Wanesy™ Management Center (End Of Life)

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====== FAQ - Multicast ======


===== What is Unicast and Multicast ? =====
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.

===== How can I know that multicast messages are correctly received by my end-devices ? =====
There is no ACK for Multicast messages. So we don't know if the multicast message has been received by all end-devices.

===== What is the mantadory information to create a Multicast group ? =====
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.

===== Can several Muticast groups have the same multicast adress ? =====
Yes. The same multicast adrress can be used by several Multicast groups.

===== Can a end-device belong to several Multicast groups ? =====
Yes. A end-device can belong to several multicast groups.

===== Which gateways are chosen for a C-Multicast DataDown ? =====
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.


===== Which gateways are choosen for a Unicast DataDown ? =====
LNS selects gateways according to their SNR (Signal/Noise ratio). The gateway with the higher SNR (lowest noise) is choosen in priority.

===== Is it possible that a end-device receive a C-Multicast DataDown from 2 different gateways at the same time ? =====
For the moment, this case is not managed.
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