Issue link: https://read.uberflip.com/i/1428383
LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 12 of 72 The authors reserve the right to change specifications without notice. 3 Physical Message Formats 302 The LoRa terminology distinguishes between uplink and downlink messages. 303 3.1 Uplink Messages 304 Uplink messages are sent by end-devices to the network server relayed by one or many 305 gateways. 306 Uplink messages use the LoRa radio packet explicit mode in which the LoRa physical header 307 (PHDR) plus a header CRC (PHDR_CRC) are included. 1 The integrity of the payload is 308 protected by a CRC. 309 The PHDR, PHDR_CRC and payload CRC fields are inserted by the radio transceiver. 310 Uplink PHY: 311 Preamble PHDR PHDR_CRC PHYPayload CRC Figure 2: Uplink PHY structure 312 3.2 Downlink Messages 313 Each downlink message is sent by the network server to only one end-device and is relayed 314 by a single gateway. 2 315 Downlink messages use the radio packet explicit mode in which the LoRa physical header 316 (PHDR) and a header CRC (PHDR_CRC) are included. 3 317 Downlink PHY: 318 Preamble PHDR PHDR_CRC PHYPayload Figure 3: Downlink PHY structure 319 3.3 Receive Windows 320 Following each uplink transmission the end-device opens two short receive windows. The 321 receive window start times are defined using the end of the transmission as a reference. 322 323 1 See the LoRa radio transceiver datasheet for a description of LoRa radio packet implicit/explicit modes. 2 This specification does not describe the transmission of multicast messages from a network server to many end-devices. 3 No payload integrity check is done at this level to keep messages as short as possible with minimum impact on any duty-cycle limitations of the ISM bands used.