access point

Wireless access point

In computer networking, a wireless access point (WAP or AP) is a device that allows wireless communication devices to connect to a wireless network using Wi-Fi, Bluetooth and related standards. The WAP usually connects to a wired network, and can relay data between the wireless devices (such as computers or printers) and wired devices on the network.

Introduction

Prior to wireless networks, setting up a computer network in a business, home, or school often required running many cables through walls and ceilings in order to deliver network access to all of the network-enabled devices in the building. With the advent of the Wireless Access Point, network users are now able to add devices that access the network with few or no new cables. Today's WAPs are built to support a standard for sending and receiving data using radio frequencies rather than cabling. Those standards, and the frequencies they use are defined by the IEEE. A current popular IEEE standard for wireless networking is the IEEE 802.11.

Common WAP Applications

A typical corporate use involves attaching several WAPs to a wired network and then providing wireless access to the office LAN. Within the range of the WAPs, the wireless end user has a full network connection with the benefit of mobility. In this instance, the WAP functions as a gateway for clients to access the wired network.

Another wireless topology, a lily-pad network, consists of a series of access points spread over a large area, each connected to a different network. This provides hot spots where wireless clients can connect to the Internet without regard for the particular networks to which they have attached for the moment. The concept can become common in large cities, where a combination of coffeehouses, libraries, other public spaces offering wireless access, as well as privately owned open access points, allow clients to stay more or less continuously connected to a network (like hopping from lily pad to lilypad), while moving around.

Home wireless networks, the majority, generally have only one WAP to connect all the computers in a home. Most are wireless routers, meaning converged devices that include a WAP, Ethernet router, and often a switch in the same package. Many also converge a broadband modem. Most owners leave their encryption settings at default, hence neighbors can use them. In places where most homes have their own WAP within range of the neighbors' WAP, it's possible for technically savvy people to turn off their encryption and set up a wireless community network, creating an intra-city communication network without the need of wired networks.

A WAP may also act as the network's arbitrator, negotiating when each nearby client device can transmit. However, the vast majority of currently installed IEEE 802.11 networks do not implement this, using a distributed pseudo-random algorithm instead.

Access Point vs. Ad-Hoc Network

Some people confuse Access Point and Ad-Hoc Network. An Ad-Hoc network uses a connection between two or more devices without using an access point: the devices communicate directly. An Ad-hoc network might be useful in some situations, such as for a quick data exchange, or for a Multiplayer LAN game, because it is easy to set up and does not require an access point. Due to its peer-to-peer layout, Ad-hoc connections are similar to Bluetooth ones, and are generally not recommended for a permanent installation.

Some people access the internet via ad-hoc networks, using features like Windows' Internet Connection Sharing. This is fine temporarily, and with a small number of devices that are close to each other, but an Ad-hoc networks don't scale well, and operate better to transfer data between nearby nodes. In contrast, internet traffic will converge to the nodes with direct internet connection, potentially congesting these nodes. For internet-enabled node, Access Points have a clear advantage, since an AP is designed to handle this load.

Limitations

One IEEE 802.11 WAP can typically communicate with 30 client systems located within a radius of 100 m. However, the actual range of communication can vary significantly, depending on such variables as indoor or outdoor placement, height above ground, nearby obstructions, other electronic devices that might actively interfere with the signal by broadcasting on the same frequency, type of antenna, the current weather, operating radio frequency, and the power output of devices. Network designers can extend the range of WAPs through the use of repeaters and reflectors, which can bounce or amplify radio signals that ordinarily would go un-received. In experimental conditions, wireless networking has operated over distances of several kilometers.

Most jurisdictions have only a limited number of frequencies legally available for use by wireless networks. Usually, adjacent WAPs will use different frequencies to communicate with their clients in order to avoid interference between the two nearby systems. But wireless devices can "listen" for data traffic on other frequencies, and can rapidly switch from one frequency to another to achieve better reception on a different frequency. However, the limited number of frequencies becomes problematic in crowded downtown areas with tall buildings using multiple WAPs. In such an environment, signal overlap becomes an issue causing interference, which results in signal dropage and data errors.

Wireless networking lags behind wired networking in terms of increasing bandwidth and throughput. While (as of 2004) typical wireless devices for the consumer market can reach speeds of 11 Mbit/s (megabits per second) (IEEE 802.11b) or 54 Mbit/s (IEEE 802.11a, IEEE 802.11g), wired hardware of similar cost reaches 1000 Mbit/s (Gigabit Ethernet). One impediment to increasing the speed of wireless communications comes from Wi-Fi's use of a shared communications medium, so a WAP is only able to use somewhat less than half the actual over-the-air rate for data throughput. Thus a typical 54 MBit/s wireless connection actually carries TCP/IP data at 20 to 25 Mbit/s. Users of legacy wired networks expect the faster speeds, and people using wireless connections keenly want to see the wireless networks catch up.

As of 2007 a new standard for wireless, 802.11n is awaiting final certification from IEEE. This new standard operates at speeds up to 540 Mbit/s and at longer distances (~50 m) than 802.11g. Use of legacy wired networks (especially in consumer applications) is expected to decline sharply as the common 100 Mbit/s speed is surpassed and users no longer need to worry about running wires to attain high bandwidth.

By the year 2008 the 802.11n based access points and client devices already take fair share of the market place. Major chipset manufacturers are Atheros and Broadcom for Access Point side and Atheros, Broadcom and Intel for client side. The MiMO operation between different manufacturers chipset is currently not supported (ie. Atheros based Access Point and Intel based client card built into a laptop will link using 802.11g instead of 802.11n).

Interference can commonly cause problems with wireless networking reception, as many devices operate using the 2.4 GHz ISM band. A nearby wireless phone or anything with greater transmission power within close proximity can markedly reduce the perceived signal strength of a wireless access point. Microwave ovens are also known to interfere with wireless networks.

Security

Wireless access has special security considerations. Many wired networks base the security on physical access control, trusting all the users on the local network, but if wireless access points are connected to the network, anyone on the street or in the neighboring office could connect.

The most common solution is wireless traffic encryption. Modern access points come with built-in encryption. The first generation encryption scheme WEP proved easy to crack; the second and third generation schemes, WPA and WPA2, are considered secure if a strong enough password or passphrase is used.

Some WAPs support hotspot style authentication using RADIUS and other authentication servers. For example, DD-WRT v24 supports Chilisoft hotspot authentication which separates the WLAN from the hard wired LAN so that your guests cannot browse the local wired network.

See also

  • Hotspots - access points or wireless networks open to the public
  • Wireless LAN - networks consisting of zero or more access points plus devices
  • LWAPP - Lightweight Access Point Protocol used to manage a large set of WAPs
  • WarXing - searching for open networks
  • Femtocell - a local-area base station using cellular network standards such as UMTS, rather than Wi-Fi
  • WiMAX - wide-area wireless standard that has a few elements in common with Wi-Fi

References

External links

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