Transmission of SCHC-compressed packets over IEEE 802.15.4 networks
draft-gomez-6lo-schc-15dot4-01

Document Type Active Internet-Draft (individual)
Authors Carles Gomez  , Ana Minaburo 
Last updated 2021-10-23
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6lo Working Group                                             C.G. Gomez
Internet-Draft                                                       UPC
Intended status: Standards Track                           A.M. Minaburo
Expires: 26 April 2022                                            Acklio
                                                            October 2021

  Transmission of SCHC-compressed packets over IEEE 802.15.4 networks
                     draft-gomez-6lo-schc-15dot4-01

Abstract

   A framework called Static Context Header Compression and
   fragmentation (SCHC) has been designed with the primary goal of
   supporting IPv6 over Low Power Wide Area Network (LPWAN) technologies
   [RFC8724].  One of the SCHC components is a header compression
   mechanism.  If used properly, SCHC header compression allows a
   greater compression ratio than that achievable with traditional
   6LoWPAN header compression [RFC6282].  For this reason, it may make
   sense to use SCHC header compression in some 6LoWPAN environments,
   including IEEE 802.15.4 networks.  This document specifies how a
   SCHC-compressed packet can be carried over IEEE 802.15.4 networks.

Status of This Memo

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   license-info) in effect on the date of publication of this document.

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements language . . . . . . . . . . . . . . . . . .   4
     2.2.  Background on SCHC  . . . . . . . . . . . . . . . . . . .   4
   3.  Architecture  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Network topologies  . . . . . . . . . . . . . . . . . . .   4
     3.2.  Protocol stack  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Frame Format  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  SCHC Dispatch . . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  SCHC Header . . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Padding . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  SCHC compression for IPv6, UDP, and CoAP headers  . . . . . .   6
     5.1.  SCHC compression for IPv6 and UDP headers . . . . . . . .   6
       5.1.1.  Compression of IPv6 addresses . . . . . . . . . . . .   7
       5.1.2.  Compression of UDP ports  . . . . . . . . . . . . . .   7
     5.2.  SCHC compression for CoAP headers . . . . . . . . . . . .   7
     5.3.  Header compression examples . . . . . . . . . . . . . . .   8
   6.  Fragmentation and reassembly  . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   RFC 6282 is the main specification for IPv6 over Low power Wireless
   Personal Area Network (6LoWPAN) IPv6 header compression [RFC6282].
   This RFC was designed assuming IEEE 802.15.4 as the layer below the
   6LoWPAN adaptation layer, and it has also been reused (with proper
   adaptations) for IPv6 header compression over many other technologies
   relatively similar to IEEE 802.15.4 in terms of characteristics such
   as physical layer bit rate, layer 2 maximum payload size, etc.
   Examples of such technologies comprise BLE, DECT-ULE, ITU G.9959, MS/
   TP, NFC, and PLC.  RFC 6282 provides additional functionality, such
   as a mechanism for UDP header compression.

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   In the best cases, RFC 6282 allows to compress a 40-byte IPv6 header
   down to a 2-byte compressed header (for link-local interactions) or a
   3-byte compressed header (when global IPv6 addresses are used).  On
   the other hand, an RFC 6282 compressed UDP header has a typical size
   of 4 bytes.  Therefore, in advantageous conditions, a 48-byte
   uncompressed IPv6/UDP header may be compressed down to a 6-byte
   format (when using link-local addresses) or a 7-byte format (for
   global interactions) by using RFC 6282.

   Recently, a framework called Static Context Header Compression (SCHC)
   has been designed with the primary goal of supporting IPv6 over Low
   Power Wide Area Network (LPWAN) technologies [RFC8724].  SCHC
   comprises header compression and fragmentation functionality tailored
   to the extraordinary constraints of LPWAN technologies, which are
   more severe than those exhibited by IEEE 802.15.4 or other relatively
   similar technologies.  SCHC header compression allows a greater
   compression ratio than that of RFC 6282.  If used properly, SCHC
   allows to compress an IPv6/UDP header down to e.g. a single byte.  In
   addition, SCHC can be used to compress Constrained Application
   Protocol (CoAP) headers as well [RFC7252][RFC8824], which further
   increases the achievable performance improvement of using SCHC header
   compression, since there is no 6LoWPAN header compression defined for
   CoAP.  Therefore, it may make sense to use SCHC header compression in
   some 6LoWPAN environments [I-D.toutain-6lo-6lo-and-schc], including
   IEEE 802.15.4 networks, considering its greater efficiency.

   If SCHC header compression is added to the panoply of header
   compression mechanisms used in 6LoWPAN environments, then there is a
   need to signal when a packet header has been compressed by using
   SCHC.  To this end, the present document specifies a 6LoWPAN Dispatch
   Type for SCHC header compression [RFC4944].

   This document specifies how a SCHC-compressed packet can be carried
   over IEEE 802.15.4 networks.  Note that, as per this document, and
   while SCHC defines fragmentation mechanisms as well, 6LoWPAN/6Lo
   fragmentation is used when necessary to transport SCHC-compressed
   packets over IEEE 802.15.4 networks [RFC4944][RFC8930][RFC8931].

   TO-DO: indicate here any specific updates of RFC 8724 for use over
   IEEE 802.15.4.

2.  Terminology

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2.1.  Requirements language

   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
   BCP14 [RFC2119], [RFC8174], when, and only when, they appear in all
   capitals, as shown here.

2.2.  Background on SCHC

   The reader is expected to be familiar with the terms and concepts
   defined in the specification of SCHC (RFC 8724).

3.  Architecture

3.1.  Network topologies

   IEEE 802.15.4 supports two main network topologies: the star
   topology, and the peer-to-peer (i.e., mesh) topology.

   SCHC has been designed for LPWAN technologies, which are typically
   based on a star topology where constrained devices (e.g., sensors)
   communicate with a less constrained, central network gateway [RFC
   8376].  However, as stated in [draft-ietf-lpwan-architecture], SCHC
   is generic and it can also be used in networking environments beyond
   the ones originally considered for SCHC.

   SCHC compression is applicable to both star topology and mesh
   topology IEEE 802.15.4 networks.

3.2.  Protocol stack

   The traditional 6LoWPAN-based protocol stack for constrained devices
   (Figure 1, left) places the 6LoWPAN adaptation layer between IPv6 and
   an underlying technology such as IEEE 802.15.4.  Suitable upper layer
   protocols include CoAP [RFC7252] and UDP.  (Note that, while CoAP has
   also been specified over TCP, and TCP may play a significant role in
   IoT environments [RFC9006], 6LoWPAN header compression has not been
   defined for TCP.)

   6LoWPAN can be envisioned as a set of two main sublayers, where the
   upper one provides header compression, while the lower one offers
   fragmentation.

   This document defines an alternative approach for packet header
   compression over IEEE 802.15.4, which leads to a modified protocol
   stack (Figure 1, right).

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        +------------+          +------------+
        | CoAP, other|          | CoAP, other|
        +------------+          +------------+
        | UDP, other |          | UDP, other |
        +------------+          +------------+
        |    IPv6    |          |    IPv6    |
        +------------+          +------------+
        | 6LoWPAN HC |          |  SCHC HC   |  <-- NEW
        +------------+          +------------+
        |6LoWPAN Frag|          |6LoWPAN Frag|
        +------------+          +------------+
        |  802.15.4  |          |  802.15.4  |
        +------------+          +------------+

        Figure 1: Traditional 6LoWPAN-based protocol stack over IEEE
       802.15.4 (left) and alternative protocol stack using SCHC for
         header compression (right).  HC and Frag stand for Header
                Compression and Fragmentation, respectively.

   SCHC header compression may be applied to the headers of different
   protocols or sets of protocols.  Some examples include: i) IPv6
   packet headers, ii) joint IPv6 and UDP packet headers, iii) joint
   IPv6, UDP and CoAP packet headers, etc.

4.  Frame Format

   This document defines the frame format to be used when a SCHC-
   compressed packet is carried over IEEE 802.15.4.  Such format is
   carried as IEEE 802.15.4 frame payload.  The format comprises a SCHC
   Dispatch Type, a SCHC Packet (i.e. a SCHC-compressed packet (RFC
   8724), and Padding bits, if any).  Figure 2 illustrates the described
   frame format.

               <---------- IEEE 802.15.4 frame payload ---------->

                               <----- SCHC Packet ----->
               +---------------+-------------+---------+ - - - - +
               | SCHC Dispatch | SCHC Header | Payload | Padding |
               +---------------+-------------+---------+ - - - - +

     Figure 2: Encapsulated, SCHC-compressed packet.  Padding bits are
                              added if needed.

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4.1.  SCHC Dispatch

   Adding SCHC header compression to the panoply of header compression
   mechanisms used in 6LoWPAN/6Lo environments creates the need to
   signal when a packet header has been compressed by using SCHC.  To
   this end, the present document specifies the SCHC Dispatch.  The SCHC
   Dispatch indicates that the next field in the frame format is a SCHC-
   compressed header (SCHC Header in Figure 2, see 4.2)).

   This document defines the SCHC Dispatch as a 6LoWPAN Dispatch Type
   for SCHC header compression [RFC4944].  With the aim to minimize
   overhead, the present document allocates a 1-byte pattern in Page 0
   [RFC8025] for the SCHC Dispatch Type:

   SCHC Dispatch Type bit pattern: 01000100 (Page 0) (Note: to be
   confirmed by IANA))

4.2.  SCHC Header

   SCHC Header (Figure 2) corresponds to a packet header that has been
   compressed by using SCHC.  As defined in [RFC8724], the SCHC Header
   comprises a RuleID, and a compression residue.  The present
   specification defines a RuleID size of 8 bits.

4.3.  Padding

   If SCHC header compression leads to a SCHC Packet size of a non-
   integer number of bytes, padding bits of value equal to zero MUST be
   appended to the SCHC Packet as appropriate to align to an octet
   boundary.

5.  SCHC compression for IPv6, UDP, and CoAP headers

   SCHC header compression may be applied to the headers of different
   protocols or sets of protocols.  Some examples include: i) IPv6
   packet headers, ii) joint IPv6 and UDP packet headers, iii) joint
   IPv6, UDP and CoAP packet headers, etc.

5.1.  SCHC compression for IPv6 and UDP headers

   With the exception of IPv6 addresses and UDP ports, IPv6 and UDP
   header fields MUST be compressed as per Section 10 of RFC 8724.

   IPv6 addresses are split into two 64-bit-long fields; one for the
   prefix and one for the Interface Identifier (IID).

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   To allow for a single Rule being used for both directions, RFC 8724
   identifies IPv6 addresses and UDP ports by their role (Dev or App)
   and not by their position in the header (source or destination).
   However, such roles are not applicable in some types of 6LoWPAN
   environments (e.g., when a sender and its destination are both nodes
   in a mesh topology network).  In such cases, the terms Uplink and
   Downlink as they have been defined in RFC 8724 are not applicable
   either.

   The present specification identifies IPv6 addresses and UDP ports by
   their position in the header (source or destination).  Accordingly,
   the present specification defines two new values for the Direction
   Indicator: Transmit (Tx) and Receive (Rx).

5.1.1.  Compression of IPv6 addresses

   Compression of IPv6 source and destination prefixes MUST be performed
   as per Section 10.7.1 of RFC 8724.

   If the source or destination IID are based on an L2 address, then the
   IID can be reconstructed with information coming from the L2 header.
   In that case, the TV is not set, the MO is set to "ignore" and the
   CDA is set to compute-IID.

   As described in [RFC8065], it may be undesirable to build the source
   IPv6 IID of a device out of the device address.  Another static value
   is used instead.  In that case, the TV contains the static value, the
   MO operator is set to "equal" and the CDA is set to "not-sent".

   If several IIDs are possible, then the TV contains the list of
   possible IIDs, the MO is set to "match-mapping" and the CDA is set to
   "mapping-sent".

   It may also happen that the IID variability only expresses itself on
   a few bytes.  In that case, the TV is set to the stable part of the
   IID, the MO is set to "MSB" and the CDA is set to "LSB".

5.1.2.  Compression of UDP ports

   TO-DO

5.2.  SCHC compression for CoAP headers

   CoAP header fields MUST be compressed as per Sections 4 to 6 of RFC
   8824.

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5.3.  Header compression examples

   TO-DO: provide examples for IPv6-only, IPv6/UDP and IPv6/UDP/CoAP.

6.  Fragmentation and reassembly

   After applying SCHC header compression to a packet intended for
   transmission, if the size of the resulting frame format (Section 4)
   exceeds the IEEE 802.15.4 frame payload space available, such frame
   format MUST be fragmented, carried and reassembled by means of
   6LoWPAN fragmentation and reassembly [RFC4944][RFC8930][RFC8931].

7.  IANA Considerations

   This document requests the allocation of the Dispatch Type Field bit
   pattern 01000100 (Page 0) as SCHC Dispatch Type.

8.  Security Considerations

   This document does not define SCHC header compression functionality
   beyond the one defined in RFC 8724.  Therefore, the security
   considerations in section 12.1 of RFC 8724 apply.

   As a safety measure, a SCHC decompressor implementing the present
   specification MUST NOT reconstruct a packet larger than 1500 bytes
   [RFC8724].

9.  Acknowledgments

   Ana Minaburo and Laurent Toutain suggested for the first time the use
   of SCHC in environments where 6LoWPAN has traditionally been used.
   Laurent Toutain, Pascal Thubert, Dominique Barthel, and Guangpeng Li
   made comments that helped shape this document.

   Carles Gomez has been funded in part by the Spanish Government
   through project PID2019-106808RA-I00, and by Secretaria
   d'Universitats i Recerca del Departament d'Empresa i Coneixement de
   la Generalitat de Catalunya 2017 through grant SGR 376.

10.  References

10.1.  Normative References

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

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   [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,
              <https://www.rfc-editor.org/info/rfc4944>.

   [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,
              <https://www.rfc-editor.org/info/rfc6282>.

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,
              <https://www.rfc-editor.org/info/rfc7252>.

   [RFC8025]  Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
              Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
              RFC 8025, DOI 10.17487/RFC8025, November 2016,
              <https://www.rfc-editor.org/info/rfc8025>.

   [RFC8065]  Thaler, D., "Privacy Considerations for IPv6 Adaptation-
              Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
              February 2017, <https://www.rfc-editor.org/info/rfc8065>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8724]  Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
              Zuniga, "SCHC: Generic Framework for Static Context Header
              Compression and Fragmentation", RFC 8724,
              DOI 10.17487/RFC8724, April 2020,
              <https://www.rfc-editor.org/info/rfc8724>.

   [RFC8824]  Minaburo, A., Toutain, L., and R. Andreasen, "Static
              Context Header Compression (SCHC) for the Constrained
              Application Protocol (CoAP)", RFC 8824,
              DOI 10.17487/RFC8824, June 2021,
              <https://www.rfc-editor.org/info/rfc8824>.

   [RFC8930]  Watteyne, T., Ed., Thubert, P., Ed., and C. Bormann, "On
              Forwarding 6LoWPAN Fragments over a Multi-Hop IPv6
              Network", RFC 8930, DOI 10.17487/RFC8930, November 2020,
              <https://www.rfc-editor.org/info/rfc8930>.

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   [RFC8931]  Thubert, P., Ed., "IPv6 over Low-Power Wireless Personal
              Area Network (6LoWPAN) Selective Fragment Recovery",
              RFC 8931, DOI 10.17487/RFC8931, November 2020,
              <https://www.rfc-editor.org/info/rfc8931>.

10.2.  Informative References

   [I-D.toutain-6lo-6lo-and-schc]
              Minaburo, A. and L. Toutain, "Comparison of 6lo and SCHC",
              Work in Progress, Internet-Draft, draft-toutain-6lo-6lo-
              and-schc-00, 4 November 2019,
              <https://www.ietf.org/archive/id/draft-toutain-6lo-6lo-
              and-schc-00.txt>.

   [RFC9006]  Gomez, C., Crowcroft, J., and M. Scharf, "TCP Usage
              Guidance in the Internet of Things (IoT)", RFC 9006,
              DOI 10.17487/RFC9006, March 2021,
              <https://www.rfc-editor.org/info/rfc9006>.

Authors' Addresses

   Carles Gomez
   UPC
   C/Esteve Terradas, 7
   08860 Castelldefels
   Spain

   Email: carlesgo@entel.upc.edu

   Ana Minaburo
   Acklio
   1137A avenue des Champs Blancs
   35510 Cesson-Sevigne Cedex
   France

   Email: ana@ackl.io

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