Wireless vs wired speeds?
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From: Andy Hewitt on 13 Jun 2010 05:01 With all my testing recently, I'm very puzzled by discrepancies in speeds between using wired and wireless networking. I realise that wireless issn't as good as wired in the main, however, the disrepancy just can't be explained by that, can it? I have 10/100 Ethernet or a selection of wireless protocols to use. Currently I have my Airport Extreme (10/100 ports only) box setup to use 5Ghz wide (dual channel), which *should* give me 2x 270Mbps, yes? I did a quick test with a 200MB file copy to the drive attached to the Extreme box, which is USB2 - 480Mbps. And yes, I know about the limitations of that, and it's only theoretical maximums. The actual speeds are *well* below the capability of the network though. The 200MB file took 4mins 5secs on Airport, and 3mins 8secs on Ethernet. iStat menu only shows a peak activity of about 18Mbps on Airport and 32Mbps on Ethernet. I know they're never going to reach full speed, but they're still very low. Is this just a rubbish transfer in the Airport between Airport/Ethernet and USB? -- Andy Hewitt <http://web.me.com/andrewhewitt1/>
From: David Empson on 13 Jun 2010 05:22 Andy Hewitt <thewildrover(a)me.com> wrote: > With all my testing recently, I'm very puzzled by discrepancies in > speeds between using wired and wireless networking. > > I realise that wireless issn't as good as wired in the main, however, > the disrepancy just can't be explained by that, can it? > > I have 10/100 Ethernet or a selection of wireless protocols to use. > Currently I have my Airport Extreme (10/100 ports only) box setup to use > 5Ghz wide (dual channel), which *should* give me 2x 270Mbps, yes? No, it will give you about 300 Mbps at best. If it wasn't wide band it would be limited to more like 130 Mbps. You can find out the nominal speed of your client's wirless connection by using Airport Utility to examine the list of clients connected to the base station. To get this, go into Manual Setup for your base station, then choose "Logs and Statistics" from the Base Station menu, and click the Wireless Clients tab. Each connected client is identified by MAC address (Airport ID). > I did a quick test with a 200MB file copy to the drive attached to the > Extreme box, which is USB2 - 480Mbps. And yes, I know about the > limitations of that, and it's only theoretical maximums. Divide that by 2 to get approximate real world maximum throughput for a hard drive connected to a USB port on a computer. Possibly somewhat slower for an Airport Extreme. > The actual speeds are *well* below the capability of the network though. > The 200MB file took 4mins 5secs on Airport, and 3mins 8secs on Ethernet. > iStat menu only shows a peak activity of about 18Mbps on Airport and > 32Mbps on Ethernet. USB is the bottleneck in the case of Ethernet (32 Mbps is actually pretty good for a USB connected hard drive). Airport has further performance overheads. Ethernet is almost always full duplex these days: it can simultaneously transfer 100 Mbps both ways. 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. If there are multiple base stations or multiple computers connected to the wireless network, the peak performance will be worse. -- David Empson dempson(a)actrix.gen.nz
From: Jaimie Vandenbergh on 13 Jun 2010 06:05 On Sun, 13 Jun 2010 10:01:25 +0100, thewildrover(a)me.com (Andy Hewitt) wrote: >With all my testing recently, I'm very puzzled by discrepancies in >speeds between using wired and wireless networking. > >I realise that wireless issn't as good as wired in the main, however, >the disrepancy just can't be explained by that, can it? > >I have 10/100 Ethernet or a selection of wireless protocols to use. >Currently I have my Airport Extreme (10/100 ports only) box setup to use >5Ghz wide (dual channel), which *should* give me 2x 270Mbps, yes? No, the AE signals on two channels but you can only attach a device to one of them. And 270Mbps is a theoretical maximum with no interference, never seen in the wild. The "line speed" that's in play can be seen on the Mac by alt-clicking the wifi fan in the menubar, "transmit rate". (starts up wifi...) Mine's 218Mbit/sec, between a 2009 iMac and a dual-channel AE 15 feet away through one set of floorboards. It's 162 now, after a renegotiation to get a better signal lock. Reliability wins over speed, it's the Apple way. >I did a quick test with a 200MB file copy to the drive attached to the >Extreme box, which is USB2 - 480Mbps. And yes, I know about the >limitations of that, and it's only theoretical maximums. You can usually trust USB2 to top out at 400Mbps, but not 480. >The actual speeds are *well* below the capability of the network though. >The 200MB file took 4mins 5secs on Airport, and 3mins 8secs on Ethernet. >iStat menu only shows a peak activity of about 18Mbps on Airport and >32Mbps on Ethernet. > >I know they're never going to reach full speed, but they're still very >low. Is this just a rubbish transfer in the Airport between >Airport/Ethernet and USB? Wifi. Remember that wifi is more like a hub (a contended shared only-one-speaker-at-a-time resource) than a switch, and is also very sensitive to environmental effects - walls, other signals. Cheers - Jaimie -- "I do not like the feel of the middle way; and I do not like the smell of the left hand way" -- J R R Tolkien
From: Andy Hewitt on 13 Jun 2010 06:54 Jaimie Vandenbergh <jaimie(a)sometimes.sessile.org> wrote: > On Sun, 13 Jun 2010 10:01:25 +0100, thewildrover(a)me.com (Andy Hewitt) > wrote: [..] > The "line speed" that's in play can be seen on the Mac by alt-clicking > the wifi fan in the menubar, "transmit rate". (starts up wifi...) > Mine's 218Mbit/sec, between a 2009 iMac and a dual-channel AE 15 feet > away through one set of floorboards. > > It's 162 now, after a renegotiation to get a better signal lock. > Reliability wins over speed, it's the Apple way. Wow, I didn't know about that one. Nice, thanks. That answers an awful lot then, mine's only showing 54Mbps. I have a very early model of the extreme boxes, is it possible it can't properly manage the 270Mbps protocol? Hmmm..... 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. > >I did a quick test with a 200MB file copy to the drive attached to the > >Extreme box, which is USB2 - 480Mbps. And yes, I know about the > >limitations of that, and it's only theoretical maximums. > > You can usually trust USB2 to top out at 400Mbps, but not 480. Yeah, I thought that was the case. Indeed, I thought it was worse than that - at least for large file transfers. > >The actual speeds are *well* below the capability of the network though. > >The 200MB file took 4mins 5secs on Airport, and 3mins 8secs on Ethernet. > >iStat menu only shows a peak activity of about 18Mbps on Airport and > >32Mbps on Ethernet. > > > >I know they're never going to reach full speed, but they're still very > >low. Is this just a rubbish transfer in the Airport between > >Airport/Ethernet and USB? > > Wifi. Remember that wifi is more like a hub (a contended shared > only-one-speaker-at-a-time resource) than a switch, and is also very > sensitive to environmental effects - walls, other signals. For sure, cheers. -- Andy Hewitt <http://web.me.com/andrewhewitt1/>
From: Rowland McDonnell on 13 Jun 2010 09:18
Andy Hewitt <thewildrover(a)me.com> wrote: [snip] > I did a quick test with a 200MB file copy to the drive attached to the > Extreme box, which is USB2 - 480Mbps. And yes, I know about the > limitations of that, and it's only theoretical maximums. I've never seen more than 2/3 of spec peak speed from any USB anything (instantaneous peaks, I don't know about - this is over a full file transfer). > The actual speeds are *well* below the capability of the network though. > The 200MB file took 4mins 5secs on Airport, and 3mins 8secs on Ethernet. > iStat menu only shows a peak activity of about 18Mbps on Airport and > 32Mbps on Ethernet. > > I know they're never going to reach full speed, but they're still very > low. Is this just a rubbish transfer in the Airport between > Airport/Ethernet and USB? If I'm using Ethernet and see 1/3-1/2 of potential max speed as the actual transfer speed, I'm happy enough. Ethernet's pretty damned inefficient from what I've been able to sniff out. 1/4 spec speed over a full file transfer ain't unusual - although if it's a big file and no other traffic's on the same cabling, you'll get faster. Big time lots faster, I've seen. Two Macs connected together without any other network traffic at all, oh yeah. Rowland. -- Remove the animal for email address: rowland.mcdonnell(a)dog.physics.org Sorry - the spam got to me http://www.mag-uk.org http://www.bmf.co.uk UK biker? Join MAG and the BMF and stop the Eurocrats banning biking |