Issue link: https://read.uberflip.com/i/1428383
LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 41 of 72 The authors reserve the right to change specifications without notice. 9 Principle of synchronous network initiated downlink (Class-B 1114 option) 1115 For a network to support end-devices of Class B, all gateways MAY synchronously broadcast 1116 a beacon providing a timing reference to the end-devices. Based on this timing reference the 1117 end-devices can periodically open receive windows, hereafter called "ping slots", which can 1118 be used by the network infrastructure to initiate a downlink communication. A network initiated 1119 downlink using one of these ping slots is called a "ping". The gateway chosen to initiate this 1120 downlink communication is selected by the Network Server.. For this reason, if an end-device 1121 moves and detects a change in the identity advertised in the received beacon, it must send 1122 an uplink to the Network Server so that the server can update the downlink routing path 1123 database. 1124 Before a device can operate in Class B mode, the following informations MUST be made 1125 available to the Network Server out-of-band. 1126 • The device's default ping-slot periodicity 1127 • Default Ping-slot data rate 1128 • Default Ping-slot channel 1129 1130 1131 All end-devices start and join the network as end-devices of Class A. The end-device 1132 application can then decide to switch to Class B. This is done through the following process: 1133 • The end-device application requests the LoRaWAN layer to switch to Class B mode. 1134 The LoRaWAN layer in the end-device searches for a beacon and returns either a 1135 BEACON_LOCKED service primitive to the application if a network beacon was found 1136 and locked or a BEACON_NOT_FOUND service primitive. To accelerate the beacon 1137 discovery the LoRaWAN layer MAY use the "DeviceTimeReq" MAC command. 1138 • Once in Class B mode, the MAC layer sets to 1 the Class B bit of the FCTRL field of 1139 every uplink frame transmitted. This bit signals to the server that the device has 1140 switched to Class B. The MAC layer will autonomously schedule a reception slot for 1141 each beacon and each ping slot. When the beacon reception is successful the end- 1142 device LoRaWAN layer forwards the beacon content to the application together with 1143 the measured radio signal strength. The end-device LoRaWAN layer takes into 1144 account the maximum possible clock drift in the scheduling of the beacon reception 1145 slot and ping slots. When a downlink is successfully demodulated during a ping slot, it 1146 is processed similarly to a downlink as described in the LoRaWAN Class A 1147 specification. 1148 • A mobile end-device should periodically inform the Network Server of its location to 1149 update the downlink route. This is done by transmitting a normal (possibly empty) 1150 "unconfirmed" or "confirmed" uplink. The end-device LoRaWAN layer will appropriately 1151 set the Class B bit to 1 in the frame's FCtrl field. Optimally this can be done more 1152 efficiently if the application detects that the node is moving by analyzing the beacon 1153 content. In that case the end-device MUST apply a random delay (as defined in Section 1154 15.5 between the beacon reception and the uplink transmission to avoid systematic 1155 uplink collisions. 1156 • At any time the Network Server MAY change the device's ping-slot downlink frequency 1157 or data rate by sending a PingSlotChannelReq MAC command. 1158 • The device MAY change the periodicity of its ping-slots at any time. To do so, it MUST 1159 temporarily stop class B operation (unset class B bit in its uplink frames) and send a 1160