Re: Faster Multicast [was Re: WatchMe-1, a VNC activity]
On Wed, 12 Aug 2009, Martin Langhoff wrote: On Wed, Aug 12, 2009 at 10:43 AM, Benjamin M. Schwartz wrote: I don't know how to test this, but I think there's a chance it could be a big win. Of course, in situations where the mDNS presence information itself is overloading the network, there's not much we can do. Get your hands on airtime.py -- and let's make sure everyone understands that in wireless networks what really matters is _airtime_. Multicast frames are sent in the slowest modulation available, and it consumes a ton of airtime. It doesn't take much to swamp the RF. I believe that the slowest modulation available is 1Mb/sec. so you would have to avoid something in the range of 30+ packets being sent before you have a chance of hitting break-even David Lang___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Re: Faster Multicast [was Re: WatchMe-1, a VNC activity]
On Wed, Aug 12, 2009 at 10:43 AM, Benjamin M. Schwartz wrote: > I don't know how to test this, but I think there's a chance it could be a > big win. Of course, in situations where the mDNS presence information > itself is overloading the network, there's not much we can do. Get your hands on airtime.py -- and let's make sure everyone understands that in wireless networks what really matters is _airtime_. Multicast frames are sent in the slowest modulation available, and it consumes a ton of airtime. It doesn't take much to swamp the RF. cheers, m -- martin.langh...@gmail.com mar...@laptop.org -- School Server Architect - ask interesting questions - don't get distracted with shiny stuff - working code first - http://wiki.laptop.org/go/User:Martinlanghoff ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
Faster Multicast [was Re: WatchMe-1, a VNC activity]
Martin Langhoff wrote: > - can we use multicast frames... and get the APs speeds bumped up to > do a "fast multicast" so as to not use up all the airtime? This would be great... and I just realized that it might also be tremendously beneficial for Telepathy-Salut. Salut uses multicast for two things: presence (mDNS) and D-Bus Tubes (a homebrew network protocol called Clique). mDNS is a classic multicast/broadcast system, where if you miss a packet, you just have to wait for the next round. Clique, however, is a "reliable multicast" system, guaranteeing in-order delivery, etc. In other words, Clique can tolerate some packet loss, because it knows how to request retransmission. My understanding is that APs use the basic rate for multicast because they presume it is an unreliable transport, and the basic rate is the least likely to drop a packet. However, for Clique, it might actually be more effective to use the highest available rate, even if it causes occasional retransmissions due to loss. I don't know how to test this, but I think there's a chance it could be a big win. Of course, in situations where the mDNS presence information itself is overloading the network, there's not much we can do. --Ben signature.asc Description: OpenPGP digital signature ___ Devel mailing list Devel@lists.laptop.org http://lists.laptop.org/listinfo/devel
