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Glossary 802.3 – The IEEE specification within project 802 for collision Sense Multiple Access / Collision Detection (CSMA / CD) networks. Access control – A method to impose controls that permit or deny users access to network resources, usually based on a user’s account or some group to which the user belongs. Active hub – A network device that regenerates received signals and sends them along the network. Active Server Pages – A technology promoted by Microsoft for creating dynamic Web pages. Address Resolution Protocol (ARP) – A protocol in TCP/IP that accepts the IP address and returns the corresponding physical address of a computer or router. Addressing – The mechanism of assigning an address to a computer. American National Standards Institute (ANSI) – ANSI creates and publishes standards for networking, communications, and programming languages. Amplifier – A hardware device that increases the power of electrical signals to maintain their original strength when transmitted across a large network. Amplitude – The strength of a signal, measured in volts or amperes. Amplitude Modulation (AM) – An analog-to-analog encoding mechanism of modifying the carrier wave with the amplitude of the incoming signal. Amplitude Shift Keying (ASK) – A digital-to-analog encoding mechanism of modifying the amplitude of the carrier wave to represent the digital bit values. Analog – The method of signal transmission used on broadband networks. Analog-to-Digital Converter (A-D) – A device that accepts analog pulses, and gives out digital bit information. Application layer – Layer 7 in the OSI reference model. The application layer provides interfaces to permit applications to request and received network services. Application Server – A specialized network server whose job is to provide access to a client/server application, and, sometimes, the data that belongs to that application as well. Asynchronous – A communication method that sends data in a stream with start and stop bits indicates where the data begins and ends. Asynchronous Transfer Mode (ATM) – A WAN technology that uses fiber–optic media to support up to 622–Mbps transmission rates. ATM uses no error checking and has a 53–byte fixed–length cell. Asynchronous transmission –A mechanism of data transmission in which the sender and the receiver do not require to synchronize before transmission begins; the sender can transmit the message at any time. ATM Layer – The second layer in the ATM protocol. Attenuation – The degradation and distortion of an electronic signal as it travels from its origin. Authentication – Establishing a proof of identity before communication can begin. Bandwidth – The range of frequencies that a communications medium can carry. Best effort delivery – A delivery mechanism that attempts to, but gives no guarantee of, the successful delivery of packet. Binary coded Decimal (BCD) – An encoding mechanism that uses four bits to encode each digit. Bit – Binary digit can have a value of 0 or 1. Bit rate – The transmission rate in case of digital signals, usually represented in Bits per second (BPS). Bits Per Second (BPS) – See Bit rate. Bridge – A networking device that works at the Data Link Layer of the OSI model. It filters traffic according to the packet’s hardware destination address is on. British Naval Connector (BNC) – Also known as bayonet nut connector, bayonet navy connector or bayonet Neill-Concelman connector. This is a matching pair of coaxial cable connectors consists of a ferrule around a hollow pin with a pair of guideposts on the outside. Broadband ISDN (B – ISDN) – ISDN that offers high data rates, suitable for video transmission. BRouter – A networking device that combines the best functionality of a bridge and a router. It routes packets that include Network layer information and bridges all other packets. Browser– based emails – A technology that allows end users to access emails using the web browser interface. Browsing – Accessing Web pages with the help of a web browser. Bus - A Major network topology in which the computers connector to a backbone cable segment to form a straight line. Bus topology – A network arrangement where in all the computers are attached to a shared medium. Byte – Usually, but not always, a combination of eight bits. Cable modem – A device that allows the transmission of Internet data over cable television networks. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) – A connection-based channel access method in which computers avoid collisions by broadcasting their intent to send data. Carrier Sense Multiple Access with Collision Detection (CSMA/CD) – A Connection-based channel access method in which computers avoid collisions by listening to the network before sending data. Cladding – A nontransparent layer of plastic or glass material inside fiberoptic that surrounds the inner core of glass or plastic fibers. Client – A computer on a network that requests resources or services from some other computer. Client/server – A model for computing in which some computers (clients) request services and others (servers) respond to such requests for services. Client/server computing – A computing environment in which the processing is divided between the client and the server. Coaxial cable – A type of cable that uses a center conductor, wrapped by an insulating layer, surrounded by a braided wire mesh and an outer jacket, to carry high-bandwidth signals such as network traffic. Collision – Occurs when two computers put data on the cable at the same time. This corrupts the electronic signals in the packet and causes data loss. Combination Network – A network that incorporates both peer-to-peer and server based capabilities. Communication server – A specialized network server that provides access to resources on the network for users not directly attached to the network. Compression – Reduction of message size without impacting its contents to reduce transmission demands. Congestion – Slow state of the network caused by too many senders, receivers or transmission. Congestion Control – A technique for monitoring network utilization and manipulating transmission to keep traffic levels from overwhelming the network medium; gets its name because it avoids “network traffic jams”. Connection-oriented – A type of protocol that establishes a formal connection between two computers, guaranteeing the data will reach its destination. Connectionless – A type of protocol that sends the data across the network to its destination without guaranteeing receipt. Crosstalk – A phenomenon that occurs when two wires lay against each other in parallel. Signals traveling down one wire can interfere with signals traveling down the other and vice versa. Cryptography – The art of encoding and decoding messages so as to product the contents of the messages from the eyes of those not authorized to read them. CPU – An abbreviation for Central Processing Unit, the collection of circuitry (a single chip on most PC’s) that supplies the “brains” for most computers. Cyclic Redundancy Check (CRC) – The CRC is calculated before transmission of a data frame and then included with the frame; on receipt, the CRC is recalculated and compared to the sent value. Data channel – The cables and infrastructure of a network. Data (D) channel – An ISDN channel used primarily for carrying control signals, which can also be used for low– speed data transfers. Data Encryption Standard (DES) – A symmetric key encryption algorithm, originally developed by IBM. Data Link control (DLC) – A network protocol used mainly by HewlettPackard printers and IBM Mainframes attached to a network. Data Link Layer – Layer 2 in the OSI reference model. This layer is responsible for managing access to the networking medium and for ensuring error-free delivery of data frames from sender to receiver. Dedicated Server – A network server that acts only as a server and is not intended for regular use as a client machine. Delta modulation – A modified version of Pulse Code Modulation, which measures only changes to adjacent signal values. Demodulator – Opposite of modulator, this equipment transforms analog signals to digital values. Demultiplexer – Opposite of multiplexer, this equipment separates multiple signals on a single medium to obtain individual signals. Device Driver – A software program that mediates communication between an operating system and a specific device for the purpose of sending and/or receiving input and output from that device. Device sharing – A primary purpose for networking: permitting users to share access to devices of all kinds, including servers and peripherals such as printers and plotters. Diagram – The term used to describe a network’s design. Digital – An encoding mechanism that consists of discrete values. Digital–to–Analog Converter (D–A) – Equipment that transforms digital pulses into analog signals. Distortion – Distortion resulting from non – uniform speed of transmission of the various frequency components of a signal through a transmission medium. Domain – A uniquely named collection of user accounts and resources that share a common security database. Domain Controller – On networks based on Windows NT server or windows 2000 Server, a directory server that also provides access controls over users, accounts, groups, computers, and other network resources. Domain model – A network based on Windows NT Server or Windows 2000 Server whose security and access controls reside in a domain controller. Domain Name System (DNS) – A TCP/IP protocol used to associate a computer’s IP address with a name. Dual bus – Two buses. Duplication control – Mechanism that prevents processing of duplicate packets. e-mail – An abbreviation for electronic mail, a networked application that permits users to send text messages, with or without attachments of many kinds, to individual or multiple users. Encryption – The mechanism of encoding messages to achieve security objectives. Error control – Detection of errors in transmission. Error-handling – The process of recognizing and responding to network transmission or reception errors. These errors are usually interminable delivery (time-out), incorrect delivery. Ethernet – A networking technology developed in the early 1970s and governed by the IEEE 802.3 specification. Ethernet remains the most popular type of networking technology in use today. Ethernet 802.2 – Ethernet frame type used by IPX / SPX on Novell Net Ware 3.12 and 4.x networks. Ethernet 802.3 – Ethernet frame type generally used by IPX / SPX on Novell Netware 2.x and 3.x networks. Ethernet II – Ethernet frame type used by TCP / IP. Even parity – A error detection mechanism based on the total number of 1 s in a message being 0. Exchange Server – A Back office component from Microsoft that acts as a sophisticated e-mail server. Extended Binary Coded Decimal Interchange Code (EBCDIC) – An encoding scheme used primarily in IBM mainframes. Extended LAN – The result of certain wireless bridges ability to expand the span of a LAN as far as three to 25 miles. Microsoft calls the resulting networks “extended LANs”. Fast Ethernet – The 100 - Mbps implementation of standard Ethernet. Fault Tolerance – A feature of a system, which allows it to continue working after an unexpected hardware or software failure. Fiber Distributed Data Interface (FDDI) – A limited–distance linking technology that uses dual, counter-rotating fiber-optic rings to provide 100Mbps fault-tolerant transmission rates. Fiber-optic – A cabling technology that uses pulses of light sent along a light conducting fiber at the heart of the cable to transfer information from sender to receiver. File Transfer Protocol (FTP) – A TCP / IP-based networked file transfer application, with an associated protocol. It’s widely used on the Internet to copy files from one machine on a network to another. Firewall – A special Internet server than sits between an Internet link and a private network, which filters both incoming and outgoing network traffic. Flow Control – An action designed to regulate the transfer of information between a sender and a receiver. Fragmentation – The process of breaking a long PDU from a higher layer into a sequence of shorter PDUs for a lower layer, ultimately for transmission as a sequence of data frames across the networking medium. Frame – Used interchangeably with “data frame”, the basic package of bits that represents a PDU sent from one computer to another across a network. Frame Relay – A WAN technology that offers transmission rates of 56Kbps to 10544 Mbps. Frame relay uses no error checking. Frame Type – One of four standards that define the structure of an Ethernet packet: Ethernet 802.3, Ethernet 802.2, Ethernet SNAP, or Ethernet II. Frequency – The number of times a signal changes its value in one second. Frequency modulation (FM) – An analog–to–analog encoding method in which the frequency of the carrier wave is a function of the modulating wave. Full-duplex Communications – A type of network communication in which a pair of networked devices can send and receive data at any given time providing two-way communications. Gateway – A networking device that translates information between protocols or between completely different networks, such as from TCP / IP to SNA. Gigabit Ethernet – An IEEE standard (802.3z) that allows for 1000-Mbps transmission using CSMA / CD and Ethernet frames. Go–back–n – An error–control mechanism in which all the frames including and after the one in error must be retransmitted. Group – Combination of smaller transmission lines. Half-duplex Communications – A type of network communication in which only one member of a pair of networked devices can transmit data at any given time. Hertz (Hz, KHz, MHz, GHz) – A measure of broadcast frequencies, in cycles per second; named after Heinrich Hertz, one of the inventors of radio communications. Hexadecimal – A mathematical notation for representing numbers in base 16. The number 10 through 15 are expressed as A through F; 10th or 0x10 (both notations indicate the number is hexadecimal) equals 16. High-level Data Link Control (HDLC) – A synchronous communication protocol. Hub – The central concentration point of a star network. Hybrid Network – A network that incorporates both peer-to-peer and server based capabilities. Hyper Text Markup Language (HTML) – The language used to create documents for the WWW. Hyper Text Transfer Protocol (HTTP) – The protocol used by the WWW to transfer files. Industry Standard Architecture (ISA) – Originally an 8-bit PC bus architecture but upgraded to 16-bit with the introduction of the IBM PC / AT in 1984. Infrared – That portion of the electromagnetic spectrum immediately below visible light. Infrared frequencies are popular for short – to medium – range (10s of meters to 40 km) point – to – point network connections. Institute of Electrical and Electronics Engineers (IEEE) – An Engineering Organization that issues standards for electrical and electronic devices, including network interfaces, cabling, and connectors. Integrated Services Digital Network (ISDN) – A WAN technology that offers increments of 64-Kbps connections, most often used by SOHO (small office/home office) users. International Standardization Organization (ISO) – The international standards-setting body, based in Geneva, Switzerland, that sets worldwide technology standards. Also called International Standards Organization. Internet – The global collection of networked computers that began with technology and equipment funded by the U.S. Department of Defense in the 1970’s. Internet Browser – A graphical tool designed to read HTML documents and access the WWW, such as Microsoft Internet Explorer or Netscape Navigator. Internet Information Server (IIS) – A Microsoft Back office component that acts as a Web-server in the Windows NT Server environment. Internet Information Services (IIS) – The Windows 2000 version of Internet Information server. Internet Protocol (IP) – TCP / IP’s primary network protocol, which provides addressing and routing information. Internet Service Provider (ISP) – A company that connects its clients to the Internet. Intranets – An in-house TCP / IP – based network, for use within accompany. Industry Request Line (IRQ) – IRQs define the mechanism whereby a peripheral device of any kind, including a network adapter, can stake a claim on the PC’s attention called “interrupt”. Jacket – The outermost layer of a cable. Jitter – A tendency toward lack of synchronization caused by mechanical or electrical changes. Latency – The amount of time a signal takes to travel from one end of a cable to the other. Layers – The functional subdivisions of the OSI reference model. The model defines each layer in terms of the services and data it handles on behalf of the layer directly above it and the layer directly below it. Local Area Network (LAN) – A collection of computers and other networked devices that fit within the scope of a single physical network and provide the building blocks for internetworks and WANs. Local host – A special DNS host name that refers whatever IP address is assigned to the machine where this name is referenced. MAC address – The unique address programmed into a NIC that the MAC layer handles. The MAC address identifies the NIC on any network in which it appears. Mail servers – A networked server that manages the flow of e-mail messages for network users. Media Access Control (MAC) - The longest legal segment of cable that a particular networking technology permits. This limitation makes sure for network designers and installers that the entire network can send and receive signals properly. Mesh – A hybrid network topology use for fault tolerance in which all computers connect to each other. Mesh Topology – A topology in which each node is connected to every other node. Metropolitan area network (MAN) - Uses WAN technologies to interconnect LANs within a specific geographic region, such as a country or a city. Microwave – Electromagnetic waves ranging from 2 GHZ to 40 GHZ. Modem (Modulator/Demodulator) – Used by computers to convert digital signals to analog signals for transmission over telephone lines. The receiving computer then converts the analog signals to digital signals. Multicast packet – A packet that uses a special network address to make itself readable to any receiving computer that wants to read its payload. Multicast packets. Multiplexer – The device that is used in multiplexing. Multiplexing – The networking technology communications on a single cable segment. that combines several Network Adapter – A synonym for network interface card (NIC). It refers to the hardware device that mediates communication between a computer and one or more types of networking media. Network Address – The number that identifies the physical address of a computer on a network. This address is hard-wired into the computer’s NIC. Network Administrator – An individual responsible for installing, configuring, and maintaining a network, usually a server-based network such as Windows 2000 Server or Novell Netware. Network Card – A synonym for network interface card (NIC). Network File System (NFS) – A distributed file system originally developed at Sun Microsystems. It supports network-based file and printer sharing using TCP/IP- based network protocols. Network Interface Card (NIC) – A PC adapter board designed to permit a computer to be attached to one or more types of networking media. Network Layer – The Network Layer handles addressing and routing of PDUs across internetworks in which multiple networks must be traversed between sender and receiver. Network Protocol – A set of rules for communicating across a network. To communicate successfully across a network, two computers must share a common protocol. Network Resources – Any kind of device, information, or service available across a network. Node – An addressable communication device, such as a computer or a router. Node–to–node delivery – Delivery of packets from one node to the next one. Noise – Random electrical signals that can be picked up transmission, causing degradation or distortion of data. during Odd parity – An error–detection method in which an extra bit is added to the data unit so that the sum of all 1–bits becomes odd. Open System Interconnection (OSI) – The family of ISO standards developed in 1970s and 1980s and designed to facilitate high-level, highfunction networking services among dissimilar computers on a global scale. Optical fiber – A high–bandwidth transmission system that sends data bits as light pulses. OSI Reference Model – It defines a frame of reference for understanding and implementing networks by breaking down the process across seven layers. Packet – A specially organized and formatted collection of data destined for network transmission; alternatively, the form in which network transmissions are received following conversion into digital form. Packet Header – Information added to the beginning of the data being sent, which contains, among other things, addressing and sequencing information. Packet Trailer – Information added to the end of the data being sent, which generally contains error-checking information such as the CRC. Parallel transmission – Transmission mechanism where multiple bits are sent at the same time, each on a separate wire. Parity bit – The additional bit added to a packet for error detection. Parity checking – The mechanism of error detection using parity bits. Passive Hub – A central connection point that signals pass through without regeneration. Peer-to-Peer – A type of networking in which each computer can be a client to other computers and act as a server as well. Period – The time required for a signal to complete one cycle. Phase – The relative signal of a position with respect to time. Physical Layer – The Physical Layer transmits and receives signals, and specifies the physical details of cables, adapter cards, connectors, and hardware behavior. Point-to-Point Protocol (PPP) – A remote access protocol that supports many protocols including TCP/IP, NetBEUI, and IPX/SPX. Presentation Layer – Platform-specific application formats are translated into generic data formats for transmission or from generic data formats into platform-specific application formats for delivery to the Application Layer. Propagation Delay – Signal delay created when a number of repeaters connect in a line. Protocol – A rigidly defined set of rules for communication across a network. Protocol Suite – A family of related protocols in which higher-layer protocols provide application services & request handling facilities, while lower-layer protocols manage the intricacies of Layer1 through 4 from the OSI reference model. Proxy Server – A special Internet server that sits between an Internet link and a private network. Pulse Code Modulation (PCM) – Digitizing analog signals using sampling and quantizing techniques. Quadrate Amplitude Modulation (QAM) – A digital–to–analog encoding technique where the amplitude and the phase values of the carrier wave can be changed to represent digital information. Quantizing – Measuring sampled analog signals to get their numeric equivalents. Radio-Frequency Interface (RFI) – Any interference caused by signals operating in the radio frequency range. Random Access Memory (RAM) – The memory cards or chips on a PC that provide working space for the CPU to use when running applications, providing network services, and so on. Raw Data – Data streams unbroken by header information. Receiver – A data communications device designed to capture and interpret signals broadcast at one or more frequencies in the Electro magnetic spectrum. Registered Jack (RJ) – Used for modular telephone and network TP jacks. Repeater – A networking device that regenerates electronic signals, so that they can accommodate additional computers on a network segment. Request-Response – A way of describing how the client/server relationship works that refers to how a request from a client leads to some kind of response from a server. Ring – Topology consisting of computers connected in a circle, forming a closed ring. Ring topology – A topology where in all the devices are connected to each other to form a ring. RJ-11 – The four-wire modular jack commonly used for home telephone handsets. RJ-45 – The eight-wire modular jack for TP networking cables and also for PBX-based telephone systems. Router – A networking device that operates at the Network Layer of the OSI model. Routing table – A table maintained by a router to decide how to route the incoming packets to its ultimate destination. RSA algorithm – A public key encryption algorithm invented by Rivest, Shamir and Adleman. Routing – The process of moving data across multiple networks via router. Sampling – The first process in Pulse Code Modulation analog signal is measured periodically. Satellite Microwave – A Microwave transmission system that uses geosynchronous satellites to send and relay signals between sender and receiver. Security – For networking, security generically describes the set of access controls and permissions in place that determine if a server can grant a request for a service or resource from a client. Segmentation – The action of decomposing a larger, upper-layer PDU into a collection of smaller, lower-layer PDUs. Serial transmission – Transmission mechanism where in one bit is sent at a time, using a single wire. Server – A computer whose job is to respond requests for services or resources from clients else where on a network. Session Layer – The session layer is responsible for setting up, maintaining, and ending ongoing sequences across a network communications on a network. Sharing – One of the fundamental justifications for networking. Sheath – The outer layer of coating on a cable; sometimes also called the jacket. Shielded Twisted Pair – A variety of TP cable, wherein a foil wrap encloses each of one or more pairs of wires for additional shielding. Shielding – Any layer of material included in cable for the purpose of mitigating the effects of interference on the signal-carrying cables it encloses. Signal – Electromagnetic wave propagating across a transmission medium. Simple Mail Transport Protocol (SMTP) – A TCP/IP protocol used to send mail messages across a network. SMTP is the basis for e-mail on the Internet. Simple Network Management Protocol (SNMP) – A TCP/IP protocol used to monitor and manage network devices. Simplex transmission – Transmission system where one side can only transmit, the other side can only receive. Sliding window – A protocol that allows several data units to transmit before an acknowledgement is received. Source address – The address of the sender of a message. Star – Major topology in which the computers connect via a central connecting point, usually a hub. Star Bus – A network topology that combines the star and bus topologies. Star Ring – A network topology wired like a star that handles traffic like a ring. Star topology – A topology in which all stations are attached to a central device (hub). Stop–and–wait– Flow control mechanism where each data unit must be acknowledged before the next one can be sent. Straight Connection (SC) – A type of one-piece fiber-optic connector that pushes on yet makes a strong and solid contact with emitters and sensors. Straight Tip (ST) – The most common type of fiber-optic connector used in Ethernet networks with fiber backbones. Switch – A special networking device that manages networked connections between any pair of star-wired devices on a network. Switching – Using a network switch to manage media or channel access. Synchronous – Communications type in which computers rely on exact timing and sync bits to maintain data synchronization. Telnet – A TCP/IP protocol that provides remote terminal emulation. Terminator – Used to absorb signals as they reach the end of a bus. Terrestrial Microwave – A wireless microwave networking technology that uses line-of-sight communications between pairs of Earth-based transmitters and receivers to relay information. Thin wire – A synonym for 10Base2, and cheapernet. Token – Used in some ring topology communications between all computers. networks to ensure fair Token bus – A LAN technology that uses token passing access method and bus topology. Token Passing – A channel access method used mostly in ring topology networks. Token Ring – A network architecture developed by IBM, which is physically wired as a star but uses token passing in a logical ring topology. Topology – A basic physical layout of a network. Transceiver – A device that both transmits and receives messages. Translation – A change from one protocol to another. Transmission Control Protocol /Internet Protocol (TCP/IP) – A protocol suite that supports communication between heterogeneous systems. TCP/IP has become the standard communications protocol for the Internet. Transmission medium – The wire that carries signals between the communicating parties. Transmitter – An electronic device capable of emitting signals for delivery through a particular networking medium. Transport Layer – The transport layer is responsible for fragmenting large PDUs from the session layer for delivery across the network. Transport Protocol – A protocol type responsible for providing reliable communication sessions between two computers. Troubleshooting – The techniques involved in detecting problems and identifying causes. Twisted-Pair (TP) – A type of cabling where two copper wires, each enclosed in some kind of sheath, are wrapped around each other. Unguided transmission media – A transmission medium that has no physical boundaries. Unshielded twisted-pair (UTP) – A form of TP cable that includes no additional shielding material in the cable composition. User Datagram Protocol (UDP) – A connectionless TCP/IP protocol that provides fast data transport. Vertical Redundancy Check (VRC) – An error– detection mechanism based on the parity checking of each character. Virtual Circuit – A logical circuit between the sender and the receiving computer. All the packets in the transmission then follow the same route and always arrive in order. Virtual LAN (VLAN) – A configuration setting that groups two or more devices attached to a switch. Web browser – The client-side software that’s used to display content from the World Wide Web (WWW). Web Server –A server that hosts HTML pages and dispatches them on request. Wide Area Network (WAN) – An internetwork that connects multiple sites, where a third-party communications carrier, such as a public or private telephone company. Wireless – Indicates that a network connection depends on transmission at some kind of electromagnetic frequency through the atmosphere to carry data transmission from one networked device to another. Wireless Bridge – A pair of devices, typically narrow-band and tight beam, that relay network traffic from one location to another. World Wide Web (WWW, W3 or web) – The TCP/IP based collection of all Web servers on the Internet. X.25 – An international standard for wide-area packet-switched communications. X.25 offers 64-Kbps network connections and uses error checking.