Wireless access point

From Freepedia

Image:Planet WAP-4000.JPG In computer networking, a wireless access point (WAP or AP) is a device that "connects" wireless communication devices together to create a wireless network. The WAP usually connects to a wired network, and can relay data between wireless devices and wired devices. Several WAPs can link together to form a larger network that allows "roaming". (In contrast, a network where the client devices manage themselves - without the need for any access points - becomes an ad-hoc network.)

Low-cost, easily-installed WAPs grew rapidly in popularity in the late 1990s and early 2000s. These devices offered a way to avoid the tangled messes of category 5 cable associated with typical ethernet networks of the day. Whereas wiring a business, home, or school often requires stringing many cables through walls and ceilings, wireless networking offers the ability to reduce, or eliminate entirely, the stringing of cables. Wireless networks also allow users greater mobility; freeing individuals from the restrictions of using a computer cabled to the wall. On the industrial and commercial side, wireless networking has had a big impact on operations: employees in these areas now often carry 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 located 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 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.

A typical corporate use of a WAP involves attaching it to a wired network, and then providing 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 functions as a gateway for clients to access the wired network. Another use invoves bridging two wired networks in conditions inappropriate for cable: 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 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 organic 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.

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.

Limitations

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 WAP. However, the limited number of frequencies becomes problematic in crowded downtown areas with tall buildings housing multiple WAPs, because enough overlap can occur between the wireless networks to cause interference.

Wireless networking lags far behind wired networking in terms of bandwidth and of 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 can actually 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.

Security

One issue with wireless access in general involves the need for security. Many early access points could not discern whether or not a particular user had authorization 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 did not usually pose a significant problem,since many organizations had reasonably good physical security. However, the fact that radio signals bleed outside of buildings and across property lines makes physical security largely irrelevant 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, client devices can easily spoof MAC addresses, leading to the need for more advanced security measures. Many access points incorporate Wired Equivalent Privacy (WEP) encryption, but security analysts have criticized WEP's inadequacies, and the U.S. FBI demonstrated the ability to break WEP protection in 3 minutes. Newer (as of 2005) encryption standards available on wireless access points and client cards include Wi-Fi Protected Access modes WPA and WPA2, both of which offer substantial improvements in security. Also, a newer system for authentication, IEEE 802.1x, promises to enhance security on both wired and wireless networks. Wireless access points that incorporate technologies like these often also have routers built in, thus becoming wireless gateways.