What is 802.11?
The 802.11 standards are a group of evolving specifications defined by the Institute of Electrical and Electronic Engineers (IEEE). Commonly referred to as Wi-Fi the 802.11 standards define a through-the-air interface between a wireless client and a base station access point or between two or more wireless clients. There are many other standards defined by the IEEE, such as the 802.3 Ethernet standard.
Why are standards important?
Standards are a set of specifications that all manufacturers must follow in order for their products to be compatible. This is important to insure interoperability between devices in the market. Standards may provide some optional requirements that individual manufacturers may or may not implement in their products.
In 1995, the Federal Communications Commission had allocated several bands of wireless spectrum for use without a license. The FCC stipulated that the use of spread spectrum technology would be required in any devices. In 1990, the IEEE began exploring a standard. In 1997 the 802.11 standard was ratified and is now obsolete. Then in July 1999 the 802.11b standard was ratified. The 802.11 standard provides a maximum theoretical 11 Megabits per second (Mbps) data rate in the 2.4 GHz Industrial, Scientific and Medical (ISM) band.
In 2003, the IEEE ratified the 802.11g standard with a maximum theoretical data rate of 54 megabits per second (Mbps) in the 2.4 GHz ISM band. As signal strength weakens due to increased distance, attenuation (signal loss) through obstacles or high noise in the frequency band, the data rate automatically adjusts to lower rates (54/48/36/24/12/9/6 Mbps) to maintain the connection.
When both 802.11b and 802.11g clients are connected to an 802.11g router, the 802.11g clients will have a lower data rate. Many routers provide the option of allowing mixed 802.11b/g clients or they may be set to either 802.11b or 802.11g clients only.
To illustrate 54 Mbps, if you have DSL or cable modem service, the data rate offered typically falls from 768 Kbps (less than 1 Mbps) to 6 Mbps. Thus 802.11g offers an attractive data rate for the majority of users. The 802.11g standard is backwards compatible with the 802.11b standard. Today 802.11g is still the most commonly deployed standard.
Ratification of 802.11a took place in 1999. The 802.11a standard uses the 5 GHz spectrum and has a maximum theoretical 54 Mbps data rate. Like in 802.11g, as signal strength weakens due to increased distance, attenuation (signal loss) through obstacles or high noise in the frequency band, the data rate automatically adjusts to lower rates (54/48/36/24/12/9/6 Mbps) to maintain the connection. The 5 GHz spectrum has higher attenuation (more signal loss) than lower frequencies, such as 2.4 GHz used in 802.11b/g standards. Penetrating walls provides poorer performance than with 2.4 GHz. Products with 802.11a are typically found in larger corporate networks or with wireless Internet service providers in outdoor backbone networks.
In January, 2004 the IEEE 802.11 task group initiated work. The standard was finally ratified in September 2009.
The goal of 802.11n is to significantly increase the data throughput rate. While there are a number of technical changes, one important change is the addition of multiple-input multiple-output (MIMO) and spatial multiplexing. Multiple antennas are used in MIMO, which use multiple radios and therefore utilizes more electrical power.
802.11n will operate on both 2.4 GHz (802.11b/b) and 5 GHz (802.11a) bands. This will require significant site planning when installing 802.11n devices. The 802.11n specifications provide both 20 MHz and 40 MHz channel options versus 20 MHz channels in 802.11a and 802.11b/g standards. By bonding two adjacent 20 MHz channels, 802.11n can provide double the data rate in utilization of 40 MHz channels. However, 40 MHz in the 2.4 GHz band will result in interference and is not recommended nor likely which inhibits data throughput in the 2.4 GHz band. It is recommended to use 20 MHz channels in the 2.4 GHz spectrum like 802.11b/g utilizes. The 5 GHz spectrum band will provide be the best utilization of 802.11n technology. Deployment of 802.11n will take some planning effort in frequency and channel selection. Some 5 GHz channels must have dynamic frequency selection (DFS) technology implemented in order to utilize those particular channels.
An IEEE working group has been working on efforts for the successor to 802.11n in the last one year. This effort is known as Very High Throughput (VHT) and focuses on changing 802.11 to support 1 Gigabit per second (Gbps) wireless LAN standard.
Which standard would be best to purchase and use?
Today, you will primarily find 802.11n products in retail. The estimates show that 94% of the buyers of these products are consumers or small businesses. These purchases are driven more out of the desire to purchase the latest technology rather than buying based on an educated decision. The majority of enterprise or corporate users have not rushed into 802.11n products. AIR802 continues to poll its customers in the USA and in other countries with over 95% reporting that they have no immediate interest in 802.11n technology for their customers. Wireless professionals are concerned about the complexity of 802.11n products, higher electrical power consumption and other issues. Most report strong signal connectivity remains most important. Since current hardware for 802.11n has lower RF power output, the majority of wireless networking professionals are continuing to deploy 802.11b/g products with more powerful RF transmit power.The common consumer equipment found in retail stores have between 30 to 65 mW of RF output power. However, within the same general price range, equipment with 250 mW of RF output power or higher can be purchased. In comparison tests, high power 802.11b/g routers provide significantly greater distance and coverage and as a result higher throughput than any typical lower powered 802.11b/g or 802.11n products in the market. For most users more data throughput is not the critical decision factor. If the wireless network is being used for Internet access and the DSL or cable modem service, which is typically less than 1 Mbps to 6 Mbps depending on the service provider or plan, the typical 25 Mbps maximum data throughput on a high RF powered 802.11b/g device is more than sufficient. In fact today, thousands of networks supporting IP video surveillance are being put into place where streaming compressed video is carried over 802.11g or 802.11a networks. The reality is that 802.11b/g equipment will be in use for many, many years. Today, the bulk of equipment manufactured and sold to wireless professionals is still 802.11b/g, particularly for outdoor use.
For those few who in the near future absolutely need higher data throughput for a particular application, then 802.11n might be a consideration. The 802.11n standard provides data throughput of up to theoretical maximum of 600 Mbps. However, real world tests, where building materials and existence of other wireless signals in the frequency band have resulted in data throughput rates of as low as 26 Mbps. There is also the risk of the product being outdated in a year should the specifications change through the IEEE working group. Thus the actual performance just might not be any better or much better than a high RF powered 802.11b/g device.
If frequency interference and congestion is a significant factor, then 802.11a should be considered. However, not all client cards in computers, etc. have 802.11a capability and this should be evaluated carefully.
In summary, most consumers or small businesses would be better off without any doubt with an high RF powered 802.11b/g device for the foreseeable future.
Comparison of 802.11 LAN Standards
|Standard||MaximumData Rate(Mbps)||TypicalThroughput(Mbps)||OperatingFrequencyBand||Maximum Non-OverlappingChannels (Americas)|
|802.11b||11||6.5||2.4 GHz||3 *1|
|802.11g||54||8 (Mixed b/g)25 (Only 802.11g)||2.4 GHz||3 *1|
|802.11a||54||25||5 GHz||24 (20 MHz channels)12 (40 MHz channels)|
|802.11n||600 (Theoretical Max)||74 to 144 *2||2.4 GHz & 5 GHz||*3|
*1 – Channels 1, 6 and 11 are the three non-overlapping channels in the Americas. Each channel is 20 MHz wide.
*2 – These are typical acheived rates. Actual throughput will depend upon various factors such as the manufacturer and model, environmental factors, whether 20 MHz or 40 MHz channels are utilized, if security is enabled and whether all clients are 802.11n or a mix of 802.11a/g/n.
*3 – For 802.11n, in the 2.4 GHz band, there are three non-overlapping 20 MHz channels or one 40 MHz channel. The use of 40 MHz is not desirable or practical in the 2.4 GHz band. However, a single 20 MHz channel could be used with lower throughput, largely defeating the gain of using 802.11n. In the 5 GHz band, twenty four non-overlapping 20 MHz or up to twelve 40 MHz channels exist.
IEEE 802.11b/g Channel Assignments
|Channel||Frequency Band (GHz)||Channel Center Frequency (GHz)||FCC – Americas||ETSI (Europe)|
– i In the America’s, with channels 1 through 11, there are three non-overlapping channels: 1, 6 and 11.
IEEE 802.11a Channel Assignments
|Channel||Center Frequency (MHz)||Americas||ETSI (Europe)||Permitted Use Location||Other Comments|
|52||5260||X||X||Indoor or Outdoor||DFS Required|
|56||5280||X||X||Indoor or Outdoor||DFS Required|
|60||5300||X||X||Indoor or Outdoor||DFS Required|
|64||5320||X||X||Indoor or Outdoor||DFS Required|
|100||5500||X||X||Indoor or Outdoor||DFS Required|
|104||5520||X||X||Indoor or Outdoor||DFS Required|
|108||5540||X||X||Indoor or Outdoor||DFS Required|
|112||5560||X||X||Indoor or Outdoor||DFS Required|
|116||5580||X||X||Indoor or Outdoor||DFS Required|
|120||5600||X||X||Indoor or Outdoor||DFS Required|
|124||5620||X||X||Indoor or Outdoor||DFS Required|
|128||5640||X||X||Indoor or Outdoor||DFS Required|
|132||5660||X||X||Indoor or Outdoor||DFS Required|
|136||5680||X||X||Indoor or Outdoor||DFS Required|
|140||5700||X||X||Indoor or Outdoor||DFS Required|
Dynamic Frequency Selection (DFS) is mandatory in the America’s and the European (ETSI) market. Access Points (APs) must constantly monitor the frequency for radar presence. If the AP detects radar, it is required to cease all transmissions within the required time frame and dynamically move to another channel.