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LPWAN                                                    P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Updates: 5172 (if approved)                                  1 July 2020
Intended status: Standards Track
Expires: 2 January 2021


                             SCHC over PPP
                 draft-thubert-intarea-schc-over-ppp-00

Abstract

   This document extends RFC 5172 to signal the use of SCHC as the
   compression method between a pair of nodes over PPP.  Combined with
   RFC 2516, this enables the use of SCHC over Ethernet and Wi-Fi.

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 2 January 2021.

Copyright Notice

   Copyright (c) 2020 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
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   provided without warranty as described in the Simplified BSD License.





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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  BCP 14  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Extending RFC 5172  . . . . . . . . . . . . . . . . . . . . .   3
   4.  Profiling SCHC for high speed links . . . . . . . . . . . . .   3
     4.1.  Mapping the SCHC Architecture . . . . . . . . . . . . . .   4
     4.2.  SCHC Parameters . . . . . . . . . . . . . . . . . . . . .   4
       4.2.1.  Resulting Packet Format . . . . . . . . . . . . . . .   5
     4.3.  Security Considerations . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The Point-to-Point Protocol (PPP) [RFC5172] provides a standard
   method of encapsulating network-layer protocol information over
   point-to-point links.  "A Method for Transmitting PPP Over Ethernet
   (PPPoE)" [RFC2516] transports PPP over Ethernet between a pair of
   nodes.  It is compatible with a translating bridge to Wi-Fi, and
   therefore enables PPP over Wi-Fi as well.

   PPP also defines an extensible Link Control Protocol, and proposes a
   family of Network Control Protocols (NCPs) for establishing and
   configuring different network-layer protocols.  "IP Version 6 over
   PPP" [RFC5072] defines the IPv6 Control Protocol (IPV6CP) , which is
   an NCP for a PPP link, and allows for the negotiation of desirable
   parameters for an IPv6 interface over PPP.

   "Negotiation for IPv6 Datagram Compression Using IPv6 Control
   Protocol" [RFC5172] defines the IPv6 datagram compression option that
   can be negotiated by a node on the link through the IPV6CP.  The
   "Static Context Header Compression (SCHC) and fragmentation for
   LPWAN, application to UDP/IPv6" [SCHC] is a compression and
   fragmentation technique that was defined after the publication of
   [RFC5172].  In order to enable SCHC over PPP and therefore Ethernet
   and Wi-Fi, [RFC5172] must be extended to signal SCHC as an additional
   compression method for use over PPP.










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2.  BCP 14

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

3.  Extending RFC 5172

   With this specification, a PPP session defines a vitual link where a
   SCHC context is established with a particular set of Rules, which is
   indicated at the set up of the PPP session as follows:

   [RFC5172] defines an IPV6CP option called the IPv6-Compression-
   Protocol Configuration option with a type of 2.  The option contains
   an IPv6-Compression-Protocol field value that indicates a compression
   protocol and an optional data field as shown in Figure 1:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |    Length     |   IPv6-Compression-Protocol   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Data ...
      +-+-+-+-+

        Figure 1: The IPv6-Compression-Protocol Configuration Option

   This specification indicates a new IPv6-Compression-Protocol field
   value for [SCHC] (see Section 5), and enables to transport a Uniform
   Resource Identifier (URI) [RFC3986] of the set of rules in the
   optional data.  The default format for the set of rules is YANG using
   the "Data Model for SCHC" [SCHC_DATA_MODEL] encoded in JSON as
   specified in [RFC7951].  The size of the URL is computed based on the
   Length of the option as Length-4.  If the encoding is asymetrical,
   the initiator of the session is considered downstream, playing the
   role of the device in an LPWAN network.

4.  Profiling SCHC for high speed links

   Appendix D of [SCHC] specifies the profile information that
   technology specifications such as this must provide.  The following
   section address this requirement.







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4.1.  Mapping the SCHC Architecture

   This specification leverages SCHC between an end point that is an IP
   Host and possibly a serial DTE (Data Terminal Equipment), and another
   that is an IP Node (either another IP Host or a Router) and possibly
   a serial DCE (Data Control Equipment), or a more modern physical or
   emulated endpoint, e.g., Ethernet devices that echange IP packets
   over PPPoE.

   Both endpoints MUST support the function of SCHC Compressor/
   Decompressor (C/D) as shown in Figure 2.


        +----------+  Wi-Fi /   +----------+                ....
        |    IP    |  Ethernet  |    IP    |            ..          )
        |   Host   +-----/------+  Router  +----------(   Internet   )
        | SCHC C/D |  Serial    | SCHC C/D |            (         )
        +----------+            +----------+               ...
                    <-- SCHC -->
                      over PPP

                        Figure 2: Typical Deployment

   The assumption for this document is that the SCHC Fragmenter/
   Reassembler (F/R) is generally not needed, because the maximum
   transmission unit (MTU) is expected to be large enough and SCHC only
   reduces the frame size vs.  native IP.

   An example use case for SCHC over PPP over Ethernet (PPPoE) would be
   to apply SCHC to streamline traffic by reducing the size of the
   frames and maintain them to a constant size and constant rate, e.g.,
   to simplify the scheduling of [DetNet] packets over TSN or one of the
   [RAW Technologies].  Scheduling on DetNet links introduces a form of
   duty cycle, but that does not affect the SCHC operation, since
   fragmentation is not provided.

   A context may be generated for a particular upper layer application,
   such as a control loop using an industrial automation protocol, to
   protect the particular flow with a DetNet service.  The context can
   be asymetric, e.g., when connecting a master and a slave, a client
   and a server, or a programmable logic controller with a sensor or an
   actuator.

4.2.  SCHC Parameters

   Compared to typical LPWANs, most serial links and emulations such as
   PPPoE are very fast and most of the constraints can be alleviated.
   For this reason, the SCHC profile for PPP is defined as follows:



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   RuleID numbering scheme: Rules are of a fixed size of two bytes,
   which allows for more than 65000 different Rules within one
   session.  Since this specification does not leverage the SCHC
      fragmentation, a SCHC packet is always in the form:


            |------- Compressed Header -------|
            +---------------------------------+--------------------+
            |  RuleID  |  Compression Residue |      Payload       |
            +---------------------------------+--------------------+
             < 2bytes >

                            Figure 3: SCHC Packet

   Maximum packet size:  MAX_PACKET_SIZE is aligned to the PPP Link MTU.

   Padding:  The L2 word is one byte, so padding is up to the next byte
      boundary.  The padding bit is a 0.

4.2.1.  Resulting Packet Format

   In the case of PPPoE, the sequence of compression and encapsulation
   is as follows:

   A packet (e.g., an IPv6 packet)
             |                                           ^ (padding bits
             v                                           |    dropped)
    +------------------+                      +--------------------+
    | SCHC Compression |                      | SCHC Decompression |
    +------------------+                      +--------------------+
             |                                           ^
             |   (No fragmentation)                      |
             v                                           |
    +--------------------+                    +--------------------+
    | PPP Session encaps |                    | PPP Session decaps |
    +--------------------+                    +--------------------+
             |                                           ^
             |                                           |
             v                                           |
     +------------------+                      +------------------+
     | PPPoE(oE) encaps |                      | PPPoE(oE) encaps |
     +------------------+                      +------------------+
             |                                           ^
             |                                           |
             +-------------------------------------------+
           Sender                                    Receiver

                         Figure 4: Stack Operation



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   In the case of PPPoE, a frame that transports an IPv6 packet
   compressed with SCHC shows as follows:


      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     +     Source MAC Address        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                               |                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   Destination MAC Address     +
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Ethernet Frame Type(0x8864)   | Ver=1 | Type=1|   Code=0      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Session ID                |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |PPP Protocol (IPv6CP) = 0x8057 |           SCHC Rule           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
    ...                        Compression                          ...
     |                           Residue                       +-+-+-+
     |                                                         | Pad |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                                                               |
     |                         Uncompressed                          |
    ...                          Original                           ...
     |                           Payload                             |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 5: SCHC over PPP over Ethernet Format

4.3.  Security Considerations

   This draft enables to use the SCHC compression and fragmentation over
   PPP and therefore Ethernet and Wi-Fi with PPPoE.  It inherits the
   possible threats against SCHC listed in the "Security considerations"
   section of [SCHC].

5.  IANA Considerations

   This document requests the allocation of a new value in the registry
   "IPv6-Compression-Protocol Types" for "SCHC".  A suggested value is
   proposed in Table 1:




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   +=======+==========================================+===============+
   | Value | Description                              | Reference     |
   +=======+==========================================+===============+
   |   4   | Static Context Header Compression (SCHC) | This document |
   +-------+------------------------------------------+---------------+

   Table 1: IP Header Compression Configuration Option Suboption Types

6.  Acknowledgments


7.  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>.

   [RFC2516]  Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,
              and R. Wheeler, "A Method for Transmitting PPP Over
              Ethernet (PPPoE)", RFC 2516, DOI 10.17487/RFC2516,
              February 1999, <https://www.rfc-editor.org/info/rfc2516>.

   [RFC5072]  Varada, S., Ed., Haskins, D., and E. Allen, "IP Version 6
              over PPP", RFC 5072, DOI 10.17487/RFC5072, September 2007,
              <https://www.rfc-editor.org/info/rfc5072>.

   [RFC5172]  Varada, S., Ed., "Negotiation for IPv6 Datagram
              Compression Using IPv6 Control Protocol", RFC 5172,
              DOI 10.17487/RFC5172, March 2008,
              <https://www.rfc-editor.org/info/rfc5172>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [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>.

   [SCHC]     Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
              Zúñiga, "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>.

8.  Informative References



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   [SCHC_DATA_MODEL]
              Minaburo, A. and L. Toutain, "Data Model for Static
              Context Header Compression (SCHC)", Work in Progress,
              Internet-Draft, draft-ietf-lpwan-schc-yang-data-model-02,
              28 February 2020, <https://tools.ietf.org/html/draft-ietf-
              lpwan-schc-yang-data-model-02>.

   [RAW Technologies]
              Thubert, P., Cavalcanti, D., Vilajosana, X., Schmitt, C.,
              and J. Farkas, "Reliable and Available Wireless
              Technologies", Work in Progress, Internet-Draft, draft-
              thubert-raw-technologies-05, 18 May 2020,
              <https://tools.ietf.org/html/draft-thubert-raw-
              technologies-05>.

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,
              <https://www.rfc-editor.org/info/rfc7951>.

   [DetNet]   Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.

Author's Address

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

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com
















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