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In this lesson, we will introduce each of the most popular 802.11 wireless standards.
The 802.11b standard was ratified in 1999. A widely deployed wireless standard, it operates in the 2.4 GHz unlicensed radio band that delivers a maximum data rate of 11 Mbps. The 802.11b standard has been widely adopted by both vendors and customers who found that its 11 Mbps data rate worked pretty well for most applications. However, 802.11b is now legacy and has been largely replaced by newer standards.
An interesting thing about all 802.11 WLAN products is that they have the ability to data rate shift while moving. This allows the person operating at 11 Mbps to shift to 5.5 Mbps, then shift to 2 Mbps, and finally still communicate farthest from the access point (AP) at 1 Mbps. Furthermore, this rate shifting happens without losing the connection and with no interaction from the user. Rate shifting also occurs on a transmission-by-transmission basis. This is important because it means that the AP can support multiple clients at varying speeds depending on the location of each client.
The problem with all 802.11b communication lies in how the data link layer is dealt with. In order to solve problems in the RF spectrum, a type of Ethernet contention management was created called carrier-sense multiple access with collision avoidance (CSMA/CA). This is needed because all the devices on a single AP are in the same collision domain.
CSMA/CA also has an optional implementation called Request to Send, Clear to Send (RTS/CTS) because of the way that hosts must communicate with the AP. For every packet sent, an RTS/CTS and acknowledgment must be received, and because of this rather cumbersome process, it is kind of hard to believe it all actually works when you use this!
To get a clear picture of this, check out the diagram below. We see a Request to Send sent from the source. The Clear to Send direction was provided by the destination. The data are sent from the source and the destination acknowledges the sent data.
The IEEE ratified the 802.11a standard in 1999, but the first 802.11a products did not begin appearing on the market until late 2001. The 802.11a standard delivers a maximum data rate of 54 Mbps with 12 nonoverlapping frequency channels. The diagram below shows the U-NII bands.
Operating in the 5 GHz radio band, 802.11a is also immune to interference from devices that operate in the 2.4 GHz band, like microwave ovens, cordless phones, and Bluetooth devices. 802.11a is not backward compatible with 802.11b because they are different frequencies, so you do not get to just upgrade part of your network and expect everything to work together in perfect harmony. A definite plus for 802.11a is that it can work in the same physical environment without interference from 802.11b users.
Similar to the 802.11b radios, all 802.11a products also have the ability to data rate shift while moving. The 802.11a products allow the person operating at 54 Mbps to shift to 48 Mbps, 36 Mbps, 24 Mbps, 18 Mbps, 12 Mbps, and 9 Mbps, and finally, still communicate farthest from the AP at 6 Mbps.
The 802.11g standard was ratified in June 2003 and is backward compatible with 802.11b. The 802.11g standard delivers the same 54 Mbps maximum data rate as you will find in the 802.11a range but runs in the 2.4 GHz range—the same as 802.11b.
Because 802.11b/g operates in the same 2.4 GHz unlicensed band, migrating to 802.11g is an affordable choice for organizations with existing 802.11b wireless infrastructures. Just keep in mind that 802.11b products cannot be software upgraded to 802.11g. This limitation is because 802.11g radios use a different chipset in order to deliver a higher data rate.
802.11b uses a modulation technique called direct-sequence spread spectrum (DSSS) that is just not as robust as the orthogonal frequency-division multiplexing (OFDM) modulation used by both 802.11g and 802.11a. 802.11g clients using OFDM enjoy much better performance at the same ranges as 802.11b clients do, but when 802.11g clients operate at the 802.11b rates (11 Mbps, 5.5 Mbps, 2 Mbps, and 1 Mbps), they actually use the same modulation 802.11b uses.
802.11b has a top throughput of 11 Mbps, and 802.11g has a top throughput of 54 Mbps. However, the actual data throughput for the user is typically much less because about 70% or more of the RF bandwidth is used for the management of the wireless network itself. The actual bandwidth the user experiences using an application is called goodput, even though you will not hear this term used a lot. Just remember that goodput refers to the actual data throughput, not the theoretical number that the standards describe.
In the United States, only 11 channels are configurable, with channels 1, 6, and 11 being nonoverlapping. This allows you to have three APs in the same area without experiencing interference. You must be aware of the channels when installing APs in a large environment so you do not overlap channels. If you configure one AP with Channel 1, then the next AP would be configured in Channel 11, the channel farthest from that configured on the first AP.
802.11n builds on previous 802.11 standards by adding multiple input, multiple output (MIMO), which employs multiple transmitters and receiver antennas to increase the data throughput. 802.11n can have up to eight antennas, but most of today’s APs use four. These are sometimes referred to as smart antennas, and if you did have four of them, two would be used for transmitting simultaneously, with the other two receiving simultaneously. This setup would allow for much higher data rates than 802.11a/b/g. In fact, the marketing people claim it will provide about 250 Mbps.
Listed next are some additional components of 802.11n that give people reason to say that 802.11n has greater reliability and predictability:
802.11ac is a Wi-Fi standard that works in the 5 GHz range and delivers up to 1 Gb throughput that was approved by the 802.11 standards committee in January 2014.
802.1ac gets more MIMO spatial streams than we can with 802.11n—up to eight, whereas 802.11n only supported four. Furthermore, and optionally, a downlink of multiuser MIMO (MU-MIMO) supports up to four clients and, most importantly, a modulation of QAM-256 compared to the modulation of QAM-64 supported by 802.11a/g.
802.11n had added fields in the wireless frame to identify 802.11a and 802.11g as high throughput (HT), whereas 802.11ac adds four fields to identify the frames as very high throughput (VHT).
802.11ax was adopted by the IEEE in 2019 as the successor to 802.11ac, and is designated by the Wi-Fi Alliance as Wi-Fi 6. 802.11x. 802.11x is a standard to be deployed in enterprise computing WLAN environments and operates simultaneously in the 2.4 GHz, 5 GHz, and 6 GHz ranges. 802.11ax is designed to provide a very high-speed wireless performance of up to 9,608 Mbps in networks that are densely populated by users.
Take a look at the table below that lists, for each of the IEEE standards in use today, the year of ratification as well as the frequency, the number of nonoverlapping channels, physical layer transmission techniques, and data rates.
| Standard | Ratified | Frequency Band | No. of Channels | Transmission | Data Rates (Mbps) | |
|---|---|---|---|---|---|---|
| 802.11 | 1997 | 2.4 GHz | 3 | IR, FHSS, DSSS | 1, 2 | |
| 802.11b | 1999 | 2.4 GHz | 3 | DSSS | 1, 2, 5.5, 11 | |
| 802.11a | 1999 | 5 GHz | Up to 23 | OFDM | 6, 9, 12, 18, 24, 36, 48, 54 | |
| 802.11g | 2003 | 2.4 GHz | 3 | DSSS, OFDM | 1, 2, 5.5, 11 | 6, 9, 12, 18, 24, 36, 48, 54 |
| 802.11n | 2010 | 2.4 GHz – 5 GHz | Varies | DSSS, CCK, OFDM | 100+ | |
| 802.11ac | 2013 | 5 GHz | Varies | OFDM | 1,000+ | |
Now, let us take a look at the illustration below, which delimits the range comparisons of each 802.11 standard and shows these different ranges using an indoor open-office environment as a factor
You can see that to get the full 54 Mbps benefit of both 802.11a and 802.11g, you need to be between 50 ft and 100 ft (maximum) away, which will likely be even less if there happen to be any obstructions between the client and the AP. 802.11n gives more distance than all three standards shown in the figure (up to twice the distance); understand that 802.11ac just will not give you more distance than 802.11n.
Source: This content and supplemental material has been adapted from CompTIA Network+ Study Guide: Exam N10-007, 4th Edition. Source Lammle: CompTIA Network+ Study Guide: Exam N10-007, 4th Edition - Instructor Companion Site (wiley.com)
