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IPv6 LoRaWAN Adaptation Layer FAQ
(recommended value). Compressed messages created by different rules (i.e., rules tailored to match
different message patterns) also use different FPort values, since the FPort value is the rule identifier
that the decompressor uses to retrieve the appropriate rule and correctly decompress the packet.
12. Does SCHC require changes in existing LoRaWAN networks?
SCHC operates on top of LoRaWAN as any other application does, as explained in How does SCHC
operate on top of LoRaWAN?. Therefore, SCHC does not require any change inside existing LoRaWAN
networks. However, SCHC needs a SCHC gateway to be implemented in the server side. The SCHC
gateway needs to be configured with a context (a set of compression and fragmentation rules) for
each end device that it intends to communicate with. The end devices need to implement a SCHC
layer in their protocol stack. That SCHC layer needs to be configured with a context identical to that in
the SCHC gateway in the network.
13. How does SCHC affect traffic?
In constrained IoT use cases, SCHC typically compresses the set of headers of IPv6/UDP and
application layer protocols down to a few bytes. This is similar to what is achieved with dedicated IoT
protocols above link layer. Compared to sending uncompressed IPv6/UDP over LoRaWAN, SCHC
significantly reduces the amount of bytes sent over LoRaWAN. Compared to using custom application
IoT protocols over LoRaWAN, SCHC provides IP interoperability, at a similar over-the-air protocol cost.
SCHC also readily provides a fragmentation mechanism. This allows transferring over LoRaWAN
application messages that are too big to fit the LoRaWAN maximum transmission unit at a given time,
without having to design an ad-hoc application layer fragmentation mechanism. SCHC fragments
going down from the network core to an end device trigger an immediate uplink transmission to send
the SCHC fragment acknowledgement. SCHC fragments going up from an end device to the core are
acknowledged in one or a few aggregated SCHC acknowledgement messages. If the uplink
transmission went without errors, only one acknowledgement is sent per upper layer packet. If there
were errors, a bitmap in the acknowledgement prompts for selective retransmission.
14. How to get started with SCHC over LoRaWAN?
For general information about the technology, a webinar is available on the LoRa
Alliance website. For actual use, SCHC can be implemented on top of the reference LoRaWAN stack
and can be supported by various hardware platforms with microcontrollers.
