azimuth. The angle that measures deviation with respect to the south in the northern hemisphere, and with respect to the north in the southern hemisphere. See also: inclination B bandwidth. A measure of fre- quency ranges, typically used for digital communications. The word bandwidth is also commonly used interchangeably with capacity to refer to the theoretical maximum data rate of a digital communica- tions line. See also: capacity, channel, throughput battery. A device used to store en- ergy in a photovoltaic system. See also: solar panel, regulator, load, converter, inverter beamwidth. The angular distance between the points on either side of the main lobe of an antenna, where the received power is half that of the main lobe. The beamwidth of an antenna is usually stated for both the horizontal and vertical planes. benchmarking. Testing the maxi- mum performance of a service or device. Benchmarking a network connection typically involves fl ood- ing the link with traf fi c and measur- ing the actual observed throughput, both on transmit and receive. BGAN see Broadband Global Ac- cess Network BNC connector. A coaxial cable connector that uses a "quick- connect" style bayonet lug. BNC connectors are typically found on 10base2 coaxial Ethernet. bridge. A network device that con- nects two networks together at the data link layer . Bridges do not route packets at the network layer . They simply repeat packets between two link-local networks. See also: router and transparent bridging fi rewall . bridge-utils. A Linux software package that is required for creat- ing 802.1d Ethernet bridges. Broadband Global Access Net- work (BGAN) . One of several stan- dards used for satellite Internet ac- cess. See also: Digital Video Broadcast (DVB-S) and Very Small Aperture Terminal (VSAT) . broadcast address. On IP net- works, the broadcast IP address is used to send data to all hosts in the local subnet. On Ethernet networks, the broadcast MAC address is used to send data to all machines in the same collision domain. bypass diodes. A feature found on some solar panels that prevents the formation of hot-spots on shaded cells, but reduces the maximum voltage of the panel. C CA see Certi fi cate Authority Cacti ( ). A popular web-based monitoring tool written in PHP. Glossary 391
capacity. The theoretical maximum amount of traf fi c provided by a digi- tal communications line. Often used interchangeably with bandwidth . captive portal. A mechanism used to transparently redirect web brows- ers to a new location. Captive por- tals are often used for authentication or for interrupting a user's online session (for example, to display an Acceptable Use Policy). cell. Solar panels are made up of several individual cells, which are electrically connected to provide a particular value of current and volt- age. Batteries are also made up of individual cells connected in series, each of which contributes about 2 volts to the battery.
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