures backward compatibility with existing
   implementations of 6LoWPAN.

   The Dispatch bits defined in [RFC4944] are used in Page 0 and are
   free to be reused in Pages 1 to 15.  In Section 4, this specification
   allocates some values in Page 1 and leaves the rest open for future
   allocations.

   Values made available by this specification in Pages 1 to 14 are to
   be assigned for new protocols whereas Page 15 is reserved for
   Experimental Use [RFC5226].





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   Note: This specification does not use the Escape Dispatch, which
   extends Page 0 to more values, but rather allocates another Dispatch
   Bit Pattern (11 11xxxx) for a new Paging Dispatch that is present in
   all Pages, including Page 0 and Pages defined in future
   specifications, to indicate the next parsing context represented by
   its Page Number.  The rationale for avoiding that approach is that
   there can be multiple occurrences of a new header indexed by this
   specification in a single frame and the overhead on an octet each
   time for the Escape Dispatch would be prohibitive.

   A Page (say Page N) is said to be active once the Page N Paging
   Dispatch is parsed, and it remains active until another Paging
   Dispatch is parsed.

4.  Page 1 Paging Dispatch

   This specification defines some special properties for Page 1,
   detailed below:

      The Dispatch bits defined for LOWPAN_IPHC by the "Compression
      Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks"
      [RFC6282] are defined with the same values in Page 1, so there is
      no need to switch context from Page 1 to Page 0 to decode a packet
      that is encoded per [RFC6282].

      Mesh Headers represent Layer 2 information and are processed
      before any Layer 3 information that is encoded in Page 1.  If a
      6LoWPAN packet requires a Mesh Header, the Mesh Header MUST always
      be placed in the packet before the first Page 1 Paging Dispatch,
      if any.

      For the same reason, Fragment Headers as defined in [RFC4944] MUST
      always be placed in the packet before the first Page 1 Paging
      Dispatch, if any.

      The NALP Dispatch Bit Pattern as defined in [RFC4944] is only
      defined for the first octet in the packet.  Switching back to Page
      0 for NALP inside a 6LoWPAN packet does not make sense.

      As a result, there is no need to restore the Page 0 parsing
      context after a context was switched to Page 1, so the value for
      the Page 0 Paging Dispatch of 11 110000 may not actually occur in
      those packets that adhere to 6LoWPAN specifications available at
      the time of writing this specification.







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5.  Security Considerations

   The security considerations of [RFC4944] and [RFC6282] apply.

6.  IANA Considerations

6.1.  Page Switch Dispatch Types

   This document allocates 16 values for "Page switch" from the
   "Dispatch Type Field" registry that was created by [RFC4944].  The
   allocated values are from 11 110000 through 11 111111 and represent
   Page Numbers 0 through 15 as discussed in this document.

6.2.  New Column in Dispatch Type Registry

   This document extends the "Dispatch Type Field" registry, which was
   created by [RFC4944] and updated by [RFC6282], by adding a new column
   called "Page".

   This document defines 16 Pages, "Page 0" to "Page 15".

   The preexisting registry content is assigned to "Page 0".

   This document also associates the Dispatch type field values that are
   allocated for LOWPAN_IPHC by [RFC6282] to Page 1.  These values range
   from 01 100000 through 01 111111 and have the same definition in Page
   1 as they do in Page 0; as a result, Page 0 and Page 1 are grouped
   together in the registry for this range.

   Values ranging from 00 000000 to 11 101111 in Page 15 (that is, all
   of Page 15 except the space used for Page switch) are reserved for
   Experimental Use [RFC5226] and shall not be assigned.

   Figure 2 represents the updates to the registry as described above.
   Refer to <http://www.iana.org/assignments/_6lowpan-parameters> for
   the complete list of updates.















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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Bit Pattern  |    Page     | Header Type         |  Reference      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               |     0       |  NALP               |  RFC 4944,      |
 |               |             |                     |  this document  |
 +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  00 xxxxxx    |    1-14     |  Unassigned         |                 |
 +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
 |               |    15       |  Reserved for       |  this document  |
 |               |             |  Experimental Use   |                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               |     0       |  ESC                |  RFC 6282,      |
 |               |             |                     |  this document  |
 +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  01 000000    |    1-14     |  Unassigned         |                 |
 +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
 |               |    15       |  Reserved for       |  this document  |
 |               |             |  Experimental Use   |                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       ...                   ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |               |    0-1      |  LOWPAN_IPHC        |  RFC 6282,      |
 |               |             |                     |  this document  |
 +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  01 1xxxxx    |    2-14     |  Unassigned         |                 |
 +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
 |               |    15       |  Reserved for       |  this document  |
 |               |             |  Experimental Use   |                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                       ...                   ...
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  11 11xxxx    |    0-15     |  Page switch        |  this document  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: Integrating the New Page Column

   Future assignments in these registries are to be coordinated via IANA
   under the policy of "Specification Required" [RFC5226].  It is
   expected that this policy will allow for other (non-IETF)
   organizations to more easily obtain assignments.











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7.  References

7.1.  Normative References

   [IEEE.802.15.4]
              IEEE, "IEEE Standard for Low-Rate Wireless Networks",
              IEEE 802.15.4-2015, DOI 10.1109/IEEESTD.2016.7460875,
              <http://ieeexplore.ieee.org/document/7460875/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
              "Transmission of IPv6 Packets over IEEE 802.15.4
              Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
              <http://www.rfc-editor.org/info/rfc4944>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
              Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
              DOI 10.17487/RFC6282, September 2011,
              <http://www.rfc-editor.org/info/rfc6282>.

7.2.  Informative References

   [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
              Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
              2014, <http://www.rfc-editor.org/info/rfc7102>.

   [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
              Constrained-Node Networks", RFC 7228,
              DOI 10.17487/RFC7228, May 2014,
              <http://www.rfc-editor.org/info/rfc7228>.












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Acknowledgments

   The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei
   Chang, Martin Turon, James Woodyatt, Samita Chakrabarti, Jonathan
   Hui, Gabriel Montenegro, and Ralph Droms for constructive reviews of
   the design in the 6lo working group.

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems
   Building D - Regus
   45 Allee des Ormes
   BP1200
   Mougins - Sophia Antipolis  06254
   France

   Phone: +33 4 97 23 26 34
   Email: pthubert@cisco.com


   Robert Cragie
   ARM Ltd.
   110 Fulbourn Road
   Cambridge  CB1 9NJ
   United Kingdom

   Email: robert.cragie@gridmerge.com























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