On Sun, Feb 1, 2015 at 6:34 PM, Andrew McGregor <[email protected]> wrote: > I missed one item in my list of potential improvements: the most braindead > thing 802.11 has to say about rates is that broadcast and multicast packets > should be sent at 'the lowest basic rate in the current supported rate set', > which is really wasteful. There are a couple of ways of dealing with this: > one, ignore the standard and pick the rate that is most likely to get the > frame to as many neighbours as possible (by a scan of the Minstrel tables). > Or two, fan it out as unicast, which might well take less airtime (due to > aggregation) as well as being much more likely to be delivered, since you > get ACKs and retries by doing that.
As far as I can see, the only sensible thing to do with multicast/broadcast is some variation of the unicast fanout, unless you've got a truly huge number of nodes. I don't know of any protocols (certainly not video streams) that actually work well with the kind of packet loss you see at medium/long range with wifi if retransmits aren't used. I've heard that openwrt already has a patch included that does this kind of fanout at the bridge layer. I've also heard of a new "reliable multicast" in some newer 802.11 variant, which essentially sends out a single multicast packet and expects an ACK from each intended recipient. Other than adding complexity, it seems like the best of both worlds. -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
