Wireless LAN

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This notebook computer is connected to a wireless access point using a PC Card wireless card. Wireless network.jpg
This notebook computer is connected to a wireless access point using a PC Card wireless card.
An example of a Wi-Fi network WI-FI Range Diagram.svg
An example of a Wi-Fi network

A wireless LAN (WLAN) is a wireless computer network that links two or more devices using wireless communication to form a local area network (LAN) within a limited area such as a home, school, computer laboratory, campus, or office building. This gives users the ability to move around within the area and remain connected to the network. Through a gateway, a WLAN can also provide a connection to the wider Internet.

Contents

Most modern WLANs are based on IEEE 802.11 standards and are marketed under the Wi-Fi brand name.

Wireless LANs have become popular for use in the home, due to their ease of installation and use. They are also popular in commercial properties that offer wireless access to their employees and customers.

History

Norman Abramson, a professor at the University of Hawaii, developed the world's first wireless computer communication network, ALOHAnet. The system became operational in 1971 and included seven computers deployed over four islands to communicate with the central computer on the Oahu island without using phone lines. [1]

54 Mbit/s WLAN PCI Card (802.11g) WLAN PCI Card cleaned.png
54 Mbit/s WLAN PCI Card (802.11g)

Wireless LAN hardware initially cost so much that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards, primarily the various versions of IEEE 802.11 (in products using the Wi-Fi brand name). Beginning in 1991, a European alternative known as HiperLAN/1 was pursued by the European Telecommunications Standards Institute (ETSI) with a first version approved in 1996. This was followed by a HiperLAN/2 functional specification with ATM influences[ citation needed ] accomplished February 2000. Neither European standard achieved the commercial success of 802.11, although much of the work on HiperLAN/2 has survived in the physical specification (PHY) for IEEE 802.11a, which is nearly identical to the PHY of HiperLAN/2.

In 2009 802.11n was added to 802.11. It operates in both the 2.4 GHz and 5 GHz bands at a maximum data transfer rate of 600 Mbit/s. Most newer routers are able to utilise both wireless bands, known as dualband. This allows data communications to avoid the crowded 2.4 GHz band, which is also shared with Bluetooth devices and microwave ovens. The 5 GHz band is also wider than the 2.4 GHz band, with more channels, which permits a greater number of devices to share the space. Not all channels are available in all regions.

A HomeRF group formed in 1997 to promote a technology aimed for residential use, but it disbanded at the end of 2002. [2]

Architecture

Stations

All components that can connect into a wireless medium in a network are referred to as stations (STA). All stations are equipped with wireless network interface controllers (WNICs). Wireless stations fall into two categories: wireless access points, and clients. Access points (APs), normally wireless routers, are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with. Wireless clients can be mobile devices such as laptops, personal digital assistants, IP phones and other smartphones, or non-portable devices such as desktop computers, printers, and workstations that are equipped with a wireless network interface.

Basic service set

The basic service set (BSS) is a set of all stations that can communicate with each other at PHY layer. Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS.

There are two types of BSS: Independent BSS (also referred to as IBSS), and infrastructure BSS. An independent BSS (IBSS) is an ad hoc network that contains no access points, which means they cannot connect to any other basic service set.

Independent basic service set

An IBSS is a set of STAs configured in ad hoc (peer-to-peer)mode.

Extended service set

An extended service set (ESS) is a set of connected BSSs. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string.

Distribution system

A distribution system (DS) connects access points in an extended service set. The concept of a DS can be used to increase network coverage through roaming between cells.

DS can be wired or wireless. Current wireless distribution systems are mostly based on WDS or MESH protocols, though other systems are in use.

Types of wireless LANs

The IEEE 802.11 has two basic modes of operation: infrastructure and ad hoc mode. In ad hoc mode, mobile units transmit directly peer-to-peer. In infrastructure mode, mobile units communicate through a wireless access point (WAP) that serves as a bridge to other networks (such as the Internet or a local area network).

Since wireless communication uses a more open medium for communication in comparison to wired LANs, the 802.11 designers also included encryption mechanisms: Wired Equivalent Privacy (WEP, now insecure), Wi-Fi Protected Access (WPA, WPA2, WPA3), to secure wireless computer networks. Many access points will also offer Wi-Fi Protected Setup, a quick (but now insecure) method of joining a new device to an encrypted network.

Infrastructure

Most Wi-Fi networks are deployed in infrastructure mode. In infrastructure mode, wireless clients, such as laptops and smartphones, connect to the WAP to join the network. The WAP usually has a wired network connection and may have permanent wireless connections to other WAPs.

WAPs are usually fixed, and provide service to their client nodes within range. Some networks will have multiple WAPs, using the same SSID and security arrangement. In that case connecting to any WAP on that network joins the client to the network and the client software will try to choose the WAP that gives the best service, such as the WAP with the strongest signal.

Peer-to-peer

Peer-to-Peer or ad hoc wireless LAN Wlan adhoc.png
Peer-to-Peer or ad hoc wireless LAN

An ad hoc network (not the same as a WiFi Direct network [3] ) is a network where stations communicate only peer to peer (P2P). There is no base and no one gives permission to talk. This is accomplished using the Independent Basic Service Set (IBSS).

A WiFi Direct network is another type of network where stations communicate peer to peer.

In a Wi-Fi P2P group, the group owner operates as an access point and all other devices are clients. There are two main methods to establish a group owner in the Wi-Fi Direct group. In one approach, the user sets up a P2P group owner manually. This method is also known as Autonomous Group Owner (autonomous GO). In the second method, also called negotiation-based group creation, two devices compete based on the group owner intent value. The device with higher intent value becomes a group owner and the second device becomes a client. Group owner intent value can depend on whether the wireless device performs a cross-connection between an infrastructure WLAN service and a P2P group, remaining power in the wireless device, whether the wireless device is already a group owner in another group or a received signal strength of the first wireless device.

A peer-to-peer network allows wireless devices to directly communicate with each other. Wireless devices within range of each other can discover and communicate directly without involving central access points. This method is typically used by two computers so that they can connect to each other to form a network. This can basically occur in devices within a closed range.

If a signal strength meter is used in this situation, it may not read the strength accurately and can be misleading, because it registers the strength of the strongest signal, which may be the closest computer.

Hidden node problem: Devices A and C are both communicating with B, but are unaware of each other Wifi hidden station problem.svg
Hidden node problem: Devices A and C are both communicating with B, but are unaware of each other

IEEE 802.11 defines the physical layer (PHY) and MAC (Media Access Control) layers based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). This is in contrast to Ethernet which uses CSMA-CD (Carrier Sense Multiple Access with Collision Detection). The 802.11 specification includes provisions designed to minimize collisions, because two mobile units may both be in range of a common access point, but out of range of each other.

Bridge

A bridge can be used to connect networks, typically of different types. A wireless Ethernet bridge allows the connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the Wireless LAN.

Wireless distribution system

A wireless distribution system (WDS) enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of a WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points. [4]

An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Connections between clients are made using MAC addresses rather than by specifying IP assignments.

All base stations in a WDS must be configured to use the same radio channel, and share WEP keys or WPA keys if they are used. They can be configured to different service set identifiers. WDS also requires that every base station be configured to forward to others in the system as mentioned above.

WDS capability may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). Throughput in this method is halved for all clients connected wirelessly.

When it is difficult to connect all of the access points in a network by wires, it is also possible to put up access points as repeaters.

Roaming

Roaming among Wireless Local Area Networks Roaming01.svg
Roaming among Wireless Local Area Networks

There are two definitions for wireless LAN roaming:

  1. Internal roaming: The Mobile Station (MS) moves from one access point (AP) to another AP within a home network if the signal strength is too weak. An authentication server (RADIUS) performs the re-authentication of MS via 802.1x (e.g. with PEAP). The billing of QoS is in the home network. A Mobile Station roaming from one access point to another often interrupts the flow of data among the Mobile Station and an application connected to the network. The Mobile Station, for instance, periodically monitors the presence of alternative access points (ones that will provide a better connection). At some point, based on proprietary mechanisms, the Mobile Station decides to re-associate with an access point having a stronger wireless signal. The Mobile Station, however, may lose a connection with an access point before associating with another access point. In order to provide reliable connections with applications, the Mobile Station must generally include software that provides session persistence. [5]
  2. External roaming: The MS (client) moves into a WLAN of another Wireless Internet Service Provider (WISP) and takes their services (Hotspot). The user can use a foreign network independently from their home network, provided that the foreign network allows visiting users on their network. There must be special authentication and billing systems for mobile services in a foreign network.[ clarification needed ][ citation needed ]

Applications

Wireless LANs have a great deal of applications. Modern implementations of WLANs range from small in-home networks to large, campus-sized ones to completely mobile networks on airplanes and trains.

Users can access the Internet from WLAN hotspots in restaurants, hotels, and now with portable devices that connect to 3G or 4G networks. Oftentimes these types of public access points require no registration or password to join the network. Others can be accessed once registration has occurred or a fee is paid.

Existing Wireless LAN infrastructures can also be used to work as indoor positioning systems with no modification to the existing hardware.

See also

Related Research Articles

IEEE 802.11 Specifications for Wi-FI wireless networks

IEEE 802.11 is part of the IEEE 802 set of local area network (LAN) protocols, and specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) Wi-Fi computer communication in various frequencies, including but not limited to 2.4 GHz, 5 GHz, 6 GHz, and 60 GHz frequency bands.

Wireless network any network at least partly not connected by physical cables of any kind

A wireless network is a computer network that uses wireless data connections between network nodes.

Wi-Fi Wireless local area networks technology based on IEEEs 802.11 standards

Wi-Fi is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access. Wi‑Fi is a trademark of the non-profit Wi-Fi Alliance, which restricts the use of the term Wi-Fi Certified to products that successfully complete interoperability certification testing. As of 2010, the Wi-Fi Alliance consisted of more than 375 companies from around the world. As of 2009, Wi-Fi-integrated circuit chips shipped approximately 580 million units yearly. Devices that can use Wi-Fi technologies include desktops and laptops, smartphones and tablets, smart TVs, printers, digital audio players, digital cameras, cars, and drones.

Wireless access point device that allows wireless devices to connect to a wired network using Wi-Fi, or related standards

In computer networking, a wireless access point (WAP), or more generally just access point (AP), is a networking hardware device that allows other Wi-Fi devices to connect to a wired network. The AP usually connects to a router as a standalone device, but it can also be an integral component of the router itself. An AP is differentiated from a hotspot which is a physical location where Wi-Fi access is available.

IEEE 802.11e-2005 or 802.11e is an approved amendment to the IEEE 802.11 standard that defines a set of quality of service (QoS) enhancements for wireless LAN applications through modifications to the media access control (MAC) layer. The standard is considered of critical importance for delay-sensitive applications, such as Voice over Wireless LAN and streaming multimedia. The amendment has been incorporated into the published IEEE 802.11-2007 standard.

Wireless mesh network network topology

A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. It can also be a form of wireless ad hoc network.

Service set (802.11 network) group of all devices on the same wireless network

In IEEE 802.11 wireless local area networking standards, a service set is a group of wireless network devices which are identified by the same SSID. SSIDs serve as "network names" and are typically natural language labels. A service set forms a logical network -- that is operating with the same level 2 networking parameters -- they are on the same logical network segment.

Wi-Fi Alliance Organization that supports the Wi-Fi alliance

Wi-Fi Alliance is a non-profit organization that promotes Wi-Fi technology and certifies Wi-Fi products for conformity to certain standards of interoperability. Not every IEEE 802.11-compliant device is submitted for certification to the Wi-Fi Alliance, sometimes because of costs associated with the certification process. The lack of the Wi-Fi logo does not necessarily imply a device is incompatible with Wi-Fi devices.

A wireless distribution system (WDS) is a system enabling the wireless bridging of access points in an IEEE 802 network. It allows an extended network to be created using wireless IEEE 802.11 (Wi-Fi) access points without the traditional requirement for wires to link them. The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client frames across links between access points, thus mixtures of ethernet and WDS connections can be treated as a single network.

Hotspot (Wi-Fi) Wi-Fi access point

A hotspot is a physical location where people may obtain Internet access, typically using Wi-Fi technology, via a wireless local-area network (WLAN) using a router connected to an Internet service provider.

Voice over WLAN

Voice over wireless LAN is the use of a wireless broadband network according to the IEEE 802.11 standards for the purpose of vocal conversation. In essence, it is voice over IP (VoIP) over a Wi-Fi network. In most cases, the Wi-Fi network and voice components supporting the voice system are privately owned.

IEEE 802.11r-2008 or fast BSS transition (FT), also called fast roaming, is an amendment to the IEEE 802.11 standard to permit continuous connectivity aboard wireless devices in motion, with fast and secure handoffs from one base station to another managed in a seamless manner. It was published on July 15, 2008. IEEE 802.11r-2008 was rolled up into 802.11-2012.

Beacon frame

Beacon frame is one of the management frames in IEEE 802.11 based WLANs. It contains all the information about the network. Beacon frames are transmitted periodically, they serve to announce the presence of a wireless LAN and to synchronise the members of the service set. Beacon frames are transmitted by the access point (AP) in an infrastructure basic service set (BSS). In IBSS network beacon generation is distributed among the stations. For the 2.4 GHz spectrum, when having more than 15 SSIDs on overlapping channels, beacon frames start to consume significant amount of air time and degrade performance even when most of the networks are idle.

Wireless security prevention of unauthorized access or damage to computers or data using wireless networks, which include Wi-Fi networks

Wireless security is the prevention of unauthorized access or damage to computers or data using wireless networks, which include Wi-Fi networks. The most common type is Wi-Fi security, which includes Wired Equivalent Privacy (WEP) and Wi-Fi Protected Access (WPA). WEP is a notoriously weak security standard: the password it uses can often be cracked in a few minutes with a basic laptop computer and widely available software tools. WEP is an old IEEE 802.11 standard from 1997, which was superseded in 2003 by WPA, or Wi-Fi Protected Access. WPA was a quick alternative to improve security over WEP. The current standard is WPA2; some hardware cannot support WPA2 without firmware upgrade or replacement. WPA2 uses an encryption device that encrypts the network with a 256-bit key; the longer key length improves security over WEP. Enterprises often enforce security using a certificate-based system to authenticate the connecting device, following the standard 802.1X.

IEEE 802.11u-2011 is an amendment to the IEEE 802.11-2007 standard to add features that improve interworking with external networks.

mylo (Sony) handheld device made by Sony

My Life Online (mylo) was a device created and marketed by Sony for portable instant messaging and other Internet-based communications, browsing Internet web sites and playback and sharing of media files. The pocket-sized, tablet-shaped handheld device, which debuted in 2006, had a screen which slid up to reveal a QWERTY keyboard. The brand name 'mylo' stands for My Life Online. Using Wi-Fi instead of cellular networks, the mylo was targeted to the 18–24 age group.

IEEE 802.11b-1999 or 802.11b, is an amendment to the IEEE 802.11 wireless networking specification that extends throughput up to 11 Mbit/s using the same 2.4 GHz band. A related amendment was incorporated into the IEEE 802.11-2007 standard.

IEEE 802.11s is Wireless LAN standard and an IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for relatively fixed topologies and wireless ad hoc networks. The IEEE 802.11s working group draws upon volunteers from university and industry to provide specifications and possible design solutions for wireless mesh networking. As a standard, the document was iterated and revised many times prior to finalization.

IEEE 802.11k-2008 is an amendment to IEEE 802.11-2007 standard for radio resource management. It defines and exposes radio and network information to facilitate the management and maintenance of a mobile Wireless LAN. IEEE 802.11k was incorporated in IEEE Std 802.11-2012; see IEEE 802.11.

IEEE 802.11ah is a wireless networking protocol published in 2017 to be called Wi-Fi HaLow(pronounced "HEY-Low") as an amendment of the IEEE 802.11-2007 wireless networking standard. It uses 900 MHz license exempt bands to provide extended range Wi-Fi networks, compared to conventional Wi-Fi networks operating in the 2.4 GHz and 5 GHz bands. It also benefits from lower energy consumption, allowing the creation of large groups of stations or sensors that cooperate to share signals, supporting the concept of the Internet of Things (IoT). The protocol's low power consumption competes with Bluetooth and has the added benefit of higher data rates and wider coverage range.

References

  1. "History of Wireless". Johns Hopkins Bloomberg School of Public Health. Archived from the original on 2007-02-10. Retrieved 2007-02-17.
  2. Wayne Caswell (November 17, 2010). "HomeRF Archives" . Retrieved July 16, 2011.
  3. http://www.wi-fi.org/knowledge-center/faq/same-ad-hoc-mode
  4. Wireless Distribution System Linked Router Network DD-WRT Wiki. Retrieved December 31, 2006.
  5. "How Wi-Fi Roaming Really Works" . Retrieved 2008-10-09.