Being new to this system but based on your responses, am i right in saying that this uses a broadcast system, i.e. all nodes on the network receive the data rather than just the target PCs? I guess that would account for such a slow down. Currently our network infrastructure is about to be revamped. We have some managed switches coming into being as part of this with the idea that we can improve access to key servers etc.
As an experiment, I plugged the two test target PCs and the fog server into a small switch. We’re using our existing DHCP server rather than running this on the fog server so I started the multicast task then re-booted the PCs. Once they’d been issued with an address, I unplugged the switch from the school’s network and the multicast ran much faster. It was still slower than a unicast but certainly acceptable and miles faster than the rate I was getting beforehand. To that end quite possibly it could be a rogue device on the network causing the problems as you suggest.
One thing I noticed was the bandwidth usage seen on the fog server’s home page. With the multicast when connected on the school’s network, this hit the ceiling constantly rather than going up and down. When I looked more closely, I noticed that this ceiling was only 1MB/minute (?) where as during the unicast or multicast on what was effectively a private network, the ceiling was much higher.