cbanier/microschc

Implementation of SCHC in microPython

microSCHC

In a nutshell

Implementation in microPython of SCHC as specified in RFC 8724 [1].

License

MIT License, Copyright (c) 2022 Orange, by Quentin Lampin

Installing microSCHC

Releases of microSCHC are available on PyPI. To install microSCHC, run

pip install microschc

Latest (pre-release) microSCHC versions can be built from source using hatch and installed using the wheel (.whl) file generated in the dist/ folder.

build:

hatch build -t wheel

installation:

pip install dist/microschc-<version>-py3-none-any.whl

microSCHC, developpement plan

microSCHC aims at implementing the SCHC Compression/Decompression (C/D) and Fragmentation/Reassembly (F/R) routines described in RFC 8724 [1].

The initial focus of this effort is on the Compression/Decompression (C/D) routines and parsers for typical IoT protocol stacks, i.e. based on IPv6 [2], UDP [3], CoAP [4], lwM2M.

Current features:

1. Parsers

   • IPv4
   • IPv6
   • UDP
   • CoAP (partial test coverage: options missing)
   • CoAP over UDP over IPv6 stack parser
   • lwM2M ( when not using CoAP options, i.e. CoAP payloads) --> postponed to after full SCHC C/D implementation

2. Matching Operators (MO)

   • equal
   • ignore
   • MSB(x)
   • match-mapping

3. Compression/Decompression Actions (CDA)

   1. Compression

      • not-sent
      • value-sent
      • mapping-sent
      • LSB
      • compute-* (e.g. UDP-checksum)
      • devIID
      • AppIID

   2. Decompression counterparts

      • not-sent
      • value-sent
      • mapping-sent
      • LSB
      • [-] compute-* (e.g. UDP-checksum)
        • UDP Checksum
        • UDP Length
        • IPv6 Payload Length
        • IPv4 Payload Length
      • devIID
      • AppIID

4. Rules

   • rule data model
   • rule matching algorithm
   • YANG model interpreter

5. Compression

   • field (left-)packet
   • field residues concatenation
   • length of variable length field encoding
   • packet compression

6. Context Management

   • Definition & implementation of custom SCHC Context (not specified in RFCs)

• [1] "RFC 8724 SCHC: Generic Framework for Static Context Header Compression and Fragmentation" , A. Minaburo et al.
• [2] "RFC 8200 Internet Protocol, Version 6 (IPv6) Specification, S. Deering et al."
• [3] "RFC 768 User Datagram Protocol, J. Postel"
• [4] "RFC 7252 The Constrained Application Protocol (CoAP), Z. Shelby et al."