Scope

1. Scope

This application note is intended for application developers building an IoT solution on Amazon Sidewalk.

On the sub-GHz LoRa link (SubG-CSS), an Endpoint reaches the medium data rate (MDR) either by holding a Gateway Session Key (GSK) session or by setting link3_data_rate to SID_LINK3_DATA_RATE_MDR at initialization. Where MDR is offered, it raises the uplink data rate, cuts airtime and allows the 500 ms asynchronous RX-window separation; link-layer acknowledgement with retries needs a session. MDR is not available in the EU region (§2.1).

On the sub-GHz FSK link (SubG-FSK), a session lets the Gateway that received the uplink authenticate its sender locally with the shared session key — the Gateway derives this Endpoint’s authentication material from the session key and resolves the device address itself, instead of obtaining that material from the Amazon Sidewalk Cloud. The keys protecting your traffic are unchanged: frame authentication and payload encryption still use the network and application keys. Nothing else on that link changes; what you design for is the transition (§2.1, §2.2).

This note covers what a session unlocks and costs on each sub-GHz link (§2.1), the lifecycle your application observes (§2.2), the three settings you own and how to size them (§3, §6), plus troubleshooting and bring-up (§7, §8).

GSK is first available in Amazon Sidewalk SDK 2.0.0; read your version from sid_sdk_version.h. On an earlier SDK, sid_gsk_config.h and sid_config.gsk_config do not exist, so code referencing either fails to compile (§5).

Whether GSK is enabled for your devices is settled out of band, not in code: the Amazon Sidewalk network decides it per sub-GHz PHY, and no public API reports it (§7, §8 step 0).

Terminology

Link types. SID_LINK_TYPE_1 (1) is Bluetooth Low Energy (Bluetooth LE). SID_LINK_TYPE_2 (2) is the 900 MHz FSK link, SubG-FSK (synchronous), with profiles SID_LINK2_PROFILE_1 (0x01) and SID_LINK2_PROFILE_2 (0x02). SID_LINK_TYPE_3 has the value 4, is the 900 MHz LoRa link, SubG-CSS (asynchronous), with profiles SID_LINK3_PROFILE_A (0x80), SID_LINK3_PROFILE_B (0x81) and SID_LINK3_PROFILE_C (0x82). A “type 3” link is not a “profile 3”.
Other recurring terms — session, non-GSK mode, ack-requested uplink, keep-alive and network synchronization — are in the Glossary.