A-F

access point

Access points are Wi-Fi transceivers that act as hubs or routers and connect clients in a wireless network operating in infrastructure mode. Access points can also provide a point of connection between a wireless network and a wired LAN.

ad hoc mode

Devices in an ad hoc network communicate directly between one another and not through an access point. Ad hoc networks are slower and less reliable than infrastructure mode networks (using access points). Ad hoc is only suited for small groups of clients or to provide temporary connectivity between notebook computers.

antenna

A component in a transceiver that directs incoming and outgoing radio waves. Antennas are inactive components and do not create or add power to a broadcast. An antenna can increase signal gain only by concentrating and directing a signal, much like a lens concentrates light to produce a brighter beam.

Asymmetric DSL (ADSL)

ADSL is the most common type of DSL and transmits data on analog phones lines. Because the download speed is greater than the upload speed, ADSL is asymmetric.

attenuation

A loss of signal power. Attenuation can occur naturally as the distance between transmitter and receiver increases. Interference from obstacles in the signal path, such as building materials, trees, and even people, can increase attenuation, especially in low-power signals.

Basic Service Set (BSS)

An access point and one or more associated wireless devices communicating in infrastructure mode.

Bluetooth

A Wireless Personal Area Networking (WPAN) technology developed that operates in the 2.4 GHz radio band. Developers named Bluetooth for the Danish King Harald Blåtand, who unified Denmark and Norway in the tenth century. Bluetooth is a complementary standard to 802.11x, replacing peripheral cables while Wi-Fi replaces Ethernet. Bluetooth’s range is too short and its throughput too slow to compete with Wi-Fi.

cantenna

A homemade Wi-Fi antenna design that uses a recycled can. The Pringles cantenna is one popular version. Cantennas are surprisingly effective and easyto make.

Denial of Service (DoS)

An attack that overwhelms a computer or service and prevents legitimate users from accessing it.

Dynamic Host Configuration Protocol (DHCP)

DHCP is a protocol used to assign IP addresses to network clients automatically, each time they connect to the network; for example, after a reboot, or when reconnecting a laptop to the network.

Ethernet

The IEEE 802.3 standard for wired networks that supports transmission speeds of up to 100 Mbps.

firewall

A hardware device or software application that acts as a traffic filter between internal and external networks. Firewalls prevent unauthorized traffic from entering a network, block access by unauthorized users, and are able to prevent a number of different attacks.

Fresnel zone

Pronounced fray-nel and named after French physicist Augustin-Jean Fresnel. The Fresnel zone refers to the pattern of radio waves between a transmitter and a receiver. The Fresnel zone between two antennas is shaped like an elongated ellipse, with the widest distribution of RF radiation occurring halfway between transceivers. If the Fresnel zone is not free of obstructions, including trees, the signal power will weaken (attenuate) significantly.