This glossary is not intended to be complete or all-encompassing. It covers common terms seen on InetDaemon.com and elsewhere dealing with computers and data communications technologies. Definitions are from InetDaemon himself--be warned.

"When I use a word," Humpty Dumpty said, in a rather scornful tone,
"it means just what I choose it to mean - neither more nor less."
 "The question is," said Alice, "whether you can make words mean
so many different things."
 "The question is," said Humpty Dumpty, "which is to be master
- that's all."

Lewis Carroll - Through the Looking Glass.
 A A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
A-Polarity (A-Pol)
Circular polarity radio antennas are described as having either A-polarity or B-polarity. A-polarity antennas use clockwise (right hand) circular polarity.
Algorithm
Term used to describe a logical framework used for solving a particular computer problem via programming. Ex. The 'shortest path' algorithm is logic that calculates the shortest path between two points.
Autonomous System (AS)
An autonomous system is a network or set of networks under one administrative authority such as a company or other organization.
Autonomous System Number (ASN or AS#)
An AS number is assigned by the American Registry for Internet Numbers (ARIN). This number must be unique, and be assigned to only one autonomous system. Companies and other organizations may have multiple AS numbers, provided they can demonstrate a need for this number. AS numbers are used by BGP to identify autonomous systems, as well as internal and external connections.
Autonomous System Path
This is a list of AS numbers which map the path through Autonomous Sysstems to the destination network. AS Paths are included in BGP Update Messages along with NLRI information as part of the routing protocol update announcements in BGP.
Amplitude
The size of the signal output. In electrical systems this is voltage, in radio systems this is radiated power.
AS Path
See Autonomous System Path.
Asynchronous Transfer Mode (ATM)
Asynchronous Transfer Mode (ATM), also referred to as Broadband-ISDN is a standards-based networking protocol utilizing 53 byte cells, and supports virtual connections, dynamic path switching and quality of service.
 B A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Bulletin Board System (BBS)
Bulletin Board System. A dial-up computer service consisting of a limited number of modems connected to a computer running Bulletin Board System software. Users may exchange e-mail with each other, play games, chat or communicate with other BBS's if the sysop has set up a mail gateway to another BBS. The invention of BBS's is generally credited to Ward Christiansen. InetDaemon once belonged to a BBS named Genesys run by SysOps Viper and EmJay.
B-Polarity (B-Pol)
Circular polarity radio antennas are described as having either A-polarity or B-polarity. B-polarity antennas use counter-clockwise (left hand) circular polarity.
Backwards Explicit Congestion Notification (BECN)
Used in frame relay to signal to the downstream device that the connection is congested.
Bandwidth
Often used erroneously to describe the total bit per second data rate, this term actually refers to the total ammount of voltage or signal spectrum that can be used to transmit data. The greater the range of values, the greater the data transfer rate.
BAUD
Number of symbols or symbol changes per second. Each symbol can cary more than one bit, so any measure of baud rate is not equivalent to bit rate or bandwidth. For example, telephone voice lines send 8,000 symbols per second and each symbol represents 8 bits. Multiplying the symbol rate times the bits per symbol gives 64,000 bits per second and the baud rate is 8,000.
Binary
The binary number system consists of the digits 0 and 1. This makes binary especially suited for working with electronic circuits that can have only two values: on and off.
Bit Rate
Number of bits per second transmitted over a communications medium. Often abbreviated as bps, kbps, mbps, gbps, tbps.
Black Hole
Black holes are the roach motels of the Internet. Black holes occur when a range of IP addresses (an IP block) is routed to a network where none of the addresses are assigned, and are not in use. This effectively causes the traffic to be dropped into what looks like a 'black hole'. Packets go in, but don't come out. Black Holes are typically caused by improper routing announcements of prefixes not assigned to an AS.
Bootstrap (boot)
The process of starting up, usually unaided. Term refers to 'pulling yourself up by your bootstraps'.
Border Gateway Protocol
BGP is a dynamic, exterior gateway protocol used for exchanging 'best-path' route information between autonomous systems. BGP does not exchage explicit hop-by-hop route information, but rather AS-paths and path-attributes.
Board
Computer chips can't be interconnected that easilly by themselves. Chips have to be inserted into specially designed pieces of fibrous plastic called "breadboard". The breadboard has metal wires running in neat little rows that connects all the chips together, so in today's computers, it's easier to work with 'boards' than it is with 'chips'. On most computers, the breadboard is the green board all the chips are soldered into. If you look closely, you can even see some of the wires inside it.
Broadcast Storm
A broadcast storm usually occurs in bridged netwrorking environments where broadcast traffic is being re-transmitted back and forth on the linked segments. Since devices are sending out repeated broadcasts, all available network capacity is used up transmitting these broadcasted frames, and none of the nodes are able to transmit or receive responses, thus initiating more broadcasts.
Broadband
A transmission system that utilizes multiple frequencies to transmit data simultaneously. Often misused when referring to the speed of a connection.
 C A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
CPU
Central Processing Unit, or simply 'processor'. Processors process 'instructions' and 'execute' program code.
Carrier (also 'common carrier')
Telecommunications provider, usually denoting an organization with nationwide or worldwide communications capability.
Carrier Signal
An electromagnetic emission used as a baseline signal for carrying information.
Central Office
A central office is a building or location where all telephone voice channels are aggregated together for multiplexing over a trunk line to another central office in a remote location.
Connectionless
Connectionless protocols do not bother to set up or check for an end-to-end connection. Connectionless systems simply transmit and don't worry whether the receiver is ready or available. TV, Radio, Walkie-Talkies and CB's are good examples of Connectionless systems. In the Internet arena, UDP is a connectionless protocol.
Connection-Oriented
A connection-oriented protocol establishes end-to-end connections for communication.
 
 D A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 
Datagram
A datagram is a unit of data of variable length. Data is produced by computer users, and chopped into pieces by some piece of software running at the Transport layer or above. It would be most correct to say that datagrams are put into packets, and that packets are put into frames.
Data Circuit-terminating Equipment (DCE)
Sometimes also seen as Data Communication Equipment. The DCE device is most commonly the device providing the communications facilities. It is the responsibility of the DCE interface to set the clock rate for the signalling so that the end stations (DTE's) can establish synchronization with the signal and communicate.
Data Terminal Equipment (DTE)
The DTE is usually and end station, the device using the communications facilities.
Decryption
The process of descrambling an encrypted sequence of data using an encryption/decoding key.
Destination Address
Address of the receiving device.
DHCP
Dynamic Host Control Protocol - Protocol that is a member of the Internet Protocol suite. Used to assign IP addresses to hosts as they bootstrap and connect to the network.
 
 
 E A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
EOF
End Of File. A sequence of characters used to indicate the end of a data file.
EOL
End Of Line sequence. A set of characters used to indicate the end of a logical line of data.
Encode
To convert data into a specific format
Endian
As in small-endian and big-endian. Computing term referring to the order in which bytes are transmitted, either low order or high order bits are sent first. This is a reference to Gulliver's Travels by Danny Cohen in his paper "On Holy Wars and a Plea for Peace". The order in which bits are transmitted becomes vitally important in comptuer to computer communications. Bits sent in what is percieved to be reverse order can cause data to be lost or scrambled and makes communication nearly impossible. Very heated discussions were very common regarding whether big-endian or little-endian transmission order was better, thus the paper and the call for peace.
Exterior Gateway Protocol (EGP)
A routing protocol used to communicate between networks administrated and owned by different organizations. Compare to Interior Gateway Protocol.
Encapsulation
The process of adding a header (and possibly trailing) information to a piece of data for the purposes of passing it through some other system. Encapsulation is used by most computers today when communicating with the Internet. Data is encapsulated in TCP or UDP, then encapsulated in IP and then transmitted over the network connection.
Encryption
The process of scrambling data in an ordered format so that it can be descrambled at the other end. Decryption of encrypted data requires the key which was used to encrypt the data. Larger/longer keys produce better encryption.
 
 
 F A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Forward Error Correction
[Radio Frequency] FEC is used in simplex communication to attempt to recover from symbol errors in a communications datastream.
Forward Explicit Congestion Notification (FECN)
FECN is used in frame relay to signal to the upstream frame relay device that there is congestion in the forward path.
Frame
  1. [Hardware] A frame is a unit of data that varies in size. It is the unit that is created by the Data Link layer.
  2. [HTML] A frame is a piece of a browser window that is created using the HTML 'frame' command within a 'frameset'.
Frame Relay
The second generation of packet switching technology put to use in the telecommunictions arena after X.25. Frame Relay is a packet-switching technology that provides non-reliable cut-through switching of frames through the network. Also known as 'fast packet'.
Frequency
Number of times per second a signal regenerates itself at a peak amplitude expressed in hertz. In general, the higher the frequency, the greater the rate it can transmit data.
 
 
 G A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Gateway
A gateway is a device used to forward data from the local network to other networks. Synonomous with the term 'router'.
 H A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
H.323
The name of the protocol standards document defining video over IP. Frequently used in IP multicast-based video-conferencing.
HSSI
High Speed Serial Interface. Cisco proprietary protocol adopted by many other network gear manufacturers. Supports up to 52Mb/sec.
Hertz
A measurement of the number of cycles per second in a signal. Higher frequency signals have higher hertz rates.
Hexadecimal
A numbering system consisting of the digits 0 through 9 and the letters A-F. This allows each column in a Hexadecimal number to represent sixteen different values. Usually designated in literature by the character combination "0x" (zero x).
Host
A host can be any device on a network that provides access or service. Host is a general term usually used to refer to a computing device. The term 'host' is used synonymously with 'computer' and 'node'.
 I A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Implement (implemented, implementation)
  1. [Programming] A particular algorithim written into computer software as program code. ie: "It's an implementation of Diffie-Hellman"
  2. [Telecom.] To install and configure a communications circuit. Most often used when discussing the process of installing a circuit for a telecommunications customer.
Interior Gateway Protocol
A routing protocol used for exchanging routes between networks that are under a single administrative control or owned by a single organization.
 J A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
JEDEC
Joint Electronic Devices Engineering Council. A group of chip manufacturers who have formed a committee to standardize size, form factor and connector issues for chips, mostly for RAM (memory).
JBOD
"Just a Bunch Of Disks" - a series of disks not utilizing a mass storage architecture such as RAID.
Jumper
A small metal bracket used to connect two pins and thereby create a short between them. The term jumper is used for both the bank of pins, and the metal bracket used to 'short' them.
 
 K A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
KVM
Keyboard Video Mouse switch. A special device used to enable multiple computers to share one keyboard, video display and mouse. Useful in server environments or where multiple computers are in use.
Kermit
Kilobit (Kb)
1,024 bits. A measure of size, most often used when referring to data transfer rates such as with modems (56 Kbps).
Kilobyte (KB)
1,024 bytes. A measure of size, most often used when referring to memory or data storage and occasionally data transfer rates.
 L A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
LLC
Logical Link Control - Layer of the 802.x protocols specifying the process of communicating with the physical link.
LAN
Local Area Network. Any network located in a single facility, usually restricted to one building.
LAPB (Link Access Procedure, Balanced mode)
LAPB is a data-link layer protocol that provides ordered, reliable communication between DCE and DTE devices in an X.25 telecommunications network.
LAPD (Link Access Procedure, D channel)
This is the data-link layer protocol used to control the 'D' or 'data' channel on an ISDN BRI connection. Also known by the ITU specification document numbers Q.920 / Q.921
Link
The term link is used loosly to describe a physical or virtual network connection.
Link-State
Link state routing algorithms are aware of the performance of physical network connections when calculating the shortest path to a destination.
 
 
 M A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
MAC
  1. The Media Access Controller (MAC) is a chip that controls access to the physical media (copper wire, optical fiber or a radio frequency). Often, a permanent address is 'burned in' to the memory of this controller. This address is also referred to as a 'MAC'.
  2. Shortened form of the word 'MacIntosh', as in the phrase "Friends don't let friends buy Macs."
MAN
Metropolitain Area Network. A network serving one city or metropolitain area.
Mainboard
This is what all the other smaller boards plug into, so sometimes it's called a MOTHERBOARD. Mainboards have 'expansion slots' allowing the computer's capabilities to be 'expanded' by adding on additional hardware. Sound, Video and Input/Output can all be 'expansion' devices.
Maximum Transmission Unit (MTU)
The MTU is a term used to refer to the maximum frame size for a particular network inerface card.
Motherboard
See 'Mainboard'.
 N A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Network
A network is a group of computers connected to each other over a common connection
Network Interface Card (NIC)
Network Interface Cards are components used in computers to allow them to connect to the network wiring.
Node
A more general term referring to any device attached to a communications or data network.
O A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 
Octet
An octet is eight binary bits.
Octal
A number system which uses only the digits 0-7 as symbols.
P A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 
Packet
A packet is the term used to describe units of data that are created by the Network Layer.
Phase
All electromagnetic signals travel in waves and thus the trigonometric functions of sine and cosine can be used to describe/calculate their behavior. The term phase is used to describe the value of the wave at a particular instant in time. By 'shifting' a signal's phase, data can be encoded.
Polarity
  1. Positive or negative voltage in electrical systems
  2. [Radio Frequency] clockwise or counter-clockwise behavior
Port
  1. A physical connector, such as for serial or ethernet connections.
  2. A number identifying a specific virtual connection.
  3. An application converted to run on a computer it was not originally designed for.

 

Q A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Q.920 / Q.921
See LAPD
Quadrant Phase Shift Keying (QPSK)
Typically used in radio frequency modulation, QPSK utilizes shifts in frequency phase to encode data into a carrier signal.
Quadrature Amplitude Modulation (QAM)
This modulation technique is most often seen in computer telephone and cable modems. QAM is a frequency-amplitude modulation technique, that uses frequency and amplitude changes to encode data into the carrier signal.
R A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
RAID
Redundant Array of Inexpensive Disks - A system of connecting a large number of smaller (thus less expensive) disks together for mass storage of data instead of buying a single large drive. RAID can be configured for redundancy (mirroring) and performance (striping). The different RAID configurations are referred to as RAID levels: 0, 1, 0+1, 3, 5).
RAM
Random Access Memory. Temporary storage on the chips inside the computer. They can store information only as long as there is electrical power.
RAM-disk
A RAM-disk is a simulation of a hard disk in RAM. This allows the system to access higher memory as if it were stored on a disk. This is the opposite of virtual memory.
ROM
Read Only Memory. These chips store what is often referred to as 'microcode' designed to perform critical functions, usually at bootstrap. Smaller devices rely upon ROMS for more complex functions.
Reliable
The term 'reliable' refers to a service or protocol that provides for recovering from errored transmission states. Examples of techniques used to assure reliability are Acknowledgements and error-checking. See also: unreliable.
Routing
A network layer process that forwards packets from a source network to a destination network.
Routing Protocol
A standard way of routing packets, which usually is implemented as a program that runs on a device that performs routing. There are two main categories of routing protocols, interior gateway protocols and exterior gateway protocols.
S A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Shout-Down
Device from the earliest days of the telephone. These were dedicated half-duplex telephone connections across trunk lines between telephone operations centers. Two-way communication required a second line strung back in the opposite direction, or a 'round-the-horn' relay back to the originating center. Engineers would pick up the handle and 'shout down' to the next telephone operations center during outages and emergencies.
Signal
An electromagnetic transmission used for the purpose of transmitting information. This transmission can be either electrical, radio freqency or light.
Source address
The address of the machine transmitting data (doing the talking). Note that in two-way communication the sender and receiver alternate roles during the communication process.
Spectrum
The total range of frequencies falling into a particular category (visible light spectrum, radio frequency spectrum).
Superframe (SF)
Superframe is a telecomunications linecoding scheme used for controlling the transmission of digital data over T1 lines. It provides for 24 timeslots of 64kbps each and an additional bit-stuffed control channel of 8 kbps.
Symbols
In the computing field, symbols are used to represent patterns of data bits. Symbols themselves are represented by specific modulation states within a communcations signal.
Symbol Rate
Symbol Rate refers to the number of symbols that are transmitted in one second. From the symbol rate, one can calculate the bandwidth (total number of bits per second) by multiplying the bits per symbol times the symbol rate.
T A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
T-carrier
Term used to classify various multiplexing levels in US and US-compatible telecommunications networks (ie. T1, T2, T3 etc.)
TCP
See Transmission Control Protocol.
TOC
See Telephone Operations Center
Telephone Operations Center
See Central Office
Terminal
1. A software application emulating a teletype terminal interface to a computer.
2. Teletype-style device providing an input/outsput mechanism composed of a monitor and keyboard or other input device that provides an interface to a remote computer system.
Terrestrial
Of or situated on terra-firma (the earth). Also referred to as 'land-based'.
Transmission Control Protocol
Transmission Control Protocol (TCP) is a reliable, connection-oriented protocol used for transporting data across one or more networks.
U A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Unreliable
This term is used to mean that a protocol or service does not provide error-checking or data-recovery mechanisms
User Datagram Protocol
User Datagram Protocol (UDP) is an unreliable, connectionless Transport Layer protocol used to transport data accross one or more networks.
V A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
VoIP / Voice over IP
Protocol that allows the encodes and encapsulates telephony data into IP datagrams for transport over an IP network such as the Internet.
Virtual Memory
Virtual memory is the process of using hard disk space as if it were RAM. This allows the computer to launch and run many more programs than it might normally be capable of. Virtual memory takes advantage of the fact that humans have difficulty doing more than one thing at a time. Thus, it is possible to move programs which the user is running, but not actively using to the hard disk while they are busy doing something else. Contrast this with a RAM-disk.

W

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Wavelength
Sometimes confused with frequency. Whereas the term frequency is used to refer to an electromagnetic signal at a particular wavelength, wavelength refers to the physical distance of 1 cycle of the signal's waveform (from peak to trough to peak). In microwave communications, the distance between waves is measured in nanometers. Radio frequencies can be measured in miles.
Wide Area Network (WAN)
Wide area networks are networks that are usually not enclosed in a single building. WANs can be as small as a college or company campus, or can span the entire globe. Compare with LAN and MAN.
 
X A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
X.25
The first true packet switching technology put into widespread use worldwide in Telecommunications systems. X.25 utilizes X.121 addressing and LAPB for ordered and reliable communication.
X-modem
X-modem was developed by Ward Christiansen for use with the first BBS. X-modem transmits data in 128 byte blocks followed by a 1-byte checksum and specifies a 1 second timeout on the data transfer connection.
Y A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Yellow Alarm
Telecommunications:  Used in T1 communications over superframe or extended superframe. A yellow alarm indicates that a Remote Alarm Indication signal was received from the upstream equipment.
Y-Modem
The second data transfer protocol developed by Chuck Forsberg as an improvement on X-Modem. Y-modem for use between computers connected with modems. This protocol was faster and provides some error correction.
Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Z-modem
Another serial data transfer protocol for use between modems deveolped by Chuck Forsberg. Z-modem is faster, does not check for receipt of data and adds the ability to resume an interrupted transfer. X-modem, Y-modem and Kermit.
ZIF socket
Zero Insertion Force socket. These sockets are used for fitting the main CPU to the mainboard. A lever is placed on the side allowing the processor to be simply dropped into place. Once the lever is pulled down and secured, the processor is held firmly in place.

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