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New IETF standard "SCHC for CoAP" to reconcile interoperability, security & energy efficiency in IoT

Marianne Laurent

The SCHC header compression (RFC 8724) published in 2020 is now extended to the entire Internet of Things (IoT) protocol stack. The IETF has released a new standard defining header compression for CoAP, the Web of Things backbone protocol and its dedicated service ecosystem.

Designed by the IETF, the Constrained application Protocol (RFC 7252) extends HTTP Web services to constrained environments. In particular, it offers a set of IoT-friendly services, including asynchronous and asymmetric communication settings, automatic device discovery and multicast. CoAP, positioned at the application level, relies on UDP/IPv6 for communication. It supports the implementation of the OMA Lightweight M2M (LwM2M) device management, as well as the new OSCORE end-to-end encryption (RFC 8613) that brings IoT the equivalent of HTTPS to IoT devices.

SCHC header compression brings drastic optimizations to CoAP implementations. And that's a key issue. Because, although designed for constrained IoT technologies, a simple use of CoAP requires an overhead of about 20 bytes. And, by stretching the protocol to its limits, in the best case the overhead may only be reduced to a minimum of 11 bytes. In contrast, SCHC makes CoAP available to all LPWAN ecosystems in a very optimized way, cutting this overhead to a single byte!

The new SCHC over CoAP standard (RFC 8824) brings core innovations to address CoAP's unique features as an asymmetric protocol using flexible headers. Besides, this compression can be defined at several levels of the protocol stack, depending on the services activated and the encryption scheme. For example, by performing several stages of compression, we preserve not only the seamless interoperability via UDP/IPv6, but also all the benefits of end-to-end encryption as defined by OSCORE, while considerably limiting signaling traffic. SCHC thus demonstrates its key role in reconciling interoperability, end-to-end security and energy efficiency in IoT deployments.

Ana Minaburo, responsible for intellectual property at Acklio, co-author of RFC 8824:

“This new standard demonstrates further the power of the SCHC header compression mechanism we designed at the IETF. Far more than UDP/IPv6, CoAP is a real challenge for compression, because it is a very flexible protocol. Our ability to run efficient and reliable compression on CoAP paves the way for an extended protocol portfolio that can be optimized with SCHC.”

Dominique Barthel, researcher expert in future networks at Orange:

“We demonstrated a tracking application with a full IPv6 stack and Acklio's SCHC implementation. SCHC reduced the data volume by 20% compared to the bare CoAP/LwM2M messages, even though we added IPv6 as part of the process, providing interoperability. Applied to a standard end-to-end secured IPv6 protocol stack, SCHC reduced the traffic by 60%.”

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