LAN 101: Networking Basics

Wireless Ethernet: 802.11n And Bluetooth

802.11n

The latest wireless network standard, 802.11n (also known as Wireless-N), was published in October 2009. 802.11n hardware uses a technology called multiple input, multiple output (MIMO) to increase throughput and range. MIMO uses multiple radios and antennas to transmit multiple data streams (also known as spatial streams) between stations. Unlike earlier 802.11 implementations, in which reflected radio signals slowed down throughput, reflected radio signals can improve throughput as well as increase useful range.

802.11n is the first wireless Ethernet standard to support two frequency ranges or bands:

  • 2.4 GHz (same as 802.11b/g)
  • 5 GHz (same as 802.11a)


Thus, depending on the specific implementation of 802.11n in use, a dual-band 802.11n device may be able to connect with 802.11b, 802.11g, and 802.11a devices, whereas a single-band 802.11n device will be able to connect with 802.11b and 802.11g devices only.

Wireless-N devices can contain radios in a number of different configurations supported by the standard. The radios are defined or categorized by the number of transmit antennas, receive antennas, and data streams (also called spatial streams) they can support. A common notation has been devised to describe these configurations, which is written as a x b:c, where a is the maximum number of transmit antennas, b is the maximum number of receive antennas, and c is the maximum number of simultaneous data streams that can be used.

The maximum performance configuration supported by the standard is 4 x 4:4, (4 transmit/receive antennas and 4 data streams), which would support bandwidths of up to 600 Mb/s, however no devices are currently on the market using that configuration. Common configurations that are used in Wireless-N devices include 1 x 1:1, 1 x 2:1, and 2 x 2:1, which include radios with 1 or 2 antennas supporting only a single data stream for up to 150 Mb/s in bandwidth. Other common configurations include 2 x 2:2, 2 x 3:2, and 3 x 3:2, which include radios with 2 or 3 antennas supporting up to two data streams for up to 300 Mb/s in bandwidth. Those using more antennas than data streams allow for increased signal diversity and range. The highest performance Wireless-N devices generally available on the market today use a 3 x 3:3 radio configuration, which supports three data streams for up to 450 Mb/s in bandwidth.

802.11n is significantly faster than 802.11g, but by how much? That depends mainly on how many data streams are supported, as well as whether a couple of other optional features are enabled or not. The base configuration uses 20 MHz wide channels with an 800 ns guard interval between transmitted signals. By using channel bonding to increase the channel width to 40 MHz, more than double the bandwidth can be achieved in theory. I say “in theory” because using the wider channels works well under very strong signal conditions, but can degrade rapidly under normal circumstances. In addition, the wider channel takes up more of the band, causing more interference with other wireless networks in range. In the real world I’ve seen throughput decrease dramatically with 40 MHz channels, such that the use of 40 MHz channels is disabled by default on most devices.

Another optional feature is using a shorter guard interval (GI), which is the amount of time (in nanoseconds) the system waits between transmitting OFDM (orthagonal frequency division multiplexing) symbols in a data stream. By decreasing the guard interval from the standard 800 ns to an optional 400 ns, the maximum bandwidth increases by about 10%. Just as with channel bonding (40 MHz channel width), this can cause problems if there is excessive interference or low signal strength, resulting in decreased overall throughput due to signal errors and retries. However, in the real world the shorter guard interval doesn’t normally cause problems, so it is enabled by the default configuration in most devices.

Combining the use of three data streams using standard 20 MHz channels and the standard 800 ns guard interval, the maximum throughput of a Wireless-N connection would be 195 Mb/s. Using the shorter 400 ns guard interval would increase this to up to 216.7 Mb/s. As with other members of the 802.11 family of standards, 802.11n supports fallback rates when a connection cannot be made at the maximum data rate.

The following table compares the standard and optional speeds supported by 802.11n to those supported by 802.11b, 802.11a, and 802.11g.

Wireless Network Speeds
Wireless TypeBand
Channel Width
GI
(Guard Interval)
Max. Speed
(1 stream)
Max. Speed
(2 streams)
Max. Speed
(3 streams)
Max. Speed
(4 streams)
802.11a5 GHz20 MHz800 ns54 Mb/s


802.11b2.4 GHz20 MHz800 ns11 Mb/s


802.11g2.4 GHz20 MHz800 ns54 Mb/s


802.11n2.4/5 GHz20 MHz800 ns65 Mb/s130 Mb/s195 Mb/s260 Mb/s
802.11n2.4/5 GHz20 MHz400 ns72.2 Mb/s144.4 Mb/s216.7 Mb/s288.9 Mb/s
802.11n2.4/5 GHz40 MHz800 ns135 Mb/s270 Mb/s405 Mb/s540 Mb/s
802.11n2.4/5 GHz40 MHz400 ns150 Mb/s300 Mb/s
450 Mb/s600 Mb/s


As you can see from the table, Wireless-N devices supporting four data streams will be able to support up to 600 Mb/s throughput, however the reality today is much less than this. Because there are no devices on the market that support four streams, the maximum throughput advertised by Wireless-N devices today is either 300 Mb/s (using two streams) or 450 Mb/s (using three streams), and those figures also assume both the use of 40 MHz wide channels (not normally recommended) and a short guard interval.

The Wi-Fi Alliance first began certifying products that support 802.11n in its Draft 2 form in June 2007. The 802.11n standard was finally published in October 2009, and 802.11n Draft 2 or later products are considered to be compliant with the final 802.11n standard. In some cases, driver or firmware updates might be necessary to insure ensure full compliance. As with previous Wi-Fi certifications, the Wi-Fi 802.11n certification requires that hardware from different makers interoperate properly with each other. 802.11n hardware uses chips from makers including Atheros, Broadcom, Cisco, Intel, Marvell, and Ralink.

Bluetooth

Bluetooth is a low-speed, low-power standard originally designed to interconnect laptop computers, PDAs, cell phones, and pagers for data synchronization and user authentication in public areas such as airports, hotels, rental car pickups, and sporting events. Bluetooth is also used for a variety of wireless devices on PCs, including printer adapters, keyboards, mice, headphones, DV camcorders, data projectors, and many others. A list of Bluetooth products and announcements is available at the official Bluetooth wireless information website.

Bluetooth devices also use the same 2.4 GHz frequency range that most Wi-Fi devices use. However, in an attempt to avoid interference with Wi-Fi, Bluetooth uses a signaling method called frequency hopping spread spectrum (FHSS), which switches the exact frequency used during a Bluetooth session 1600 times per second over the 79 channels Bluetooth uses. Unlike Wi-Fi, which is designed to allow a device to be part of a network at all times, Bluetooth is designed for ad hoc temporary networks (known as piconets) in which two devices connect only long enough to transfer data and then break the connection. The basic data rate supported by Bluetooth is currently 1 Mb/s (up from 700 Kb/s in earlier versions), but devices that support enhanced data rate (EDR) can reach a transfer rate up to 2.1 Mb/s.

The current version of Bluetooth is 4.0, however versions 2.1 and later supports easier connections between devices such as phones and headsets (a process known as pairing), longer battery life, and improved security compared to older versions. Version 3.0 adds a high-speed mode based on Wi-Fi, while 4.0 adds low energy protocols for devices using extremely low power consumption.

Interference Issues Between Bluetooth and 802.11b/g/n Wireless

Despite the frequency-hopping nature of Bluetooth, studies have shown that Bluetooth 802.11b/g/n devices can interfere with each other, particularly at close range (under 2 meters) or when users attempt to use both types of wireless networking at the same time (as with a wireless network connection on a computer also using a Bluetooth wireless keyboard and/or mouse). Interference reduces throughput and in some circumstances can cause data loss.

Bluetooth version 1.2 adds adaptive frequency hopping to solve interference problems when devices are more than 1 meter (3.3 feet) away from each other. However, close-range (less than 1 meter) interference can still take place. IEEE has developed 802.15.2, a specification for enabling coexistence between 802.11b/g/n and Bluetooth. It can use various time-sharing or time-division methods to enable coexistence. Bluetooth version 2.1 is designed to minimize interference by using an improved adaptive hopping method, whereas 3.0 and later adds the ability to use 802.11 radios for high-speed transfers. Companies that build both Bluetooth and 802.11-family chipsets, such as Atheros and Texas Instruments (TI), have developed methods for avoiding interference that work especially well when same-vendor products are teamed together.

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  • gerchokas
    Last time I tried to set up a LAN I messed it all up and ended up reconfiguring services and drivers for a good while... Now I just settle for an internet (WiFi) connection for games and the like, and transfer files with a pen-drive. MUCH simpler...
    -11
  • iam2thecrowe
    I know a lot of so called "I.T." companies that could learn a thing or two, like how to plug a cable in and how to diagnose a fualty cable/patch point, instead of calling the printer guy out to troubleshoot their network problems for them. IT guys are so lazy sometimes.
    9
  • LORD_ORION
    OK seriously, you cannot even do a book prize internationally?

    Lame.

    You suck etc...
    -5
  • nevertell
    A true fileserver is running linux :>
    0
  • Pyree
    I think this should become a sticky on the network forum.
    6
  • amk-aka-Phantom
    Nice article. Bookmarked for future reference... some of my friends could use these basics and the article is well-written and simple to understand :)
    0
  • cangelini
    LORD_ORIONOK seriously, you cannot even do a book prize internationally?Lame.You suck etc...


    Nope, we can't unfortunately. The same tax laws and rules that apply to $100 motherboards and $1000 CPUs also apply to $60 books.

    A letter to your congressman about our ridiculous tax laws would be more productive ;)
    8
  • amk-aka-Phantom
    134065 said:
    Nope, we can't unfortunately. The same tax laws and rules that apply to $100 motherboards and $1000 CPUs also apply to $60 books. A letter to your congressman about our ridiculous tax laws would be more productive ;)


    Lol, I accept that explanation readily, as much as I hate all these kick-ass US-only draws. Taxes are a party crasher...
    1
  • jryan388
    I was under the impression that cat6 cable was required for gigabit ethernet...
    1
  • Proximon
    It really is an impressively clear and complete book. It's quite a skill to cover topics like this in a way that doesn't require too much background knowledge first.
    0
  • soccerdocks
    jryan388I was under the impression that cat6 cable was required for gigabit ethernet...


    I was too. But it sounds like as long as your CAT5e cable is short enough it will work. Although probably not optimally.
    0
  • michaelahess
    Cat5e is fine for gigabit. I've had runs over 300ft work fine at 1Gb speeds.

    I didn't read very carefully but I didn't see anything in the wifi section about true transmission speeds. 54g will only net you 18-24Mb at the best, consistently. Fastest I've gotten outa any N gear is just shy of 250Mb/sec. And that was with high end Cisco gear at very short distance. Wireless is just too fickle for real high bandwidth stuff.

    I've been in the network provider (ISP) field for over 15 years. Anyone has any questions, just ask me. ;) Ok don't really, I don't have the time!
    2
  • Onus
    ARCNet, Token Ring...that brings back a lot of memories. Then there was Corvus' Omninet...
    0
  • chickenhoagie
    guess my cisco class taught me a lot in highschool. still learned a few pointers in this article though
    0
  • sysa
    I did a little checking and found out that the 6200 series processors are Interlagos.
    0
  • zodiacfml
    wow, didn't know our ordinary ethernet only need two pairs of wires.
    i wonder why it had those extra pairs before gigabit ethernet.
    1
  • thegame8019
    I am currently enrolled in Cisco's academy and this article has made a few things a little more clear to me.
    1
  • PhoneyVirus
    I have this book 10 feet from me but I'm not aloud with it until Christmas because the girlfriend would kill me, the only way I could look at it is I would have to where a pair of rubber gloves so there wouldn't be any finger prints on the hard cover and not to break the book in so I'll wait until Christmas and it can't come fast enough.

    Also amk-aka-phantom this book should be on your book shelf and NOT Bookmarked in the browser, Read this book remember all you can build your self a system, Read Microsoft Windows Inside Out, Remember your Keyboard Short Cuts aka Run Commands, Conquer the Command prompt, program simple VBScripts, Batch files and you will have no problem running a little PC Repair shop.

    PhoneyVirus
    0
  • amk-aka-Phantom
    189013 said:
    Also amk-aka-phantom this book should be on your book shelf and NOT Bookmarked in the browser, Read this book remember all you can build your self a system, Read Microsoft Windows Inside Out, Remember your Keyboard Short Cuts aka Run Commands, Conquer the Command prompt, program simple VBScripts, Batch files and you will have no problem running a little PC Repair shop.


    Umm... thank you, but I know enough about PCs and networking without any books.
    0