This glossary of terms is designed to help you understand some of the terms associated with Internet and Wireless connectivity.
Absorbtion occurs when RF waves are absorbed by the materials that they are attempting to pass through. Absorption typically occurs when the waves pass through walls or dense materials. Water and concrete have high RF absorption properties. If you need coverage in stairwells, remember that they are mostly concrete tubes with a bunch of diagonal concrete dividers.
A measure of frequency 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 communications line.
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.
A coaxial cable connector that uses a "quickconnect" style bayonet lug. BNC connectors are typically found on 10base2 coaxial Ethernet.
A network device that connects 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.
The theoretical maximum amount of traffic provided by a digital communications line. Often used interchangeably with bandwidth.
A well defined range of frequencies used for communications. 802.11 channels use 22 MHz of bandwidth, but are only separated by 5 MHz.
An access point that does not broadcast its SSID, often used as a security measure.
When two identical waves merge and are in phase, the amplitude of the resulting wave is twice that of either of the components. This is called constructive
interference. See also: destructive interference
Network equipment (such as a router or bridge) that is installed at a customer's location.
The speed at which 802.11 radios exchange symbols, which is always higher than the available throughput. For example, the nominal data rate of 802.11g is
54 Mbps, while the maximum throughput is about 20 Mbps). See also: throughput
A logarithmic unit of measurement that expresses the magnitude of power relative to a reference level. Commonly used units are dBi (decibels relative to an
isotropic radiator) and dBm (decibels relative to a milliwatt).
When a router receives a packet destined for a network for which it has no explicit route, the packet is forwarded to the default gateway. The default gateway
then repeats the process, possibly sending the packet to its own default gateway, until the packet reaches its ultimate destination.
An attack on network resources, usually achieved by flooding a network with traffic or exploiting a bug in an application or network protocol.
When two identical waves merge and are exactly out of phase, the amplitude of the resulting wave is zero. This is called destructive interference. See
also: constructive interference
The simplest form of omnidirectional antenna.
An antenna that radiates very strongly in a particular direction. Examples of directional antennas include the yagi, dish, and waveguide antennas.
The ability of an antenna to focus energy in a particular direction when transmitting, or to receive energy from a particular direction when receiving.
The widely used network protocol that maps IP addresses to names.
A protocol used by hosts to automatically determine their IP address.
The place where one organization's network meets another. Edges are defined by the location of the external router, which often acts as a firewall.
The very wide range of possible frequencies of electromagnetic energy. Parts of the electromagnetic spectrum include radio, microwave, visible light, and X rays.
A wave that propagates through space without the need for a propagating medium. It contains an electric and a magnetic component. See also: mechanical wave
A router that accepts or denies traffic based on some criteria. Firewalls are one basic tool used to protect entire networks from undesirable traffic.
Power diminished by geometric spreading of the wavefront, as the wave propagates through space. See also: attenuation, free space loss
The number of whole waves that pass a fixed point in a period of time. See also: wavelength, Hertz
The ratio of the maximum directivity of an antenna to its directivity in the opposite direction.
Communications equipment that can send and receive at the same time (such as a telephone). See also: half duplex
The ability of a radio component (such as an antenna or amplifier) to increase the power of a signal. See also: decibel
Communications equipment that can send or receive, but never both at once (such as a handheld radio). See also: full duplex.
A measure of frequency, denoting some number of cycles per second.
Radio waves from 3 to 30 MHz are referred to as HF. Data networks can be built on HF that operate at very long range, but with very low data
capacity.
Data that crosses one network connection. A web server may be several hops away from your local computer, as packets are forwarded from router to router, eventually reaching their ultimate destination.
In wireless networks, a hot-spot is a location that provides Internet access via Wi-Fi, typically by use of a captive portal. In photovoltaic systems, a hot-spot occurs when a single cell in a solar panel is shaded, causing it to act as a resistive load rather than to generate power.
An Ethernet networking device that repeats received data on all connected ports. See also: switch
The quotient of voltage over current of a transmission line, consisting of a resistance and a reactance. The load impedance must match the source impedance for maximum power transfer (50 for most communications equipment).
The most common network layer protocol in use. IP defines the hosts and networks that
make up the global Internet.
The family of communication protocols that make up the Internet. Some of these protocols include TCP, IP, ICMP, and UDP. Also called the TCP/IP protocol suite, or simply TCP/IP.
The amount of time it takes for a packet to cross a network connection. It is often (incorrectly) used interchangeably with Round Trip Time (RTT), since measuring the RTT of a wide-area connection is trivial compared to measuring the actual latency. See also: Round Trip Time.
If a person standing at point A has an unobstructed view of point B, then point A is said to have a clear Line of Sight to point B.
The amount of radio energy available to overcome path losses. If the available link budget exceeds the path loss, minimum receive sensitivity of the receiving radio, and any obstacles, then communications should be possible.
A network (typically Ethernet) used within an organization. The part of a network that exists just behind an ISP's router is generally considered to be part of the LAN. See also: WAN.
A network connection (such as VSAT) that has high capacity and high latency. In order to achieve the best possible performance, TCP/IP must be tuned
to match the traffic on such links.
A network with no hierarchical organization, where every node on the network carries the traffic of every other as needed. Good mesh network implementations are selfhealing, which means that they automatically detect routing problems and fix them as needed.
The phenomenon of reflections of a signal reaching their target along different paths, and therefore at different times.
See mesh
The lowest IP number in a subnet. The network address is used in routing tables to specify the destination to be used when sending packets to a logical group of IP addresses.
NAT is a networking technology that allows many computers to share a single, globally routable IP address. While NAT can help to solve the problem of limited IP address space, it creates a technical challenge for two-way services, such as Voice over IP.
Network diagnostic tools that display information about wireless networks, such as the network name, channel, and encryption method used.
Also called the Internet layer. This is the third layer of the OSI and TCP/IP network models, where IP operates and Internet routing takes place.
Any device capable of sending and receiving data on a network. Access points, routers, computers, and laptops are all examples of nodes.
An antenna that radiates almost equally in every direction in the horizontal plane. See also: directional antenna, sectorial antenna
A wireless repeater that only uses a single radio, at significantly reduced throughput. See also: repeater
A popular model of network communications defined by the ISO/IEC 7498-1 standard. The OSI model consists of seven interdependent layers, from
the physical through the application. See also: TCP/IP network model.
On IP networks, messages sent between computers are broken into small pieces called packets. Each packet includes a source, destination,
and other routing information that is used to route it to its ultimate destination. Packets are reassembled again at the remote end by
TCP (or another protocol) before being passed to the application.
A ubiquitous network diagnostic utility that uses ICMP echo request and reply messages to determine the round trip time to a network host. Ping can be used to determine the location of network problems by "pinging" computers in the path between the local machine and the ultimate destination.
see Power over Ethernet
A wireless network where several nodes connect back to a central location. The classic example of a point-to-multipoint network is an access point at an office with several laptops using it for Internet access. See also: point-to-point, multipoint-to-multipoint
A wireless network consisting of only two stations, usually separated by a great distance. See also: point-to-multipoint, multipoint-to-multipoint
A network protocol typically used on serial lines (such as a dial-up connection) to provide IP connectivity.
The direction of the electric component of an electromagnetic wave as it leaves the transmitting antenna. See also: horizontal polarization, vertical polarization, circular polarization
A technique used to supply DC power to devices using the Ethernet data cable. See also: end span injectors, mid span injectors
The portion of the electromagnetic spectrum in which waves can be generated by applying alternating current to an antenna.
A mesh implementation where routes are computed only when it is necessary to send data to a specific node. See also: proactive routing
A network monitoring tool that performs unattended monitoring over long periods, and notifies administrators immediately when problems arise.
Reflection occurs when RF waves cannot penetrate a surface and are returned or bounced off the surface. Reflection is common with metal and glass surfaces. Reflection is the principle behind a Faraday cage, where the holes on the cage surface are smaller than the wavelength of the radiation or signal that they are attempting to block, thereby blocking the signal that is striking its surface. So even a thin layer of metal containing no holes can effectively block wireless signals from passing through it.
A node that is configured to rebroadcast traffic that is not destined for the node itself, often used to extend the useful range of a network.
The amount of time it takes for a packet to be acknowledged from the remote end of a connection. Frequently confused with latency.
A database that stores information in a very compact way that does not expand over time. This is the data format used by RRDtool and other network monitoring tools.
A device that forwards packets between different networks. The process of forwarding packets to the next hop is called routing. routing. The process of forwarding packets between different networks. A device that does this is called a router.
A list of networks and IP addresses kept by a router to determine how packets should be forwarded. If a router receives a packet for a network that is not in the routing table, the router uses its default gateway. Routers operate at the Network Layer. See also: bridge and default gateway.
Scattering occurs when the reflective surface is uneven, which causes many random bounces. A reflective signal may still have enough of its original properties to be used, but a scattered signal does not. In some cases where you cannot get a direct signal through to your location, you may be able to get a strong enough signal from a bounced RF wave, but only if that wave gets bounced off of a smooth surface; if the surface is uneven then the bounced signal will be useless.
An antenna that radiates primarily in a specific area. The beam can be as wide as 180 degrees, or as narrow as 60 degrees. See also: directional antenna,
omnidirectional antenna
An end-to-end encryption technology built into virtually all web browsers. SSL uses public key cryptography and a trusted public key infrastructure to secure data communications on the web. Whenever you visit a web URL that starts with https, you are using SSL.
No antenna is able to radiate all the energy in one preferred direction. Some is inevitably radiated in other directions. These smaller peaks are referred to as
sidelobes.
A protocol designed to facilitate the exchange of management information between network devices. SNMP is typically used to poll network switches and routers to gather operating statistics.
A device that provides a visual representation of the electromagnetic spectrum.
A generic term used to refer to the responsiveness of a network connection. A "high-speed" network should have low latency and more than enough capacity to carry the traffic of its users. See also: bandwidth, capacity, and latency.
A subset of a range of IP networks, defined by netmasks.
A network device that provides a temporary, dedicated connection between communicating devices. See also: hub.
A popular simplification of the OSI network model that is used with Internet networks. The TCP/IP model consists of five interdependent layers, from the physical through the application.
The actual amount of information per second flowing through a network connection, disregarding protocol overhead.
Tools that measure the actual bandwidth available between two points on a network.
A TTL value acts as a deadline or emergency brake to signal a time when the data should be discarded. In TCP/IP networks, the TTL is a counter that starts at some value (such as 64) and is decremented at each router hop. If the TTL reaches zero, the packet is discarded. This mechanism helps reduce damage caused by routing loops. In DNS, the TTL defines the amount of time that a particular zone record should be kept before it must be refreshed. In Squid, the TTL defines how long a cached object may be kept before it must be again retrieved from the original website.
A ubiquitous network diagnostic utility often used in conjunction with ping to determine the location of network problems. The Unix version is called traceroute, while the Windows version is tracert. Both use ICMP echo requests with increasing TTL values to determine which routers are used to connect to a remote host, and also display latency statistics. Another variant is tracepath, which uses a similar technique with UDP packets. See also: mtr.
A session oriented protocol that operates at the Transport Layer, providing packet reassembly, congestion avoidance, and reliable delivery. TCP is an integral protocol used by many Internet applications, including HTTP and SMTP.
A form of data encapsulation that wraps one protocol stack within another. This is often used in conjunction with encryption to protect communications from potential eavesdroppers, while eliminating the need to support encryption within the application itself. Tunnels are often used conjunction with VPNs.
One of several standards used for satellite Internet access. VSAT is the most widely deployed satellite technology used in Africa. See also: Broadband Global Access Network (BGAN) and Digital Video Broadcast (DVB-S).
A tool used to join two networks together over an untrusted network (such as the Internet). VPNs are often used to connect remote users to an organization's network when traveling or working from home. VPNs use a combination of encryption and tunneling to secure all network traffic, regardless of the application
being used. See also: tunnel.
A technology that provides telephone-like features over an Internet connection. Examples of popular VoIP clients include Skype, Gizmo Project, MSN Messenger, and iChat.
The distance measured from a point on one wave to the equivalent part of the next, for example from the top of one peak to the next. Also known as lambda.
A marketing brand owned by the Wi-Fi Alliance that is used to refer to various wireless networking technologies (including 802.11a, 802.11b, and 802.11g). Wi-Fi is short for Wireless Fidelity.
A fairly strong link layer encryption protocol supported by most modern Wi-Fi equipment.
Any long distance networking technology. Leased lines, frame relay, DSL, fixed wireless, and satellite all typically implement wide area networks. See also: LAN.
A web site that allows any user to edit the contents of any page. One of the most popular public wikis is http://www.wikipedia.org/
A somewhat secure link layer encryption protocol supported by virtually all 802.11a/b/g equipment.
A free network protocol analyzer for Unix and Windows. http://www.wireshark.org/
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