Wireless access point

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Wireless access point Planet WAP-4000

A wireless access point (WAP or AP) is a device that "connects" wireless communication devices together to create a wireless network. The WAP is usually connected to a wired network, and can relay data between devices on each side. Many WAPs can be connected together to create a larger network that allows "roaming". In contrast, a network where the client devices manage themselves is called an ad-hoc network.

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

Low-cost, easily-installed WAPs grew rapidly in popularity in the late 1990s and early 2000s. These devices offered a way to avoid tangled messes of Category 5 cable associated with typical Ethernet networks of the day. While wiring a business, home, or school often requires stringing many cables through walls and ceilings, wireless networking offers the ability to cut down on, or eliminate entirely, the number of cables needing to be strung. Wireless networks also allow users greater mobility; freeing individuals from the need to be stuck at a computer cabled to the wall. On the industrial and commercial side, wireless networking has had a big impact on operations: employees are often armed with Portable Data Terminals integrating barcode scanners and wireless links, allowing them to update work-in-progress and inventory in real-time.

One IEEE 802.11 WAP can typically communicate with 30 client systems within a radius of 100 m. However, communication range can vary a lot depending on such variables as indoor or outdoor placement, height above ground, nearby obstructions, type of antenna, the current weather, operating radio frequency, and power output of the device. The range of WAPs can be extended through the use of repeaters and reflectors, which can bounce or amplify radio signals that ordinarily could not be received. Some experiments have been carried out to allow wireless networking over distances of several kilometers.

A typical corporate use of a WAP is to attach it to a wired network, and then provide wireless client adapters for users who need them. Within the range of the WAP, the wireless end-user has a full network connection with the benefit of mobility. In this instance, the WAP is a gateway for clients to access the wired network. Another use is to bridge two wired networks where cable is not appropriate; for example, a manufacturer can wirelessly connect a remote warehouse's wired network with a separate (though within line of sight) office's wired network.

Another wireless topography is called a lily pad network: a series of access points spread over a large area, each connected to a different network, providing hot spots where wireless clients can connect to the Internet without regard for the particular networks to which it's attached at the moment. The concept is somewhat incidental in large cities, where a combination of coffeehouses, libraries, and other public spaces offering wireless access allow clients to roam over a large area (like hopping from lily pad to lily pad), staying more or less continuously connected.

There are 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. Wireless devices are able to "listen" for data traffic on other frequencies, and can rapidly switch from one frequency to another to achieve better reception on a different WAP. However, the limited number of frequencies becomes problematic in crowded downtown areas with tall buildings housing multiple WAPs, because there can be enough overlap between the wireless networks to cause interference.

Wireless networking is far behind wired networking in terms of bandwidth and throughput. While (as of 2004) typical wireless devices for the consumer market can reach speeds of 11 (IEEE 802.11b) or 54 Mbit/s (megabits per second) (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 is that Wi-Fi uses a shared communications medium, so the actual usable data throughput of a WAP is somewhat less than half the over-the-air rate. Thus, a typical 54 MBit/s wireless connection actually carries TCP/IP data at 20 to 25 Mbit/s. Because users of legacy wired networks are used to the faster speeds, people using wireless connections are anxious to see the wireless networks catch up.

Another issue with wireless access in general is the need for security. Many early access points were not able to discern whether or not a particular user was authorized to access the network. Although this problem reflects issues that have long troubled many types of wired networks (it has been possible in the past for individuals to plug computers into randomly available Ethernet jacks and get access to the network), this was usually not a significant problem since many businesses had reasonably good physical security. However, the fact that radio signals bleed outside of buildings and across property lines means that physical security is not as much of a deterrent to war drivers.

In response, several new security technologies have emerged. One of the simplest techniques involves only allowing access from certain MAC addresses. However, MAC addresses can be easily spoofed, leading to the development of more advanced security measures. Many access points incorporate Wired Equivalent Privacy encryption, but that also has been criticized by many security analysts as not good enough. Newer (as of 2004) encryption standards available on WAPs and client cards include TKIP and AES, both of which offer substantial improvements in security. Also, a newer system for authentication is IEEE 802.1x, which promises to enhance security on both wired and wireless networks. WAPs that incorporate technologies like these often also have routers built in, so they are somewhat more accurately described as wireless gateways.de:Wireless Access Point ja:アクセスポイント (無線LAN) pl:Access Point

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