Static Context Header Compression (SCHC) is a standard compression and fragmentation mechanism defined in th
IPv6 over LPWAN working group
at the

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and ...

. It offers compression and fragmentation of

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. I ...

/ UDP/

CoAP Constrained Application Protocol (CoAP) is a specialized Internet application protocol for constrained devices, as defined iRFC 7252 It enables those constrained devices called "nodes" to communicate with the wider Internet using similar protocols ...

packets to allow their transmission over the Low-Power Wide-Area Networks (LPWAN).

Compression scheme tailored to LPWAN

About LPWAN

Low-Power Wide-Area Network (

LPWAN A low-power wide-area network (LPWAN or LPWA network) is a type of wireless telecommunication wide area network designed to allow long-range communications at a low bit rate among things (connected objects), such as sensors operated on a batter ...

) gathers the connectivity technologies tailored for

Internet of Things The Internet of things (IoT) describes physical objects (or groups of such objects) with sensors, processing ability, software and other technologies that connect and exchange data with other devices and systems over the Internet or other com ...

(IoT), allowing for: * long-range communication (up to 40 km), * very low energy consumption (on the device side), * and energy efficiency (for networks). The trade-off for achieving these features includes severe limitation in terms of

throughput Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered ov ...

and packet size supported. Also, LPWAN come with limitations on transmission modalities since, in order to save battery, devices are dormant most of the time and wake up only episodically to transmit and receive data for a short time window. As a result, the LPWAN use their specific protocols, each adapted to their own specificities. Most importantly, they cannot carry

, which was designed to allocate addresses to the billions of IoT connected devices.

IETF compression standards

''In the early 2000s, the IETF produced the first wave of mature standards for compression and fragmentation:'' * '' RoHC (Robust Header Compression) in 2001,'' * ''and

6LoWPAN 6LoWPAN (acronym of "IPv6 over Low-Power Wireless Personal Area Networks") in '6LoWPAN: The Embedded Internet', Shelby and Bormann redefine the 6LoWPAN acronym as "IPv6 over lowpower wireless area networks," arguing that "Personal" is no longer rel ...

(IPv6 over Low-Power Wireless Personal Area Networks) in 2007.'' Yet, these compression schemes cannot fit the LPWAN specificities.'''' SCHC associates the benefits of the RoHC context, which provides high flexibility in the fields processing, and of the 6LoWPAN operations to avoid transiting fields that are known by the other side.''''

SCHC compression

SCHC takes advantage of the

characteristics (no routing, highly predictable traffic format and content of messages) to reduce the overhead to a few bytes and save network traffic. The SCHC compression is based on the notion of context. A context is a set of rules that describes the communication context, meaning the header fields. It is shared and pre-provisioned in both the end-devices and the core network. The "static context" assumes that the rule description does not change during transmission. Thanks to this mechanism, IPv6/UDP headers are in most cases reduced to a small identifier.

SCHC fragmentation

When compression is not enough, SCHC provides a fragmentation mechanism that works in 3 different ways:

No-Ack

In this mode the SCHC packet is separated in multiple fragments that are blindly sent to the receiver, if the receiver missed any one packet then it won't be able to re build the sent packet.

Ack-On-Error

In this mode the concept of "windows" is used, windows have a predefined size, allowing the receiver to keep a count of which windows or windows parts have been received, at the moment the receiver gets the last fragment from the sender it will calculate which parts of the packets it has missed and send a message describing that to the sender. The sender will then initialize the retransmission of the missing packet parts.

Ack-Always

In Ack-Always mode the same retransmission mechanism as for Ack-On-Error is used except that it is not done at the end of the transmission but for each window.

Standardization efforts

The Generic Framework for Static Context Header Compression and Fragmentation
RFC 8724
has been published in April 2020. It describes the generic framework that can be used on all

technologies, and more generally on all Internet networks. Additional work is dedicated to the definition of standard parameter settings and modes of operation to optimize SCHC's performance according to the implemented protocols and the underlying LPWAN technologies:
RFC 9011
SCHC over LoRaWAN

SCHC for CoAP
SCHC over NB-IoT

SCHC over SigfoxSCHC over IEEE 802.15.4 networks
In May 17 2022, The LoRa Alliance (global association of companies backing the open LoRaWAN® standard for the internet of things low-power wide-area networks) announced that LoRaWAN now seamlessly supports Internet Protocol version 6 (IPv6) from end-to-end. By expanding the breadth of device-to-application solutions with IPv6, LoRaWAN’s addressable IoT market is also broadened to include internet based standards required in smart electricity metering and new applications in smart buildings, industries, logistics, and homes. The Alliance released a technical specification TS 10-1.0.0 to explain how to use SCHC as an adaptation layer to enable LoRaWAN end-devices to use IPv6-based stacks over LoRaWAN. In addition, SCHC is being adopted in a joint standardization effort carried out by the

DLMS IEC 62056 is a set of standards for electricity metering data exchange by International Electrotechnical Commission. The IEC 62056 standards are the international standard versions of the DLMS/COSEM specification. DLMS or Device Langua ...

User Association and the LoRa Alliance for the

smart metering A smart meter is an electronic device that records information such as consumption of electric energy, voltage levels, current, and power factor. Smart meters communicate the information to the consumer for greater clarity of consumption beha ...

industries.

References

{{reflist

External links

IPv6 over Low Power Wide-Area Networks (LPWAN) Working group
at IETF
RFC 8724
– SCHC: Generic Framework for Static Context Header Compression and Fragmentation
RFC 9011
– SCHC over LoRaWAN
RFC 8824
– SCHC for CoAP
RFC 8376
– Low-Power Wide Area Network (LPWAN) Overview IPv6 Wireless networking standards Data compression Internet protocols Internet layer protocols