Abilene network: The Abilene network is the part of Internet2 that is run by Indiana University.
access layer: The access layer is the part of a network that connects clients or servers to the rest of the network. It is often a LAN.
access point (AP): The part of the wireless LAN that connects the LAN to other networks.
acknowledgment (ACK): A character indicating a positive acknowledgment that a message has been received correctly.
ACM: Association for Computing Machinery. The ACM is an association of computer professionals.
acronym: A word formed from the initial letters or groups of letters of words in a phrase. An example is the word laser, which means light amplification by stimulated emission of radiation.
address: A coded representation of the destination of data or of its originating source. For example, multiple computers on one communication circuit must each have a unique data link layer address.
address resolution: The process of determining the lower-layer address from a higher-layer address. For example, IP address resolution means determining the IP address from the application-layer address, whereas data link layer address resolution means determining the data link layer address from an IP address.
Address Resolution Protocol (ARP): The network-layer protocol standard for data link layer address resolution requests.
ADSL: See asymmetric DSL (ADSL).
Advanced Encryption Standard (AES): A new single-key encryption standard authorized by NIST that replaces DES. It uses the Rijndael (pronounced "rain doll") algorithm and has key sizes of 128, 192, and 256 bits. NIST estimates that using the most advanced computers and techniques available today, it will require about 150 trillion years to crack AES by brute force.
Advanced Research and Development Network Operations Center (ARDNOC):
The agency funded by the Canadian government to develop new Internet2 technologies and protocols.
American National Standards Institute (ANSI): The principal standards-setting body in the United States. ANSI is a nonprofit, nongovernmental organization supported by more than 1,000 trade organizations, professional societies, and companies. It belongs to the ITU-T CCITT and the ISO.
amplifier: A device used to boost the strength of a signal. Amplifiers are spaced at intervals throughout the length of a communication circuit to increase the distance a signal can travel.
analog: Pertaining to representation by means of continuously variable quantity, such as varying frequencies. Physical quantities such as temperature are continuous variable, and therefore are "analog."
analog signal: A signal in the form of a continuously varying quantity such as amplitude, which reflects variations in the loudness of the human voice.
analog transmission: Transmission of a continuously variable signal as opposed to a discrete on/off signal. The traditional way of transmitting a telephone or voice signal is analog.
API: Application Program Interface. API is the way IBM links incompatible equipment for microcomputer-to-mainframe links. API allows applications on microcomputers and mainframes to speak directly to each other at the application software level, even though the equipment is from different vendors.
Apple Talk: A set of communication protocols that defines networking for Apple computers. Rarely used today.
application service provider (ASP): An application service develops an application system (e.g., an airline reservation system, a payroll system) and companies purchase the service, without ever installing the software on their own computers. They simply use the service the same way you might use a Web hosting service to publish your own Web pages rather than attempting to purchase and operate your own Web server.
ARCnet: Attached Resource Computing network. A proprietary token-bus LAN developed by the Datapoint Corporation.
ARDNOC: See Advanced Research and Development Network Operations Center (ARDNOC).
ARPANET: One of the early packet-switching networks. ARPANET was developed by the U.S. Department of Defense Advanced Research Projects Agency. It was the predecessor of the Internet.
ARQ: Automatic Repeat reQuest. A system employing an error-detecting code so conceived that any error initiates a repetition of the transmission of the incorrectly received message.
ASCII: American Standard Code for Information Interchange. Pronounced "ask-e." An eight-level code for data transfer adopted by the ANSI to achieve compatibility among data devices.
asymmetric DSL (ADSL): A data link layer technology that provides high-speed ("broadband") communication over traditional telephone lines. A DSL modem is used to provide three channels: a traditional voice channel, an upstream channel for communicating from the client to the ISP (often at speeds of 64 to 640 Kbps), and a downstream channel for communicating from the ISP to the client (often at speeds of 640 Kbps to 6 Mbps).
asynchronous transfer mode (ATM): A communication switch that handles interface speeds ranging from 25 million to 622 million bps. It multiplexes data streams onto the same BN by using cell relay techniques. ATM switches can handle multimedia traffic, such as data, graphics, voice, and video.
asynchronous transmission: Transmission in which each information character is individually synchronized, usually by start and stop bits. The gap between each character is not a fixed length. Compare with synchronous transmission.
ATM: See asynchronous transfer mode (ATM). In banking, an automated teller machine.
attenuation: As a signal travels through a circuit, it gradually attenuates, or loses power. Expressed in decibels, attenuation is the difference between the transmitted and received power caused by loss of signal strength through the equipment, communication circuits, or other devices.
authentication: A security method of guaranteeing that a message is genuine,that it has arrived unaltered, and that it comes from the source indicated.
automatic number identification (ANI): The process whereby a long-distance common carrier provides its customers with a visual display of an incoming caller’s telephone number.
backbone network (BN): A large network to which many networks within an organization are connected. It usually is a network that interconnects all networks on a single site, but it can be larger if it connects all the organization’s terminals, microcomputers, mainframes, LANs, and other communication equipment.
BALUN: balanced/unbalanced. An impedance-matching device to connect balanced twisted-pair cabling with unbalanced coaxial cable.
bandwidth: The difference between the highest and lowest frequencies in a band. For example, a voice-grade circuit has a 4,000-Hz bandwidth. In common usage, bandwidth refers to circuit capacity; when people say they need more bandwidth, they need a higher transmission speed.
basic rate interface (BRI): In ISDN, two 64,000-bps B circuits for data transmission and one 16,000-bps D circuit for signaling (2 B+D). Also called basic rate access. See also primary rate interface (PRI).
baud: Unit of signaling speed. Now obsolete and replaced by the term symbol rate. The speed in baud is the number of signal elements per second. If each signal represents only 1 bit, baud is the same as bits per second (bps). When each signal contains more than 1 bit, baud does not equal bps.
BER: bit-error rate. The number of bits received in error divided by the total number of bits received. An indicator of circuit quality.
BERT: bit-error rate testing. Testing a data line with a pattern of bits that are compared before and after the transmission to detect errors.
BGP: See Border Gateway Protocol (BGP).
binary: A number system using only the two symbols 0 and 1 that is especially well adapted to computer usage because 0 and 1 can be represented as "on" and "off," respectively, or as negative charges and positive charges, respectively. The binary digits appear in strings of 0′s and 1′s. bipolar transmission: A method of digital transmission in which binary 0 is sent as a negative pulse and binary 1 is sent as a positive pulse.
bit: 1. An abbreviation of the term binary digit. 2. A single pulse in a group of pulses. 3. A unit of information capacity.
bit rate: The rate at which bits are transmitted over a communication path, normally expressed in bits per second (bps). The bit rate should not be confused with the data signaling rate (baud), which measures the rate of signal changes being transmitted. See also bps.
bit stream: A continuous series of bits being transmitted on a transmission line.
BKER: Block-error rate. The number of blocks received in error divided by the total number of blocks received.
BKERT: Block-error rate testing. Testing a data link with groups of information arranged into transmission blocks for error checking.
block: Sets of contiguous bits or bytes that make up a message, frame, or packet.
block check character (BCC): The character(s) at the end of a binary synchronous communications (BSC) message used to check for errors.
Bluetooth: A standard for short-distance wireless communication.
BONDING: BONDING (Bandwidth on Demand Interoperatibility Networking Group) is an inverse multiplexing proposal for combining several 56-Kbps or 64-Kbps circuits into one higher-speed circuit.
Border Gateway Protocol (BGP): A network-layer standard protocol used to exchange route information between routers using dynamic decentralized routing. Used only between different TCP/IP autonomous systems (i.e., major sections of the Internet). bps: Bits per second. The basic unit of data communication rate measurement. Usually refers to rate of information bits transmitted. Contrast with baud and bit rate.
bridge: A device that connects two similar networks using the same data link and network protocols. Compare with gateway, router, and brouter. broadband circuit: An analog communication circuit.
broadband communications: Originally, the term referred to analog communications, but it has become corrupted in common usage so that it now usually means high-speed communications networks, typically Internet access technologies with access speeds of 1 Mbps or higher.
broadband Ethernet: The 10Broad36 version of Ethernet IEEE 802.3, meaning that it transmits at 10 millions bps in broadband with a maximum distance of 3,600 meters. broadcast routing: See decentralized routing.
brouter: A piece of hardware that combines the functions of a bridge and a router. See also bridge and router. brute-force attack: A way of breaking an encrypted message by trying all possible values of the key.
buffer: A device used for the temporary storage of data, primarily to compensate for differences in data flow rates (for example, between a terminal and its transmission circuit) but also as a security measure to allow retransmission of data if an error is detected during transmission.
burst error: A series of consecutive errors in data transmission. Refers to the phenomenon on communication circuits in which errors are highly prone to occurring in groups or clusters.
bus: A transmission path or circuit. Typically an electrical connection with one or more conductors in which all attached devices receive all transmissions at the same time.
byte: A small group of data bits that is handled as a unit. In most cases, it is an 8-bit byte and it is known as a character.
call-back modem: When a user calls a host computer, the modem disconnects the call after receiving the password and calls back to the caller’s predefined telephone number to establish a connection.
CA*net: CA*net is the Canadian network that forms part of Internet2.
carrier: An analog signal at some fixed amplitude and frequency that then is combined with an information-bearing signal to produce an intelligent output signal suitable for transmission of meaningful information. Also called carrier wave or carrier frequency.
carrier frequency: The basic frequency or pulse repetition rate of a signal bearing no intelligence until it is modulated by another signal that does impart intelligence.
CCITT: See Consultative Committee on International Telegraph and Telephone (CCITT). Now obsolete and renamed International Telecommunications Union—Telecommunications (ITU-T).
CD: 1. Collision detection in the CSMA (Carrier Sense Multiple Access) protocol for LANs. 2. Carrier detect occurs when a modem detects a carrier signal to be received.
central office: The switching and control facility set up by the local telephone company (common carrier) where the subscriber’s local loop terminates. Central offices handle calls within a specified geographic area, which is identified by the first three digits of the telephone number. Also called an end office or exchange office.
CENTREX: A widespread telephone company switching service that uses dedicated central office switching equipment. CENTREX CPE is where the user site also has customer premises equipment (CPE).
certificate authority (CA): A CA is a trusted organization that can vouch for the authenticity of the person or organization using authentication (e.g., VeriSign). A person wanting to use a CA registers with the CA and must provide some proof of identify. CA issues a digital certificate that is the requestor’s public key encrypted using the CA’s private key as proof of identity that can be attached to the user’s e-mail or Web transactions.
channel: 1. A path for transmission of electromagnetic signals. Synonym for line or link. Compare with circuit. 2. A data communications path. Circuits may be divided into subcircuits.
character: A member of a set of elements used for the organization, control, or representation of data. Characters may be letters, digits, punctuation marks, or other symbols. Also called a byte.
checking, echo: A method of checking the accuracy of transmitted data in which the received data are returned to the sending end for comparison with the original data.
circuit: The path over which the voice, data, or image transmission travels. Circuits can be twisted-wire pairs, coaxial cables, fiber-optic cables, microwave transmissions, and so forth. Compare with channel, line, and link.
circuit switching: A method of communications whereby an electrical connection between calling and called stations is established on demand for exclusive use of the circuit until the connection is terminated.
cladding: A layer of material (usually glass) that surrounds the glass core of an optical fiber. Prevents loss of signal by reflecting light back into the core.
client: The input-output hardware device at the user’s end of a communication circuit. There are three major categories of clients: microcomputers, terminals, and special-purpose terminals.
cluster controller: A device that controls the input-output operations of the cluster of devices (microcomputers, terminals, printers, and so forth) attached to it. Also called a terminal controller. For example, the 3274 Control Unit is a cluster controller that directs all communications between the host computer and remote devices attached to it. CMIP: See Common Management Interface Protocol (CMIP).
coaxial cable: An insulated wire that runs through the middle of a cable. A second braided wire surrounds the insulation of the inner wire like a sheath. Used on LANs for transmitting messages between devices.
code: A transformation or representation of information in a different form according to some set of pre-established conventions.
codec: A codec translates analog voice data into digital data for transmission over computer networks. Two codecs are needed—one at the sender’s end and one at the receiver’s end.
code conversion: A hardware box or software that converts from one code to another, such as from ASCII to EBCDIC.
collapsed backbone network: In a collapsed BN, the set of routers in a typical BN is replaced by one switch and a set of circuits to each LAN. The collapsed backbone has more cable but fewer devices. There is no backbone cable. The "backbone" exists only in the switch.
collision: When two computers or devices transmit at the same time on a shared multipoint circuit, their signals collide and destroy each other.
common carrier: An organization in the business of providing regulated telephone, telegraph, telex, and data communications services, such as AT&T, MCI, Bell-South, and NYNEX. This term is applied most often to U.S. and Canadian commercial organizations, but sometimes it is used to refer to telecommunication entities, such as government-operated suppliers of communication services in other countries.
Common Management Interface Protocol (CMIP): CMIP is a network management system that monitors and tracks network usage and other parameters for user workstations and other nodes. It is similar to SNMP, but it is more complete and is better in many ways.
communication services: A group of transmission facilities that is available for lease or purchase.
comparison risk ranking: The process by which the members of a Delphi team reach a consensus on which network threats have the highest risk. It produces a ranked list from high risk to low risk.
component: One of the specific pieces of a network, system, or application. When these components are assembled, they become the network, system, or application. Components are the individual parts of the network that we want to safeguard or restrict by using controls.
Computer Emergency Response Team (CERT): The job of CERT, located at Carnegie Mellon University, is to respond to computer security problems on the Internet, raise awareness of computer security issues, and prevent security breaches. It was established by the U.S. Department of Defense in 1988 after a virus shut down almost 10 percent of the computers on the Internet. Many organizations are starting their own computer emergency response teams, so the term is beginning to refer to any response team, not just the one at Carnegie Mellon University.
concentrator: A device that multiplexes several low-speed communication circuits onto a single high-speed trunk. A remote data concentrator (RDC) is similar in function to a multiplexer but differs because the host computer software usually must be rewritten to accommodate the RDC. RDCs differ from statistical multiplexes because the total capacity of the high-speed outgoing circuit, in characters per second, is equal to the total capacity of the incoming low-speed circuits. On the other hand, output capacity of a statistical multiplexer (stat mux) is less than the total capacity of the incoming circuits.
conditioning: A technique of applying electronic filtering elements to a communication line to improve the capability of that line so it can support higher data transmission rates.
configuration: The actual or practical layout of a network that takes into account its software, hardware, and cabling. Configurations may be multidrop, point-to-point, LANs, and the like. By contrast, a topology is the geometric layout (ring, bus, star) of the configuration. Topologies are the building blocks of configurations. Compare with topology.
connectionless routing: Connectionless routing means each packet is treated separately and makes its own way through the network. It is possible that different packets will take different routes through the network depending on the type of routing used and the amount of traffic.
connection-oriented routing:
Connection-oriented routing sets up a virtual circuit (one that appears to use point-to-point circuit switching) between the sender and receiver. The network layer makes one routing decision when the connection is established, and all packets follow the same route. All packets in the same message arrive at the destination in the same order in which they were sent.
Consultative Committee on International Telegraph and Telephone (CCITT): An international organization that sets worldwide communication standards. Its new name is International Telecommunications Union—Telecommunications (ITU-T).
content caching: Storing content from other Web sites on your network to reduce traffic on your Internet connection. A content engine regularly stores incoming static content such as banners and graphics files so that future requests for those items can be processed internally.
content delivery: Storing content for your Web sites on the content delivery provider’s servers spread around the Internet to reduce traffic on your Internet connection. The content delivery provider’s servers contain the static content on your pages such as banners and graphics files. Software on your Web server locates the nearest content delivery server to the user (based on his or her IP address) and changes the references on your Web pages to draw the static content from that server. Content delivery was pioneered by Akamai, which is one of the leading content delivery services on the Internet.
contention: A method by which devices on the same shared multipoint circuit compete for time on the circuit.
control: A mechanism to ensure that the threats to a network are mitigated. There are two levels of controls: system-level controls and application-level controls.
control character: A character whose occurrence in a particular context specifies some network operation or function.
control spreadsheet: A two-dimensional matrix showing the relationship between the controls in a network, the threats that are being mitigated, and the components that are being protected. The controls listed in each cell represent the specific control enacted to reduce or eliminate the exposure.
core layer: The core layer is the central part of a network that provides access to the distribution layer. It is often a very fast BN that runs through the center of a campus or office complex.
COS: Corporation for Open Systems. An organization of computer and communications equipment vendors and users formed to accelerate the introduction of products based on the seven-layer OSI model. Its primary interest is the application layer (layer 7) of the OSI model and the X.400 e-mail standard.
CPU: central processing unit.
CRC: Cyclical redundancy check. An error-checking control technique using a specific binary prime divisor that results in a unique remainder. It usually is a 16- to 32-bit character.
CSMA/CA: Carrier Sense Multiple Access (CSMA) with Collision Avoidance (CA). This protocol is similar to the Carrier Sense Multiple Access (CSMA) with Collision Detection (CD) protocol. Whereas CSMA/CD sends a data packet and then reports back if it collides with another packet, CSMA/CA sends a small preliminary packet to determine whether the network is busy. If there is a collision, it is with the small packet rather than with the entire message. CA is thought to be more efficient because it reduces the time required to recover from collisions.
CSMA/CD: Carrier Sense Multiple Access (CSMA) with Collision Detection (CD). A system used in contention networks. The network interface unit listens for the presence of a carrier before attempting to send and detects the presence of a collision by monitoring for a distorted pulse.
customer premises equipment (CPE):Equipment that provides the interface between the customer’s CENTREX system and the telephone network. It physically resides at the customer’s site rather than the telephone company’s end office. CPE generally refers to voice telephone equipment instead of data transmission equipment.
cut through switching: A type of switching in which messages are forwarded as they arrive, almost on a bit-by-bit basis.
data: 1. Specific individual facts or a list of such items. 2. Facts from which conclusions can be drawn.
data compression: The technique that provides for the transmission of fewer data bits without the loss of information. The receiving location expands the received data bits into the original bit sequence.
Specification (DOCSIS): A de facto data link layer standard for transmitting data via a cable modem using Ethernet-like protocols.
Data-over-Voice (DOV): When data and voice share the same transmission medium. Data transmissions are superimposed over the voice transmission.
datagram: A datagram is a connectionless service in packet-switched networks. Each packet has a destination and sequence number and may follow a different route through the network. Different routes may deliver packets at different speeds, so data packets often arrive out of sequence. The sequence number tells the network how to reassemble the packets into a continuous message.
DCE: Data circuit terminating equipment. The equipment (usually the modem) installed at the user’s site that provides all the functions required to establish, maintain, and terminate a connection, including the signal conversion and coding between the data terminal equipment (DTE) and the common carrier’s line.
decentralized routing: With decentralized routing, all computers in the network make their own routing decisions. There are three major types of decentralized routing. With static routing, the routing table is developed by the network manager and remains unchanged until the network manager updates it. With dynamic routing, the goal is to improve network performance by routing messages over the fastest possible route; an initial routing table is developed by the network manager but is continuously updated to reflect changing network conditions, such as message traffic. With broadcast routing, the message is sent to all computers, but it is processed only by the computer to which it is addressed.
decibel (dB): A tenth of a bel. A unit for measuring relative strength of a signal parameter such as power and voltage. The number of decibels is ten times the logarithm (base 10) of the ratio of the power of two signals, or ratio of the power of one signal to a reference level. The reference level always must be indicated, such as 1 milli watt for power ratio.
dedicated circuit: A leased communication circuit that goes from your site to some other location. It is a clear, unbroken communication path that is yours to use 24 hours per day, 7 days per week. Also called a private circuit or leased circuit.
delay distortion: A distortion on communication lines that is caused because some frequencies travel more slowly than others in a given transmission medium and therefore arrive at the destination at slightly different times. Delay distortion is measured in microseconds of delay relative to the delay at 1,700 Hz. This type of distortion does not affect voice, but it can have a serious effect on data transmissions.
delay equalizer: A corrective device for making the phase delay or envelope delay of a circuit substantially constant over a desired frequency range. See also equalizer.
Delphi group: A small group of experts (three to nine people) who meet to develop a consensus when it may be impossible or too expensive to collect more accurate data. For example, a Delphi group of communication experts might assemble to reach a consensus on the various threats to a communication network, the potential dollar losses for each occurrence of each threat, and the estimated frequency of occurrence for each threat.
denial of service (DoS) attack: A DoS attempts to disrupt the network by flooding the network with messages so that the network cannot process messages from normal users.
DES: Data Encryption Standard. Developed by IBM and the U.S. National Institute of Standards, this widely used single-key encryption algorithm uses a 64-bit key.
desktop videoconferencing: With desktop videoconferencing, small cameras are installed on top of each user’s computer so that participants can hold meetings from their offices.
digital signal: A discrete or discontinuous signal whose various states are discrete intervals apart, such as +15 volts and -15 volts.
digital subscriber line (DSL): A data link layer technology that provides high-speed ("broadband") communication over traditional telephone lines. A DSL modem is used to provide three channels: a traditional voice channel, an upstream channel for communicating from the client to the ISP (often at speeds of 64 to 640 Kbps), and a downstream channel for communicating from the ISP to the client (often at speeds of 640 Kbps to 6 Mbps).
distortion: The unwanted modification or change of signals from their true form by some characteristic of the communication line or equipment being used for transmission—for example, delay distortion and amplitude distortion.
distortion types: 1. Bias: A type of distortion resulting when the intervals of modulation do not all have exactly their normal durations. 2. Characteristic: Distortion caused by transient disturbances that are present in the transmission circuit because of modulation. 3.
Delay: Distortion occurring when the envelope delay of a circuit is not consistent over the frequency range required for transmission. 4.
End: Distortion of start-stop signals. The shifting of the end of all marking pulses from their proper positions in relation to the beginning of the start pulse. 5. Jitter: A type of distortion that results in the intermittent shortening or lengthening of the signals. This distortion is entirely random in nature and can be caused by hits on the line. 6. Harmonic: The resultant process of harmonic frequencies (due to nonlinear characteristics of a transmission circuit) in the response when a sinusoidal stimulus is applied.
distributed denial of service (DDoS) attack: With a DDoS attack, a hacker breaks into and takes control of many computers on the Internet (often several hundred to several thousand) and uses them to launch the DoS attack from thousands of computers at the same time.
distribution layer: The distribution layer is the part of a network that connects the access layer to other access layers and to the core layer. It is often a BN in a building.
Domain Name Service (DNS): A server that provides a directory used to supply IP addresses for application-layer addresses— that is, a server that performs IP address resolution.
download: The process of loading software and data into the nodes of a network from the central node. Downloading usually refers to the movement of data from a host mainframe computer to a remote terminal or microcomputer.
