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. 802.11b 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. 802.11g 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. IEEE 802.11 a/b/g/n Wi‐Fi Standards and Facts Page 1 802.11a 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. 802.11n In January, 2004 the IEEE 802.11 task group initiated work. There have been numerous draft specifications, delays and lack of agreement among committee members. Yes, even in the process of standards development, politics are involved. The Proposed amendment has now been pushed back to early 2010. It should be noted it has been delayed many times already. Thus 802.11n is only in draft status. Therefore, it is possible that changes could be made to the specifications prior to final ratification. 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 thus 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. For best results of 802.11n, the 5 GHz spectrum will be the best option. 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. Another consideration of 802.11n is the significantly increased electrical power demand in comparison to the current 802.11b/g or 802.11a products. This is primarily due to multiple transmitters. The Wi‐Fi Alliance is testing and certifying compatibility of 802.11n radio draft 2.0 specifications. There are several realities to consider. They are only testing against some basic criteria and interoperability points. Also the number of devices being tested against each other is low. This certification does not provide any protection against changes to the 802.11n standard prior to ratification. IEEE 802.11 a/b/g/n Wi‐Fi Standards and Facts Page 2 VHT 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 wireless standard, 802.11b, 802.11g or 802.11n should I buy? Today, you will find the stores full of draft‐802.11n products. The estimates show that 94% of the buyers of these products are consumers or small businesses, who frankly don’t know about standards issues. The majority of enterprise or corporate users are not investing into these draft products. At issue is both the possibility of these products not being compliant with any final standards and the desire not to suffer potential headaches until the technology is fully ready. Interestingly technical writers for trade journals or the press tend to promote heavily 802.11n despite the fact that AIR802 has polled its customers in the USA and in other countries with over 98% reporting that they have no interest in 802.11n until the standard is ratified and the technology and products have been proven. For reference, the majority of AIR802 customers are government agencies; value added resellers, computer networking companies (installing wireless products in both residential and small business environments), consumers and distributors. Therefore, it appears that most buyers have taken a very cautious wait and see approach despite optimistic editorial articles. For the majority of residential and small and medium size business users, the single largest concern among users is to provide the desired signal coverage followed by reliability. For these users current 802.11b/g products with high RF power output would provide the most desirable results. 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 draft product in the market. For most users more data throughput is not a 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 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. IEEE 802.11 a/b/g/n Wi‐Fi Standards and Facts Page 3 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 has been expected to provide data throughput of 100 Mbps or greater. 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 Maximum Data Rate (Mbps) Typical Throughput (Mbps) Operating Frequency Band 802.11b 802.11g 11 54 2.4 GHz
2.4 GHz
802.11a 54 6.5
8 (Mixed b/g) 25 (Only 802.11g)
25
5 GHz
24 (20 MHz channels) 12 (40 MHz channels)
802.11n 248 74 *2
2.4 GHz & 5 GHz *3 Maximum Non‐
Overlapping Channels (Americas)
3 *1 3 *1 *1 – Channels 1, 6 and 11 are the three non‐overlapping channels in the Americas. Each channel is 20 MHz wide. *2 – 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 802.11 a/b/g/n Wi‐Fi Standards and Facts Page 4 IEEE 802.11b/g Channel Assignments Channel 1 2 3 4 5 6 7 8 9 10 11 12 13 14 •
Frequency Band (GHz) 2.401‐2.423 2.406‐2.428 2.411‐2.433 2.416‐2.438 2.421‐2.443 2.426‐2.448 2.431‐2.453 2.436‐2.458 2.441‐2.463 2.446‐2.468 2.451‐2.473 2.456‐2.478 2.461‐2.483 2.473‐2.495 Channel Center Frequency (GHz) 2.412 2.417 2.422 2.427 2.432 2.437 2.442 2.447 2.452 2.457 2.462 2.467 2.472 2.484 FCC – Americas ETSI (Europe) X X X X X X X X X X X ‐ ‐ ‐ X X X X X X X X X X X X X ‐ In the America’s, with channels 1 through 11, there are three non‐overlapping channels: 1, 6 and 11. IEEE 802.11 a/b/g/n Wi‐Fi Standards and Facts Page 5 IEEE 802.11a Channel Assignments Channel Center Frequency (MHz) 34 5170 36 5180 38 5190 40 5200 42 5210 44 5220 46 5230 48 5240 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140 149 5260 5280 5300 5320 5500 5520 5540 5560 5580 5600 5620 5640 5660 5680 5700 5745 153 5765 157 5785 161 5805 165 5825 •
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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. IEEE 802.11 a/b/g/n Wi‐Fi Standards and Facts Page 6