Multipurpose Internet Mail Extension (MIME): An application-layer standard protocol that enables SMTP mail messages to transfer nontext characters such as graphics and software. The sending e-mail client translates the nontext characters into something that resembles text using MIME codes and attaches it to the message. The receiving e-mail client translates the MIME codes back into the original graphic or software file.
nanosecond: One billionth (1/1,000,000,000) of a second or 10-9.
National Institute of Standards and Technology (NIST): Formerly the National Bureau of Standards. The agency of the U.S. government responsible for developing information processing standards for the federal government.
negative acknowledgment (NAK): The return signal that reports an error in the message received. The opposite of acknowledgment (ACK).
network: 1. A series of points connected by communication circuits. 2. The switched telephone network is the network of telephone lines normally used for dialed telephone calls. 3. A private network is a network of communication circuits confined to the use of one customer.
network access point (NAP): An "intersection" on the Internet where many national and regional ISPs connect to exchange data.
network address translation (NAT): NAT is the process of translating between one set of private IP addresses inside a network and a set of public IP addresses outside the network for use on the Internet. NAT is transparent in that no computer notices that it is being done.
network cost of ownership (NCO): NCO is a measure of how much it costs per year to keep one computer operating. NCO includes the cost of support staff to attach it to the network, install software, administer the network (e.g., create user IDs, back up user data), provide training and technical support, and upgrade hardware and software. NCO is often $1,500 to $3,500 per computer per year. Compare with total cost of ownership (TCO).
network interface card (NIC): An NIC allows the computer to be physically connected to the network cable; the NIC provides the physical-layer connection from the computer to the network.
network operating system (NOS): The NOS is the software that controls the network. The NOS provides the data link and the network layers and must interact with the application software and the computer’s own operating system. Every NOS provides two sets of software: one that runs on the network server(s) and one that runs on the network client(s).
network operations center (NOC): Any centralized network management control site.
network profile: Every LAN microcomputer has a profile that outlines what resources it has available to other microcomputers in the network and what resources it can use elsewhere in the network.
network service: An application available on a network—for example, file storage. and Technology (NIST).
node: In a description of a network, the point at which the links join input-output devices. It could be a computer or a special-purpose device such as a router.
noise: The unwanted change in waveform that occurs between two points in a transmission circuit.
noise, amplitude: A sudden change in the level of power with differing effects, depending on the type of modulation used by the modem.
noise, cross-talk: Noise resulting from the interchange of signals on two adjacent circuits; manifests itself when it is possible to hear other people’s telephone conversations.
noise, echo: The "hollow" or echoing characteristic that is heard on voice-grade lines with improper echo suppression.
noise, Gaussian: Noise that is characterized statistically by a Gaussian, or random, distribution.
noise, impulse: Noise caused by individual impulses on the circuit.
noise, intermodulation: Noise that occurs when signals from two independent lines intermodulate. A new signal forms and falls into a frequency band differing from those of both inputs. The new signal may fall into a frequency band reserved for another signal.
NRZ: Nonreturn to zero. A binary encoding and transmission scheme in which 1′s and 0′s are represented by opposite and alternating high and low voltages, and in which there is no return to a reference (zero) voltage between encoded bits.
NRZI: Nonreturn to zero inverted. A binary encoding scheme that inverts the signal on a 1 and leaves the signal unchanged for a 0, and in which a change in the voltage state signals a 1-bit value and the absence of a change denotes a 0-bit value.
null character: A control character that can be inserted into or withdrawn from a sequence of characters without altering the message.
null modem cable: A 6- to 8-foot RS232 cable that makes the two microcomputers connected at each end of the cable think they are talking through modems.
office, central or end: The common carrier’s switching office closest to the subscriber.
100Base-T: An Ethernet LAN standard that runs at 100 million bps and uses unshielded twisted-pair wires.
1000Base-T: An Ethernet LAN standard the runs at 1 billion bps and uses unshielded twisted-pair wires.
Open Shortest Path First (OSPF): A network-layer standard protocol used to exchange route information between routers using dynamic decentralized routing.
optical fibers: Hair-thin strands of very pure glass (sometimes plastic) over which light waves travel. They are used as a medium over which information is transmitted.
OSI model: The seven-layer Open Systems Interconnection (OSI) Reference model developed by the ISO subcommittee. The OSI model serves as a logical framework of protocols for computer-to-computer communications. Its purpose is to facilitate the interconnection of networks.
out-of-band signaling: A method of signaling that uses a frequency that is within the passband of the transmission facility but outside of a carrier circuit normally used for data transmission.
overhead: Computer time used to keep track of or run the system, as compared with computer time used to process data.
overlay network: A network (usually a WLAN) used to supplement a primary network (usually a wired LAN).
packet: A group of binary digits, including data and control signals, that is switched as a composite whole. The data, control signals, and error-control information are arranged in a specific format. A packet often is a 128-character block of data.
packet switching: Process whereby messages are broken into finite-size packets that always are accepted by the network. The message packets are forwarded to the other party over a multitude of different circuit paths. At the other end of the circuit, the packets are reassembled into the message, which is then passed on to the receiving terminal.
packet switching network (PSN): A network designed to carry data in the form of packets. The packet and its format are internal to that network. The external interfaces may handle data in different formats, and format conversion may be done by the user’s computer.
PAD: Packet assembly/disassembly. Equipment providing packet assembly and disassembly between asynchronous transmission and the packet-switching network.
parallel: Describes the way the internal transfer of binary data takes place within a computer. It may be transmitted as a parallel word, but it is converted to a serial or bit-by-bit data stream for transmission.
parity bit: A binary bit appended to an array of bits to make the number of 1 bits always be odd or even for an individual character. For example, odd parity may require three 1 bits and even parity may require four 1 bits.
parity check: Addition of noninformation bits to a message to detect any changes in the original bit structure from the time it leaves the sending device to the time it is received.
Pbps: Petabits per second. A data rate equal to 1 quadrillion bits per second (1,000,000,000,000,000).
PBX: private branch exchange. Telephone switch located at a customer’s site that primarily establishes voice communications over tie lines or circuits as well as between individual users and the switched telephone network. Typically also provides switching within a customer site and usually offers numerous other enhanced features, such as least-cost routing and call detail recording.
PDU: Protocol Data Unit.
peer: A dictionary definition of peer is "a person who is equal to another in abilities." A peer-to-peer network, therefore, is one in which each microcomputer node has equal abilities. In communications, a peer is a node or station that is on the same protocol layer as another.
peer-to-peer communications: 1. Communication between two or more processes or programs by which both ends of the session exchange data with equal privilege. 2. Communication between two or more network nodes in which either side can initiate sessions because no primary-secondary relationship exists.
peer-to-peer LAN: A network in which a microcomputer can serve as both a server and a user. Every microcomputer has access to all the network’s resources on an equal basis.
permanent virtual circuit (PVC): A virtual circuit that resembles a leased line because it can be dedicated to a single user. Its connections are controlled by software.
pirate: A person who obtains the latest software programs without paying for them. A skilled software pirate is able to break the protection scheme that is designed to prevent copying.
plain old telephone network (POTS): The nickname for the public switched telephone network. Often used when referring to dial-up Internet access using a modem.
PLP: Packet Layer Protocol (PLP) is the routing protocol that performs the network layer functions (e.g., routing and addressing) in X.25 networks.
point of presence (POP): The physical access location of an ISP or voice or data communications carrier. point-to-point: Denoting a circuit or line that has only two terminals. A link. An example is a single microcomputer connected to a mainframe. polling: Any procedure that sequentially queries several terminals in a network.
polling, hub: A type of sequential polling in which the polling device contacts a terminal, that terminal contacts the next terminal, and so on, until all the terminals have been contacted.
polling, roll call: Polling accomplished from a pre-specified list in a fixed sequence, with polling restarted when the list is completed.
polynomial checking: A checking method using polynomial functions to test for errors in data in transmission. Also called cyclical redundancy check (CRC).
port: One of the circuit connection points on a front-end processor or local intelligent controller.
Post Office Protocol (POP): An application-layer standard used to communicate between the client and the e-mail server. POTS: See plain old telephone network (POTS).
PPP: PPP (multilink Point-to-Point Protocol) is an inverse multiplexing protocol for combining circuits of different speeds (e.g., a 64,000-bps circuit with a 14,400-bps circuit), with data allocated to each circuit is based on speed and need. PPP enables the user to change the circuits allocated to the PPP multiplexed circuit in mid-transmission so that the PPP circuit can increase or decrease the capacity. PPP is the successor to SLIP.
primary rate interface (PRI): In ISDN, twenty-three 64,000 bits per second D circuits for data and one 64,000 bits per second B circuit for signaling (23 B+D).
propagation delay: The time necessary for a signal to travel from one point on the circuit to another, such as from a satellite dish up to a satellite or from Los Angeles to New York.
protocol: A formal set of conventions governing the format and control of inputs and outputs between two communicating devices. This includes the rules by which these two devices communicate as well as handshaking and line discipline.
protocol stack: The set of software required to process a set of protocols.
PTT: Postal, telephone, and telegraph. These are the common carriers owned by governments; the government is the sole or monopoly supplier of communication facilities.
public data network (PDN): A network established and operated for the specific purpose of providing data transmission services to the public. It can be a public packet-switched network or a circuit-switched network. Public data networks normally offer value-added services for resource sharing at reduced costs and with high reliability. These time-sharing networks are available to anyone with a modem.
public key encryption: Public key encryption uses two keys. The public key is used to encrypt the message and a second, very different private key is used to decrypt the message. Even though the sender knows both the contents of the outgoing message and the public encryption key, once it is encrypted, the message cannot be decrypted without the private key. Public key encryption is one of the most secure encryption techniques available.
public key infrastructure (PKI): The PKI is the process of using public key encryption on the Internet. PKI begins with a certificate authority (CA), which is a trusted organization that can vouch for the authenticity of the person or organization using authentication (e.g., VeriSign). The CA issues a digital certificate that is the requestor’s public key encrypted using the CA’s private key as proof of identity. This certificate is then attached to the user’s e-mail or Web transactions. The receiver then verifies the certificate by decrypting it with the CA’s public key—and must also contact the CA to ensure that the user’s certificate has not been revoked by the CA.
pulse amplitude modulation (PAM):Amplitude modulation of a pulse carrier. PAM is used to translate analog voice data into a series of binary digits before they are transmitted.
pulse code modulation (PCM):Representation of a speech signal by sampling at a regular rate and converting each sample to a binary number. In PCM, the information signals are sampled at regular intervals and a series of pulses in coded form are transmitted, representing the amplitude of the information signal at that time.
QAM: Quadrature amplitude modulation. A sophisticated modulation technique that uses variations in signal amplitude, which allows data-encoded symbols to be represented as any of 16 states to send 4 bits on each signal.
Quality of Service (QoS): The ability of devices to give different priorities to different types of messages so that some messages (e.g., voice telephone data) are transmitted faster than other messages (e.g., e-mail).
quantizing error: The difference between the PAM signal and the original voice signal. The original signal has a smooth flow, but the PAM signal has jagged "steps."
RBOC: Regional Bell operating company. One of the seven companies created after divestiture of the old Bell system to provide local communications. Includes Ameritech, Bell Atlantic, BellSouth, NYNEX, Pacific Telesis, Southwestern Bell, and US West.
redundancy: The portion of the total information contained in a message that can be eliminated without loss of essential information.
reliability: A characteristic of the equipment, software, or network that relates to the integrity of the system against failure. Reliability usually is measured in terms of mean time between failures (MTBF), the statistical measure of the interval between successive failures of the hardware or software under consideration.
repeater: A device used to boost the strength of a signal. Repeaters are spaced at intervals throughout the length of a communication circuit.
request for comment (RFC): A proposed standard for the Internet on which anyone in the world is invited to comment.
request for proposal (RFP): A request for proposal is used to solicit bids from vendors for new network hardware, software, and services. RFPs specify what equipment, software, and services are desired and ask vendors to provide their best prices.
response time: The time the system takes to react to a given input; the time interval from when the user presses the last key to the terminal’s typing the first letter of the reply. Response time includes
(1) transmission time to the computer;
(2) processing time at the computer, including access time to obtain any file records needed to answer the inquiry; and (3) transmission time back to the terminal.
ring: 1. The hot wire in a telephone circuit.
2. An audible sound used for signaling the recipient of an incoming telephone call.
3. A LAN topology having a logical geometric arrangement in the shape of a ring.
risk: The level or amount of exposure to an item when compared with other items. It is a hazard or chance of loss. Risk is the degree of difference, as in, "What level of risk does one threat have when compared to the other threats?"
risk assessment: The process by which one identifies threats, uses a methodology to determine the tangible or intangible exposures, and develops a sequenced list of the threats from the one having the highest risk to the one having the lowest risk. The list may be in a sequence based on tangible dollar losses or on intangible criteria such as public embarrassment, likelihood of occurrence, most dangerous, most critical to the organization, and greatest delay. Also called risk ranking or risk analysis.
RMON: Remote monitoring. The definitions of what is stored and therefore retrievable from a remote user microcomputer when using the Simple Network Management Protocol (SNMP). It is referred to as the RMON MIB (management information base).
router: A device that connects two similar networks having the same network protocol. It also chooses the best route between two networks when there are multiple paths between them. Compare with bridge, brouter, and gateway.
Routing Information Protocol (RIP): A network-layer standard protocol used to exchange route information between routers using dynamic decentralized routing.
RS232: A technical specification published by the Electronic Industries Association that specifies the mechanical and electrical characteristics of the interface for connecting data terminal equipment (DTE) and data circuit terminating equipment (DCE). It defines interface circuit functions and their corresponding connector pin assignments.
RS449: An Electronic Industries Association standard for data terminal equipment (DTE) and data circuit terminating equipment (DCE) connection that specifies interface requirements for expanded transmission speeds (up to 2 million bps), longer cable lengths, and 10 additional functions.
serial: 1. Transmitting bits one at a time and in sequence. 2. The sequential or consecutive occurrence of two or more related activities in a single device or circuit.
server: A computer that provides a particular service to the client computers on the network. In larger LANs, the server is dedicated to being a server. In a peer-to-peer LANs, the server may be both a server and a client computer. There may be file, database, network, access, modem, facsimile, printer, and gateway servers.
server farm: A LAN segment containing many servers.
service-level agreement (SLA): An SLA specifies the exact type of performance and fault conditions that the organization will accept and what compensation the service provider must provide if it fails to meet the SLA. For example, the SLA might state that network availability must be 99 percent or higher and that the MTBF for T1 circuits must be 120 days or more.
Service Set Identifier (SSId): A simple, easily broken approach to WLAN security.
session: A logical connection between two terminals. This is the part of the message transmission when the two parties are exchanging messages. It takes place after the communication circuit has been set up and is functioning.
signal: A signal is something that is sent over a communication circuit. It might be a control signal used by the network to control itself.
signal-to-noise ratio: The ratio, expressed in dB, of the usable signal to the noise signal present.
Simple Mail Transfer Protocol (SMTP): An application-layer protocol standard used to transfer e-mail messages across the Internet.
simplex: A circuit capable of transmission in one direction only. Contrast with full duplex and half-duplex.
Simple Network Management Protocol (SNMP): An application-layer protocol standard used in network management for monitoring and configuring network devices.
single cable: A one-cable system in broadband LANs in which a portion of the bandwidth is allocated for "send" signals and a portion for "receive" signals, with a guardband in between to provide isolation from interference.
SLIP: Serial Line Internet Protocol (SLIP) is a proposed standard for inverse multiplexing. It has been surpassed by PPP.
spanning tree protocol: A data link layer protocol used to prevent broadcast storm in networks that have redundant links providing multiple paths between LAN segments.
spike: A sudden increase of electrical power on a communication circuit. Spike is a term used in the communication industry. Contrast with surge.
spread spectrum: The U.S. military developed spread spectrum through-the-air radio transmission technology primarily to overcome the problem of intentional interference by hostile jamming and secondarily for security. A spread spectrum signal is created by modulating the original transmitted radio frequency (RF) signal with a spreading code that causes "hopping" of the frequency from one frequency to another. By contrast, conventional AM and FM radio uses only one frequency to transmit its signal.
start bit: A bit that precedes the group of bits representing a character. Used to signal the arrival of the character in asynchronous transmission.
statistical multiplexer: Stat mux or STDM. A time division multiplexer (TDM) that dynamically allocates communication circuit time to each of the various attached terminals, according to whether a terminal is active or inactive at a particular moment. Buffering and queuing functions also are included.
stop bit: A bit that follows the group of bits representing a character. Used to signal the end of a character in asynchronous transmission.
store and forward switching: A switching technique that accepts messages, stores them, and then forwards them to the next location after ensuring they contain no errors as addressed in the message header.
STX: A control character used in ASCII and EBCDIC data communications to mean start of text.
surge: A sudden increase in voltage on a 120-volt electrical power line. A term used in the electric utilities industry. Contrast with spike.
switch: Switches connect more than two LAN segments that use the same data link and network protocol. They may connect the same or different types of cable. Switches typically provide ports for 4, 8, 16, or 32 separate LAN segments, and most enable all ports to be in use simultaneously, so they are faster than bridges.
switched circuit: A dial-up circuit in which the communication path is established by dialing. If the entire circuit path is unavailable, there is a busy signal, which prevents completion of the circuit connection.
switched network: Any network that has switches used for directing messages from the sender to the ultimate recipient.
switched network, circuit switched: A switched network in which switching is accomplished by disconnecting and reconnecting lines in different configurations to set up a continuous pathway between the sender and the recipient. See also circuit switching.
switched network, store and forward: A switched network in which the store-and-forward principle is used to handle transmission between senders and recipients. See also store-and-forward-switching.
switching: Identifying and connecting independent transmission links to form a continuous path from one location to another.
symbol rate: The speed in baud is the number of symbols per second. If each signal represents only one bit, symbol rate is the same as bits per second. When each signal contains more than one bit, symbol rate does not equal bits per second.
Synchronization character (SYN): An 8-bit control character that is sent at the beginning of a message block to establish synchronization (timing) between the sender and the receiver. Term used for the characters preceding an Ethernet packet. Term used for a TCP open connection request.
synchronous data link control (SDLC): A protocol for managing synchronous, code-transparent, serial bit-by-bit information transfer over a link connection. Transmission exchanges may be full-duplex or half-duplex and over switched or non switched links. The configurations of the link connection may be point-to-point, multipoint, or loop. SDLC is the protocol used in IBM’s systems network architecture.
synchronous optical network (SONET): The National Exchange Carriers Association standard for optical transmission at gigabits-per-second speeds. For example, digital signals transmit on T1 circuits at 1,544,000 bps and on T3 circuits at 44,376,000 bps. The slowest SONET OC-1 optical transmission rate of 51,840,000 bps is slightly faster than the T3 rate.
synchronous transmission: Form of transmission in which data is sent as a fixed-length block or frame. Compare with asynchonous transmission.
systems network architecture (SNA): The name of IBM’s conceptual framework that defines the data communication interaction between computer systems or terminals.
T carrier: A hierarchy of digital circuits designed to carry speech and other signals in digital form. Designated T1 (1.544 Mbps), T2 (6.313 Mbps), T3 (44.736 Mbps), and T4 (274.176 Mbps).
tariff: The formal schedule of rates and regulations pertaining to the communication services, equipment, and facilities that constitute the contract between the user and the common carrier. Tariffs are filed with the appropriate regulatory agency (FCC or state public utilities commission) for approval and published when approved.
TASI: Time assisted speech interpolation. The process of interleaving two or more voice calls on the same telephone circuit simultaneously.
Tbps: Terabits per second. A data rate equal to 1 trillion bits per second (1,000,000,000,000).
TCM: Trellis-coded modulation (TCM) is a modulation technique related to QAM that combines phase modulation and amplitude modulation. There are several different forms of TCM that transmit 5, 6, 7, or 8 bits per signal, respectively.
TCP/IP: Transmission Control Protocol/Internet Protocol is probably the oldest networking standard, developed for ARPANET, and now used on the Internet. One of the most commonly used network protocols.
telecommunications: A term encompassing voice, data, and image transmissions that are sent over some medium in the form of coded signals.
telecommuting: Telecommuting employees perform some or all of their work at home instead of going to the office each day.
teleconferencing: With teleconferencing, people from diverse geographic locations can "attend" a business meeting in both voice and picture format. In fact, even documents can be shown and copied at any of the remote locations.
telephony: A generic term to describe voice communications. Pronounced "tel-ef-on-e," not "tel-e-fon-e."
Telnet: Telnet enables users on one computer to log in to other computers on the Internet.
10Base-T: An Ethernet LAN standard (IEEE 802.3) that runs at 10 million bps and uses unshielded twisted-pair wires.
10Base2: An Ethernet LAN standard that runs at 10 million bps, uses baseband transmission techniques, and allows 200 meters maximum cable length.
10Base5: An Ethernet LAN standard that runs at 10 million bps, uses baseband transmission techniques, and allows 500 meters maximum cable length.
10Broad36: An Ethernet LAN standard that runs at 10 million bps, uses broadband transmission techniques, and allows 3,600 meters maximum cable length.
thick Ethernet: Refers to the original Ethernet specification that uses thick coaxial cable that is both grounded and shielded. The many layers of shielding are of polyvinyl and aluminum, which make the cable wider in diameter than other Ethernet cables. The heavy shielding also makes the cable more expensive and less flexible; therefore, it is impractical for many installations.
thin Ethernet: Refers to the 10Base2 baseband Ethernet, meaning the version that transmits at 10 million bps in baseband at 200 meters maximum. It uses thin coaxial cable. Also called cheapnet.
threat: A potentially adverse occurrence or unwanted event that could be injurious to the network, the computing environment, the organization, or a business application. Threats are acts or events the organization wants to prevent from taking place, such as lost data, theft, disasters, virus infections, errors, illegal access, and unauthorized disclosure. In other words, threats are events no one wants to occur.
throughput: The total amount of useful information that is processed or communicated during a specific time period.
token: The special sequence of characters used to gain access to a token ring or token-bus network to transmit a packet.
token bus: A LAN with a bus topology that uses a token-passing approach to network access. In a token-bus LAN, the next logical node or station is not necessarily the next physical node because it uses preassigned priority algorithms. Message requests are not handled in consecutive order by stations. Contrast with token ring.
token passing: A method of allocating network access wherein a terminal can send a message only after it has acquired the network’s electronic token.
token ring: A LAN with a ring topology that uses a token-passing approach to network access. In a token ring LAN, the next logical station also is the next physical station because the token passes from node to node. Contrast with token bus.
topology: The basic physical or geometric arrangement of the network—for example, a ring, star, or bus layout. The topology is the network’s logical arrangement, but it is influenced by the physical connections of its links and nodes. This is in contrast to its configuration, which is the actual or practical layout, including software and hardware constraints. Topologies are the building blocks of a network configuration. Compare with configuration.
total cost of ownership (TCO): TCO is a measure of how much it costs per year to keep one computer operating. TCO includes the cost of support staff to attach it to the network, install software, administer the network (e.g., create user IDs, back up user data), provide training and technical support, and upgrade hardware and software, along with the cost of "wasted time" when the network is down. TCO is often $10,000 per computer per year. Compare to network cost of ownership (NCO). transceiver: A device that transmits and/or receives data to or from computers on an Ethernet LAN. Also a hub.
tree: A network arrangement in which the stations hang off a common "branch," or data bus, like leaves on the branch of a tree.
TRIB: Transmission rate of information bits. A TRIB is the network’s throughput. It is the effective rate of data transfer over a communication circuit per unit of time. Usually expressed in bits per second.
triple DES (3DES): 3DES is a symmetric encryption technique that involves using DES three times, usually with three different keys, to produce the encrypted text, which produces a stronger level of security than DES, because it has a total of 168 bits as the key (i.e., 3 x 56 bits).
trunk: A voice communication circuit between switching devices or end offices.
turnaround time: The time required to reverse the direction of transmission from send to receive or vice versa on a half-duplex circuit.
twisted pair: A pair of wires used in standard telephone wiring. They are twisted to reduce interference caused by the other twisted pairs in the same cable bundle.
Twisted-pair wires go from homes and offices to the telephone company end office.
uninterruptible power supply (UPS):Provides backup electrical power if the normal electrical power fails or if the voltage drops to unacceptably low levels.
unipolar transmission: A form of digital transmission in which the voltage changes between 0 volts to represent a binary 0 and some positive value (e.g., +15 volts) to represent a binary 1. See also bipolar transmission.
unshielded twisted-pair (UTP) wires: The type of wiring used in 10Base-T Ethernet networks. Same as twisted pair.
upload: The process of loading software and data from the nodes of a network (terminals or microcomputers), over the network media, and to the host mainframe computer.
URL: To use a browser to access a Web server, you must enter the server’s addresses or URL (uniform resource locator). All Web addresses begin with seven characters: http://.
User Datagram Protocol (UDP): A connectionless transport layer protocol standard used by TCP to send short messages such as DNS requests.
user profile: The user profile specifies what data and network resources a user can access, and the type of access (read-only, write, create, delete, etc.).
V.nn: The V.nn series of ITU-T standards relating to the connection of digital equipment to the analog telephone network. Primarily concerned with the modem interface.
value-added network (VAN): A corporation that sells services of a value-added network. Such a network is built using the communication offerings of traditional common carriers, connected to computers that permit new types of telecommunication tariffs to be offered. The network may be a packet switching or message switching network. VBNS: See very-high-performance backbone network service (vBNS).
VDT: Video display terminal.
very-high-data-rate digital subscriber line (VDSL): A form of DSL that provides very high speed transmission (e.g., up to 51 Mbps) over traditional telephone lines for very short distances.
very-high-performance backbone network service (vBNS): One part of Internet2 run by MCI World-Com. video teleconferencing: Video teleconferencing provides real-time transmission of video and audio signals to enable people in two or more locations to have a meeting. virtual: Conceptual or appearing to be, rather than actually being.
virtual circuit: A temporary transmission circuit in which sequential data packets are routed between two points. It is created by the software in such a way that users think they have a dedicated point-to-point leased circuit.
virtual private network (VPN): A hybrid network that includes both public and private facilities. The user leases a bundle of circuits and configures the VPN on an as-needed basis so that some traffic travels on the private leased network and some travels on the common carrier’s public network.
virus: Viruses are executable programs that copy themselves onto other computers.Most viruses attach themselves to other programs or to special parts on disks, and as those files execute or are accessed, the virus spreads. Viruses cause unwanted events—some are harmless (such as nuisance messages) and others are serious (such as the destruction of data). Some viruses change their appearances as they spread, making detection more difficult.
voice-grade circuit: A term that applies to circuits suitable for transmission of speech, digital or analog data, or facsimile, generally with a frequency range of about 300 to 3,300 Hz contained within a 4,000-Hz circuit.
VRC: Vertical redundancy check. Same as parity check.
warchalk: marking (usually using chalk on pavement) the location and information for unsecured WLANs.
wardriving: The act of finding unsecured WLAN access points (usually by driving around).
weather map: A network map showing real-time utilization on each circuit.
Web browser: A software package on the client computer that enables a user to access a Web server.
Web crawler: A Web crawler searches through all the Web servers it knows to find information about a particular topic.
Web server: A Web server stores information in a series of text files called pages. These text files or pages use a structured language called HTML (Hypertext Markup Language) to store their information.
Wide Area Network (WAN): A network spanning a large geographical area. Its nodes can span city, state, or national boundaries. WANs typically use circuits provided by common carriers. Contrast with backbone network (BN), local area network (LAN), and metropolitan area network (MAN).
Wi-Fi: The trademarked name for 802.11b.
Wi-Fi Protected Access (WPA): A technique for providing security in WLANs.
Wired Equivalent Privacy (WEP): A technique for providing security in WLANs that is not very effective.
Wireless Application Protocol (WAP): A de facto standard set of protocols for connecting wireless devices to the Web. WAP provides a variety of protocols at the application, transport, and network layers to enable devices with a very small display screen to display standard Web information.
wire speed: Operating at the same speed as the incoming circuit; having extremely low latency.
wiring closet: A central point at which all the circuits in a system begin or end, to allow cross-connection.
World Wide Web: The Web provides a graphical user interface and enables the display of rich graphical images, pictures, full-motion video, and sound clips.
X.nn: The X.nn series of ITU-T standards relating to transmission over public data networks.
X.400: An OSI standard that defines how messages are to be encoded for the transmission of e-mail and graphics between dissimilar computers and terminals. X.400 defines what is in an electronic address and what the electronic envelope should look like. Approved by the CCITT.
X.500: An OSI standard that defines where to find the address to put on the electronic envelope of a X.400 transmission. X.500 is the directory of names and addresses similar to the yellow pages of a telephone directory.
Xmodem: Xmodem is an asynchronous file transmission protocol that takes the data being transmitted and divides it into blocks. Each block has a start of header (SOH) character, a 1-byte block number, 128 bytes of data, and a 1-byte checksum for error checking.
Ymodem: Ymodem is an asynchronous file transmission protocol. The primary benefit of the Ymodem protocol is CRC-16 error checking.
Zmodem: Zmodem is a newer asynchronous file transmission protocol written to overcome some of the problems in older protocols. It uses CRC-32 with continuous ARQ and dynamically adjusts its packet size according to communication circuit conditions to increase efficiency. It usually is the preferred protocol of most bulletin board systems.
