WiFi Will Never Be As Fast As Ethernet

With "Fast" Ethernet, you expect (and generally get) 100Mbps performance from the network. With Gigabit Ethernet, you expect (and possibly get) 1000Mbps. With 802.11g WiFi, you expect 54Mbps, but you seldom get that. Why is WiFi less reliable?

Ethernet (IEEE 802.3), and WiFi (IEEE 802.11) are Layer 2 specifications of the OSI Network Model. Physical Ethernet also occupies Layer 1 of the model.

If you observe the limitations imposed by IEEE specifications, you get predictable results - those limitations should exceed your operating requirements. For instance, 100M Ethernet is provided for cable runs of up to 100 Metres (300 feet) between the computer, and the other network device (generally a hub / router / switch, or another computer).

With Ethernet, you control the environment completely. That is, you own the physical network, and you control what you own. With WiFi, you use the radio frequency spectrum included in IEEE 802.11, but share that spectrum with other electronic devices. Some devices may be non compliant with 802.11 (baby monitors, portable phones, and microwave ovens may transmit on that frequency band), and may be treated as analogue interference. Other devices may be 802.11 compliant, but owned by your neighbours, may also operate in the same frequency spectrum, and may be treated as digital interference.

The bottom line - with WiFi, there are things you can't control easily, and others that you can't control at all.

• Ethernet is a full duplex, dedicated medium. WiFi is half duplex, and shared - it has one media, the WiFi channel, which has to be shared for both sending and receiving the packets. And it's shared with your neighbours.


• Ethernet is a mature technology - it's been around for much longer than WiFi. WiFi components have frequently upgraded firmware. Any time you ask the vendor for help, their first question will be "What version firmware are you running?". This is not a delaying tactic, or needless protocol - it's an attempt to ensure that your drivers are up to date, so they can help you effectively.


• Any time you get new hardware, you should always consider the possibility that the firmware was upgraded after your unit was packaged. Always get up to date firmware - and get it from the vendor.


• Ethernet is a scalable medium. With Ethernet, each computer has its own cable connecting it to the network. With "n" number of computers in an Ethernet network, you can theoretically have "n/2" simultaneous conversations between computers. As you add computers, and cables (and higher rate cables), the total amount of bits being passed in any network, simultaneously, increases constantly. With WiFi, there is a ceiling. At any location in a WiFi neighbourhood, you can have a maximum number of bits being passed, "simultaneously", shared among all WiFi devices near that location. WiFi is not scalable.


• Ethernet is a much more stable medium. With switched Ethernet, you have two hosts, for instance a router / switch, and a client computer. The two hosts are connected by a physical cable. The firmware and hardware on each host has to manage the conversation only with the other host.


• With WiFi, each host is managing / blocking conversations with dozens of other hosts (multiple channels, locations, and networks) constantly, and no two hosts are seeing the same complement of other hosts at any time or in any place. Managing relationships in the constantly changing WiFi population takes resources - and can make the WiFi device slower than it should be.


• Besides the constantly changing and differing population issue, there's the security needs. WEP, WPA, WPA2, AES, CCMP, TKIP... The list of security protocols and standards is endless, and changes frequently. Managing security in any WiFi conversation takes resources - and can make the WiFi device slower than it should be.


• Can you actually see a computer from the Access Point? With WiFi, if you don't have a clear line of sight visibility between the network devices, you'll not get a full strength signal. Distance is another factor. Signal strength falls off as distance increases. Put the computer in one room, and the AP in another (a normal use for WiFi), and see what signal strength you get. Walls and floors are a major signal problem. Signal loss will be higher if the signal has to travel diagonally thru the wall or floor, rather than at a right angle.


• Look at the antennas on the AP and the computer, and see how much they are parallel - you will get maximum signal strength only when the 2 are perfectly parallel. Draw an imaginary line, extending at a right angle, from one antenna towards the other. Does it intersect the other? Try and make a line between the two intersect at a right angle. Signal loss will be higher if one network device is located directly above the other, and on another floor, if both antennas are pointed vertically.

To make this simplest to understand, look at some examples.

• If the AP and a computer are in the same room, locate both devices so both antennas are the same height off the floor. Point both antennas vertically.
• If the AP and a computer are on different floors, locate both devices so the antennas are immediately above and below each other. Point both antennas horizontally.


• If the AP and a computer are in different rooms, position both so a line from one to the other goes at a right angle thru the wall. Locate both devices so both antennas are the same height off the floor. Point both antennas vertically.


• When you can't be so precise in physical placement, point both antennas parallel to each other, per the above strategies.


• An Ethernet cable is a media that YOU own, and physically control. With WiFi, you have to share the channel with all of your neighbours. And, with CSMA/CA, the sum of your usable bandwidth plus your neighbours usable bandwidth will never add up to 54M (for 802.11g) or 108M (or whatever is promised, for 802.11n). Relying upon Collision Avoidance will always require wait time, where neither of you is transmitting. And the more neighbours that you have, the more time that your equipment will be waiting to use the channel.


• If your equipment is compatible, you may benefit from using NetStumbler, or a similar product. Find out how many of your neighbours are also using WiFi, and how close each is.


• Try using a channel that isn't being used by a neighbour close to you. With 802.11G 54M, only channels 1, 6, and 11 don't overlap in frequency. If you have 2 neighbours - one on channel 1, and the other on channel 6, your best choice (avoiding digital interference) is channel 11. Analogue interference, or noise, may make this conclusion less certain.


• Remember that wireless networks may come and go, so watch over a period of hours, if not days. NetStumbler is great for this - leave it running, and it will make a running list, showing each observed access point, and graphing its signal strength by time.
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• Your wireless neighbours are interference sources outside your home. You probably also have interference sources inside your home.
  
  • Baby monitors.
  • Computers.
  • Cordless phones.
  • Microwave ovens.
  • Wireless stereo speakers.
  If you install a WiFi device on your desktop computer, try and get one with an antenna that you can move above, and away from, the computer. Signal loss will be higher with a PCI WiFi card, with the antenna stuck at the back of the computer. This is particularly the case if your computer is a tower, sitting on the floor. The higher the antenna from the floor, the better the signal level.


• You will only get maximum performance from similar equipment, and with no WiFi neighbours. You will have to share the channels with your neighbours. In any WiFi neighbourhood, no two WiFi devices will be within range of the same complement of other WiFi devices. The hidden node problem, where it is recognised that no two networks have to share the spectrum with the identical complement of other networks, is a well known WiFi issue.


• Maybe the router configuration has a setting that's causing your problem. Start by checking your Transmission Rate setting.


• If it's on Auto, try setting it to a realistic rate. Start by setting it at the rate you think you're getting, and see if your bandwidth improves even slightly. If there is any problem with your signal, auto may make the router spend more time recovering from problems, and less time actually sending and receiving.
• If it's on a low rate, try setting it at a higher rate. See if your bandwidth improves.
• When tuning your Transmission Rate, using NetStumbler to analyse performance would be a very good idea.


• For more thoughts on this subject, see BBR Forums How Can I Boost My Range? (#10944).


• And consider that, even though WiFi doesn't use wires as heavily, general physical networking principles may still apply.