Wireless vs wired speeds?
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From: Andy Hewitt on 13 Jun 2010 18:32 David Empson <dempson(a)actrix.gen.nz> wrote: > Andy Hewitt <thewildrover(a)me.com> wrote: [..] > > Even more 'wow', I switched it back to 2.4GHz, and now get 78Mbps. I > > then tried 'Interference Robustness', and it went down to 7Mbps. > > Any walls in the way? Lower frequencies (2.4 GHz) travel better through > solid objects than higher frequencies (5 GHz). Yeah, there was two, now it's one (see other reply). -- Andy Hewitt <http://web.me.com/andrewhewitt1/>
From: David Empson on 13 Jun 2010 20:10 Fred McKenzie <fmmck(a)aol.com> wrote: > In article <1jk1mwd.9ordk41gg4898N%dempson(a)actrix.gen.nz>, > dempson(a)actrix.gen.nz (David Empson) wrote: > > > Any form of wireless networking is half duplex - each end must take > > turns transmitting. This limits the maximum throughput due to having to > > stop and wait for the other device to respond. A file transfer involves > > a constant stream of acknowledgement going the other way, which slows > > down the transfer. > > > > That combined with the actual bit rate for your client may explain the > > apparent lack of speed for Airport. > > David- > > AirPort is a two step system. Each data packet is sent to the AirPort, > and then the AirPort sends it to the destination. The acknowledgement > returns the same way. Doesn't this divide the theoretical data rate by > 2? Or is that factored into the calculation? In this case the hard drive is connected to the Airport Extreme, so there is only one wireless communication "hop" involved, thus the maximum speed of file transfer is probably somewhere in the order of 60% to 70% of the theoretical data rate. Acknowledgements are sent in response to every second data packet, and there is some overhead for contention; the acknowledgement packets are shorter but not short enough to make a huge difference. If you were doing file sharing between two computers via a WiFi router, then the rate would roughly halve again, due to all data packets being transmitted twice (computer A to router, router to computer B) and ditto for acknowledgements, i.e. the rate would be closer to 30% to 35% of the lowest nominal wireless network speed of the two computers. That's all assuming no other devices active on the same WiFi network, and all devices involved are doing nothing on the network apart from this single file transfer. It also assumes the hard drive at each end can keep up with that transfer rate. -- David Empson dempson(a)actrix.gen.nz
From: Andy Hewitt on 14 Jun 2010 07:29
Jaimie Vandenbergh <jaimie(a)sometimes.sessile.org> wrote: > On Sun, 13 Jun 2010 20:45:00 +0100, thewildrover(a)me.com (Andy Hewitt) > wrote: [..] > >> Even more 'wow', I switched it back to 2.4GHz, and now get 78Mbps. I > >> then tried 'Interference Robustness', and it went down to 7Mbps. > > > >Right. Couldn't let that go, so I've been messing about now. I've > >relocated the Airport box from the cupboard it was in, and now have a > >Transmit Rate of 243 :-). Much betterer! It pushed the peak data > >transfer rate to 44.5Mbps. > > I've been glancing at mine through the day, and it's varied from the > numbers up top down as far as 71, now at around 140Mbps. Not suitable > for guaranteed bandwidth! Ooh, now I've got it moving between 243 and 270 ;-) -- Andy Hewitt <http://web.me.com/andrewhewitt1/> |