IP Number for SCHC
draft-moskowitz-lpwan-ipnumber-01
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| Authors | Robert Moskowitz , Stuart W. Card , Adam Wiethuechter | ||
| Last updated | 2022-08-05 | ||
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draft-moskowitz-lpwan-ipnumber-01
LPWAN R. Moskowitz
Internet-Draft HTT Consulting
Intended status: Standards Track S. Card
Expires: 6 February 2023 A. Wiethuechter
AX Enterprize, LLC
5 August 2022
IP Number for SCHC
draft-moskowitz-lpwan-ipnumber-01
Abstract
This document requests an Internet Protocol Number assignment for
SCHC so that SCHC can be used for IP independent SCHC of other
transports such as UDP and ESP.
With SCHC at, effectively, the Transport Layer, this document
describes how to provide Forward Error Correction (FEC), enabled via
SCHC, at the IP datagram level. This is the most efficient bandwidth
consumption approach to FEC. As it is done outside any security
envelope, it does come with the risk of DoS attacks against the FEC.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 6 February 2023.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
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
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 IP Number . . . . . . . . . 3
1.2. FEC use case for SCHC as an IP Number . . . . . . . . . . 4
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4
3. Internet Protocol Number for SCHC . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. IANA IP Number Registry Update . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. FEC applied to IP Datagram Example . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
LPWAN Static Context Header Compression (SCHC) Architecture
[lpwan-architecture] originally envisioned SCHC used at the Network
layer, encompassing IP and Transport, by the network provider. Then
SCHC would be used by the application; this would include any
security envelope.
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.
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DTLS 1.3 [RFC9147] further complicates this. 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.
Once SCHC is available as an IP Number, it effectively becomes a new
Transport Layer and some interesting options are now possible to
support communications like UAS Command and Control (C2) that must
reach the Unmanned Aircraft (UA) from the Ground Control Station
(GCS). Forward Error Correction (FEC) can be provided at the IP
datagram level as a function of this new SCHC Transport Layer. This
addition of FEC as described in Appendix A can significantly reduce
the risk of losing a message from either lossy wireless or RED
(Random Early Discard) within the Internet routing fabric.
1.1. Basic use case for SCHC as an IP 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 UA that uses different links over the duration of
an operation (i.e. flight).
* Operation starts using 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.
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A more complex example is an Unmanned 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. FEC use case for SCHC as an IP Number
UAS C2 often requires that a command must reach the UA. There are
multiple ways, with at least one wireless link in path, to achieve a
high to mandatory level of delivery assurance. A common aviation
approach is to use a highly reliable radio band. These RF bands tend
to be narrow and are data constrained and thus typically receiver
density constrained. That is, they can only send limited, short
messages to a limited number of UA per ground antenna.
Even within this performance constraint, this RF approach requires
both the UA and GCS to be on the same wireless network, or the
intervening Internet path having an assured level of packet delivery.
This effectively rules out general purpose Internet paths where RED
practically assures packet loss at a critical time.
FEC is a long-established methodology to ensure that the message
(data) gets through. It can selectively be used on a per message
basis with the application signaling SCHC which RuleID to use. For
example there can be two RuleIDs, one for basic compression
(Section 1.1) and one that adds FEC to this (see Appendix A). Or
there could be three rules so that there can be two levels of
delivery assurance (and FEC overhead) for different levels of must
deliver.
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: 144) as shown below:
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+=========+=========+================+================+===========+
| Decimal | Keyword | Protocol | IPv6 Extension | Reference |
| | | | Header | |
+=========+=========+================+================+===========+
| TBD1 | SCHC | Static Context | | This RFC |
| (144) | | Header | | |
| | | Compression | | |
+---------+---------+----------------+----------------+-----------+
Table 1: Internet Protocol Numbers
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. IANA Considerations
4.1. IANA IP Number Registry Update
This document requests IANA to make the following change to the
"Assigned Internet Protocol Numbers" [IANA-IPN] registry:
IP Number:
This document defines the new IP Number value TBD1 (suggested:
144) (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 |
| (144) | | Header | | |
| | | Compression | | |
+---------+---------+----------------+----------------+-----------+
Table 2
5. Security Considerations
TBD
6. References
6.1. 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>.
6.2. Informative References
[diet-esp] Migault, D., Guggemos, T., Bormann, C., and D. Schinazi,
"ESP Header Compression and Diet-ESP", Work in Progress,
Internet-Draft, draft-mglt-ipsecme-diet-esp-08, 13 May
2022, <https://datatracker.ietf.org/doc/html/draft-mglt-
ipsecme-diet-esp-08>.
[IANA-IPN] IANA, "Assigned Internet Protocol Numbers",
<https://www.iana.org/assignments/protocol-numbers/
protocol-numbers.xhtml>.
[ikev2-diet-esp]
Migault, D., Guggemos, T., and D. Schinazi, "Internet Key
Exchange version 2 (IKEv2) extension for the ESP Header
Compression (EHC) Strategy", Work in Progress, Internet-
Draft, draft-mglt-ipsecme-ikev2-diet-esp-extension-02, 13
May 2022, <https://datatracker.ietf.org/doc/html/draft-
mglt-ipsecme-ikev2-diet-esp-extension-02>.
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[lpwan-architecture]
Pelov, A., Thubert, P., and A. Minaburo, "LPWAN Static
Context Header Compression (SCHC) Architecture", Work in
Progress, Internet-Draft, draft-ietf-lpwan-architecture-
02, 30 June 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-lpwan-architecture-02>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[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>.
[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>.
Appendix A. FEC applied to IP Datagram Example
FEC, applied at the IP Datagram level, is the most efficient
implementation in terms of data transmission overhead. Only the IP
Header is repeated for each message fragment and FEC frame. Reed-
Solomon FEC is used in this example.
This does come at the potential risk and overhead caused by malicious
alteration of content. The fragments have to be assembled with the
potential help of FEC before any security layer Integrity Check can
be validated. But this is just one of many DoS attacks and as these
messages will tend to be small, any memory allocation or FEC
processing should be minimal.
All SCHC rules applying to the datagram are applied first. If the
compressed residue is N bytes, then a Reed-Solomon block of N/2 is
generated across the compressed residue. The compressed residue is
now divided into 2 IP datagrams with the Reed-Solomon block being a
3rd IP datagram. The SCHC RuleID's lower 2 bits are used as a block
sequence number.
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The receiver of these blocks uses the SCHC RuleID's lower 2 bits
block sequence number to rebuild the message. If either block 1 or 2
is missing, then it is replaced with a null block and Reed-Solomon is
used to reconstruct it. The SCHC RuleID represented in the upper
bits is then used to decompress the message which is then passed to
the proper Transport Layer.
If Reed-Solomon is used to generate one parity block of length N/2 at
a transmission cost of 40 + N/2 bytes (where 40 is the size of the
IPv6 header), this is only a transmission savings where N greater
than 80. If N is less, then just sending the message twice should
result in the same recovery rate with lower transmission cost. Note
that if SCHC is independently used to compress the IPv6 header, the
resulting IPv6 residue size is used above.
Acknowledgments
Discussions with Pascal Thubert, lpwan co-chair, helped develop this
approach of using SCHC E2E below the current Transport Layers.
The addition of using SCHC as an actual Transport Layer for FEC
support came from discussions with long-range wireless providers on
mandates to assure C2 delivery and the need of an E2E approach.
Authors' Addresses
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
Email: rgm@labs.htt-consult.com
Stuart W. Card
AX Enterprize, LLC
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: stu.card@axenterprize.com
Adam Wiethuechter
AX Enterprize, LLC
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: adam.wiethuechter@axenterprize.com
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