



INTAREA                                                R. Moskowitz, Ed.
Internet-Draft                                            HTT Consulting
Intended status: Standards Track                              P. Thubert
Expires: 13 April 2026                                                  
                                                                C. Gomez
                                                                     UPC
                                                             A. Minaburo
                                                              Consultant
                                                         10 October 2025


                       Protocol Numbers for SCHC
                  draft-ietf-schc-protocol-numbers-03

Abstract

   This document requests an Internet Protocol Number, an Ethertype
   assignment and well known ports for SCHC.  The SCHC architecture, the
   SCHC instance establishment, and the SCHC compression/decompression
   processes are simplified when SCHC is easily recognised.  Well-known
   protocol and port numbers are needed.  The Internet Protocol Number
   request is so that SCHC can be used for IP independent of other
   transports such as UDP and ESP.  The Ethertype is to support generic
   use of native SCHC over any IEEE 802 technology for IP and non-IP
   protocols.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 13 April 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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 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 Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Basic use case for SCHC as an Internet Protocol Number  .   4
     1.2.  Basic use case for SCHC as an Ethertype . . . . . . . . .   4
     1.3.  Basic use case for SCHC as a UDP port . . . . . . . . . .   5
     1.4.  Basic Use case for SCHC over connection-oriented
           communication . . . . . . . . . . . . . . . . . . . . . .   5
     1.5.  SCHC Port Numbers and protocol number as identifiers  . .   6
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   6
   3.  Internet Protocol Number for SCHC . . . . . . . . . . . . . .   6
   4.  Ethertype for SCHC  . . . . . . . . . . . . . . . . . . . . .   7
   5.  Transport Port Numbers for SCHC . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  IANA Internet Protocol Number Registry Update . . . . . .   7
     6.2.  IANA Ethertype Request  . . . . . . . . . . . . . . . . .   8
     6.3.  IANA SCHC Ethertype Registry  . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The Static Context Header Compression (SCHC) Architecture
   [schc-architecture] originally envisioned SCHC used at the Network
   layer to enable IPv6 over selected Low-Power Wide Area Networking
   (LPWAN) radio technologies, encompassing IP and Transport, by the
   network provider.  Then SCHC would be used by the application; this
   would include any security envelope.

   In the evolution of SCHC, compression and fragmentation are available
   at any layer.  After applying SCHC, the protocol information is
   reduced to a RuleID and the compression residue (if any).  We need to
   identify SCHC to recognise when a protocol header has been compressed
   by SCHC.



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   The identifier to be used depends on the protocol/layer in the stack
   where SCHC is applied.  It MUST be unambiguous to transform SCHC into
   an application.  And this identifier could be a protocol number and
   port numbers.

   This approach brakes down when dealing with Diet ESP [diet-esp].
   When Next Header is ESP, it is challenging for the ESP process to
   determine if an incoming ESP payload is regular ESP [RFC4303] or a
   diet ESP payload.  Careful allocation of the incoming SPI
   [ikev2-diet-esp] can mitigate this and have an implicit SCHC header,
   but it is not sound protocol design.  If the Next Header in the IP
   header were SCHC, not ESP, a clear segregation of incoming traffic is
   directly supportable.

   Additionally, SCHC can then be the Next Header within the ESP header
   with 'regular' SCHC rules for processing this content.  This approach
   will greatly simplify [diet-esp].

   DTLS 1.3 [RFC9147] adds further complications.  DTLS 1.3 headers
   themselves are typically already very compressed and SCHC would not
   provide much value.  But the UDP header in front of DTLS would
   benefit of a separate compression from the IP Header compression.
   Where it is possible with ESP's SPI to mitigate inbound packet
   processing challenges implicit SCHC would generate, DTLS header does
   not safely even provide this and a SCHC IP number is necessary to
   separate traffic.

   New IETF work has started with the SCHC WG that is chartered to:

   |  provide specifications for the application of SCHC over underlying
   |  layers, where underlying layers include but are not limited to UDP
   |  tunnels, IP, PPP, and Ethernet, as well as the use of SCHC by
   |  upper-layer protocols.

   To achieve its charter, the SCHC working group needs the allocations
   that are requested in this document.

   These issues carry over to IP Header compression if SCHC were
   available as an Ethertype (for 802 networking) and if SCHC were
   available as a TCP/UDP port number (for the application layer).  At
   each layer, SCHC solves a problem that protocol designers, using
   constrained networks, currently have to design around.









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1.1.  Basic use case for SCHC as an Internet Protocol Number

   A mobile node, or network, may use different links over a period of
   time.  In some cases the node has the multiple interfaces and, in
   theory, could tune the compression to each interface.  In other
   cases, it is the whole network that is mobile and individual nodes
   have no "knowledge" of which link with what characteristics is
   actively handling the traffic.  In either case, the node
   administrator is aware that some links are constrained and use of
   SCHC compression is highly recommended.

   One example is an Uncrewed Aircraft (UA) that uses different links
   over the duration of an operation (i.e. flight).

   *  Operation starts using a veriport's WiFi service.

   *  On gaining altitude, UA transitions to a Cellular service.

   *  On gaining more altitude, UA transitions to a constrained 700MHz
      UHF service.

   *  On approach to destination vertiport, link transition is reversed.

   The UA could use SCHC compression only on the UHF link, but this may
   complicate the implementation.

   A more complex example is an Uncrewed Cargo Aircraft that has
   multiple avionics systems, all Ethernet connected to an onboard
   router that has the multiple interfaces.  Here the nodes each manage
   their own secure path to their ground-based server, but have no
   knowledge of which link is in use to intelligently use compression.

1.2.  Basic use case for SCHC as an Ethertype

   In the case of a classical LPWAN link such as LoRa [RFC9011], the use
   of SCHC to compress the transported protocol, as well as the SCHC
   session (called instance) to use, are implicit.  The MAC-Layer
   endpoints are preconfigured so there can be only one session, and
   there can be only SCHC.  When extended to Ethernet and more powerful
   endpoint, this model is way too restrictive, and it is necessary to
   signal both the use of SCHC and the SCHC session to be used.  While
   the SCHC WG is charterd to produce the latter, the Ethertype defined
   in this document will be used to signal SCHC as the upper-layer
   protocol.

   As an example that will leverage this, Aircraft-to-anything (A2X)
   [drip-a2x-adhoc-session] and Aircraft-to-Ground
   [drip-efficient-a2g-comm] protocols are specific cases that can



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   benefit from SCHC as an Ethertype.  These can use IEEE 802 wireless
   technology and lessen spectrum contention in high traffic or long-
   range situations by minimizing the datagram size via SCHC.

   In the above uses, SCHC compresses the IPv6 header completely (all 40
   bytes), leaving only destination address (32 bytes, source address
   calcuated from content), or only 8 bytes (needs both addresses) at
   the cost of a 1-byte SCHC RuleID.  The 2-byte payload length may be
   needed in some cases (as in Section 4).

   Since the whole point of SCHC is to reduce payload size, SCHC
   directly over an 802 technology cannot be addressed via the Ethernet
   Protocol Assignment under the IANA OUI.  A distinct Ethertype is
   needed by SCHC to actually reduce payload overhead.

1.3.  Basic use case for SCHC as a UDP port

   There is a need to allow carrying SCHC-compressed data units (i.e.,
   SCHC datagrams [draft-ietf-schc-architecture]) atop UDP.  For
   example, SCHC-based header compression for Constrained Application
   Protocol (CoAP) has been specified [RFC8824].  The document entitled
   'Transmission of SCHC-compressed packets over IEEE 802.15.4 networks'
   [6lo-15dot4-schc] aims to exploit the opportunity of carrying SCHC-
   compressed CoAP messages on top of UDP.  To support this
   functionality, there is a need for UDP port numbers known by both
   endpoints (sender and receiver) that identifies the presence of a
   SCHC Stratum atop UDP, i.e., that the UDP payload is a SCHC datagram
   (in this case, a SCHC-compressed CoAP message).

   In addition, note that it is possible to use traditional 6LoWPAN
   header compression [RFC6282] to compress IPv6 and UDP headers, but
   not to compress CoAP headers.  Therefore, the only way to support
   CoAP header compression on devices running 6LoWPAN is by means of
   SCHC, which again requires to place a SCHC Stratum on top of UDP.

   SCHC header compression is also being developed for further protocols
   carried by UDP (e.g., QUIC [schc-quic-compression]).  In the future,
   SCHC may be applied to any protocol at any layer, such as DTLS and
   TCP.

1.4.  Basic Use case for SCHC over connection-oriented communication

   In a connection-oriented communication, two endpoints establish a
   session to transfer data reliably, with error detection and
   reordering of received data.  During the connection establishment
   (3-way handshake), both hosts must identify SCHC with the layer-4
   port number and exchange and agree on the SoR.  Through the data
   transfer, the management of the SoR uses the Yang data model as



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   described in the [draft-toutain-schc-coreconf-management].  Both
   endpoints must make the same changes to keep the integrity of the
   flow control.

   The SoR may contain dedicated Rules for Acknowledgements and
   connection termination.

   This approach is essential for critical business applications where
   data loss or corruption could have serious financial or legal
   consequences.

1.5.  SCHC Port Numbers and protocol number as identifiers

   In the current SCHC architecture, the SCHC Stratum Header adds
   signalling information to the SCHC packet.  It may be fully
   compressed, and it does not add any overhead in that case.  The SCHC
   Stratum Header helps to identify the use of SCHC and selects the
   correct instance and SoR in the SCHC process.  The SCHC Stratum
   Header format includes an identifier that depends on the compressed
   stack layer.  These identifiers are the protocol number at layer
   three and port numbers at layer four.

2.  Terms and Definitions

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

3.  Internet Protocol Number for SCHC

   SCHC as the IP payload SHOULD be indicated in the IPv4 "Protocol"
   field or the IPv6 "Next Header" field with a value of TBD1
   (recommended: 145) as shown below:

    +=========+=========+================+================+===========+
    | Decimal | Keyword | Protocol       | IPv6 Extension | Reference |
    |         |         |                | Header         |           |
    +=========+=========+================+================+===========+
    |    TBD1 | SCHC    | Static Context |                | This RFC  |
    |   (145) |         | Header         |                |           |
    |         |         | Compression    |                |           |
    +---------+---------+----------------+----------------+-----------+

                     Table 1: Internet Protocol Numbers



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   The SCHC compressed header with payload is shown below.  The size of
   the SCHC RuleID is variable as described in [RFC8724].  An
   implementation should have a table of source IP address and RuleID
   size.  The addresses should be represented in prefix format to allow
   for groups of addresses having the same RuleID size.

       |------- Compressed Header -------|
       +---------------------------------+--------------------+
       |  RuleID  |  Compression Residue |      Payload       |
       +---------------------------------+--------------------+

                           Figure 1: SCHC Packet

   The RuleID may be statically configured per [RFC8724], or may be
   negotiated within a protocol as in IKE [ikev2-diet-esp].

4.  Ethertype for SCHC

   The use of SCHC as an Ethertype is similar to that as in Section 3,
   above.  Immediately after the SCHC Ethertype is the RuleID as in
   Figure 1.  If the rules for the RuleID does not provide the datagram
   length, the datagram length MUST be explicit in the Compression
   Residue, as the 802 header may not provide the needed length
   information to properly process the datagram.

5.  Transport Port Numbers for SCHC

   SCHC's first function is to compress the header; with this action,
   the protocol ports are hidden from the application.  To identify SCHC
   in the upper layers, the protocols do not have a next header field.
   The port numbers are necessary to be aware that the protocol's header
   has been compressed.

6.  IANA Considerations

6.1.  IANA Internet Protocol Number Registry Update

   This document requests IANA to make the following change to the
   "Assigned Internet Protocol Numbers" [IANA-IPN] registry:

   Internet Protocol Number:
      This document defines the new Internet Protocol Number value TBD1
      (suggested: 145) (Section 3) in the "Assigned Internet Protocol
      Numbers" registry.







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    +=========+=========+================+================+===========+
    | Decimal | Keyword | Protocol       | IPv6 Extension | Reference |
    |         |         |                | Header         |           |
    +=========+=========+================+================+===========+
    |    TBD1 | SCHC    | Static Context |                | This RFC  |
    |   (145) |         | Header         |                |           |
    |         |         | Compression    |                |           |
    +---------+---------+----------------+----------------+-----------+

                                  Table 2

6.2.  IANA Ethertype Request

   IANA is requested using the process in Section 5.5 of
   [intarea-rfc7042bis], to request the Ethertype for SCHC.

6.3.  IANA SCHC Ethertype Registry

   A registry of SCHC RuleIDs for SCHC as an Ethertype may be needed.
   More discussion is needed to resolve this.  For example, split a
   1-byte RuleID in half.  The top half of 1-14 assigned to different
   domains of use, like for aviation.  A value of 15 designates that a
   2-byte RuleID is used.

7.  Security Considerations

   TBD

8.  References

8.1.  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>.

   [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>.

8.2.  Informative References









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   [6lo-15dot4-schc]
              Gomez, C. and A. Minaburo, "Transmission of SCHC-
              compressed packets over IEEE 802.15.4 networks", Work in
              Progress, Internet-Draft, draft-ietf-6lo-schc-15dot4-10, 5
              July 2025, <https://datatracker.ietf.org/doc/html/draft-
              ietf-6lo-schc-15dot4-10>.

   [diet-esp] Migault, D., Hatami, M., Cespedes, S., Atwood, J. W., Liu,
              D., Guggemos, T., Bormann, C., and D. Schinazi, "ESP
              Header Compression with Diet-ESP", Work in Progress,
              Internet-Draft, draft-ietf-ipsecme-diet-esp-09, 17 August
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              ipsecme-diet-esp-09>.

   [drip-a2x-adhoc-session]
              Moskowitz, R., Card, S. W., and A. Gurtov, "Aircraft to
              Anything AdHoc Broadcasts and Session", Work in Progress,
              Internet-Draft, draft-moskowitz-drip-a2x-adhoc-session-06,
              22 April 2025, <https://datatracker.ietf.org/doc/html/
              draft-moskowitz-drip-a2x-adhoc-session-06>.

   [drip-efficient-a2g-comm]
              Moskowitz, R., Card, S. W., and A. Gurtov, "Efficient Air-
              Ground Communications", Work in Progress, Internet-Draft,
              draft-moskowitz-drip-efficient-a2g-comm-05, 17 September
              2025, <https://datatracker.ietf.org/doc/html/draft-
              moskowitz-drip-efficient-a2g-comm-05>.

   [IANA-IPN] IANA, "Assigned Internet Protocol Numbers",
              <https://www.iana.org/assignments/protocol-numbers/
              protocol-numbers.xhtml>.

   [ikev2-diet-esp]
              Migault, D., Hatami, M., Liu, D., Preda, S., Atwood, J.
              W., Cespedes, S., Guggemos, T., and D. Schinazi, "Internet
              Key Exchange version 2 (IKEv2) extension for Header
              Compression Profile (HCP)", Work in Progress, Internet-
              Draft, draft-ietf-ipsecme-ikev2-diet-esp-extension-06, 21
              August 2025, <https://datatracker.ietf.org/doc/html/draft-
              ietf-ipsecme-ikev2-diet-esp-extension-06>.

   [intarea-rfc7042bis]
              Eastlake, D. E., Abley, J., and Y. Li, "IANA
              Considerations and IETF Protocol and Documentation Usage
              for IEEE 802 Parameters", Work in Progress, Internet-
              Draft, draft-ietf-intarea-rfc7042bis-11, 6 November 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
              rfc7042bis-11>.



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   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [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>.

   [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>.

   [RFC9011]  Gimenez, O., Ed. and I. Petrov, Ed., "Static Context
              Header Compression and Fragmentation (SCHC) over LoRaWAN",
              RFC 9011, DOI 10.17487/RFC9011, April 2021,
              <https://www.rfc-editor.org/info/rfc9011>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/info/rfc9147>.

   [schc-architecture]
              Pelov, A., Thubert, P., and A. Minaburo, "Static Context
              Header Compression (SCHC) Architecture", Work in Progress,
              Internet-Draft, draft-ietf-schc-architecture-04, 6
              February 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-schc-architecture-04>.

   [schc-quic-compression]
              Sirohi, S. and L. Toutain, "QUIC compression using SCHC",
              Work in Progress, Internet-Draft, draft-sirohi-schc-quic-
              compression-00, 12 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-sirohi-schc-
              quic-compression-00>.







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Acknowledgments

   Discussions with Pascal Thubert, lpwan co-chair, helped develop this
   approach of using SCHC E2E below the current Transport Layers.

   Adam Wiethuechter and Stuart W.  Card of AX Enterprize, LLC provided
   extensive input and review for use of SCHC for aviation air-to-air
   and air-to-ground communications.

   Carles Gomez has been funded in part by
   MCIU/AEI/10.13039/501100011033/FEDER/UE through project PID2023-
   146378NB-I00, and by Secretaria d'Universitats i Recerca del
   Departament d'Empresa i Coneixement de la Generalitat de Catalunya
   with the grant number 2021 SGR 00330.

Authors' Addresses

   Robert Moskowitz (editor)
   HTT Consulting
   Oak Park, MI 48237
   United States of America
   Email: rgm@labs.htt-consult.com


   Pascal Thubert
   06330 Roquefort-les-Pins
   France
   Email: pascal.thubert@gmail.com


   Carles Gomez
   UPC
   C/Esteve Terradas, 7
   08860 Castelldefels
   Spain
   Email: carles.gomez@upc.edu


   Ana Minaburo
   Consultant
   Rue de Rennes
   35510 Cesson-Sevigne
   France
   Email: anaminaburo@gmail.com







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