What is Wireless LAN?

January 9, 2016 by afaqahmad

Filed under Wireless LAN

Last modified June 9, 2016

What is Wireless LAN?

wireless

A wireless local area network (WLAN) is a wireless computer network that two or more devices via a wireless distribution method (often spread spectrum or OFDM radio) links within a limited area such as a home, school, computer lab or office. This provides users with the ability to move around within a local coverage area and still be connected to the network, and can connect to the broader internet. Most modern WLANs are based on the IEEE 802.11 standards, placed on the market in the course of the Wi-Fi brand name.

Wireless LANs have become popular in the home due to the ease of installation and use, and commercial complexes offer wireless access to their customers; often free.New York, for instance, has begun a pilot program to city employees in all five boroughs of the city with wireless Internet.

History:-

Norman Abramson, a professor at the University of Hawaii, has developed the world’s first wireless computer communication network, ALOHANET (operational in 1971), using cheap ham-like radios. The system consisted of seven computers deployed in four islands to communicate with the central computer on the island of Oahu without the use of telephone lines.
WLAN (Wireless Local Area Network) initial hardware cost so much that it was only used as an alternative to cabled LAN in places where cabling is 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 the IEEE 802.11 (in products using the Wi-Fi brand name). Beginning in 1991, a European alternative became known as HiperLAN / 1 by the European Telecommunications Standards Institute (ETSI) has continued with a first version was adopted in 1996 followed by a HiperLAN / 2 functional specification with ATM influences accomplished February 2000. Neither the European standard achieved the commercial success of 802.11, although much of the work to HiperLAN / 2 has survived in the PHY specification for IEEE 802.11a, which is almost 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 band with a maximum transfer rate of 600 Mbit / s. Most newer routers are able to utilize both wireless bands, known as dual-band. This enables data communication to the crowded 2.4 GHz band, which is also shared with Bluetooth devices avoid andmicrowave ovens. The 5 GHz band is wider than the 2.4 GHz band, with more channels, thus allowing 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.

Types of wireless LANs:-

The IEEE 802.11 has two basic modes: infrastructure or ad hoc mode. In the ad-hoc mode, mobile broadcast units directly peer-to-peer. In mode infrastructure, mobile units communicate via anaccess point that serves as a bridge to other networks (such as the Internet or LAN).

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

Infrastructure:-

Most Wi-Fi networks are deployed in the infrastructure mode.

In the infrastructure mode, a base station functions as a wireless access hub, and nodes communicate via the hub. The hub usually, but not always, a wired or fiber network and can cause permanent wireless connections to other nodes.

Wireless access points are usually fixed, and provide service to their customers nodes within range.

Wireless clients such as laptops, smartphones etc. Connect to connect to the access point to the network.

Sometimes a network will be a multiple access points, with the same “SSID and security control. In this case connects one network access point that connects the client to the network. In that case, the client software to try the access point choose to try to give the best service as the access point with the strongest signal.

Peer to Peer:-

Peer-to-peer or ad hoc wireless LAN
An ad-hoc network (not the same as a Wi-Fi Direct network) is a network where stations communicate only peer-to-peer (P2P). There is no basis and no one gives permission to talk. This is achieved with the aid of the Independent Basic Service Set (IBSS).

A Wi-Fi Direct network is a different type of network where stations communicate peer to peer.

In a Wi-Fi P2P group, the group owner works as an Access Point and all other devices are clients. There are two ways to create a group entitled the Wi-Fi Direct group. In one approach of the user is a P2P group owner of the hand. This method is also known as autonomic Group owner (autonomous GO). In the second method, also called negotiations based group creation, two devices compete on the basis of the group owner intention value. The device with a higher intention value is a group owner and the second device is a client. Group owner intention value may depend on whether the wireless device performs a cross-connection between a WLAN infrastructure service and a P2P group, the remaining power in the wireless device, or wireless device has a group owner in another group and / or a received signal strength of the first wireless device.

A peer-to-peer network allows wireless devices to communicate directly with each other. Wireless devices within range can discover each other directly, without going through the central access points. This method is usually used two computers so that they together form a network. This can take place in principle in devices within a closed range.

If a signal strength meter is in this situation, it can not be read accurately and the power can be misleading because records the strength of the strongest signal that the closest computer can be.
Hidden node problem: both devices A and C interact with B, but 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). 802.11 specification contains provisions to reduce collisions, because the two mobile units can be both within range of a common access point, but out of range of each other.

Bridge:-

“” A bridge can be used to connect networks, typically comprised of different types. A wireless Ethernet bridge allows the devices connected to an Ethernet network to a wireless network. The bridge serves as a connection with the wireless LAN.

Wireless Distribution System:-

Main article: Wireless Distribution System
A Wireless Distribution System allows the wireless connection of access points in an IEEE 802.11 network. It can be a wireless network with multiple access points to be extended without the need to link a wired backbone, as traditionally required. The notable advantage of WDS over other solutions is that the preservation of the MAC addresses of client packets across links between access points.

An access point can be an important relay or remote base station. One of the main base station is typically connected to the wired Ethernet. A relay base station transmits data between remote base stations, wireless clients or other relay stations to either a main or another relay 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 instead of IP commands.

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

WDS can also be referred to as a repeater mode because it appears to bridge and accept wireless clients at the same time (as opposed to traditional bridging). It should be noted, however, that in this process throughput halved all clients connected wirelessly.

If it is difficult to set up all the access points in a network of threads, can also be access points as a regenerator.

Roaming:-

There are two definitions for wireless LAN roaming:
Internal Roaming: The Mobile Station (MS) from one access point (AP) to another AP within a home network as the signal strength is too weak. An authentication server (RADIUS), the re-authentication of MS performs via 802.1x (eg with PEAP). The billing for QoS in the home network. A mobile station roaming from one access point to another is often interrupts the flow of data between the mobile station and an application connected to the network. The Mobile Station for example, periodically monitors the presence of other access points (those that provide a better connection). At any given time, based on its own mechanisms, the Mobile Station decides to re-associate with an access point with a stronger wireless signal. However, the Mobile Station may lose a connection to an access point for dealing with a different access point. To provide reliable connectivity applications, the mobile station must generally software that provides session persistence.
External Roaming: The MS (client) is moving in a WLAN from another Wireless Internet Service Provider (WISP) and take their services (hotspot). The user can independently of his home network using another foreign network, if it is open to visitors. There have dedicated authentication and billing systems for mobile services in a foreign network.
Applications

Wireless LANs have many applications. Modern implementations of WLAN range from small in-home networks to large, campus-sized fully mobile networks in airplanes and trains.

Users can access the Internet from wireless hotspots in restaurants, hotels, and now with portable devices that connect to 3G or 4G networks. Often these forms of public access points do not require registration or password to connect to the network. Others can be accessed after registration has been completed and / or paid.

Performance and throughput:-

WLAN, organized in different layers 2 variants (IEEE 802.11), have different characteristics. In all the flavors of 802.11, its maximum achievable throughput, or data based on measurements under ideal conditions, or in the layer 2 data rates. However, this is not for typical implementations in which data is transferred between two end points of which at least one of which is typically connected to a fixed infrastructure, and the other endpoint is connected to an infrastructure via a wireless connection.
This usually means that data frames fit a 802.11 (WLAN) medium and converted 802.3 (Ethernet) or vice versa.

Because of the difference in the frame (header) lengths of the two media, the packet size of a request determines the speed of the data transfer. This means that an application which small packets (e.g. VoIP) is using a data stream with a high overhead traffic (for example, a low goodput).

Other factors that contribute to the overall application data rate, the rate at which the request transmits the packets (i.e., the data rate), and the energy with which the wireless signal is received.

The latter is determined by the distance and the configured output of the communicating devices.

The same is true references to the attached flow charts which show measurements of UDP throughput measurements. Each an average (UDP) throughput (the error bars are barely visible due to the small variation) of 25 measurements.

Each room comes with a specific package size (small or large) and a specific data rate (10 kbit / s – 100 Mbit / s). Markers for the traffic profiles of common applications are also included. This text and measurements do not cover package errors, but information can be found at found above. The table below shows the maximum achievable (application-specific) UDP throughput in the same scenarios (again the same references) with several difference WLAN (802.11) flavors. The measurement hosts have been 25 meters apart from each other; loss is ignored again.

 

WLAN flavor Small packets (64 B) Large packets(1460 B)
Maximum application-specific UDP throughput in Mbit/s Maximum application-specific UDP throughput in Mbit/s
802.11b 0.5 5.5
802.11g 2.2 25.1
802.11a 2.5  28.3
 802.11n (20 MHz channel, 2.4 GHz)  9.3 73
802.11n (40 MHz channel, 2.4 GHz) 9.0 100
802.11ac (5 GHz)

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