Introduction

A wireless LAN, or WLAN, is simply a local area network that doesn't rely on wired Ethernet connections. A WLAN can be either an extension to a current wired network or an alternative to it. Use of a WLAN adds flexibility to networking. A WLAN allows users to move around while keeping their computer connected, without having to depend on Ethernet cables.

WLANs try to provide all the features of wired LANs, but without the wires. The only noticeable differences to the end user tend to be in speed (ranging from 1 to 54Mbps, with some manufacturers currently offering proprietary 108Mbps solutions) and security (the wireless access point is shared among everybody nearby, so security issues exist with WLANs that don't exist for wired networks). WLANs can cover areas ranging in size from a small office to a large campus, with neighborhood and city-wide ranges planned for the future. Most commonly, WLANs employ access points that provide access within a radius of 65 to 300 feet. Many companies are developing WLAN technology. The information below was adapted from the Wireless LAN Association web page.

WLAN types
Following are the general types of WLANs:

The private home or small business WLAN: This consists of one or two access points covering around a 100- to 200-foot radius. The equipment is common enough to be found in most office supply or electronics stores, or even some retail stores like Target or Wal-Mart. With few exceptions, hardware in this category subscribes to the 802.11a, b, or g standards (also known as Wi-Fi).

The enterprise class WLAN: This type has a larger number of individual access points covering a wider area. The access points themselves have features not needed for a home or small office, like better security, authentication, remote management, and tools to help integrate with existing networks. Each access point has a larger coverage area than home or small office products, and all are designed to work together to cover a much larger area. Equipment here also adheres to the 802.11a, b, or g standard, and in the future will likely adhere to further security-refining standards such as 802.1x.

The Wireless Metropolitan Area Network (WMAN): The Indiana University wireless network is an example of this. A WMAN covers an area from multiple city blocks up to a city's boundaries. The most common type of WMAN is a collection of individual enterprise class wireless networks that collectively allow users to access all of them. For example, IU's WMAN is a collection of individual buildings' and departments' WLANs taken together as a whole.
In most places, WMANs usually consist of wireless networks belonging to several businesses or Internet service providers. Take the Kiva Everywhere network as a limited example of this (limited because it's open only to IU users): IU's wireless network (already a WMAN in itself) and Kiva Everywhere's network of KSpots together serve as a Bloomington area WMAN for IU users.

The WMAN is also the point where you start seeing different technologies and standards. Again, the most common WMAN is basically a group of individual access points and WLANs. But different designs, like Angel Technologies' developmental project called the HALO (High Altitude Long Operation) Network would use specially equipped airplanes as airborne wireless access points.

While you will see the term Metropolitan Area Network (MAN), don't confuse it with a Wireless Metropolitan Area Network (WMAN). Aside from the fact that MANs tend to be wired networks, they usually exist to provide connectivity to local ISPs, or to business and enterprise class LANs. In contrast, a WMAN exists to provide connectivity directly to an end user. In other words, a MAN normally acts as a backbone, while a WMAN acts as the "last mile" connection directly to a user's computer. Exceptions exists, but in broad terms this is true.

Wireless WAN (Wide Area Network): Although a WAN by definition is the exact opposite of a LAN, Wireless WANs (WWANs) deserve brief mention here. Most WANs exist to connect LANs that are not in the same geographical area (for more information, see What is the difference between a LAN, a MAN, and a WAN, and what is a LAN connection?), and until recently this was also the case for WWANs. But recently, cellular phone companies like Sprint (for BroadBand Direct) and AT&T (among others) have begun offering WWAN technology that the end user can access directly. Those WWANs use cellular data technology to cover extremely wide areas. While they are considerably slower than wireless LAN speeds (most advertise between 50 to 144Kbps; compare this to dial-up speeds, which are around 56Kbps), they're still better than the lowest end of DSL speeds (128Kbps), plus they allow far greater mobility than standard 802.11a, b, or g wireless. Since they rely on coverage by the major cellular network providers, coverage areas for wireless Internet access tend to be more or less the same as they are for cell phones. There are many different standards competing at this level (GSM, CDMA, GPRS, 3G, to name a few). Most of them are mobile data standards that previously were used only on cell phones.
WLAN standards
WLAN standards below the metropolitan level are fairly well defined; most people have heard about 802.11b and g Wi-Fi standards. Some upcoming standards like 3G are attempting to increase range and seamless availability. Others like 802.1x, EAP, and 802.11i are attempting to increase security. Currently, the industry emphasis is on extending range or strengthening security rather than trying to increase speed, but that may change in the future.

802.11a, b, and g: The big three standards
The 802.11a, b, and g standards are by far the most common ones for home wireless access points up through large business wireless systems. The differences in the protocols are these:

802.11a

Shortest range of the big three standards (generally around 60 to 100 feet)

Broadcasts in the 5GHz frequency

Supports up to 54Mbps (megabits per second) speed

Less able to penetrate physical barriers like walls

Better speed than 802.11b, supports more simultaneous connections, and because it operates in a more regulated frequency, gets less signal interference from other devices, so is considered to be more consistent in terms of maintaining a connection. In certain circumstances, such as areas with major radio interference (e.g., airports, business call centers), 802.11a will outperform and actually outrange 802.11b.
802.11b

Better range than 802.11a: up to 300 feet in ideal circumstances, and better than 802.11a even in real-world circumstances (Tests by independent reviewers tend to achieve anywhere from 70 to 150 feet.)

Broadcasts in the 2.4GHz frequency

Supports up to 11Mbps speed

Hardware tends to be lower in cost nowadays.

Better able than 802.11a to penetrate physical barriers, and lower in cost, but cannot support as many simultaneous connections. Also, it operates on the same frequency as many cordless phones and other appliances; therefore, it is more susceptible to interference and other things that degrade its performance, so it's not considered a good technology for certain applications requiring absolutely reliable connections, such as live video streaming.
802.11g

Very close to 802.11b in certain aspects; is actually backwards compatible with 802.11b products (but will run only at 802.11b speeds when operating with them)

Faster speed than 802.11b; supports up to 54Mbps. Some proprietary solutions (Netgear, Linksys) manage to get 108Mbps out of the 802.11g standard by broadcasting on more than one of the eight channels that 802.11b uses.

Also uses the 2.4GHz frequency

Slightly shorter range than 802.11b, but still better than 802.11a. Most independent reviews report around 65 to 120 feet in real-world situations.

Suffers from the same problems, such as interference and absolute reliability, as 802.11b
Security standards
Wireless 802.11 does provide for some basic security, but as it has become more widespread, the basic security has come to be seen as inadequate. Further security standards have been created, some to extend the basic ones, others to replace the basic standard entirely.

WEP (Wired Equivalent Privacy): One of the earliest security schemas, WEP was originally created for 802.11b, but migrated to 802.11a as well. It simply encrypts the data traffic between the wireless access point and the client computer.
WEP is generally considered insufficient security nowadays. For starters, WEP simply encrypts the traffic; it doesn't actually secure either end of the transmission. Also, the encryption level is 40 bits, which now is considered very weak.

WPA (Wi-Fi Protected Access): WPA was created in response to the flaws discovered in WEP. WPA implements higher security and addresses the flaws in WEP, but is intended to be only an intermediate measure until further 802.11i security measures are developed. When used in PSK (pre-shared key) mode, WPA-PSK is considered safe enough for most home and small business use, and when combined with technologies like RADIUS and VPN, is considered secure enough for all but the most sensitive enterprise applications.

802.1x: This standard is part of a full WPA security standard. WPA consists of a pair of smaller standards that address different aspects of security: TKIP (Temporal Key Integrity Protocol encryption), which is what encrypts the wireless signal, and 802.1x, which handles the authentication of users to the network. Currently, many wireless systems either have you log into individual wireless access points (home systems work like this), or let you onto the wireless network but keep you from getting anywhere without either further authentication or technology being used. (This is how IU's network works; any wireless device can see the wireless signal and get on the wireless network, but until the device is registered for DHCP and a VPN connection is established, you cannot use the connection to access the Internet. VPN is what authenticates you, but you're already on the wireless network at that point). 802.1x makes you authenticate to the wireless network itself, not an individual access point, and not to some other level like VPN. This is more secure, as unauthorized traffic can be denied right at the wireless access point.

802.11i: This is basically the end point of the process that began with WPA-PSK. It combines that standard with the highest level of encryption yet for a wireless connection (called Advanced Encryption Standard [AES]). The encryption level is high enough that additional dedicated chips are needed on the access points and wireless interface cards to handle the encryption. In summary, 802.11i is the "adult", or finished version of WPA-PSK/TKIP/802.1x/AES.