Unicast messages are sent to a single end-device and multicast messages are sent to multiple end-devices. All devices of a multicast group must share the same multicast address and associated encryption keys. All end-devices must listen to the multicast channel in order to get multicast messages (end-devices must be C-class). The best use-cases for Multicast is Lighting domain and Firmware update.

There is no ACK for Multicast messages. So we don't know if the multicast message has been received by all end-devices.

The mandatory information is :

• a Cluster name
• a Multicast address: DevAddr, a 32 bit network address (must be unique and not belong to an existing end-device)
  
• the Application session key (AppSKey) and Network session key (NWkSKey) used for frames encryption, 32 digits hexadecimal string.
• radio settings: a fixed frequency in MHz (float32)and a DataRate (a string formatted as “SFxxBWyyy” with xx from 7 to 12 and yyy = 125/250/500 for LoRa modulation or yyy=5000 for FSK modulation)
• a frame counter: FCntDown
• the LoRaWAN MAC version: for Europe 868 MHz, select 1.0.2 MAC version and Regional parameters B revision to be compatible with WMC 2.x

The multicast address and associated network session key and application session key must come from the application layer.
Class-C Multicast downlinks SHALL NOT carry MAC commands.

Yes. The same multicast adrress can be used by several Multicast groups.

Yes. A end-device can belong to several multicast groups.

LNS selects gateways according to the following :

• Retrieve all end-devices owned by the group.
• Retrieve gateways used by these end-devices to send DataUp messages.
• Check duty cycle.
• Check DLAllowed.
• Compute coverage of each gateway.
• If one gateway covers all end-devices, select it.
• If several gateways cover all-devices, select the one with with the lower duty cycle.
• If no gateways cover all end-devices:
  • Remove end-devices not covered by any gateways.
  • Select gateways covering end-devices covered by only one gateway.
  • For remaining end-devices (covered by several gateways), select the gateway with the best coverage.

In all cases, a gateway cannot be selected if its duty cycle is over the maximum limit or if downlink is not allowed by its owner.

If a end-device has never transmitted data, it won't be taken into account for the choice of gateways used for multicast DataDown.

Here are some specific main cases:

• Case 1 :
  • Gateway 1 covers all-devices
  • Duty cycle is under its maximum limit
  • ⇒ Gateway 1 is selected to send the multicast DataDown message

• Case 2 :
• Gateway 1 and Gateway 2 cover all end-devices
• Duty cycle is under its maximum limit for both gateways
• Gateway 2 duty cycle is lower
• ⇒ Gateway 2 is selected to send the multicast DataDown message

• Case 3 :
  • Gateway 1 covers all end-devices
  • Gateway 2 covers 80% of the end-devices
  • Duty cycle is under its maximum for both gateways
  • ⇒ Gateway 1 is selected to send the multicast DataDown message

• Case 4 :
  • Gateway 1 covers 70% of the end-devices (4, 5, 6, 7, 8, 9, 10)
  • Gateway 2 covers 80% of the end-devices (1, 2 ,3 ,4, 5, 6, 7, 8)
  • Duty cycle is under its maximum limit for both gateways
  • ⇒ Gateway 1 and 2 are selected to send the multicast DataDown message

• Case 5 :
  • Gateway 1 covers 90% of the end-devices (1, 2 ,3 ,4, 5, 6, 7, 8, 9)
  • Gateway 2 covers 70% of the end-devices (1, 2 ,3 ,4, 5, 6, 7, 8)
  • Gateway 3 covers 10% of the end-devices (10)
  • Duty cycle is under its maximum limit for all gateways
  • ⇒ Gateway 1 and 3 are selected to send the multicast DataDown message

• Case 6 :
  • Gateway 1 covers 90% of the end-devices (1, 2 ,3 ,4, 5, 6, 7, 8, 9)
  • Gateway 2 covers 70% of the end-devices (1, 2 ,3 ,4, 5, 6, 7, 8)
  • Gateway 3 covers 10% of the end-devices (10)
  • Duty cycle is over for Gateway 1
  • Duty cycle is under its maximum limit for Gateway 2 and 3
  • ⇒ Due to its duty cycle, Gateway 1 cannot be used to send the multicast DataDown message. So Gateways 2 and 3 are selected. End-devices 8 and 9 may not be covered.

LNS selects gateways according to their SNR (Signal/Noise ratio). The gateway with the higher SNR (lowest noise) is choosen in priority.

For the moment, this case is not managed.