Realistic WiFi throughput on a 54Mb/sec connection? - Page 1
Forum section: electronics / general

author: Delta
author_rank: Super Contributor
timestamp: April 21, 2016, 12:26:48 am
content: I've been messing around with a Raspberry Pi 2 (running Ubuntu Server), trying to find my way around Ubuntu server and generally doing stuff for the hell of it. Anyway....Setup:RPi onboard ethernet <---cat5e---> Cable modem / router <---WiFi---> T410s Thinkpad running Ubuntu MATE^|cat5e|Ancient laptop running Ubuntu ServerThe router is a Virgin Media Superhub, Netgear manufactured. The router is about 4m away from me, through a platerboard ceiling, I've got a very strong signal, as you can see from iwconfig's output below...When playing with NFS and Samba, I noticed it was a bit slow, and runningCode:iperfI noticed my network speeds were a pretty poor. I blamed the poor Pi's ethernet....However with a fully wired connection on an ancient laptop I can iperf from the Pi at over 90Mbits/s, on my T410s I struggle to hit 20Mbits/s over WiFi. Is this par for the course for supposedly 54Mbits/s WiFi?I've followed all the advicehere, with little improvement.WiFiCode:wlan0 IEEE 802.11abg ESSID:"WiFi"Mode:Managed Frequency:2.437 GHz Access Point: A0:21:B7:FE:59:18Bit Rate=54 Mb/s Tx-Power=15 dBmRetry short limit:7 RTS thr:off Fragment thr:offPower Management:offLink Quality=63/70 Signal level=-47 dBmRx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0Tx excessive retries:21 Invalid misc:15926 Missed beacon:0------------------------------------------------------------Client connecting to 192.168.0.15, TCP port 5001TCP window size: 85.0 KByte (default)------------------------------------------------------------[ 3] local 192.168.0.12 port 56485 connected with 192.168.0.15 port 5001[ ID] Interval Transfer Bandwidth[ 3] 0.0-10.1 sec 23.2 MBytes 19.3 Mbits/secWiredCode:------------------------------------------------------------Client connecting to 192.168.0.15, TCP port 5001TCP window size: 43.8 KByte (default)------------------------------------------------------------[ 3] local 192.168.0.27 port 50775 connected with 192.168.0.15 port 5001[ ID] Interval Transfer Bandwidth[ 3] 0.0-10.0 sec 111 MBytes 93.2 Mbits/sec

author: Halcyon
author_rank: Unknown
timestamp: April 21, 2016, 12:39:42 am
content: General rule of thumb I like to use is half of whatever speed your device and WiFi router is negotiating a connection at. It's not scientific by any means but it has suited me fairly well.For example, if I try to stream a video file with a codec rate of around 20-23Mbps over a 54Mbps WiFi connection, it struggles to do so and I'm in an area with very little interference from other devices and neighbouring networks. If you're in a built up area with many WiFi networks on the same band, expect far worse performance.A friend of mine living in North Sydney was struggling with his WiFi router. There were probably around 20 other networks around him. Even though it "connected" at 54Mbps, he was lucky to get 1Mbps and regular dropouts. I ended up installing an enterprise Cisco access point for him to drown out all his neighbours -- Worked perfectly (for him).Also depending on the access point, if you have clients connecting at slower rates, other clients need to wait longer for them to finish transmitting. That can slow things down quite a bit.If you can, use the 5Ghz band. So far it's much less populated and there are more channels to choose from.

author: Delta
author_rank: Super Contributor
timestamp: April 21, 2016, 01:07:46 am
content: Quote from: Halcyon on April 21, 2016, 12:39:42 amYour rule of thumb seems pretty accurate; I've just enabled 802.11n, and now get the followingCode:wlan0 IEEE 802.11abgn ESSID:"WiFi"Mode:Managed Frequency:2.437 GHz Access Point: A0:21:B7:FE:59:18Bit Rate=144.4 Mb/s Tx-Power=15 dBmRetry short limit:7 RTS thr:off Fragment thr:offPower Management:onLink Quality=65/70 Signal level=-45 dBmRx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0Tx excessive retries:0 Invalid misc:30 Missed beacon:0~$ iperf -c 192.168.0.15------------------------------------------------------------Client connecting to 192.168.0.15, TCP port 5001TCP window size: 85.0 KByte (default)------------------------------------------------------------[ 3] local 192.168.0.12 port 35635 connected with 192.168.0.15 port 5001[ ID] Interval Transfer Bandwidth[ 3] 0.0-10.0 sec 74.2 MBytes 62.2 Mbits/secCan the advertised speeds EVER be reached?I don't think we're 2.4GHz congested here, whilst I'm in an Urban area, the house is pretty isolated. I can just get a glimps of the neighbour's WiFi if I'm at the far end of the house, but not here in the living room...

author: uncle_bob
author_rank: Unknown
timestamp: April 21, 2016, 01:19:49 am
content: Quote from: Delta on April 21, 2016, 01:07:46 amHiIf you measure them the way *some* router specs apparently do, you certainly can:1) First take the wired bit load into the router, that's A2) Then take the max RF bit load out of the router, that's B3) Next comes the max RF bit load into the router, that's C4) Finally there is the wired bit load out of the router, that's DThe "speed of the router" according to some is A + B + C + D. You *might* observe that what comes in on the wire is the same as what goes out on the RF. You might also observe that you rarely transmit and receive at the same time through a single device.No, not everybody rates routers this way. After I saw the first guy doing this (on a multi band device), I started reading the fine print a *lot* closer.So - simply put - the speed their "marketing genius" came up with is not the speed your program reports. His speed is about 4X the max speed your device can ever hope to achieve through the router. Yes, that's nuts. I suspect it results in a lot of phone calls to their tech support line.Bob

author: Delta
author_rank: Super Contributor
timestamp: April 21, 2016, 01:27:44 am
content: That's proper dodgy Bob! those sneaky marketing guys!But what I meant was can you even get throughput approaching the link speed? If it says connected at XXX Mbits/s, why can we only achieve half of that at best?

author: Halcyon
author_rank: Unknown
timestamp: April 21, 2016, 02:03:40 am
content: Quote from: Delta on April 21, 2016, 01:07:46 amNot in the real world. They are theoretical maximums but don't take into account the capabilities of client devices, interference, bandwidth, protocol overheads etc... etc...Don't forget too that WiFi is half-duplex, in that when a client is transmitting, the access point is receiving and waiting for TX to finish before sending the next packet. Data isn't sent and received simultaneously like Ethernet.

author: stmdude
author_rank: Frequent Contributor
timestamp: April 21, 2016, 02:44:56 am
content: Another thing to keep in mind is that the slowest device on an AP sets the speed (for that radio).I.e, if you have your phone/ipad/whatever far away from the AP, it'll lower the bit-rate to something that gets a reasonable error-rate. 11Mbps for example.If you then sit down next to the router with your laptop, the maximum speed you can expect is 11Mbps.This is one of the main reasons I have dual-band WiFi at home (i don't have neighbors, so 2.4 and 5GHz is all mine). The devices that doesn't need speed are all on the 2.4GHz, even if they're 5GHz capable. The 5GHz is for things that will need speed, like my laptop and the HTPC.

author: Halcyon
author_rank: Unknown
timestamp: April 21, 2016, 03:01:22 am
content: Quote from: stmdude on April 21, 2016, 02:44:56 amThat only applies to broadcast messages, beacons, control channel stuff. The actual data throughput will be at whatever that device is connected at. Yes it's argued that in reality that the "slowest device" will bring networks to a grinding halt but I believe that was back in the bad old days when WiFi was new and for some reason people just believe that it's true today -- It's generally not. For example, right now I have a machine associated to an AP next door hovering between 2 and 5.5Mbps however a machine with a stronger signal will happily communicate at 13Mbps to the same AP.it's important not to confuse the number of antennas with the number of physical radios. Antenna diversity is a totally different concept. Even some enterprise dual-band access points these days have one physical radio and can only communicate on one band at any one time. I have an Aruba AP which is one of the ones I use at home, it's capable of both 2.4GHz and 5GHz but not simultaneously.

author: uncle_bob
author_rank: Unknown
timestamp: April 21, 2016, 11:41:05 am
content: HiOk, well if we are going to get into all the messy details ...The "link speed" is a theory based number. If I send bits continuously over the link without stopping under ideal conditions I hit the link speed. This is very much like talking for 20 minutes without taking a breath. It does not happen. In the real world, you put your data into packets. You send some number of packets and wait (take a breath). While you wait, the other end of the transaction lets you know the packets have made it through. That acknowledge process involves a radio "turn around". One end stops sending and the other end starts.Net result is that things like packet size, buffer size and turn around time very much get into the speed equation.Bob

author: mariush
author_rank: Super Contributor
timestamp: April 21, 2016, 11:48:00 am
content: I get up to 2.45 MB/s when transferring files through FTP. I'd say 2.1 MB/s consistent at around 2-3 meters from the router.PC with ftp server connected through cat5e cable to cable modem/router that has 2.4 ghz / 5 ghz wireless built in, download is made on old centrino laptop with 54mbps network card .

author: Kevman
author_rank: Regular Contributor
timestamp: April 21, 2016, 04:51:13 pm
content: I'm almost positive that all wirelesss network traffic must go through the AP. If you have two wireless devices communicating, theoretical throughput is therefore halved straight off, as it must go from the first device to the AP and then the AP send must send to the destination.In practice its even worse due to all the overhead, collisions, collision avoidance wait-states, and dropped packet timeouts/retransmissions that eat up time. All this means Performance degrades heavily as more devices are added.I'm lucky to get 100mbit out of my 866mbit wireless AC, even in a very non-congested area like mine and only 1 device active on the network.I. hate. Wifi.

author: Delta
author_rank: Super Contributor
timestamp: April 21, 2016, 05:02:03 pm
content: Quote from: Kevman on April 21, 2016, 04:51:13 pmI hear you, brother! But it has its place, for browsing on phones and tablets etc, or sitting on the sofa with a laptop, but it is NOT a replacement for Ethernet!

author: rrinker
author_rank: Super Contributor
timestamp: April 21, 2016, 07:11:31 pm
content: I just built a small cube PC that has 801.11ac MIMO (which my router also has). Speed tests show the limiting factor of this connection is my internet connection, at 160mbps down and 12mbps up. That's with the PC in a different room, with an interior stud wall and closet between the router and computer. In approximately the same place where the 5.8GHz 802.11n Roku can't transfer fast enough to stream HD video - which it did when located 10 feet closer to the wall.

author: borjam
author_rank: Unknown
timestamp: April 21, 2016, 07:52:08 pm
content: Quote from: Halcyon on April 21, 2016, 03:01:22 amSlow devices are a problem. A slow device transmitting data keeps the radio busy for a longer time than another device with a faster connection. Worse, a 802.11g device associated to a 802.11n network will force the AP to incur in additional handshake to guarantee coexistence. That hurts throughout.That's why it's better to prevent low signal devices to associate and, sometimes, it's even better to lower the power of the access points.

author: Halcyon
author_rank: Unknown
timestamp: April 21, 2016, 08:49:48 pm
content: Quote from: borjam on April 21, 2016, 07:52:08 pmOh 100% it hassomeimpact, but not as much as people think. Many are under the illusion that if you have a device communicating at say 2 Mbps because of signal strength or whatever, then all other devices will be forced down to 2 Mbps. This just isn't true.

author: MrSlack
author_rank: Frequent Contributor
timestamp: April 21, 2016, 09:04:53 pm
content: WiFi is bloody awful. I've got a 300Mbit network and I'll be lucky if I can pull 3-4mbytes a second over it. There's so much noise where I live it's impossible. I've had to sling Ethernet around everywhere.

author: miguelvp
author_rank: Super Contributor
timestamp: April 21, 2016, 09:43:06 pm
content: Don't get me started with WiFi and why there is such a thing as a game console that uses WiFi for online gaming.Developing for the PS Vita that only had WiFi for networking was eye opening enough. Every day during lunch all our online testing will break because of the number of people walking by with cell phones on their way out to get lunch. On top of all the dev kits around the full office building and adding new AP nodes didn't make a huge difference because of the density of wireless devices.Even going to the parking lot to test wasn't good enough, I guess if we ever were to support a WiFi only device again, I would ask for an anechoic chamber like the ones Apple have:http://www.engadget.com/2010/07/16/inside-apples-black-lab-wireless-testing-facilities/WiFi packet capture is also non trivial if you actually want to get a good picture of what is happening at the access point itself.

author: FireFlower
author_rank: Regular Contributor
timestamp: April 21, 2016, 09:52:16 pm
content: If you actually have wireless spectrum analyzer you might see noteable noises around your room.Bluetooth works on 2.4GHz range, microwave works on 2.4GHz, just you being physically between antennas slows down connection speed. Why is it so? Well the thing is 54Mbps uses modulation where in same signal you see different bits. For example putting microwave on and your QAM-64 (visual) small bits become so large that it cannot make out sense what they are anymore thus reducing modulation bits to 16, to 4 etc until it gets signal trough.I wasn't able to find a good demo picture but on above row is very noisy and at least 8-QAM is not anymore readable for receiver, 16-QAM is also very borderline.

author: uncle_bob
author_rank: Unknown
timestamp: April 22, 2016, 12:13:58 am
content: Quote from: FireFlower on April 21, 2016, 09:52:16 pmHi.... there also is the minor issue that WiFi works on the 2.4 GHz bandIf I sit here for a while with a monitor program, I can spot close to 100 network ID's in less than 20 minutes. I'm not using a fancy directional antenna. I'm just using the built in laptop WiFi. It's nothing special, I'm typing this message on the laptop. The "in band signals" represent a lot more crud than my microwave puts out....Bob