 a range of 6 km from the phone exchange. Asynchronous: In an asynchronous service, such as a generic file transfer, the transmission of packets within a data stream can be separated by random intervals. This compares with the more stringent time requirements of isochronous or synchronous services (q.v.). Backhaul: Backhaul refers to the transmission of network traffic from a remote site, such as a wireless MAN base station, back to an ISP or other Internet point-of-presence. A DSL link might provide backhaul for an urban Wi-Fi hotspot, while a remote rural network might require a long- range wireless or satellite link. Bandwidth: Bandwidth is a measure either of the frequency width of a signal (measured in Hertz), or the total amount of data that can be transmit- ted in a certain period of time over a particular medium or using a particu- lar device (measured in bps). The bandwidth of a transmitted signal is measured between the frequencies at which the signal drops to half its peak power (the 3dB points). Barker Code: A Barker code is a binary sequence that has low correlation with a time-shifted version of itself (low auto-correlation). The 11-bit Barker code (10110111000) is used as the spreading or chipping code in 802.11 DSSS. Baseband: Baseband refers to the signal in a communication system before it is modulated and multiplexed onto its carrier. The term is commonly used to refer both to the signal and to the hardware/software that processes the signal. Beamwidth: The coverage angle of a radio antenna, ranging from 360 degrees for an omnidirectional antenna to a narrow pencil beam with a high gain directional antenna such as a Yagi or parabolic dish. Binary Phase Shift Keying (BPSK): A modulation technique, using two phases of the carrier to represent data symbols 1 and 0. Bluetooth: A wireless PAN technology used for voice and data links with a typical range of 10 metres. Bluetooth delivers a standard data rate of 720 kbps Glossary using frequency hopping spread spectrum in the 2.4 GHz ISM radio band. Wi