Issue link: https://read.uberflip.com/i/1428383
LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 57 of 72 The authors reserve the right to change specifications without notice. 16 Class B unicast & multicast downlink channel frequencies 1514 The class B downlink channel selection mechanism depends on the way the class B beacon 1515 is being broadcasted. 1516 16.1 Single channel beacon transmission 1517 In certain regions (ex EU868) the beacon is transmitted on a single channel. In that case, all 1518 unicast&multicastClass B downlinks use a single frequency channel defined by the 1519 "PingSlotChannelReq" MAC command. The default frequency is defined in [PHY]. 1520 16.2 Frequency-hopping beacon transmission 1521 In certain regions (ex US902-928 or CN470-510) the class B beacon is transmitted following 1522 a frequency hopping pattern. 1523 In that case, by default Class B downlinks use a channel which is a function of the Time field 1524 of the last beacon (see Beacon Frame content) and the DevAddr. 1525 Class B downlink channel = [DevAddr + floor ( Beacon_Time Beacon_period )] modulo NbChannel 1526 • Whereby Beacon_Time is the 32 bit Time field of the current beacon period 1527 • Beacon_period is the length of the beacon period (defined as 128sec in the 1528 specification) 1529 • Floor designates rounding to the immediately lower integer value 1530 • DevAddr is the 32 bits network address of the device 1531 • NbChannel is the number of channel over which the beacon is frequency hopping 1532 Class B downlinks therefore hop across NbChannel channels (identical to the beacon 1533 transmission channels) in the ISM band and all Class B end-devices are equally spread 1534 amongst the NbChannel downlink channels. 1535 If the "PingSlotChannelReq" command with a valid non-zero argument is used to set the 1536 Class B downlink frequency then all subsequent ping slots should be opened on this single 1537 frequency independently of the last beacon frequency. 1538 If the "PingSlotChannelReq" command with a zero argument is sent, the end-device should 1539 resume the default frequency plan, id Class B ping slots hoping across 8 channels. 1540 The underlying idea is to allow network operators to configure end-devices to use a single 1541 proprietary dedicated frequency band for the Class B downlinks if available, and to keep as 1542 much frequency diversity as possible when the ISM band is used. 1543 1544 1545