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Appendix A. GLOSSARY

access permission

The level of access or the rights assigned to a user in relation to a particular resource on a network.

access protocol

A protocol that is used to move network data across a WAN connection. Access protocols provide the encapsulation that creates the virtual tunnel.

See also [tunneling]

access time

Measured in milliseconds, access time is the time it takes a drive to access data. The lower the access time, the faster the drive. For example, an 11-millisecond drive would be faster than a 28-millisecond drive.

Active Directory

This name refers to both the hierarchical tree structure provided in the Windows 2000 network environment and the utility used to manage users, computers, and other devices such as printers in the Windows 2000 network environment.


An alarm or notification you can configure on the Windows Server Performance Monitor that alerts you when a particular threshold for a process, such as hard drive usage, has been reached.

American Registry for Internet Numbers

The central registry for IP addresses used in a number of countries. ARIN is a not-for-profit organization established to register (and administer) IP addresses for North America, South America, the Caribbean, and sub-Sahara Africa.

American Standard Code for Information Interchange

The basic character set used by most computer operating systems.

Anonymous FTP site

An FTP site that allows anonymous logons. FTP typically requires a logon name and password.

See also [File Transfer Protocol]


The built-in networking language (protocol stack) used by the Apple Macintosh OS.

Application layer (DoD)

This layer in the DoD stack is equivalent to the OSI Application, Presentation, and Session layers. This layer provides the user interface for the various protocols and applications that access the network, and it handles file transfer, remote login to other nodes, e-mail functionality, and network monitoring. It also sets up the session between communicating nodes and manages the transport of data between them.

Application layer (OSI Model)

The top and seventh layer of the OSI conceptual model. This layer provides the user interface and services such as message handling and file transfer on the network.


A internetwork developed by the U.S. government and various universities that provided a redundant, packet-switching infrastructure for the movement of data across wide geographical areas.

asynchronous modem

A device designed to move data over a regular analog voice-grade telephone line.

See also [modem]

Asynchronous Transfer Mode

A high-speed packet-switching WAN technology used on optical networks. ATM is typically deployed on high-speed backbones such as SONET.

See also [Synchronous Optical Network/Synchronous Digital Hierarchy]


The degradation of the data signal over a run of cable or other medium.

Automatic Private IP Addressing

The ability of computers running Windows 2000, Me, or XP to automatically assign themselves an IP address when they cannot find a DHCP server on the network.

B channel

The data-carrying channels on an ISDN connection. Basic Rate ISDN uses three channels. Two data-carrying channels, called B channels, each provide 64Kbps of bandwidth for data transfer. The third channel, the D channel, is not used for data transfer. Instead, operating at 16Kbps, the D channel is used exclusively for setup and control information used during the communication session.

See also [ISDN modem]

backup domain controller

An additional server computer used on a Microsoft domain to provide some help to the domain controller for logging on and authenticating network users.


The data pipe or conduit provided by a particular network architecture. Bandwidth is the amount of data that can ultimately be pushed along the network medium under ideal conditions.


Data that flows in a single bit stream. Ethernet, token ring, and other LAN technologies use baseband transmissions.


A set of initial performance readings taken on a server or a network and then used for later comparison.

Basic Rate ISDN

A form of ISDN that provides two B channels for the movement of data over regular phone lines.

See also [ISDN modem]
See also [B channel]


The oscillation of a sound wave on which one bit of data is carried. Baud was once used as a way to classify modem speeds; it has now been replaced by bits per second.

See also [bits per second]


The smallest unit of data found on a computer; bits are represented by either a one (1) or a zero (0).

bits per second

The number of bits moved per second by a device such as a modem. Modems and other devices are typically classified by bps.

boot sector virus

A virus that is typically spread to a system when an infected disk is left in the floppy drive when a user boots up a computer. The virus then replicates to the boot sector of the computer's hard drive.


A hardware component on a server, such as the processor or the memory, that is being overtaxed and is slowing down overall system performance.


A internetworking device used to segment networks that have grown to a point where the amount of data traffic on the network media is slowing the overall transfer of information. Bridges use MAC addresses to keep local data traffic on each segment of the network.

See also [MAC address]


Data transmission where a single line can carry multiple transmissions on different channels.

bus topology

A LAN topology where computers are connected at intervals to a main trunk line or network backbone. Bus topologies typically use a passive network architecture, where the computers on a bus just sit and listen. When they "hear" data on the wire that belongs to them, they accept that data.


A 53-byte packet used by ATM to move data, such as voice and video, across public networks (such as the POTS) and private wide area networks.

See also [Asynchronous Transfer Mode]

central office

The nearest POTS switching station to a company or institution.


One carrier unit on a T-Carrier line. Each channel can provide up to 64Kbps of throughput, and channels can be combined to provide greater amounts of bandwidth.

See also [T-Carrier system]
See also [multiplexer]

Channel Service Unit/Digital Service Unit

A piece of equipment that sits between a LAN multiplexer and the network's connection to the local loop. It provides for the timing of the data transfer.

See also [local loop]
See also [customer premise equipment]


The virtual path created for a communication session on a circuit- switching network.

See also [circuit switching]

circuit switching

Establishes a circuit during the communication session between the sender and receiver. This means that, temporarily, the lines are dedicated to that communication session. Then, when the session is over, the circuit is immediately "torn down" and becomes available for another communication session. ISDN is an example of circuit switching.

See also [ISDN modem]

Class A

A category of IP addresses used for very large networks. A Class A network provides over 16 million node addresses.

Class B

A category of IP addresses used for large and medium-size companies and institutions. There are 16,384 Class B network addresses available, with each Class B network supplying over 65,000 host addresses.

Class C

A category of IP addresses used for small networks. There are over 2 million Class C network addresses available. Class C networks only provide 254 node addresses, however.


A computer on a network that accesses resources provided by server computers.

connection-oriented transport

A protocol operating at the Transport layer of the OSI model that uses a system of acknowledgements to ensure data delivery and defines a static route on the network so that packets are delivered along the same route during the session. This is considered a reliable connection.

connectionless transport

A protocol operating at the Transport layer of the OSI model that does not use acknowledgements or a defined route on a network to move data from one node to another. Connectionless protocols do not require the network resources that a connection-oriented protocol does, but connectionless transport is considered an unreliable method of data delivery.


The real-time graphs added to the Windows Performance Monitor. Graphs are used to monitor the performance of an object.

See also [object]
See also [Performance Monitor]


Renegade computer users who attack computer systems and networks; their arsenal includes viruses and a variety of attack strategies, such as denial-of-service attacks and IP spoofing.

crossover cable

A twisted-pair cable that has been configured to allow the direct connection of two computers that are outfitted with Ethernet NICs.


Interference passed between two closely located data wires.


Carrier Sense Multiple Access with Collision Avoidance.A network access strategy used by AppleTalk. A device that is ready to send data out onto the network will notify the other network nodes of its intention to place data on the network.


Carrier Sense Multiple Access with Collision Detection.A network access strategy used by Ethernet networks. If a node sending data detects that there has been a collision, it will wait to resend the data until the line is determined to be free of other data.

customer premise equipment

The LAN devices and the telephone system inside a company or an institution.

cyclic redundancy check

A mathematical calculation that is included in the trailer of a data frame. The CRC is calculated on both the sending and receiving computer. If the CRC checks are in agreement, the data contained in the frame is considered to be intact.

data bus

The parallel collection of wires provided by a motherboard for the movement of data between devices on the motherboard and the computer's processor.

data frame

Data packets moving down the OSI model are encapsulated by particular network architecture, such as Ethernet or token ring, into a frame. The frame makes the data packet compatible with the network architecture's media-access strategy.

Data Link Control protocol

A mainframe communication protocol that is also used to allow computers on a network to communicate with printers directly connected to a network using devices such as an HP DirectJet box or HP DirectJet card.

Data Link layer (OSI model)

Responsible for the movement of data across the actual physical link between computers. It is also responsible for assuring that the data is received error free.

database engine

The software on a database server that accepts requests for information from clients on the network.


The process of moving raw data received by a node up the OSI stack into a format that can be accessed by a network user using a particular application.

default gateway

On IP networks that have been divided up into subnets, the default gateway is the router that provides the connection for a subnet to access the rest of the network.


The place where the CPE ends and the phone company's equipment begins.


The conversion of data from analog to digital. This data-conversion process is provided by a modem.

Department of Defense

model A network communications conceptual model that was developed by the Department of Defense in the infancy of the Internet. The DoD model has four layers: Application layer, Host-to-Host layer, Internet layer, and Network Access layer.

differential backup

This type of backup only backs up the files that have changed since the last backup. The differential backup does not, however, change the marker attribute, which indicates that the file has been backed up.

Digital Data Service

Digital lines supplied by the POTS or other service provider that are used for data transfer. DDS lines include the T-Carrier system.

See also [T-Carrier system]

Digital Subscriber Line

One of the newest technologies for data transfer over the POTS, the DSL technology allows for digital communication over existing phone lines.

Digital Subscriber Line Access Multiplexer

A device located at a provider's central office that receives signals from multiple customer Digital Subscriber Line connections and puts these signals on a high-speed backbone using multiplexing techniques.

See also [Digital Subscriber Line]
See also [multiplexer]

direct connect printer

A printer that contains its own network interface, processor, and memory for print serving. Such printers are typically attached directly to a network hub using twisted-pair cable.

disk duplexing

Disk mirroring where separate drive controllers are used on drives in a mirror set.

See also [Redundant Array of Inexpensive Disks]
See also [disk mirroring]

disk mirroring
(RAID 1)

This type of RAID is used to create an exact duplicate of a drive or drive partition. If the main drive fails, the mirror-image drive can be used to keep the server running.

See also [Redundant Array of Inexpensive Disks]

DNS domain

A friendly name assigned to a company or institution that has a presence on the Internet. Domain names must be leased by an organization for use on the Internet.

DNS server

A server that resolves friendly domain names (URLs) to IP addresses (and vice versa). There are seven core DNS servers on the Internet.


The basic structure or administrative unit for Microsoft networks running the Windows NT, 2000, and XP network operating systems. Each domain is managed by a server called the domain controller.

See also [DNS domain]
See also [domain controller]

domain controller

The server on a Microsoft network domain that maintains the database of user accounts. The domain controller can also offer network resources, such as printers and shared files.

domain name space

The actual structure or scheme used for DNS names. The domain name space is basically an upside-down tree in which the different domains branch out from a central branch or root.

Domain Name System

The hierarchical, friendly naming system devised for the Internet. DNS servers are used to resolve these friendly DNS names to actual IP addresses.

dotted decimal

The format used to display IP addresses. This format consists of four decimal octets separated by periods.

electronic mail

A network service that allows users to send and receive messages.


The process of moving user data down the OSI stack on a sending node through a number of intermediary formats.

enterprise network

The network infrastructure for a large company or institution that consists of multiple sites across a geographical area, a country, or even the world.

Event Viewer

A utility available on a Microsoft server that allows you to view different event logs related to the server's system and security. This utility is useful in determining whether drivers for devices such as a NIC have loaded correctly on the server.

Fast Ethernet

So named because of its "faster" throughput speed (when compared to the original 10Mbps flavor of Ethernet), Fast Ethernet provides a bandwidth of 100Mbps.


Stands for File Allocation Table. It is the file system originally developed for use in the DOS environment. It uses a file allocation table to store the name and location of files that have been saved to a disk. The original version of FAT is referred to as FAT16. A newer version of FAT called FAT32 was developed by Microsoft to provide support for larger drive sizes.

fault tolerance

The ability for a hardware system or software to recover from errors or physical problems. Fault tolerance on networks is increased by strategies such as server backups, RAID arrays, and antivirus software.

Fiber Distributed Data Interface

A network architecture that provides high-speed network backbones that can be used to connect and extend the range of LANs.

file sharing

The ability of an NOS or OS to allow network users to connect to files or resources on a server or peer computer on the network. A number of operating systems and all the network operating systems provide strategies for sharing file and drive resources on peer-to-peer and server-based networks.

File Transfer Protocol

A member of the TCP/IP protocol stack used to send and receive data between computers on the Internet or an intranet.

file virus

A virus that actually infects an executable file such as an EXE or COM file.


A device designed to sit between your network and the Internet that protects the internal network from outside attack. A firewall will examine data leaving and entering the internal network and can actually filter the data traveling in both directions.

forward lookup zones

Records held on a DNS server that are used to resolve friendly names to IP addresses.

See also [DNS server]

fractional-T connection

A connection that uses a portion of the channels provided by a full T-Carrier line.

See also [T-Carrier system]

FTP server

A server that provides FTP services to network clients.

See also [File Transfer Protocol]

full backup

This type of backup can also be called a normal backup or daily backup (depending on the backup software you are using). A full backup takes all the files you select for backup and backs them up (no matter how the files are currently marked).


Allows communication between a sending and a receiving device in both directions simultaneously.

fully qualified domain name

The complete DNS name for a computer on a TCP/IP network. An FQDN will include the Internet domain name and the name of the computer.


A computer or other device that uses software as a communication bridge between incompatible platforms or network architectures.

Gigabit Ethernet

Uses the same IEEE Ethernet specifications and the same data format as other versions of Ethernet. Gigabit Ethernet provides a data transmission speed of 1,000Mbps.


A TCP/IP protocol developed at the University of Minnesota (the school mascot is the gopher) that provides a client/server system that allows a Gopher client to access data on a Gopher server (or servers) using a hierarchical directory, much like an index.


A logical administrative container that holds a collection of user accounts.


A suite of client communication software that is used to communicate with a communication server package.


An extremely knowledgeable computer aficionado. A criminal hacker would be a cracker.

See also [crackers]


Transmission of data can take place in two directions between a sending and a receiving device, but with half-duplex, data can only be transmitted in one direction at a time.


An electronic communication agreement between two computers exchanging data over a network.

hardware sharing

The ability to share hardware devices such as printers, CD-ROM drives, and hard drives on the network. The ability to share peripherals is built in to many operating systems. Network operating systems also provide the ability for a server to share hardware devices.


Designates the number of routers that packets pass through on an internetwork as they move from source to destination. Each hop would be one router.

Host-to-Host layer (DoD)

Equivalent to the OSI Transport layer, this layer provides flow control and connection reliability as data moves from a sending to a receiving computer. This layer takes the data from the Application layer protocols and begins the process of readying the data for movement out over the network.


The machine-level designation provided to a computer or other device on an IP network.


A device with typically no active electronics that supplies a central connection point for computers arranged in a star topology.


Basically a pointer that allows you to refer to Web pages, graphics, and multimedia content that are listed on a particular Web page. When a hyperlink is clicked on in a Web browser window, a user is taken to that page or activates a particular event (such as the playing of video or audio content or the displaying of a picture).

Hypertext Markup Language

The programming language used to create Web documents that can be read by a Web browser such as Microsoft Internet Explorer or Netscape Navigator. HTML consists of tags that are used to format a document so that it can be viewed in a Web browser.

Hypertext Transfer Protocol

A TCP/IP stack member that provides the connection between an HTTP client (a computer outfitted with a Web browser) and a Web server.

(Institute of Electrical and Electronics Engineers)

An international organization whose mandate is to develop and share electrical and Information Technology specifications worldwide.


The resistance of a wire to data transmission. All cable types have impedance, which is measured in Ohms. The greater the impedance, the more energy required to move the signal over the wire.

incremental backup

This type of backup backs up only the files that have been changed since the last backup (just as a differential backup does).

Interface Message Processor

A hardware switch that was the precursor to the router. IMPs were used during the initial testing of ARPAnet.

See also [ARPAnet]


Signals or noise from nearby devices that interfere with a wire's ability to move a transmission signal.


A giant, global internetwork that connects millions of computers. The current Internet evolved from government-sponsored packet-switching networks such as the ARPAnet.

Internet access provider

A communications company that provides a connection to the Internet backbone. IAPs typically serve larger corporations that maintain their own DNS servers and other Internet services servers, such as e-mail servers, and only require an onramp to the Internet infrastructure.

Internet layer (DoD)

This layer corresponds to the OSI Network layer and is responsible for the routing of data across logical network paths and provides an addressing system to the upper layers of the DoD stack. This layer also defines the packet format used for the data as it moves onto the network.

Internet Message Access Protocol

An e-mail transport program that provides an alternative to the POP3 protocol. IMAP mail servers do not immediately dump all the available mail from the server to the IMAP client when the client connects.

See also [POP3]

Internet service provider

A provider of Internet-based services. An ISP provides an Internet connection to users or companies in addition to other services, such as Internet e-mail, Web browsing, FTP, and newsgroups. An ISP also typically offers space on its Web server for personal or corporate Web sites.


A network of networks. An internetwork is a collection of LANS that uses different internetworking devices, such as routers and switches, to expand the range of the LANs.


The central authority for domain names in the United States.


A private, internal network that uses the TCP/IP protocol stack and different Internet technologies and servers to create an Internet-like environment for the users on the network.

IP Address

The unique logical address assigned to every computer and other devices, such as routers, on a network that uses the TCP/IP protocol.

IP Version 6

A new IP addressing system that provides a greater number of bits (128 bits). IPV6 will offer billions more IP addresses than are currently available with IPV4.


A suite of cryptography-based protection services and security protocols that can be used to secure internal networks, networks that use WAN solutions for connectivity, and networks that take advantage of remote access solutions.

(Internetwork Packet Exchange/Sequenced Packet Exchange)

A proprietary LAN protocol stack developed by Novell. IPX/SPX provides its own unique system for node addressing and was originally developed for LANs using the Novell NetWare NOS.


A suite of protocols defined by the ITU-T (International Telecommunication Union-Telecommunication Standardization sector) that provides digital communication over existing phone lines.

ISDN modem

A terminal adapter that is used to connect a LAN to the POTS local loop.

See also [ISDN modem]


The lag time it takes data to move from one place to another. Some WAN technologies, such as ATM, use fixed-size packets to increase the potential throughput and decrease latency.


A Unix clone created by Linus Torvalds when he was a student at the University of Helsinki. Linux is an open-system OS/NOS, and the source code is free.

local area network

A collection of personal computers and other peripheral devices connected at one location.

local loop

The actual physical wires that connect a business to the nearest phone company switching station.

local printer

A printer that is directly attached to a server. The printer is only local, however, in relation to the server it is attached to.


The actual hardware devices, such as the built-in ports, on the back of Mac computers and the special shielded twisted-pair cables that make up the physical connection for Apple networks.

Logical Link Control sublayer

This sublayer of the OSI's Data Link layer maintains the link between sending and receiving computers as data is moved across the physical media of the network.

See also [Data Link layer (OSI model)]

MAC address

The hardware address provided by the MAC sublayer of the OSI's Data Link layer. MAC addresses are actually burned into devices such as NICs and router interfaces. Each MAC address is unique.

See also [Data Link layer (OSI model)]

macro virus

Typically written in Visual Basic code, this type of virus affects documents and spreadsheet data files rather than executables. A number of Microsoft Word and Excel macro viruses have surfaced in recent years.


Viruses, worms, and other software that are designed to mess up a computer.


An attribute placed on files by the OS that differentiates files that have been backed up from those that have changed since the last backup.

Media Access Control sublayer (OSI model)

The sublayer of the Data Link layer that provides access with the network media and provides the addressing system used to move data frames on the network.

See also [MAC address]


A device that can modulate and demodulate an analog transmission, providing for data communication over a regular phone line.

modem pool

A collection of modems on a remote access server. The modem pool provides for multiple dial-in connections.


The conversion of digital information on a computer to analog data carried on a phone line (modulation is handled by a modem).

See also [demodulation]
See also [modem]

multipartite virus

A virus that has the characteristics of both a boot sector virus and a file virus. It can spread from the boot sector of a drive to another drive, and it can also attack executable files on the computer.

See also [boot sector virus]
See also [file virus]

multiplayer gaming

A number of PC-based games are designed to allow multiple players to interact during a gaming session on a network. Individuals who set up home-based, peer-to-peer networks can take advantage of a large number of computer games that provide support for multiple players.


The device that combines or divides the signals carried on the separate channels of a digital carrier line.

See also [T-Carrier system]

Multistation Access Unit

A connectivity device containing an internal, logical ring that is used as the central connection point for computers on a token-ring network.

(Nearest Active Downstream Neighbor)

The computer being passed a token is the nearest active downstream neighbor.

(Nearest Active Upstream Neighbor)

The computer that passes a token to the next computer on the logical ring is called the nearest active upstream neighbor.


Stands for Novell Directory Services. It is the logical, hierarchical directory tree used to manage users and devices on a Novell network. NDS became the structure for Novell networks with the release of NetWare 4.

NetBIOS Extended User Interface

A simple but fast LAN protocol stack designed for small networks. NetBEUI is a nonroutable protocol and was designed as an extension of Microsoft and IBM's NetBIOS protocol.


A group of connected computers that can share resources. Networks can be as small as two computers connected in a peer-to-peer arrangement or as large as global networks, such as the Internet, that use a number of different WAN connectivity strategies, including satellite technology.

Network Access layer (DoD)

This layer is equivalent to the Data Link layer of the OSI model and consists of the protocols that take the packets from the Internet layer and package them in an appropriate frame type.

Network Address Translation

The ability to hide a group of computers using IP addresses behind one or more IP address. NAT is often used to hide friendly networks behind a proxy server.

See also [proxy server]

network architecture

The defining strategy for how computers on the network access the network media. The network architecture will also play some part in the network topology deployed on the network. Examples of network architectures are Ethernet and token ring.

network interface card

A peripheral device containing a transceiver (a transmitter and receiver) that is able to convert data from parallel to serial, and vice versa. A NIC is the computer's connection to the network media.

Network layer (OSI model)

Responsible for the addressing of packets and their routing on the network.

Network Monitor

A Windows Server utility that allows you to monitor and track network performance and traffic.

network operating system

Software that imparts special server capabilities to a computer. A server running an NOS can authenticate users to the network and share network resources.

network share

A drive or folder on a server that is made available to users on the network. Shares cannot consist of individual files.


An electronic bulletin board provided by a news server, such as those provided by Usenet. Information on news servers is broken into categories. Each subject area is called a newsgroup.


A client computer, server, or other device (such as a router) that is connected to the network.


Stands for New Technology File System. It is a file system available on computers running Windows NT and Windows 2000 that supports the spanning of large volumes and uses transaction logs, making it easier to recover data on a failed disk. NTFS is an improvement over the FAT file system that was originally developed for the DOS/Windows environment.

See also [FAT]


Microsoft's clone of the IPX/SPX protocol stack.

See also [IPX/SPX (Internetwork Packet Exchange/Sequenced Packet Exchange)]


On a Windows server, any process that can be measured using the Performance Monitor is referred to as an object.

See also [Performance Monitor]


One portion of the four-part IP address. Each octet in an IP address is equivalent to 8 bits of address information. Each IP address consists of four octets (or 32 bits).


Stands for Original Equipment Manufacturer. It refers to large resellers of computer equipment. Software manufacturers such as Microsoft often supply OEMs with special versions of their software that is highly compatible with the OEM's hardware.

(Open Systems Interconnection)

reference model A conceptual model developed to illustrate how network protocols allow computers to communicate on the network. The OSI model consists of seven layers. Each layer serves a specific function as data moves through several intermediary forms before it is transmitted by a computer onto the network.


A blanket term for data that is being processed to be sent over a network. In theory, a packet is created at the Transport layer of the OSI model when data is segmented into small data packages.

packet switching

In WAN connections that use packet switching, the data is divided into packets. The small packet size used in packet switching provides fast and efficient delivery of data.

parity bit

Extra bits placed in a data stream sent by a modem. The parity bits are used to check for errors in the transmission.


A logical portion of a hard drive that is actually read by the computer's operating system as a separate drive.


In a peer-to-peer network, the computers on the network functions as peers. Each peer has the capability to access and serve up resources such as files and printers.

peer communication

Information placed by a protocol operating at a particular layer of the OSI model in a data packet's header that is intended for a protocol operating at the same layer of the OSI model on the receiving computer.

peer-to-peer networking

A simple, low-cost method for connecting personal computers in situations where you want to share files and other resources, such as a printer. The capability to provide peer services is built in to the OS that is running on the peer computers.

Performance Monitor

A utility available on Microsoft servers that allows you to monitor server hardware performance, such as the processor and RAM.

permanent virtual circuit

A connection route set up between a sending device and a receiving device on a public switched network. The PVC is identified by a Data Link Connection Identifier (DLCI). Logical addresses, such as IP addresses, are then mapped to the PVC, providing a path through the WAN for the movement of data between the connected LANs.

Personal Digital Assistant

A handheld computing device that provides productivity software for managing appointments, contacts, and other personal information.

Physical layer (OSI model)

This layer defines the actual physical aspects of how cabling is connected on a particular network topology.

(Packet Internet Gopher)

A simple diagnostic command that uses echo packets to test the IP connection between two computers on a TCP/IP network.

Plain Old Telephone System

The infrastructure of the public switched telephone network in the United States. The POTS provides a number of different WAN technologies.

plug and play

An operating system service that allows for the automatic recognition and installation of peripheral devices such as modems and printers.

Point-to-Point Protocol

A TCP/IP protocol that provides a reliable connection between computers. PPP supports multiple network protocols, such as IP, IPX, and NetBEUI. PPP also provides compression and error checking and is therefore more reliable than a SLIP connection.


A TCP/IP stack protocol used by e-mail clients to connect to a POP3 e-mail server. The POP3 e-mail server basically functions as a mail drop.

Presentation layer (OSI Model)

The converter layer of the OSI model. This layer converts the data into a format that can be read by the receiving computer.

primary DNS server

A DNS server on a network that serves as the premier DNS name–to–IP address resolver on the network. It is called the primary DNS server because client machines are configured to consult it first when trying to resolve friendly names to IP addresses (or vice versa).

Primary Rate ISDN

A faster version of ISDN for businesses. Primary Rate ISDN uses a T1 line and provides 23 B channels (each operating at 64Kbps). One D channel is also necessary (as with BRI) to handle setup and to control the connection. All or any number of the 23 B channels available can be combined for data transfer. Some channels can also be used for voice communication.

print queue

The list of print jobs waiting to be printed. These print jobs are held in the print server's memory or hard drive in the form of a print queue.

print server

A computer used to queue up print jobs and control printer access. A print server typically has a printer directly connected to it.

print spooler

Software on a print server that accepts print jobs from network clients and readies them for printing.

printer pool

Several identical printers that have been configured to appear as one printer on the network. Because multiple printers can accept print jobs sent to the pool, print services are provided faster to network users.

program sharing

Involves applications such as spreadsheets and word processors being run over a network. File servers and special applications servers provide the platform for sharing different applications over a network.


Software code that provides the rules for how computers communicate on a network. LAN protocols such as TCP/IP or IPX/SPX actually are made up of a number of protocols in a stack. There must be a common protocol for the computers to communicate.

protocol stack

A group of tightly associated protocols, each with its own function, that work together to prepare data for the communication process.

proxy server

A server that sits between your network (considered a trusted network) and an untrusted network, such as the Internet. The proxy server masks the computers that are hidden behind it on the trusted network.

public folder

A folder on a network server that can be accessed by network users who have the appropriate permissions.


A request to a database server for information from a network client.


A method of combining several drives into one RAID array that provides for faster access time. RAID 0 does not actually provide any fault tolerance.

See also [Redundant Array of Inexpensive Disks]


A method of combining several drives into one RAID array so that the information is striped across the drives. If one drive in the array fails, the data can be regenerated using parity information contained on the other drives in the array.


Software on a client computer that handles the little "bait and switch" operation that makes the computer think a network resource is still just a local resource.

Redundant Array of Inexpensive Disks

A group or array of hard drives that provides fault tolerance on a server and is seen by network clients as a single drive.

remote access server

A server that accepts incoming dial-in connections or virtual connections from remote client computers.

remote printer

A printer attached to a computer other than your server. The computer that the printer is attached to would consider the printer local. Whether a printer is local or remote will depend on which computer on the network you are using as your reference point.


A device that takes the signal received from computers and network devices and regenerates the signal so that it maintains its integrity along a longer cable run than is normally possible. Repeaters are also referred to as concentrators.


The software on an application such as a Web browser that contacts a DNS server for resolving a friendly name to an IP address.


A hardware component on a server or a computer. A resource can be the memory, processor, or hard drive space on a computer.

reverse lookup zones

Zones on a DNS server that resolve IP addresses to friendly names.

See also [DNS server]

ring topology

A LAN topology where computers are arranged in a physical circle. The ring topology moves information on the wire in one direction and is considered an active topology. Computers on the network actually retransmit the packets they receive and then send them on to the next computer in the ring.

RJ-11 jack

A small jack that accepts RJ-11 or telephone connectors.

RJ-45 connector

The male end on a twisted-pair cable used to connect to various network devices such as a computer's NIC.


A internetworking device used to connect LANs via LAN and WAN connections. The router uses a combination of hardware to route packets between networks.

routing protocol

A protocol used by routers to build routing tables and determine the best path for data on a routed network.

RS-232 cable

A cable used to connect a device such as a modem to a COM port on a computer.


A Linux add-on program that allows Linux computers to participate in Windows workgroups. Samba derives its name from Server Message Block (SMB). SMB is an important part of the NetBIOS/NetBEUI protocol stack and supplies the data blocks that make requests between client and server or between peers on a Microsoft network.

scalable networks

Networks designed so that any number of clients or additional servers can be added to them. The scalability of a network will often depend on the network operating system being used on the network.

Secure Electronic Transaction

A system developed to secure credit card purchases on the World Wide Web. SET was developed by Visa and MasterCard and provides very strong 128-bit encryption. The more bits, the better encryption. Therefore, 128-bit encryption is harder to decode than 64-bit encryption.

Secure HTTP

A superset of the HTTP protocol that provides mechanisms to secure online transactions. SHTTP was developed by Enterprise Integration Technologies and is now the property of Terisia Systems. SHTTP provides for the encryption of transmissions between servers and clients.

Secure Socket Layer

A system used to secure online transactions on the Internet. SSL was developed by Netscape to secure online transactions and uses a combination of encryption and digital certificates (the certificates are used to verify a merchant's identity) to secure the transfer of information from a Web browser to a Web site store.

Serial Line Internet Protocol

An access protocol developed primarily to allow PCs to connect to the Internet using a modem. It operates at the OSI model's Physical layer and allows data to flow across the telephone line to a remote system.

serial ports

The communication (COM) ports on a computer. Serial ports are typically used to connect communication devices such as modems to a computer.

serial transmission

Data bits are lined up in a single bit stream for transfer over a network medium such as copper wire.


A computer that actually serves up the resources available on the network—everything from files to electronic mail post offices. A server running a network operating system also controls access to the network and authenticates users based on login name and password.

server-based networking

A networking model where user access and the sharing of resources is centrally controlled. Resources and user logon are controlled by a specialized network server.


A resource, such as e-mail, newsgroups, or teleconferencing, provided by a communication server.

service access points

Communication channels that are provided by the Logical Link Control (LLC) sublayer of the Data Link layer of the OSI model. SAPs are used so that lower layers of the OSI model can communicate with upper layers in the OSI stack.

Session layer (OSI model)

The layer of the OSI model responsible for setting up the communication link or session between the sending and receiving computers.


A resource such as a drive, folder, or printer that is made available to other users on a network.

share-level security

A security scheme in which each resource on a network is managed separately and often requires a unique password for access. Share-level security is typical for the peer-to-peer networking environment.

shared database

A client/server environment where a shared database is held on a database server and is accessed using database client software on network client computers.

shared printer

A printer on a network that accepts print jobs from more than one computer.

shielded twisted pair

Network-grade twisted-pair cabling that is encased in a protective shielding.

Simple Mail Transport Protocol

A protocol that allows e-mail servers to send and receive messages. This protocol operates at the Application, Presentation, and Session layers of the OSI model.


A type of transmission in which data can only be sent in one direction between a sending and a receiving device. Your thermostat and furnace are good examples of simplex transmission.


Sharing information from computer to computer by physically passing a disk holding the information.

(Structured Query Language)

A language used to build complex client/server databases. SQL is also used by the database client software to send queries to the database server.

star topology

A LAN topology where each computer or device on the network is connected to a central device called a hub. Each computer is connected with its own cable (typically twisted-pair cable) to a port on the hub. Star LANs typically deploy a passive network architecture.


A logical division or subset of a large IP network. Each subnet is connected to the other subnets on the network by a router.


A term typically reserved for some of the large mainframe and miniframe computers built in the last few decades. Cray Corporation actually marketed a powerful mini called the Cray Supercomputer.

(Samba Web Administration Tool)

A Samba configuration tool that can be accessed using a Web browser on a Linux computer.

See also [Samba]

switched network

A WAN connectivity strategy that allows multiple users to take advantage of the same line. Switched networks can take advantage of two different strategies: circuit switching and packet switching.

See also [circuit switching]
See also [packet switching]


An internetworking device that can be used to preserve the bandwidth on your network using segmentation. Switches are used to forward packets to a particular segment using MAC hardware addressing (the same as bridges).

See also [bridge]

Synchronous Optical Network/Synchronous Digital Hierarchy

A Physical layer specification for high-speed fiber-optic networks. SONET networks typically used ATM as their WAN protocol.

T-Carrier system

High-speed digital lines made up of multiple channels provided by the POTS or other service provider. The T-Carrier system can be used for the high-speed transfer of voice, video, and data. Each channel on a line can provide 64Kbps of throughput.


A heavy-gauge coaxial cable that is fairly inflexible and requires special equipment (over and above a simple network card) to connect a computer to the network backbone.


A fairly flexible coaxial cable (RG-58A/U) used on Ethernet LANs.

time domain reflectometer

A sophisticated device that can diagnose shorts and breaks in a cable and can provide you with information on where a short or break exists on the cable.


A data packet that is passed from computer to computer on a network using a ring topology. Possession of the token is necessary for the computer to transmit data onto the network.


The overall physical layout of a network.


A diagnostic command that can be used to see the route that data packets take between two computers on a TCP/IP network.


A protocol that has the ability to transform data packets from one format to another. Translator protocols typically reside at the Presentation layer of the OSI model and make sure that data will be understandable when received by a computer on the network.

Transmission Control Protocol/Internet Protocol (TCP/IP)

A suite of protocols developed for the Internet. It is a routable protocol stack that is universally embraced by client operating systems and network operating systems.

Transport layer (OSI model)

Responsible for the flow control of data between communicating computers.

trusted network

Another name for the internal or corporate network. It is trusted because of the administrator's ability to control user activity.

See also [untrusted network]

tunnel client

A computer that remotely connects to a tunnel server using a VPN.

See also [Virtual Private Network]

tunnel server

A server that provides the network connection for a Virtual Private Network session.


Remote access servers encapsulate packets in a frame so that they can move through a virtual route or tunnel across the public switched telephone network. Virtual tunnel encapsulation is provided by the wide area networking protocol or access protocol that is being used to host the connection.

uniform resource locator

The friendly name of an Internet resource such as a Web server on the World Wide Web. A URL is defined by the registered domain name of a company and the domain name system hierarchy.

uninterruptible power supply

A device outfitted with some type of battery that can supply temporary power to a server when there is a power failure.

Universal Naming Convention

A naming system that uses "friendly names" to refer to resources on a network. The UNC for a share on a server takes the format \\ server name \ share name .


A multiuser, multitasking operating system that provides a client/server networking environment on a wide variety of hardware platforms.

unshielded twisted pair

Network-grade twisted-pair cabling that is not encased in a protective shielding.

untrusted network

An external network such as the Internet that will be connected to the internal or trusted network. It is untrusted because the network administrator has no control over the users or activity on the external network.

See also [trusted network]


A network of Internet servers that allows users to post and read messages in newsgroups.

See also [newsgroup]

user authentication

The process where the user is allowed access to the network by virtue of his login name and password.

user communication

A term that encompasses any number of different mediums for user communication on a network. These different communication mediums include electronic mail, newsgroups, and video conferencing.


The name that a user must provide when logging on to a server-based network.

Virtual Private Network

A secure, dedicated point-to-point connection over a public IP network such as the Internet.


A malicious, self-replicating piece of software code. Because a virus can copy itself, it can easily (and unfortunately) be spread from computer to computer.


A simple device that can be connected to a cable to test the cable for a break or a short.


A portion of a hard drive or parts of several hard drives that can function as a separate and discrete drive. In the case of RAID, a volume (which appears to the computer as one drive) is actually spread over two or more drives.

well-known port numbers

Conduit numbers that have been assigned to TCP/IP protocols and are used in conjunction with IP addresses to form a connection between protocols functioning on a sending and receiving computer. For example, SMTP uses port 25, and POP3 uses port 110.

wide area network

LANs at different locations connected together using various WAN technologies.

WINS server

A special server on a Microsoft network that resolves NetBIOS names to IP addresses.


A group of peer computers that operate in the same logical network space.


A powerful standalone or network client computer that provides the memory and processing power to run more complex software, such as the design software used by engineers.


A program that spreads itself from computer to computer on a network. Worms are self-replicating and do not require user interaction to spread throughout a network.


See [Digital Subscriber Line (DSL)]

AppleTalk networks can be divided into logical subsets. Each of these subsets is called a zone. Zones are used to group users into logical workgroups, making it easy for them to share network resources.



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