Do multiple programs listening to multicast cause more network traffic?

I have sever开发者_Go百科al programs listening to the same multicast stream, I'm wondering will this doubling the traffic compared with only one program listening or the traffic/bandwidth usage are the same? thanks!

The short answer is no, the amount of traffic is the same. I'll caveat that with "in most cases". Multicast packets are written to the wire using a MAC address constructed from the multicast group address. Joining a multicast group is essentially telling the NIC to listen to the appropriate MAC address. This makes each listener receive the same ethernet frame. The caveat has to do with how multicast routing may or may not work. If you have a multicast aware router then multicast traffic may traverse the router onto other networks if someone has joined the group on another subnet.

I recommend reading "TCP/IP Illustrated, Volume 1" if you plan on doing a lot of network programming. This is the best way to really understand how all of the protocols fit together.

Are the clients on the same network?

For wireless 802.11 multicast, it depends on the implementation of Multicast at the wireless access point.

Some wireless access points do multicast to unicast conversion at the datalink layer and thus send a data separately to EACH client that has joined the multicast group.

If the AP is not doing unicast conversion, generally, your network utilization does not increase.