WiFi Glossary

802.11
802.11 (known colloquially as wifi) is a radio technology used for wireless local area networks (WLANs). Compared to other networking technologies, wifi is quick to setup and inexpensive. Its main disadvantage is its relative insecurity.

Wifi comprises several standards developed by the IEEE. The most notable of these are 802.11a, 802.11b, and 802.11g.

The 802.11 (without the added letters) standard was released in 1997. Though it was too rudimentary (and too slow) for commercial acceptance and though it has been superseded by 802.11a, 802.11b, etc., it did lay the foundation for what has grown into a huge market. It provided fragmentation, DSSS, FHSS, diffused infrared, and most of the essential technology of today's consumer-grade wireless computer networks.

802.11a
Issued in 1999, 802.11a is one of a family of standards for wireless local area networks (WLANs). It is also sometimes termed WiFi5.

802.11a employs a set of radio channels at the frequencies of 5.725 GHz to 5.850 GHz (in the U-NII band).

802.11a's main advantages over the more popular 802.11b are:

The reasons for its relative unpopularity include: The 802.11a standard includes a strategy for falling back to slower bandwidths when noise is high or signal strength is low. These slower bandwidths are 48, 36, 24, 18, 12, 9, and 6 Mbps. Some implementations of 802.11a include a proprietary "Turbo" mode (also termed "2X") of 108 Mbps.

802.11a and 802.11b use the same MAC layer designs; where they differ is in their PHY layers. 802.11a achieves its higher bandwidth by using multiplexing and a more efficient error correction scheme (forward error correction (FEC)).

802.11a uses the following modulation techniques:

802.11b
The specification for 802.11b was first released in 1999. It was an amendment to 802.11 which ran at 1 and 2 Mbps. 802.11b was initially termed "High Rate" and added 5.5 and 11 Mbps. It permits up to 1 watt of power output but most 802.11b devices use less for battery power conservation.

802.11b uses 2.4 GHz (details in table below) and offers a bandwidth of up to 11 Mbps. 2.4 GHz is a crowded part of the radio spectrum. It is shared by microwave ovens, cordless phones, medical and scientific equipment, Bluetooth devices, and many consumer and industrial applications. Here are the exact frequencies used by 802.11b and 802.11g.
USA/FCC, Canada2.412-2.462 GHz11 channels
Europe CE/ETSI2.412-2.472 GHz13 channels
Japan2.412-2.484 GHz14 channels
France2.457-2.472 GHz4 channels

802.11g
Like 802.11b, 802.11g operates in the 2.4 GHz band (details in table above). It offers a bandwidth of up to 54 Mbps. However, it uses a different radio technology than 802.11b. When conceived, 802.11g sought to provide the best of both worlds -- the high speed of 802.11a and the low cost of 802.11b. Its design is a compromise between chip manufacturers with large investments in incompatible technologies.

802.11g has a total of fourteen channels (in most of the world) or eleven (in the USA) but, like 802.11b, only three are non-overlapping, unlike 802.11a's eight. This enables it to squeeze into a narrower band. There is 5 MHz between each pair of adjacent channels. The centerpoint of the bottom frequency is 2.412 GHz. Each channel is 22 MHz wide. Hence, the bottom of the bottom frequency is 2.401 GHz (2.412 GHz minus half of 22 MHz). The three non-overlapping channels (in practice, the only usable ones) are 1, 6, and 11.

802.11g has two mandatory modes (every manufacturer must provide these): CCK and OFDM, and two optional modes: Packet Binary Convolutional Coding (PBCC-22) -- 22 Mbps -- and CCK-OFDM-33 -- 33Mbps.

802.11h
This IEEE standard is a refinement to 802.11a. It unifies standards for the 5 GHz band. It adapts 802.11a for European regulatory requirements. It improves the 802.11 MAC and PHY layers to give:

802.11i
Security enhancements to 802.11 -- This IEEE standard will remedy weaknesses in 802.11 wireless network security, particularly WEP. It is currently under development by an IEEE working group. For a superb set of definitions of security terminology, see RFC 2828.

802.11s
See mesh network.

802.16
See WiMAX.

802.1x
When completed, this IEEE standard will provide strong security for both wireless and wired networks. It will support several authentication modes including RADIUS.

access control list (ACL)
One rudimentary security mechanism is the ACL in which the enforcer has a list of the physical (hardware) addresses of the devices (usually computers) permitted to access a network. These addresses are stored in MAC format. Drawbacks of this mechanism are that it's less useful to authenticate a hardware device than a user, and that MAC addresses can be spoofed by imposters. The advantage is that it's simple and easily administered.

access point
A device that connects to a wired network and which transmits and receives 802.11 signals. Thus, it acts as the interface between nearby wireless devices such as users' laptop computers and the wired network. (Devices that interconnect networks are termed bridges. Access points are sometime referred-to as bridges.) Often, the wired network is itself connected to the Internet. Thus, the access point serves to enable wireless computer users to connect to the Internet.

The device itself consists of:

  1. A radio transmitter and receiver
  2. An RJ-45 wired network interface
  3. Bridging software

Occasionally, access points are used without wired networks. In such "standalone" wireless networks, access points serve as communication buffers, for example when communication is attempted with a laptop that is in standby mode. (Laptop computers enter standby mode to conserve battery power.) To catch them up on data they missed while standing by, access points buffer the data for these laptops until they awaken.

ad hoc mode
See IBSS.

address resolution protocol (ARP)
Within an ethernet local area network (LAN), machines identify each other by MAC addresses. On the Internet, however, machines identify each other by Internet Protocol (IP) addresses (see DNS below) such as 192.100.68.211. Thus, to reach its final destination, a message must be delivered to a MAC address which must be resolved from its IP address. The ARP protocol does this. Within an ethernet LAN, it broadcasts a message to all the machines asking, "If this is your IP address, tell me your MAC address." The responding machine (if any) sends back its MAC address. Then the sender can deliver the message and stores the address in its ARP cache for future reference.

advanced encryption standard (AES)
This encryption is strong and will replace WEP in 802.1x. It was developed to replace DES, the algorithm chosen for use by U.S. government organizations. It will also be widely used outside of the government. AES uses the Rijndael algorithm which was developed by Drs. Daemen and Rijmen of Belgium. The National Institute of Standards and technology (NIST) selected the Rijndael algorithm for AES because it offers a combination of security, performance, efficiency, ease of implementation, and flexibility. The AES specifies three key sizes: 128, 192 and 256 bits.

analog modulation
One set of techniques for delivering information electronically uses a constant-frequency signal (the carrier) to which a variation of some kind is applied, varying with the information to be delivered. Several types of variations can be applied:

association
When a client becomes part of a network it is said to have associated. This is accomplished by scanning.

asynchronous transfer mode (ATM)
A technology for wide area networking. Uses fiber-optic media. 622 Mbps.

authentication
Authentication is the process of determining the identity of a user. The most common form of authentication is by user name and password. Other forms use digital certificates, digital signatures, etc. Many have been tried with wifi including:

attenuation
Transmitted signals weaken (are attenuated) for a variety of reasons: These attenuations are more pronounced at higher frequencies, e.g. 5 GHz signals tend to be attenuated more easily than 2.4 GHz signals.

authorization
Authorization is the process of determining which service(s) a user is permitted to use and to what extent. It requires that the identity of the user be previously established by some authentication process. The authenticated user ID is then authorized by lookup in a file, table, database, or authorization service such as LDAP.

automatic private IP address (APIPA)
On TCP/IP networks (including wireless ones) devices can communicate only if they are equipped with IP addresses. The two most common mechanisms by means of which devices receive these addresses are static and DHCP. However, it may occasionally happen that a wireless network has neither of these. It is reasonable that a collection of devices on an isolated wireless network to be able to communicate among themselves without an extensive infrastructure nor network configuration expertise on the part of its users. In consumer situations it should just work. In home networks where a printer is often shared among several computers, such a scheme is especially useful.

APIPA is Microsoft's solution to this problem. It is meant for nonrouted small home or business environments with up to 25 clients. When a client boots up, has no static IP address, and cannot find a DHCP server, it uses APIPA to assign itself an IP address in the 169.254.xxx.xxx block. Since this block is not routable (Internet routers ignore it) there is no risk of conflicts with devices on networks elsewhere in the world even if the isolated network becomes Internet-connected.

The client also configures itself with a default class B subnet mask of 255.255.0.0. It uses the self-configured IP address until a DHCP server becomes available, checking every five minutes. If it detects a DHCP server on the network, APIPA stops and the DHCP server replaces the IP address with a dynamic one.

APIPA is a fairly new solution (available starting with Windows 98.) Previously, devices received 0.0.0.0 as their default addresses which, because it was duplicated on several devices, prevented them from communicating at all.

basic service set (BSS)
Collectively, an access point plus a set of wireless clients (usually laptop computers). See also EBSS and IBSS.

beacon frame
Access points periodically announce the time, the data rates they support and, optionally, their SSID. (This latter datum can be withheld for security; withholding it prevents passive scanning.) These broadcasts enable wireless clients to find and connect to wireless networks. The data are grouped in a standardized sequence termed a beacon frame.

Bluetooth
Named for a Norwegian pirate by Ericsson, the Norwegian company that invented it, Bluetooth is a wireless technology that, like 802.11b and 802.11g operates in the 2.4GHz band of the radio spectrum. It is also called piconet, scatternet, and personal area networking (PAN). Its application is "walk-up connectivity" -- low-power wireless and data communications by cellphones, PDAs, and other personal devices. Communication occurs over short distances, typically within a room. It uses a "discovery" process in which Bluetooth devices, without user intervention, detect each other and exchange capabilities and permissions. Bluetooth radio modules operate at Power Class 2 (2.5 mW). Transmission rate is 1 Mbps. Within the 2.4 GHz ISM band, Bluetooth uses all 79 channels. Its modulation technique is 2-GFSK with FHSS at 1600 hops/second. A piconet is a group of Bluetooth devices communicating together. One member of the group acts as a master and determines the hop sequence. A scatternet is a bunch of piconets. The Bluetooth standard defines five modes. A Bluetooth device is, at any given moment, in one of these modes:

bridge
Devices that interconnect two or more networks are termed bridges. As they are often used to connect local area networks (LANs) to wireless LANs (WLANs), access points are often termed bridges.

broadband wireless communications
Broadband wireless is a collection of overlapping technologies that enable wireless high-speed communications. The collection includes wifi, WiMAX, 3G and Ultra-Wideband (UWB) technologies.

broadband wireless access (BWA)
See WiMAX

Carrier Sense Multiple Access (CSMA)
When two transmitters transmit simultaneously, a collision occurs and communication fails. There are two strategies for dealing with this. One strategy is point coordination function (PCF) (also called polling) in which the transmitters take turns in a defined sequence. The other strategy is CSMA: transmitters listen before sending and, if they detect other traffic, they wait before transmitting. There are two variations on CSMA: CSMA/CD and CSMA/CA.

Cisco
A Californian manufacturer of networking equipment of all kinds, Cisco is the dominant wifi vendor. Some of the terminology they use is their own. Here is a translation table.

Cisco TermGeneric Term
home radio network nameSSID
home networkad hoc (IBSS) mode
Aironet Client Utility (ACU)access point configuration software
Link Status Meter (LSM)NetStumbler and others
Client Encryption Manager (CEM)WEP configuration software

code division multiple access (CDMA)
A technique for sharing a medium using spread spectrum and simultaneous transmissions, each with its own encoding.

Colubris
A Canadian manufacturer of industrial-strength wifi equipment. See www.colubris.com. Other manufacturers include 3Com, Belkin, Cisco, D-Link, Linksys (recently acquired by Cisco) and Netgear.

complementary code keying (CCK)
An error detection and correction technique that involves XORing the data with 64 eight-bit code words. By adding redundant information to a transmission, it enables the receiver to detect and correct errors without requiring retransmission.

content filtering
In a variety of situations -- particularly public ones -- it is inappropriate to permit computer users to access pornography or other inappropriate material. Techniques for restricting such access are termed content filtering. One way to accomplish this is by means of a DNS proxy.

dBm (decibels)
The decibel (abbreviated dBm) is a unit of measure of the power of transmission signals. Another way of measuring the strength of these signals is in milliwatts (mW -- thousandths of a watt). The milliwatt is a linear measure whereas the decibel is logarithmic (computed as powers of the base of natural logarithms, 2.71828 which for ease of computation is often rounded to 3). dBm measures power relative to one milliwatt. 1 mW equals 0 dBm. The strength of a signal having power less than 1 mW is measured in negative numbers of dBm. For example, -35 dBm is a good, healthy signal whereas -90 dBm is barely usable or perhaps even too weak to use. Because dBm is logarithmic, increasing a signal's strength by 3 dBm means doubling it. Decreasing it by 3 dBm means halving it. Increasing it by 10 dBm means increasing it tenfold. Thus, 0 dBm is 1 mW, 10 dBm is 10 mW, 20 dBm is 100 mW, and 30 dBm is 1000 mW (1 watt). 200 mW, the maximum wifi transmission power permitted by the FCC in the United States, equals 23 dBm.

digital modulation
Techniques include: See also modulation and analog modulation.

direct-sequence spread spectrum (DSSS)
Wifi is a spread spectrum radio technology; it uses several frequencies at once, not just one frequency like, say, the FM radio we listen to in our cars. DSSS is one of two spread spectrum techniques used in wireless computer networks. (The other is frequency-hopping spread spectrum, FHSS.) 802.11 explicitly calls for DSSS.

In DSSS, data at the sending station is combined with a fixed bit sequence called a chipping code. The chipping code divides the data according to a spreading ratio. It is a redundant bit pattern that is applied to each bit that is transmitted. This enables error detection and correction. If a bit is lost or garbled in transmission, thanks to the redundancy it can be reconstructed at the receiving end without requiring retransmission.

Several chipping codes have been designed. At transmission rates of 1 or 2 Mbps, DSSS uses one called a Barker code which is four bits in length. The Barker code is XOR'ed with each data bit. Thus, the number of bits that must be transmitted is four times the actual amount of data. The apparent inefficiency of chipping codes is more than compensated by the use of the spread spectrum. At transmission rates of 5.5 or 11 Mbps, DSSS uses Complementary Code Keying (CCK) which XORs the data with 64 eight-bit code words.

dynamic host configuration protocol (DHCP)
DHCP is a computer network protocol for centrally assigning and keeping track of Internet Protocol (IP) addresses. Each computer that accesses the Internet must first have an IP address. The IP address can be manually entered into the computer or it can be done automatically by a DHCP server. The automatic method requires less effort by the user and enables centralized management of this network resource. Access points often provide DHCP server service as one of their features.

distributed coordination function (DCF)
The set of rules in 802.11 that call for carrier sense multiple access collision avoidance (CSMA/CA).

demilitarized zone (DMZ)
Occasionally, NAT firewalls cause problems. For example, an application program such as a game or videoconferencing will be unable to function under NAT. To bypass NAT, some access points offer a feature named DMZ. This enables a computer on the local area network to be placed outside of the NAT firewall. Computers in the DMZ are not protected from hacker attacks. Hence, it is best to place them there only temporarily. The details of how to use the DMZ vary from one access point to another; see the user manual.

diversity antenna system
At high frequencies such as those used by wifi (2.4 GHz and 5 GHz) multipath distortion is a difficult problem. One solution -- termed diversity -- is to use two identical antennas separated by a space of several inches and switch from one to the other (only one is active at any given moment) when the signal-to-noise ratio (SNR) is high. Transmission is done on the antenna on which a signal was most recently received. The best access points use diversity antennas. When setting up such an access point, be careful to do it properly:

domain name system (DNS)
DNS is the mechanism by means of which text names such as www.wifi-italia.com are translated to numerical Internet Protocol (IP) addresses such as 192.100.68.211. Humans prefer (and can remember) the text names but internally the Internet communicates numerically.

DNS proxy
A software application that runs on a server computer. It intercepts requests for Internet resources and sometimes redirects them. A common purpose for doing this is content filtering.

digital subscriber line (DSL)
A DSL line is an ordinary telephone wire used for digital data. It is a consumer-grade service provided by local phone companies for Internet access from the home. DSL circuits are faster than conventional analog modems and have largely replaced them. DSL delivers 1.5 Mbps of bandwidth over conventional copper pairs (wire). It achieves this speed by using OFDM. The ordinary telephone (POTS) can be used simultaneously. Two common types of DSL are ADSL (Asymmetric DSL -- fast downloading, slow uploading -- less expensive and commonly used for consumer applications) and SDSL (Symmetric DSL -- fast communication in both directions, used for connecting server computers to the Internet. At the customer's end of the wire, a device named a DSL router is required (sometimes incorrectly called a DSL modem.) The computers and access points connect to the router.

extended basic service set (EBSS)
Collectively, several access points perhaps with some overlapping coverage area, plus a set of wireless clients (usually laptop computers). See also BSS and IBSS.

extensible authentication protocol (EAP)
EAP is the generic concept of protocols for the secure transportation of authentication data such as passwords over 802.11 wireless networks. For a superb set of definitions of security terminology, see RFC 2828.

An EAP-based protocol is communicated between an access point and an authentication server such as a RADIUS. The access point initiates the conversation with the server when it is contacted by a client (most often a PC) requesting access to the wireless network. A "back-end" server actually does the authentication while the access point merely passes through the authentication exchange. Typically, the server will send an initial Identity Request followed by one or more Requests for authentication information. The client sends a Response packet in reply to each Request. The server ends the authentication phase with a Success or Failure packet.

EAP is not an implementation, it is a framework for implementations. It is defined in RFC 2284. It supports a variety of authentication mechanisms. Several implementations have been created and others are under development. Implementations include:

frequency division multiple access (FDMA)
A technique for sharing a transmission medium in which a band of frequencies is split into narrow channels.

FireWire
The trade name for the communication protocol standardized as IEEE 1394. 400 Mbps.

forward error correction (FEC)
FEC is an error correction scheme used by 802.11a. Of 802.11a's 52 subchannels (distinct carrier signals, each with its own frequency, 300 kHz apart): The error correction channels carry secondary copies of the data. They eliminate the need for retransmission in the event of errors.

fragmentation
The 802.11 specification calls for the use of a technique named fragmentation in order to provide communication of acceptable reliability. Fragmentation is defined as part of the MAC sublayer of OSI's link layer (layer 2).

Fragmentation is a collision-avoidance strategy. A collision occurs when two transmitters transmit simultaneously. Their transmissions become garbled. Several strategies have been devised to prevent this; fragmentation is the one espoused by 802.11.

The underlying principle is that transmssions that are shorter in duration are less likely to collide with other transmissions. Fragmentation keeps transmissions brief. Longer transmissions are divided into several shorter ones. Each of these shorter transmissions is termed a frame. Smaller frames can be communicated with greater reliability because they present fewer opportunities for transmission errors.

However, fragmentation comes at a cost. Because each frame must be acknowledged by the recipient and also has its own header and demands a complete program cycle to be processed, smaller frames demand more computing resources for a given amount of data, i.e. are less efficient. The overhead can be substantial, but in a noisy environment this may be unavoidable.

fragmentation threshold
One of the settings on an access point (don't mess with this unless you know what you're doing!) is the maximum frame size, termed fragmentation threshold. Transmissions whose size exceeds this threshold are divided into smaller ones. The purpose of this fragmentation is to improve the reliability of transmission. Where there is strong radio interference or other impediments to reliable communication, it may be necessary to reduce the fragmentation threshold.

frequency hopping spread spectrum (FHSS)
This is a spread spectrum technique in which, for purposes of security, a transmission consists of a short burst at one frequency, then a short burst at another, etc. In order for the receiver to receive the transmission, it must correctly hop from one frequency to the next in the same sequence as the transmitter. This demands a hopping code that is known at both ends of the transmission but not to eavesdroppers. The FHSS algorithm includes error detection and re-sending.

In orthogonal FHSS, several messages are delivered simultaneously, each with its own hopping code, none of which use the same frequency simultaneously.

FHSS has several parameters including:

As implemented in 802.11, FHSS uses channels whose frequencies are separated by 1 MHz, 78 hopping sequences, minimum hopping distances of 6 MHz, and a minimum hop rate of 2.5 hops/second.

Gaussian frequency shift keying (GFSK)
A digital modulation technique, GFSK is implemented in the PMD. As implemented in 802.11, at a transmission speed of 1 Mbps it uses 2 levels of frequency shift. At 2 Mbps it uses 4 levels.

hidden node problem Transmitter 1 can 'hear' the access point but not transmitter 2. Transmitter 2 can 'hear' the access point but not transmitter 1. Hence the two transmitters might attempt to transmit simultaneously.
One of the difficult problems in wireless networks is the hidden node problem. If two clients were to transmit simultaneously ("collide"), their transmissions would become garbled. For reliable communication, only one transmitter can transmit at a time. To ensure this, a node in the network first "listens" to make sure no others are transmitting before it transmits. Ordinarily, all the clients on a wireless network can "hear" each other and thus coordinate their transmissions to prevent collisions. However, occasionally two clients will each be capable of communicating with the access point but not with each other and thus may collide. (In the diagram, transmitter 1 can "hear" the access point but not transmitter 2; transmitter 2 can "hear" the access point but not transmitter 1; hence the two transmitters might attempt to transmit simultaneously.) This is termed the hidden node problem.

This technique of sharing a medium by first making sure it's not already in use belongs to a class of solutions termed carrier sense multiple access (CSMA).

There are two ways to overcome the hidden node problem: request-to-send (RTS) protocol and point coordination function (PCF) (sometimes called polling).

Hiperlan-2
Hiperlan is a European competitor to 802.11. It is developed by the European Telecommunication Standards Institute (ETSI). The current release is Hiperlan-2. Like 802.11a, Hiperlan uses the 5 GHz band with a transmission speed of 54 Mbps. It has some advantages over 802.11 though it is losing the marketing war.

Here is a technical comparison of Hiperlan and 802.11. In the PHY layer, Hiperlan and 802.11 are the same. The differences are in the link layer (see OSI). In Hiperlan's version of the link layer, two features are added:

  • Radio link control
  • Logical link control
Like 802.11, Hiperlan has error correction. Unlike 802.11, it has automatic channel selection (in 802.11 a channel is selected manually at the time of configuration.) Also unlike 802.11, Hiperlan supports roaming. In addition to laptop computers, it supports a broad variety of clients including cell phones, ATM, and Firewire.

Hiperlan manages media contention differently than 802.11. It does not use CSMA/CD; instead, control of the RF medium is centralized at the access point. The access point informs its clients (called mobile terminals, MTs) when they may transmit, using a TDMA algorithm. During transmission, each client has use of the entire frequency band for a brief time slot. Time slots are allocated dynamically with a Quality of Service (QoS) priority algorithm. Thus, unlike 802.11, Hiperlan can reliably deliver time-sensitive data especially audio and video.

Hiperlan has a complete complement of security features, especially including encryption. Access points and MTs each authenticate the other.

hypertext transport protocol (HTTP)
Essentially an adaptation of the protocol of e-mail, HTTP is the "language" spoken between browsers and web servers for requesting and delivering web pages and multimedia.

infrared
Infrared is a portion of the electromagnetic spectrum just below light. It is another technology (other than the radio waves used by wifi) for wireless networking. It is promoted and standardized by the Infrared Developers Association (IrDA), especially a wireless printer protocol. Communication via infrared light uses pulse position modulation (PPM) and slot times.

Infrared is more secure than wifi because it is line-of-sight; it cannot pass through walls or obstacles. Its range is shorter than that of wifi.

independent basic service set (IBSS)
Collectively, a set of wireless clients connected without an access point, also known as peer-to-peer and ad hoc operating modes. See also BSS and EBSS.

Industrial, Scientific and Medical (ISM) band
ISM is one of many portions of the radio frequency spectrum allocated by the FCC for a particular type of use. The ISM band is intended for use without requiring a license. Transmissions are restricted to low power. Wifi is one of the unlicensed uses of the ISM band. The ISM band consists of a set of frequencies 83.5 MHz wide, from 2.4 GHz to 2.4835 GHz.

The Institute of Electrical and Electronic Engineers (IEEE)
The IEEE is an international organization that develops standards for hundreds of electronic and electrical technologies. It uses numerical codes (like the Dewey Decimal system in libraries) to identify the various technology families. The 802 subgroup of the IEEE develops standards for local and wide area networks with the 802.11 section of the subgroup responsible for standards for wireless local area networks.

interframe space (IFS)
A frame (sometimes called a packet) is a unit of transmission. Typically, a large message is divided into several frames which are transmitted independently and reassembled at the receiving end. A frame consists of: preamble + header + data. Separating pairs of frames are interframe spaces (IFS). There are several types of IFS:

Internet Engineering Task Force (IETF)
The IETF is an industry consortium like the IEEE. It establishes and documents the technology "standards" upon which the Internet is built. (They're not really standards because those can be established only by governmental decree. However, they are accepted as such.) The official documents created by the IETF are termed Requests for Comments (RFCs).

logical link control (LLC) sublayer
One of two sublayers of the link layer (second from the bottom) of the OSI model of network communication protocols. 802.11's LLC sublayer is identical to that of wired networks. All 802.11-specific features of the link layer are confined to the other sublayer, the MAC sublayer.

media access control (MAC) sublayer
One of two sublayers of the link layer (second from the bottom) of the OSI model of network communication protocols. For purposes of discussing the architecture of wifi networking protocols, the OSI link layer is divided into two sublayers: LLC and MAC. All 802.11 link layer features are confined to the MAC sublayer. 802.11's LLC sublayer is identical to that of wired networks. 802.11's MAC sublayer calls for CSMA/CA (collision avoidance) instead of CSMA/CD (collision detection). It also calls for RTS and fragmentation.

media access control (MAC) address
Within an ethernet local area network (LAN), machines identify each other by 48-bit MAC addresses, sometimes called ethernet or physical addresses. Every device that can be connected to a LAN has a unique MAC address. This address is assigned at the time the device is manufactured. It is burned into the device's firmware chip. Each manufacturer receives a block of millions of addresses for this purpose. (Here is a list of all the manufacturers of ethernet devices and their address blocks.)

These adresses are usually notated as sequences of hexadecimal digits such as 00-50-00-7B-D2-77. These are sometimes written with colons, e.g. 00:50:00:7B:D2:77 instead of dashes. For broadcasting (sending to all devices on a network) a special MAC address is reserved: FF-FF-FF-FF-FF-FF.

mesh network (MWLAN)
Mesh technology seeks to overcome the short range of 802.11 networks. As of this writing, it is hampered by a lack of standards. There are several incompatible MWLAN systems from different manufacturers. Mesh extension is included in the 802.16 standard, but it appears likely that 802.11 will develop standardized interoperable wireless mesh first. The yet-to-be-developed standard already has a designation -- 802.11s -- and the IEEE has set up an 802.11s working group to write the specification. The result may be that when WiMAX is finally deployed it will face healthy competition from 802.11s.

Mesh network topology is like that of ad hoc wifi networks. In a full mesh network, each node is connected directly to each of the others. In a partial mesh topology, nodes are connected to some but not all of the other nodes. It is able to support nodes that are mobile (roaming). Clients may be laptop computers, PDAs, mobile phones, etc. There are also static nodes that form the infrastructure.

The official IEEE definition of 802.11s:

An IEEE 802.11 Extended Service Set (ESS) Mesh* is a collection of APs interconnected with wireless links that enable automatic topology learning and dynamic path configuration. [It is] an extension to the IEEE 802.11 MAC. [It] supports both broadcast/multicast and unicast delivery at the MAC layer using radio-aware metrics over self-configuring multi-hop topologies. [It uses] IEEE 802.11i security mechanisms... in which all of the APs are controlled by a single logical administrative entity.

michael
With 802.11 and WEP, data integrity is provided by a 32-bit integrity check value (ICV) that is appended to the 802.11 payload and encrypted with WEP. However, this does not prevent a hacker using cryptanalysis from changing bits in the encrypted payload and updating the encrypted ICV without being detected by the receiver. In WPA, this form of attack is prevented by an algorithm called Michael. Michael calculates an 8-byte message integrity code (MIC) that is placed between the data portion of the 802.11 frame and the 4-byte ICV. The MIC field is encrypted together with the frame data and the ICV. Michael also provides replay protection. A new frame counter in the IEEE 802.11 frame is used to prevent replay attacks.

modem
"Modulator-demodulator" -- a device that converts digital signals to and from computers from and to analog signals as required for for transmission over telephone lines.

modulation
To modulate a signal is to add information to it. At the receiving end, the signal is demodulated; the information is extracted from it. There are numerous modulation techniques. Some are analog, such as frequency modulation (FM) in which the information is encoded as a series of variations to the frequency of the signal, and amplitude modulation (AM) in which the magnitude of the signal is varied. By these means music and speech is transmitted to ordinary radios. (See analog modulation.) Other modulation techniques are digital. These include phase shift keying (PSK) and pulse position modulation (PPM). (See digital modulation.)

multipath distortion
When a radio signal arrives at a receiver by two different paths, it becomes garbled because the paths are inevitably of unequal lengths. Multiple paths are typically due to reflections off metallic objects in the path between transmitter and receiver.

netmon
Netmon is a program that monitors networks. It (or programs like it) is an essential part of every NOC. Its primary function is to periodically ping each of the sites it monitors and alert someone if there's no reply. It also records the results of this activity and generates a variety of historical displays and analyses of performance.

network access server (NAS)
A NAS is a piece of equipment that directly accepts users' connections. For example, in a wireless network the device serving as the NAS is the access point. In a dialup network, the NAS is the switch that connects the receiving modems to the computers providing the dialup services (e.g. e-mail and web browsing.)

network address translation (NAT)
NAT is used on local area networks for two purposes: security and Internet access. To the external network (outside the organization) only the NAT server is visible, and it appears as a single Internet address. However, inside the network there can be dozens or even hundreds of machines. The NAT server assigns to each its own unique internal address. These addresses are not revealed to the outside world and in any case are not routable. Hence, these machines cannot be contacted from the outside and thus are protected from attack. The second purpose is achieved by not requiring each machine to have an Internet-wide unique IP address; it must be unique only within the local network. Access to the Internet is provided through the NAT server which conceals the internal addresses.

network operations center (NOC)
Networks are administered by experts working in a physical location termed a NOC.

Network Stumbler (NetStumbler)
This is our favorite Windows program for detecting 802.11a, b, and g WLANs. It has several uses: measuring signal coverage ("site surveying"), detecting other networks that may be causing interference, detecting rogue (unauthorized) access points, and wardriving (see scan). Download it for free from www.netstumbler.com.

Open Systems Interconnection (OSI) model
To help in decomposing into manageable pieces (termed layers) the problem of designing networks, the telecommunications industry has generally adopted a theoretical model called OSI. It was originally proposed by the International Standards Organization (ISO). The elements of wifi technology apply to the bottom two layers (layers 1 and 2).

Layer NumberLayer NameWifi Component
7application
6presentation
5session
4transport
3network
2linkLLC
MAC
1physicalPLCP
PMD

What Happens at Each Layer
Layer NumberLayer NameDescription
7ApplicationThe application layer provides the network services that users see, such as e-mail, the web, ftp, telnet, DNS, NIS, NFS, and instant messaging.
6PresentationThis layer provides independence from differences in data representation (e.g. encryption) by translating from application to network format and back. In the presentation layer, data is transformed into the form that the application layer can accept. This layer formats and encrypts data for transmission, providing freedom from compatibility problems. It is sometimes called the syntax layer.
5SessionThis layer establishes, manages and terminates connections between applications. It layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.
4TransportThis layer provides transparent transfer of data between nodes (sometimes termed hosts and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) operate in this layer.
3NetworkThis layer provides switching and routing technologies, creating logical paths ("virtual circuits") for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing. Internet Protocol (IP) addresses (such as 192.100.68.37) operate in this layer.
2Data LinkThe data link layer defines the format of data on the network. A commonly-used data format is the network data frame, often called a packet. It includes a checksum, source and destination address, and data. The largest packet that can be sent through the data link layer defines the Maximum Transmission Unit (MTU). The data link layer handles the physical and logical connections to the packet's destination, using a network interface. For example, a host connected to an ethernet network would have an ethernet interface to connect to the outside world, and a loopback interface to send packets to itself. MAC addresses are defined in this layer.
1PhysicalThe physical layer is the medium itself, e.g. coaxial cable, fiber, unshielded twisted pairs (UTP), or radio waves. All media are functionally equivalent. The main difference is in convenience and cost of installation and maintenance. Converters from one media to another operate at this level.

orthogonal frequency division multiplexing (OFDM)
This is the the technique by which 802.11a and others overcome the physical limitation to 20 Mbps due to multipath distortion which it would otherwise have. It splits the data into several streams. Each stream is sent on a distinct channel in parallel (simultaneously). Each channel actually uses a lower speed hence there is less multipath distortion yet higher speed in the aggregate. The streams are reassembled into the original data at the receiving end.

physical layer convergence procedure (PLCP)
PLCP is one of the two sublayers of wifi's PHY layer in the OSI network model. The other sublayer is PMD. Located in the PLCP software is the logic that listens to the airwaves for silence before broadcasting, and that receives data from the MAC sublayer and formats it into frames and the interframe spaces that separate them. A frame consists of a preamble + a header + data. The preamble and header are always transmitted at 1 Mbps. Depending on how well the medium is performing, the data portion of the frame is transmitted at 1, 2, 5.5, or 11 Mbps.

physical medium dependent (PMD)
PMD is one of the components of the OSI PHY layer as adapted for 802.11. In this layer is implemented the electrical transmission method: DSSS, FHSS, or diffused infrared, and, for error correction, Barker code (at 1 or 2 Mbps) or CCK (above 2 Mbps).

phase shift keying (PSK)
Phase shift keying is a digital modulation technique in which the phase of the carrier signal is varied. In the simplest type of phase shift keying, the phase is shifted by 180 degrees to indicate a one. A zero is indicated by no shift. By increasing the number of phase variations, more bits can be delivered. For example, in quadrature PSK (QPSK) the phase is shifted by 90, 180, or 270 degrees hence delivering two bits of data instead of just one.

plain old telephone service (POTS)
Also sometimes called dial tone.

point coordination function (PCF)
PCF (also termed polling) is a technique for enabling multiple transmitters to share a medium. Other such techniques include RTS and CSMA/CD. If two transmitters transmitted at the same time their transmissions would be garbled. The set of techniques known collectively as CSMA seek to prevent that. PCF is one such technique.

In wifi with PCF, the access point acts as "point coordinator". It broadcasts a beacon frame that tells the clients to shut up for some period of time. Then it grants exclusive use of the medium to a single client. That client proceeds to transmit. When it's done, the client lets the access point know by transmitting a null data frame.

This technique is especially suited for time-sensitive data such as video. 802.11 implements PCF in the MAC sublayer of OSI's link layer.

polling
See PCF

port
A port is a number in one of the fields of a TCP packet. It is used by the recipient of the packet to determine which program (if any) to pass it to. Usually, the software that makes this determination is the operating system of the server computer (or, on some Unix machines, a program named inetd). This computer is typically running several programs simultaneously, each providing some service to other programs or to other computers on the network. Examples of these services include e-mail, name service (DNS), web service, database management, and many more. Each of these services communicates with its clients by means of a specialized protocol. For example, port 80 and the HTTP protocol are used by browsers communicating with web servers. Port 110 and the Post Office Protocol (POP) are used by e-mail clients communicating with a common type of e-mail server. Here is the up-to-date, exhaustive list of port numbers.

Point-to-Point Protocol over Ethernet (PPPoE)
PPPoE is a protocol used by many DSL Internet Service Providers.

power management
For laptop computers and other portable devices, power management is always an engineering challenge. A number of strategies have been devised to exact the maxiumum possible battery life. For example, built in to the device controllers in the operating systems of laptop computers are such modes as sleep, standby and hibernation. In these modes, the screen is dimmed or blanked, disk drives are spun down, and wireless network interfaces are disabled except for brief, periodic reawakenings to check for new data.

To support this latter power management feature, many access points buffer data for sleeping clients. When the client awakes and contacts the access point it then collects its buffered data.

There are several power management modes in which a wireless device may operate, including:

power over ethernet (PoE)
This is a technique by which 48V electrical power can be delivered to network devices. Thus, they needn't be plugged-in to wall outlets in the conventional manner. Power is delivered through the unused conductors in standard unshielded twisted pair (UTP) ethernet cable. It is especially useful for access points that, for maximum coverage, must be installed on a ceiling or other prominent location where electricity is not easily available.

probe
See scan.

proxy
A proxy is an intermediary server that redirects a client's requests. One common type of proxy provides content filtering. When the client computer requests access to some network resource deemed inappropriate, it is redirected to a "request denied" document.

pulse position modulation (PPM)
PPM is the modulation technique employed by devices that communicate wirelessly by means of infrared light.

quadrature amplitude modulation (QAM)
Implementations include 16 levels (16-QAM) and 64 levels (64-QAM).

quadrature phase shift keying (QPSK)
See phase shift keying (PSK).

radadmin
A program that serves as the user interface to the radius server. Typically, it is operated by network administrators and is password-protected.

RADIUS server
The acronym RADIUS stands for Remote Authentication Dial In User Service. It is both a protocol (defined in RFCs 2138, 2865, and 2866) and a server. The server is a software package that provides authentication and accounting services. The latest radius servers not only authenticate and charge users on dial-in connections; they provide complete control of access to networks. Thus, they are the appropriate tool for managing public-access wireless networks. Included in the software suite is the server program itself, radiusd, which responds to authentication and accounting requests, and accompanying programs to monitor the activity of the server and analyze the information it provides. This information includes user activity logs and more. One of the suppliers of this software is GNU; here is the GNU Radius Reference Manual.

Request for Information (RFI)
An initial contact made by a purchaser to a vendor requesting general information about products or services offered.

Request for Proposal (RFP)
A request from a purchaser to a vendor for specific pricing and description of deliverables.

request-to-send (RTS) protocol
The request-to-send (RTS) protocol (sometimes called RTS/CTS for request-to-send/clear-to-send) is a technique for sharing a medium among several transmitters. It is a collision-avoidance strategy; it prevents more than one transmitter from transmitting at the same time. In RTS in wifi, each client requests permission from the access point before transmitting. Next, the access point alerts all clients to back off, then it gives a CTS to the requestor.

802.11 specifies RTS as part of its MAC sublayer of OSI's link layer. It doesn't demand that RTS be used at all times, but only for long (typically over 3000 bytes) data packets. It is preferable to avoid using RTS when possible because it imposes significant overhead. With short data packets, the probability of collision is acceptably small. The length of the packets for which RTS should be used is termed the RTS threshold (an access point configuration parameter -- don't mess with it unless you know what you're doing!) Only packets that are longer than the RTS threshold are transmitted using RTS. Lowering the RTS threshold can improve communications when clients are far apart or there are many of them.

request-to-send (RTS) threshold
See hidden node problem.

Reverse Address Resolution Protocol (RARP)
RARP does the opposite of the Address Resolution Protocol (ARP). When a device knows its own MAC address but not its IP number, it broadcasts to the LAN a message that says, "Here is my MAC address; tell me my IP address (from your ARP cache) if you know it."

Request for Comments (RFC)
The generic name given to a document in the set managed by the IETF. Though RFC documents are not explicitly defined as standards, they are generally perceived as such. Most manufacturers and developers of Internet-based products and software adhere to them rigorously. A more complete definition is here and the RFCs themselves are here.

roaming
Roaming is a feature of wireless communication that transparently (i.e. without involving the user) enables a client to disconnect from one access point, cell, or base station and, without interruption, connect to another. This requires that the access points, base stations, or cells have a protocol for communicating between themselves to enable the handoff. For example when a user in a car talks on a cell phone and travels from one cell to the next, the roaming feature of the cell phone protocol seamlessly hands off the connection from one cell to the next while the user chatters obliviously.

Unfortunately, 802.11 does not include such a protocol. Rather, it delegates this service to < href="#osi">OSI layers 3 (network) and 4 (transport). Hence, it is a vendor-proprietary feature and not standardized. If you carry your laptop from one wifi network to another, it's very likely that your connection will be dropped.

scan
Scanning is the process by means of which a wireless network client finds a wireless network. There are two ways this is done, passive and active.

Secure wireless networks withhold their SSIDs (see SSID) thus making unauthorized association more difficult.

secure HTTP (HTTPS)
For electronic commerce on the World Wide Web, ordinary HTTP is inadequate because it lacks security; it communicates in plain text. HTTPS is HTTP with encryption added. It was invented by Netscape Communications Corporation. HTTPS encrypts the session data with one of two methods: either the SSL (Secure Socket Layer) protocol or the TLS (Transport Layer Security) protocol. HTTPS uses port 443. In web pages that use HTTPS, the URL begins with https:// rather than http://.

service set ID (SSID)
Every wireless network has a name (such as "123ElmStreet") called a service set ID (SSID). Most access points come preconfigured with a default SSID, often the name of the manufacturer. One purpose of the SSID is to enable overlapping wireless networks to be distinguished. A client would associate (connect) to one chosen from a list of SSIDs. Most access points can, for security, be configured to withhold broadcasting their SSIDs. Thus, to associate with it, a client would have to know the SSID by some means other than simply scanning for wireless networks.

shared wireless access protocol (SWAP)
A competitor to 802.11, SWAP (also called HomeRF) is another wireless protocol for consumer applications. The first version, released in 2000, ran at 1.6 Mbps. Version 2, released in 2001, ran at 10 Mbps. Its main advantage over 802.11 is that it includes a QoS (quality of service) metric that enables it to guarantee priority for time-sensitive data especially audio and video. Nonetheless, it has gained very little market share.

signal-to-noise ratio (SNR)
The ratio between the power level of the desired signal at the receiver and the power level of noise (undesired RF energy) at the receiver. It is expressed as the difference in decibels between the signal and the noise. Thus, a higher value means better reception.

simple network management protocol (SNMP)
A standardized mechanism for remotely monitoring and managing network resources such as modems, access points, printers, computers, routers, etc.

spread spectrum transmission
The opposite of narrowband (in which a radio transmission is on a single frequency), spread spectrum transmissions use several frequencies simultaneously. This is done for security and/or bandwidth. These techniques include frequency hopping spread spectrum (FHSS) and direct sequence spread spectrum (DSSS).

static IP address
One means by which a device on a TCP/IP network (such as a wireless one) is assigned an address is statically. A static IP address is assigned and hand-entered into the device as part of its setup configuration and it is rarely or never changed thereafter. The advantage of this message is its simplicity. The drawback is that on many networks there is a shortage of IP addresses and static addressing monopolizes this scarce resource. Even when the device is turned off the address remains unavailable for use by other devices. DHCP is the most commonly-used dynamic (as opposed to static) addressing scheme to overcome this problem.

Temporal Key Integrity Protocol (TKIP)
This new mechanism replaces WEP with a stronger encryption algorithm. TKIP changes the key for every frame, and the change is synchronized between the wireless client and the AP. TKIP also verifies the security configuration after the encryption keys are determined.

time division multiple access (TDMA)
A technique for sharing a transmission medium in which the use of the medium is divided into time slots which are then allocated to the transmitters according to some algorithm. Some cell phones use this technique for sharing the airwaves, as does Hiperlan.

tunnel
A tunnel is an encrypted connection that connects two computers across an untrusted network. For example, retrieving e-mail from a POP server ordinarily requires sending a login and password "in the clear." This is vulnerable to eavesdroppers such as network sniffers. To protect from such threats, tunneling can be done with an encryption program such as Secure Shell (SSH). Rather than connecting to the POP server directly, the user establishes an SSH connection to the internal network where the mail server resides. The SSH client software then sets up a port forwarding mechanism so that POP traffic is forwarded through the encrypted tunnel. At the server end, it is delivered to the POP port. At the client end, the e-mail program thinks it is talking to the POP server though in fact it is connected to the SSH program. Transparently to both client and server, all communication between them is encrypted.

virtual private network (VPN)
VPNs are used by workers working at home, on the road, or at branch offices to connect in a secure fashion to remote corporate servers via the Internet. This is done by means of a type of tunnel. For example, by tunneling the SMB file server protocol, VPNs are often used to grant remote access to files on corporate file servers. Users thus have access from home to all the data on their PCs in the office.

wifi
Wireless Fidelity (a wordplay on the 1960s term Hi Fi for High Fidelity) meaning the technology of short-range wireless access to the Internet via IEEE 802.11 transmission protocols.

transmission power
One of the settings in wifi equipment is the amount of electrical energy (the transmission power) it feeds to the antenna when it broadcasts. It may in some cases not be desirable to transmit at full power, for example when the transmissions cause interference to a neighbor's wireless activity, or when security (transmission beyond the boundaries of an enterprise) is a concern. The power of wireless transmissions is measured in milliwatts (mW). In some countries, the permitted transmission power is considerably less, e.g. 30 mW. In the United States, FCC regulations do not permit wifi transmissions to exceed 200 mW (one-fifth of a watt). Another commonly-used unit of measure for signal strength is the decibel, abbreviated dBm. See dBm for details.

unlicensed national information infrastructure (U-NII) band
The U-NII band is a portion of the radio spectrum whose use requires no license from the FCC. It is divided into three portions, the highest of which is 100 MHz wide between 5.725 and 5.825 GHz and is used by 802.11a.

Frequency RangeMaximum Permitted
Transmission Power
low band5.15-5.25 GHz40 mW
middle band5.25-5.35 GHz200 mW
high band5.725-5.825 GHz800 mW (outdoors)

WiFi Alliance
Formerly named WECA, the WiFi Alliance was formed in 1999. Having as its members over 200 companies, its primary purpose is to certify compliance of products with the IEEE 802.11 family of standards. Those that do are permitted to bear the logo.

WiMAX
WiMAX is an "emerging technology" (translation: nobody uses it yet and the vendors can't agree on a standard) intended to meet business demand for rapid Internet connection and integrated data, voice and video services. WiMAX proponents claim it can extend fiber optic networks and provide more capacity than cable networks or digital subscriber lines (DSL). It will have a range of up to 30 km, will integrate seamlessly with the existing infrastructure used by wireless carriers, and will operate in either licensed or unlicensed spectrum in frequency bands between 700 MHz and 6 GHz. It uses OFDM to overcome multipath distortion. One of the most compelling aspects of WiMAX technology is that networks can be created in just weeks by deploying a small number of base stations on buildings or poles to create high-capacity wireless access systems. WiMAX will deliver "last mile" broadband connectivity in a larger geographic area than Wi-Fi, enabling T1 type service to business customers and cable/DSL-equivalent access to residential users. WiMAX will provide "canopies" of coverage up to six miles wide. This range and high throughput will enable it to be used as backhaul carrier infrastructure and for enterprise campuses and Wi-Fi hotspots.

WiMAX will be deployed in three phases.

(See IEEE 802.16 Backgrounder (24 May 2002) and Intel's white paper on Broadband Wireless.)

wired equivalent privacy (WEP)
WEP is the original, flawed encryption mechanism included with the IEEE 802.11 standard for wireless networks. (Encryption is the process of encoding transmissions to thwart eavesdroppers.) WEP is an optional part of the 802.11 standard; access point manufacturers can adhere to the standard yet omit it from their products. We know of none that have done so.

WEP uses a key (encryption password) that is known at both ends of the connection (the wirelessly-networked computer and the access point). This is known as a shared private key. Flaws in WEP's algorithm are notorious; the implementation of the algorithm (RC4) is poor, and the 24-bit initialization vector can be cracked with conventional equipment. Using software that today is freely available on the Internet, a hacker can deduce a WEP key in under an hour. Furthermore, good security practice dictates that shared private keys should be replaced periodically yet network administrators find it cumbersome to do so. When the key is changed on the access point, all the wireless computer users must be notified of the new key and they must update it in their configurations in order to continue to use the WLAN. Even with access points that can support several keys simultaneously, key management is difficult and therefore rarely done. Fortunately, new mechanisms are under development (802.11i) that will remove the necessity of conducting this onerous task.

wireless application protocol (WAP)
To deliver services like those on the World Wide Web to wireless devices such as cell phones, WAP has been developed. Wireless devices are typically far more limited than their desktop counterparts in terms of transmission bandwidth. The verbosity of standard HTTP makes it too slow for a wireless context. WAP is essentially a simplified, economized HTTP. To support WAP, there are gateways between the web and wireless networks; they translate from HTTP to WAP. Thus, web servers needn't support both protocols. The gateways take web servers' HTTP output and translate it to WAP thus enabling existing servers to serve both audiences.

wired equivalent privacy (WEP)
This is the name given to the encryption scheme originally specified for 802.11. This specification includes only 40-bit WEP (also called 64-bit WEP assuming a 24-bit initialization vector -- 40+24=64). Some vendors offer 104-bit (also called 128-bit for the same reason) but this is not described in the 802.11 spec because it's proprietary.

WEP is being replaced due to the following flaws:

The IEEE is working on a complete redesign. In the interim, another scheme is offered and is widely available, named wireless protected access (WPA). The redesigned security mechanism will be released as two IEEE standards:

Wireless Ethernet Compatibility Alliance (WECA)
See WiFi Alliance

wireless Internet service provider (WISP)
Companies that provide any of a variety of Internet-related services -- such as web site hosting, e-mail service, network access, etc. -- are termed Internet service providers (ISPs). Those that provide these services on WLANs are termed WISPs.

wireless local area network (WLAN)
A WLAN is a local area network (LAN) that interconnects computers and related devices with radio waves instead of wires.

wireless markup language (WML)
For displaying World Wide Web pages, wireless devices are typically far more limited in their resources such as screen real estate than their desktop counterparts. Thus, for this purpose WML has been developed. It is essentially "HTML lite", tuned for slower transmission speed and smaller display devices (such as cell phones.) WML is an XML-based tagged language. It has yet to become popular in North America. However, in Japan a similar language -- cHTML (compact HTML) -- a product of DoCoMo, delivered by the protocol termed i-mode (Internet for cell phones) is in wide usage.

wireless modes
Depending on its components and their relationships, a wireless network can be constructed in a variety of ways, termed wireless modes:

wireless protected access
This interim implementation of wireless security is not perfect but is better than WEP and serves as a temporary fix while 802.11i is under development. It is designed so that existing access point equipment can be upgraded by means of firmware updates and thus won't need to be replaced. WPA includes the following features: 802.1x authentication is required in WPA. In the 802.11 standard, 802.1x authentication was optional.