Is there any real implementation of LoRaWAN multicasting? According to v1.0.2 LoRaWAN specification it is possible to send multicast frames but I have not found neither a node nor a network server for doing so. Nobody knows a way?
Multicasting requires that all the devices you want to talk to are listening, so you have to start with a LoRaWAN class C stack, where devices are always listening. Using a "group address" is a trivial modification of the stack: you just have to add some code so that the device filter incoming frames that contains either its address, or the group address.
What is complicated is making the communication secure as, if you use a group shared secret key, any device in that group that is compromised gives an attacker control of the whole group. Public key cryptography can be a solution but the math is quite intensive and takes a really long time to compute on a typical small embedded processor.
On this site http://www.scoop.it/t/the-french-wireless-connection/p/4055120530/2015/11/12/lorawan-class-c-and-multicast there is link to presentation about a street lightning solution made with lorawan and they say (direct quote):
Because the downlink traffic is more significant and because of the restrictions imposed by different telecommunications authorities, the use of multicasting in LoRa™ is a must.
This means, in their solution made with LoRa their only way to send data in meaningful way is to use multicasting. At 2015 year they were communicating with almost 75k street lights all around the world on that way.