multicast and data loss

[ded]

hello !

i would like to stream in multicast over a wifi network.there is more than one wifi accesspoint and a clients could forward 3 or 4 wifi routers.
this network has data loss and latency is really variable.
i read on wikipedia that TS use Reed-Solomon code like parchive(PAR2) to correct small data loss or transmission errors.is that possible to increase the number of correction symbols ? or there and other way to stream over this network(unicast is not possible)?

[Rémi Denis-Courmont]

Most access points can't tolerate multicast at streaming rate. This is a bandwidth problem. No error correction can fix that.

[ded]

thanks for this reply.

is there a way to check the maximum multicast bandwith like iperf on linux?

[thannoy]

multicast implies UDP, so unreliable especially over wifi and loaded networks.
If another peer send a packet to the wifi AP at the time one of yours is being sent, both packets will be merged and unreadable, they will need to be resent. In fact the same occurs on cabled network and UDP packets are not re-emitted whereas TCP are re-asked by receiver so re-emitted..

A bench will only give an idea. If one day someone use the wifi for a HTTP download while you are streaming, your streaming performances will decrease dramatically for example.
And in fact, are you sure multicasted packets are not duplicated for each peer on a wifi access point (and sent sequentially to each one), in which case performances decrease very fast depending on the number of connected/listening peers?