For UDP broadcast gurus: Problems achieving high-bandwidth audio UDP broadcast over WiFi (802.11N and 802.11G)

Question

I\'m attempting to send multichannel audio over WiFi from one server to multiple client computers using UDP broadcast on a private network.

I\'m using software calle

Answer 1

Are all parties connected via WiFi or is the sender using a wired connection to the Access Point? Broadcast data will be transmitted as unicast data from a station to an access point and the access point will then retransmit the data as broadcast/multicast traffic so it will use twice the on-air bandwidth compared to when the sender sits on the wired side of the AP.

When sending a unicast frame the AP will wait for an ACK from the receiving station and it will retransmit the frame until the ACK arrives (or it times out). Broadcast/multicast frames are not ACKed and therefore not retransmitted. If you have a busy/noisy radio environment this will cause the likelyhood of dropped packets to increase, potentially a lot, for multicast traffic compared to unicast traffic. In an audio application this could certainly be audible.

Also, IIRC, broadcast/multicast traffic does not use the RTS/CTS procedure for reserving the media which exarbates the dropped packets problem.

It could actually be the case that multiple unicast streams work better than a single multicast stream under less-than-ideal radio conditions given that the aggregated bandwidth is high enough.

If you can I would suggest that you use wireshark to sniff the WiFi traffic and take a look at the destination address in the 802.11 header. Then you can verify if the packets are actually broadcast or not over the air.