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Toggit's Encyclopedia of Networking Terms and Computer Dictionary.

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Search Alphabetical Listings for the letter 'C' C2 One of a series of seven levels of computer security defined by the National Security Agency. C2-level security requires that users are logged in and tracked during their session, that all resources have owners, that objects such as files be protected from processes that might damage them, that events can be audited, and that the system has adequate protection against intrusion. C2 security applies to a stand-alone system, so in theory a networked computer cannot be C2-compliant; following the guidelines can certainly help you to set up a more secure system. CA See certificate authority. cable modem A modem that sends and receives signals through a coaxial cable connected to a cable-television system, rather than through conventional telephone lines. Cable modems, with speeds of up to 500Kbps, are faster than current conventional modems, but are subject to performance changes as system load increases. Theoretical data rates are much higher than those achieved with conventional modems; downstream rates of up to 36Mbps are possible, with 3Mbps to 10Mbps likely, and upstream rates up to 10Mbps. Cabletron Systems A leading producer of Internet and intranet hardware and management solutions, Cabletron is also moving into Gigabit Ethernet and data, voice, and video systems. For more information about Cabletron, see www.cabletron.com. cabling standards National cabling standards, concerned with the performance of cables and connectors under conditions of actual use, are specified by the National Electric Code, American National Standards Institute, and Underwriters Laboratories. Other standards have been specified by the Electronics Industry Association/ Telecommunications Industries Association (EIA/TIA). Standards include: _ ANSI/EIA/TIA-568-1991 Commercial Building Telecommunications Wiring. _ EIA/TIA TSB-36 Additional Cable Specifications for UTP Cables. 1991. _ EIA/TIA TSB-40 Telecommunications Systems Bulletin—Additional Transmission Specifications for UTP Connecting Hardware. 1992. _ ANSI/EIA/TIA-568A 1995 revises the original 568 document and adds material from TSB-36 and TSB-40. _ ANSI/EIA/TIA-569-1990 Commercial Building Standard for Telecommunications Pathways and Spaces. _ ANSI/EIA/TIA-570-1991 Residential and Light Commercial Telecommunications Wiring Standard.   cache buffer _ ANSI/EIA/TIA-606-1993 Administration Standard for the Telecommunications Infrastructure of Commercial Buildings. _ ANSI/EIA/TIA-607-1994 Commercial Building Grounding and Bonding Requirements for Telecommunications. Local codes and standards may impose additional requirements. Underwriters Laboratories (UL) tests cable and other devices to determine the conditions under which the device will function safely. Two important tests for cable performance are: _ UL-910, which tests smoke emission and flame spread for plenum cable _ UL-1666, which tests smoke emission and flame spread for riser cable CAC See Connection Admission Control. cache Pronounced “cash.” A special area of memory, managed by a cache controller, that improves performance by storing the contents of frequently accessed memory locations and their addresses. A memory cache and a disk cache are not the same. A memory cache is implemented in hardware and speeds up access to memory. A disk cache is software that improves hard-disk performance. When the processor references a memory address, the cache checks to see if it holds that address. If it does, the information is passed directly to the processor, so RAM access is not necessary. A cache can speed up operations in a computer whose RAM access is slow compared with its processor speed, because cache memory is always faster than normal RAM. There are several types of caches: _ Direct-mapped cache A location in the cache corresponds to several specific locations in memory, so when the processor calls for certain data, the cache can locate it quickly. However, since several blocks in RAM correspond to that same location in the cache, the cache may spend its time refreshing itself and calling main memory. _ Fully associative cache Information from RAM may be placed in any free blocks in the cache so that the most recently accessed data is usually present; however, the search to find that information may be slow because the cache has to index the data in order to find it. _ Set-associative cache Information from RAM is kept in sets, and these sets may have multiple locations, each holding a block of data; each block may be in any of the sets, but it will only be in one location within that set. Search time is shortened, and frequently used data are less likely to be overwritten. A set-associative cache may use two, four, or eight sets. See also disk cache; wait state; write-back cache; write-through cache. cache buffer A Novell NetWare implementation of a disk cache used to speed server disk accesses, thereby allowing workstations to access data more quickly. Reading data from cache memory is much faster than reading data from the hard disk. NetWare uses cache buffers for a variety of purposes: _ For use by NetWare Loadable Modules (NLMs), such as LAN drivers, database servers, communications servers, and print servers   cache buffer pool _ To cache each volume’s FAT _ To cache files currently in use _ To build a hash table of directory information See also disk cache. cache buffer pool In Novell NetWare, the amount of memory available for use after the SERVER.EXE file has been loaded into memory. Memory in the pool can be used for a variety of purposes, including caching the file allocation tables for each volume and creating a hash table of directory information. See also hash table. cache controller Pronounced “cash controller.” A special-purpose processor whose sole task is to manage cache memory. On newer processors, such as the Intel Pentium II, cache management is integrated directly into the processor. See also cache. cache memory Pronounced “cash memory.” A relatively small section of very fast memory (often static RAM) reserved for the temporary storage of the data or instructions likely to be needed next by the processor. Cache memory integrated directly onto the microprocessor is called primary cache or L1 cache, and cache memory located in an external circuit is known as secondary cache or L2 cache. See also cache. caddy The flat plastic container used to load a compact disc into certain CD-ROM disk drives. Most current CD-ROM drives do not require a caddy. CAE See Common Application Environment. CAI See Computer Associates International. Caldera, Inc. A software company in Provo, Utah, that repackages one of the most popular versions of Linux under the name of OpenLinux. For more information on Caldera, see www.caldera.com. callback modem Also known as a dialback modem. A special modem that does not answer an incoming call, but instead requires the caller to enter a code and hang up so that the modem can return the call. As long as the entered code matches a previously authorized number, the modem dials the number. Callback modems are useful in installations for which communications lines must be available for remote users but data must be protected from intruders. caller ID See automatic number identification. call packet A block of data that carries addressing information, as well as any other information needed to establish an X.25 switched virtual circuit. campus network A network that connects LANs from multiple departments inside a single building or set of buildings. Campus networks are LANs because they do not include WAN services, even though they may extend for several miles. canonical The usual standard Unix way of doing something. This term has a more   carrier signal precise meaning in mathematics, in which rules dictate the way that formulas are written, but in Unix, it tends to mean “according to ancient or religious law.” See also holy wars. Canon, Inc. One of the world’s leading suppliers of imaging products, electronic equipment, computer printers, fax machines, and scanners. For more information on Canon, see www.canon.com. CAPI See Cryptography API. card A printed circuit board or adapter that you plug into a computer to add support for a specific piece of hardware. See also expansion board; expansion bus. card services Part of the software support needed for PCMCIA hardware devices in a portable computer. Card services control the use of system interrupts, memory, and power management. When an application wants to access a PCMCIA card, it always goes through the card services software and never communicates directly with the underlying hardware. For example, if you use a PCMCIA modem, it is the card services, not the applications program, that establishes which communications port and which interrupts and I/O addresses are in use. See also device driver; PC Memory Card International Association; socket services. carriage return A control character (ASCII 13) that signals the print head or display cursor to return to the first position of the current line. See also line feed. carrier An analog signal of fixed amplitude and frequency that is combined with a data-carrying signal to produce an output signal suitable for transmitting data. See also carrier signal. carrier detect Abbreviated CD. An electrical signal sent from a modem to the attached computer to indicate that the modem is online. See also Data Carrier Detect; RS-232-C. Carrier Sense Multiple Access/ Collision Detection Abbreviated CSMA/CD. A baseband protocol with a built-in collision-detection technique. Each node on the network listens first and transmits only when the line is free. If two nodes transmit at exactly the same time and a collision occurs, both nodes stop transmitting. Then, to avoid a subsequent collision, each node waits for a different random length of time before attempting to transmit again. Ethernet and 802.3 LANs use CSMA/CD access methods. See also collision; demand priority; Fast Ethernet; token passing. carrier signal A signal of chosen frequency generated to carry data; often used for long-distance transmissions. A carrier signal does not convey any information until the data is added to the signal by modulation and then decoded on the receiving end by demodulation.   cascaded star cascaded star A network topology in which multiple hubs or data centers are connected in a succession of levels, which permits many more connections than a single level. CASCADED STAR cascading menus In Microsoft Windows 2000, a function that presents the contents of network drives or special folders such as Control Panel as menu items that can be selected by name. See also personalized menus. Castanet A collection of software-update tools from Marimba, Inc. that operate over the Internet. Based on Java technology, Castanet can automatically deliver software updates not only for Java programs, but also for those written in C, C++, and Visual Basic, and because only the updated content is downloaded, performance is optimized. For more information on Castanet, see www.marimba.com. See also server push. Category 1–5 The Electronics Industry Association/Telecommunications Industry Association (EIA/TIA) 586 cabling standards, sometimes abbreviated CAT 1-5, as follows: _ Category 1 For unshielded twisted-pair (UTP) telephone cable. This cable may be used for voice, but is not suitable for data transmissions.   CCITT V Series _ Category 2 For UTP cable use at speeds up to 4Mbps. Category 2 cable is similar to IBM Cabling System Type 3 cable. _ Category 3 For UTP cable use at speeds up to 10Mbps. Category 3 cable is the minimum requirement for 10BaseT and is required for Token Ring. This cable has four pairs of conductors and three twists per foot. _ Category 4 For the lowest acceptable grade of UTP cable for use with 16Mbps Token Ring. _ Category 5 For 100-ohm, four-wire twisted-pair copper cable for use at speeds up to 100Mbps with Ethernet or ATM (Asynchronous Transfer Mode). This cable is low-capacitance and shows low crosstalk when installed according to specifications. See also cabling standards; Type 1–9 cable. CAU See Controlled Access Unit. CAV See constant angular velocity. CBCP See Certified Business Continuity Professional. CBE See Certified Banyan Engineer. CBR See Constant Bit Rate. CBS See Certified Banyan Specialist. CCDA See Cisco Certified Design Associate. CCDP See Cisco Certified Design Professional. CCIE See Cisco Certified Internetworking Expert. CCITT See Consultative Committee for International Telephony and Telegraphy. CCITT Groups 1–4 A set of four standards for facsimile transmissions. Groups 1 and 2, which are no longer used, define analog facsimile transmissions. Groups 3 and 4 describe digital systems, as follows: _ CCITT Group 3 Specifies a 9600bps modem to transmit standard images of 203 dpi horizontally by 98 dpi vertically in standard mode, and 203 dpi by 198 dpi in fine mode. _ CCITT Group 4 Supports images up to 400 dpi for high-speed transmission over a digital data network (for example, ISDN), rather than over a dial-up telephone line. _ CCITT is now known as the International Telecommunication Union. See also International Telecommunication Union. CCITT V Series A set of recommended standards for data communications, including transmission speeds and operational modes, issued by CCITT, now known as the International Telecommunication Union. Each standard is assigned a number, although not in chronological order. Higher numbers do not always indicate a newer standard. A second or revised version is indicated by bis , and ter indicates a third version. See also International Telecommunication Union.   CCITT X Series CCITT X Series A set of recommended standards issued by CCITT to standardize protocols and equipment used in public and private computer networks. The standards include transmission speeds, interfaces to and between networks, and operation of user hardware. CCITT is now known as the International Telecommunication Union. See also International Telecommunication Union. CCNA See Cisco Certified Network Associate. CCNP See Cisco Certified Network Professional. CCP See Certified Computing Professional. CCP See Compression Control Protocol. CD See carrier detect. CDA See Certified Database Administrator. CDDI See Copper Distributed Data Interface. CDE See Common Desktop Environment. CD-I See Compact Disc-Interactive. CDIA See Certified Document Imaging Architect. CDMA See Code Division Multiple Access. CDP See Cisco Discovery Protocol. CDPD See Cellular Digital Packet Data. CD-R See CD-Recordable. CD-Recordable Abbreviated CD-R. Using CD-R, you can write to the disc only once; after that, the disc can only be read from and not written to. From a functional point of view, a CD-R and a CD-ROM are identical; you can read CD-R discs using almost any CD-ROM drive, although the processes that create the discs are slightly different. Low-cost CD-R drives are available from several manufacturers, including Kao, Kodak, Mitsui, Phillips, Ricoh, Sony, TDK, 3M, and Verbatim. See also CD ReWritable; digital video disc; Magneto-optical storage; WORM. CD ReWritable Abbreviated CD-RW. A CD format that can be written to and erased as many as 1000 times. From a functional point of view, a CD-RW and a CD-ROM are identical, but not all CD-ROM drives can read CD-RW discs. Low-cost CD-RW drives are available from several manufacturers, including Kodak, Mitsui, Phillips, and Sony. See also CD-Recordable; digital video disc; Magneto-optical storage; WORM. CD-ROM See Compact Disc—Read- Only Memory. CD-ROM disk drive A disk device that uses compact disc technology for information storage. Many CD-ROM disk drives also have headphone jacks, external speaker jacks, and a volume control. CD-ROM disk drives designed for computer use are more expensive than audio CD players, because CD-ROM disk drives   central processing unit are manufactured to much higher tolerances. If a CD player misreads a small amount of data, the human ear probably will not detect the difference; if a CDROM disk drive misreads a few bytes of a program, the program will not run. The two most popular CD-ROM drive interface cards are SCSI and ATAPI (AT Attachment Packet Interface). ATAPI is part of the Enhanced IDE specification introduced by Western Digital in 1994 and lets you plug an IDE CD-ROM directly into an IDE controller on the system’s motherboard. Other CD-ROM drives may use the computer’s parallel port or a PCMCIA connection. See also Compact Disc—Read-Only Memory. CD-ROM Extended Architecture Abbreviated CD-ROM/XA. An extension to the CD-ROM format, developed by Microsoft, Phillips, and Sony, that allows for the storage of audio and visual information on compact disc so that you can play the audio at the same time you view the visual data. CD-ROM/XA is compatible with the High Sierra specification, also known as ISO standard 9660. CD-ROM/XA See CD-ROM Extended Architecture. CD-RW See CD ReWritable. cell Any fixed-length data packet. For example, Asynchronous Transfer Mode (ATM) uses 53-byte cells, consisting of 48 bytes of data and 5 bytes of header information. Cell Loss Priority Abbreviated CLP. In an Asynchronous Transfer Mode (ATM) cell, a field contained in the 5-byte cell header that defines how to drop a cell if network congestion occurs. The value holds priority values, with 0 indicating a cell with the highest priority. See also Header Error Control; Payload Type Identifier; Virtual Channel Identifier; Virtual Path Identifier. cell relay A form of packet transmission used in Broadcast Integrated Services Digital Network (B-ISDN) networks that uses a fixed-length, 53-byte cell over a packetswitched network. Also known as Asynchronous Transfer Mode (ATM). cell switching A term that describes how a cellular telephone system switches from one cell to the next as the signal strength fades. The switch takes about 300 milliseconds to complete and is not noticeable by the user. Cellular Digital Packet Data Abbreviated CDPD. A method used in cellular communications and wireless modems for sending data more efficiently by using any idle cellular channel. Capacity becomes available for data transmissions when a voice call is terminated or when a call is switched from cell to cell. CDPD uses voice channels, but can switch to a new frequency if a voice transmission begins in the cell currently in use. central processing unit Abbreviated CPU. The computing and control part of the computer. The CPU in a mainframe computer may be contained on many printed circuit   Centrex boards. In a minicomputer, the CPU may be contained on several boards. The CPU in a PC is usually contained in a single, extremely powerful microprocessor. Centrex Acronym formed from Central Exchange. Services provided to a company by the local telephone company. All the switching takes place at the telephone company’s central office rather than at the customer site, so Centrex services are easy to expand. Centronics parallel interface A standard 36-pin interface used to connect a PC to a peripheral device, such as a printer; originally developed by the printer manufacturer Centronics, Inc. The standard defines eight parallel data lines, plus additional lines for status and control information. See also parallel port. CERN See Conseil Européen pour la Researche Nucléaire. CERT See Computer Emergency Response Team. certificate An encrypted digital signature used for authentication to prove that you are who you claim to be, either as an individual, the provider of a service, the vendor of a product, or a corporation, or to guarantee that an e-mail message is actually from the person you think it is from and that it has not been altered in any way during transmission. See also authentication; certificate authority; Secure Sockets Layer. certificate authority Abbreviated CA. A trusted organization that validates and issues certificates; often called a “trusted authority.” Certified Application Developer for Developer/2000 A certification from Oracle consisting of a set of exams covering Structured Query Language, the creation of procedures using Oracle Procedure Builder, using Developer/2000, and managing the user interface. Certified Banyan Engineer Abbreviated CBE. A premium certification from Banyan designed to evaluate technical knowledge of the Banyan VINES network operating system. A candidate must complete two required courses and pass two exams. Certified Banyan Specialist Abbreviated CBS. A basic certification from Banyan designed to evaluate technical knowledge of the Banyan VINES network operating system. A candidate must complete one required course and pass three exams. An additional certification concentrates on the integration of Banyan’s StreetTalk onto Microsoft Windows 2000 servers; to complete this certification, you must first become a Microsoft Certified Professional. Certified Business Continuity Professional Abbreviated CBCP. A certification from Disaster Recovery Institute International (DRII) that covers intermediate information on business continuity planning and disaster recovery and associated work experience and board certification. See also Associate Business Continuity Professional; Master Business Continuity Professional.   Certified Lotus Specialist Certified Computing Professional Abbreviated CCP. A certification from the Institute for Certification of Computing Professionals designed for experienced professionals with more than four years experience in a wide variety of computing and related tasks. Certified Database Administrator 1. Abbreviated CDA. A certification from Oracle that covers knowledge of Structured Query Language, administration of Oracle products, along with backup and recovery, and system performance tuning. 2. Abbreviated CDA. A certification from Sybase that covers designing, building, and supporting Sybase SQL Server databases. See also Certified Performance and Tuning Specialist. Certified Document Imaging Architect Abbreviated CDIA. A certification from the Computer Technology Industry Association (CompTIA) that assesses skills in document management, including scanning and storing documents in digital form and using optical character recognition software. Certified Information System Auditor Abbreviated CISA. A certification from the Information Systems Audit and Control Association (ISACA) that covers ethics, security, system organization and management, and system development, acquisition, and maintenance. Certified Information Systems Security Professional Abbreviated CISSP. A certification from the International Information System Security Certification Consortium (ISC) 2 designed for system security experts with at least three years of practical experience. The exam covers access control systems, operations security, cryptography, applications and systems planning, business continuity and disaster planning, telecommunications and network security, ethics, and the law. Certified Java Developer Abbreviated CJD. An advanced certification from Sun Microsystems designed to evaluate Java programming language skills. See also Certified Java Programmer. Certified Java Programmer Abbreviated CJP. A certification from Sun Microsystems designed to evaluate Java programming language skills. See also Certified Java Developer. Certified Lotus Professional Abbreviated CLP. A certification from Lotus designed to evaluate a wide range of skills and knowledge of Lotus products. Several certifications are available, including CLP: Application Developer, CLP: Principal Application Developer, CLP: System Administrator, CLP: Principal System Administrator, CLP: cc:Mail System Administrator. See also Certified Lotus Specialist. Certified Lotus Specialist Abbreviated CLS. A certification from Lotus designed to evaluate knowledge of a single Lotus product. Options include certification in Lotus Domino, Lotus 1-2-3, Lotus Notes, and cc:Mail. See also Certified Lotus Professional.   Certified Network Professional Certified Network Professional Abbreviated CNP. A certification from the Network Professional Association (NPA) that involves meeting requirements in the areas of client operating systems, networking hardware, network operating systems, communications protocols, and network topologies. Two years of relevant work experience and two vendor-based certifications are required to complete the program. Certified Novell Administrator Abbreviated CNA. A Novell certification program for network administrators responsible for the day-to-day operation of a network. Within the CNA program, a candidate can specialize in one or more Novell products, including IntranetWare, NetWare, or GroupWise. See also Certified Novell Engineer; Master Certified Novell Engineer. Certified Novell Engineer Abbreviated CNE. A Novell certification program for technical professionals concerned with network system design, implementation, and maintenance. Within the CNE program, a candidate can specialize in one or more Novell products, including IntranetWare, Net- Ware, or GroupWise. See also Certified Novell Administrator; Master Certified Novell Engineer. Certified Novell Engineer Professional Association Abbreviated CNEPA. An association of Certified Novell Engineers (CNEs) that provides benefits, such as workshops demonstrating how to configure and troubleshoot Novell products, as well as admission to network-related events and complementary subscriptions. See also Certified Novell Engineer. Certified Novell Instructor Abbreviated CNI. A Novell certification program for trainers who want to teach Novell courses. Once certified, by passing the appropriate exam at the instructor level, a CNI can teach any instructor-led Novell course, including those for Certified Novell Administrator (CNA), Certified Novell Engineer (CNE), and Master CNE (MCNE). See also Master Certified Novell Instructor. Certified Performance and Tuning Specialist Abbreviated CPTS. A certification from Sybase that tests for proficiency across a wide range of database administration, tuning, and performance concepts. See also Certified Database Administrator. Certified PowerBuilder Developer Associate Abbreviated CPDA. A certification from Sybase designed for experienced PowerBuilder developers that tests knowledge in the areas of client/server architecture, object-oriented programming, relational databases, and Structured Query Language. See also Certified PowerBuilder Developer Professional. Certified PowerBuilder Developer Professional Abbreviated CPDP. A certification from Sybase designed for experienced PowerBuilder developers that requires hands-on experience building PowerBuilder applications as well as a demonstration of good development practices.   character See also Certified PowerBuilder Developer Associate. Certified Solutions Expert Abbreviated CSE. A pair of Internet certifications from IBM. CSE: Net.Commerce is aimed at the developers of Internet store fronts and other financial transactions over the Internet. CSE: Firewall is a security-related certification. Certified Unicenter Engineer Abbreviated CUE. A certification from Computer Associates designed to evaluate expertise in the Unicenter TNG product line. CGI See Common Gateway Interface. Challenge-Handshake Authentication Protocol Abbreviated CHAP. A method of authentication that you can use when connecting to an ISP that allows you to log on automatically. See also Password Authentication Protocol. challenge-response authentication A method of authentication used by Microsoft Windows 2000 and other operating systems. When a user contacts a server, the server responds with a challenge, upon which the user then performs a cryptographic operation and returns the result to the server. The server then performs the same operation, and if the two results are the same, the user is considered authentic. See also clear text authentication. channel 1. In communications, any connecting path that carries information from a sending device to a receiving device. A channel may refer to a physical medium (for example, a coaxial cable) or to a specific frequency within a larger channel. 2. In Internet Relay Chat (IRC), a named forum where you can chat in real time with other users; also known as a chat room. channelization The process of dividing the bandwidth of a communications circuit into smaller increments. See also T1. channelized T1 See T1. Channel Service Unit Abbreviated CSU. A device that functions as a certified safe electrical circuit, acting as a buffer between the customer’s equipment and a public carrier’s WAN. A CSU prevents faulty CPE (customer-premises equipment), such as DSUs (data service units), from affecting a public carrier’s transmission systems and ensures that all signals placed on the line are appropriately timed and formed. All CSU designs must be approved and certified by the FCC. See also Data Service Unit. CHAP See Challenge-Handshake Authentication Protocol. character A symbol that corresponds to a key on the keyboard. A character can be a letter, a number, punctuation, or a special symbol and is usually stored as a single byte. A collection of related characters is known as a character set , and the most common character set on PC systems is the American Standard Code for Information Interchange (ASCII). Some larger IBM systems still use Extended Binary Coded Decimal Interchange   character-based interface Code (EBCDIC). In an attempt to rationalize the many international character sets in use these days, some systems use more than one byte to store a character. See also American Standard Code for Information Interchange; Extended Binary Coded Decimal Interchange Code; Unicode. character-based interface An operating system or application that uses text characters rather than graphical techniques for the user interface. See also command line; graphical user interface. character code A code that represents one specific alphanumeric or control character in a set of characters. See also American Standard Code for Information Interchange; Extended Binary Coded Decimal Interchange Code; Unicode. character mode A mode in which the computer displays characters on the screen using the built-in character set, but does not show any graphics characters or a mouse pointer. Also known as text mode. character set A standard group of letters, numbers, punctuation marks, special symbols, and control characters used by a computer. See also American Standard Code for Information Interchange; Extended Binary Coded Decimal Interchange Code; Unicode. characters per second Abbreviated cps. The number of characters, or bytes, transmitted every second during a data transfer. A measurement of the speed of operation of equipment, such as serial printers and terminals. character string Any group of alphanumeric characters treated as a single unit. Also known as a string. cheapernet wire See thin Ethernet. checkpointing The process of moving transactions from the transaction log to their permanent disk location. checksum A method of providing information for error detection, usually calculated by summing a set of values. The checksum is usually appended to the end of the data that it is calculated from so that they can be compared. For example, Xmodem, a popular file-transfer protocol, uses a 1-byte checksum calculated by adding all the ASCII values for all 128 data bytes and ignoring any numeric overflow. The checksum is added to the end of the Xmodem data packet. This type of checksum does not always detect all errors. In later versions of the Xmodem protocol, cyclical redundancy check (CRC) is used instead for more rigorous error control. See also cyclical redundancy check; error detection and correction. child domain In Microsoft Windows 2000 Server, a secondary domain beneath the top-level domain in a Windows 2000 domain tree.   Cisco Certified Internetworking Expert See also first-layer domain; parent domain; root domain. chip A slang expression for integrated circuit. See also integrated circuit. choke packet A packet used for flow control. A node that notices congestion on the network generates a choke packet and sends it toward the source of the congestion, which is then required to reduce its sending rate. CHRP See Common Hardware Reference Platform. CICS See Customer Information Control System. CIDR See Classless Inter-Domain Routing. CIFS See Common Internet File System. CIOS See Internetworking Operating System. circuit 1. A communications channel or path between two devices capable of carrying electrical current. 2. A set of components connected to perform a specific task. circuit switching A temporary communications connection established as required between the sending and receiving nodes. Circuit switching is often used in modem communications over dial-up telephone lines. It is also used in some privately maintained communications networks. See also message switching; packet switching; virtual circuit. Cirrus Logic, Inc. A leading manufacturer of integrated circuits, particularly semiconductor wafers, Cirrus Logic has also moved into the areas of 56K modem chip sets and sound-card chip sets. For more information on Cirrus Logic, see www.cirrus.com . CIS See CompuServe. CISA See Certified Information System Auditor. CISC See complex instruction set computing. ciscoBus The bus used in routers from Cisco Systems, Inc. See also Cisco Extended Bus; switch processor. ciscoBus controller See switch processor. Cisco Certified Design Associate Abbreviated CCDA. A certification from Cisco designed to evaluate knowledge of relatively simple networks. See also Cisco Certified Design Professional. Cisco Certified Design Professional Abbreviated CCDP. A certification from Cisco designed to evaluate knowledge of complex networks based on Cisco LAN and WAN routers and LAN switches. See also Cisco Certified Design Associate. Cisco Certified Internetworking Expert Abbreviated CCIE. An advanced certification from Cisco offered in three   Cisco Certified Network Associate areas: CCIE-Routing and Switching, CCIEInternet Service Provider (ISP) Dial, and CCIE-WAN Switching. Cisco Certified Network Associate Abbreviated CCNA. A certification from Cisco designed to evaluate network support knowledge. See also Cisco Certified Network Professional. Cisco Certified Network Professional Abbreviated CCNP. An advanced certification from Cisco designed to evaluate network support knowledge. See also Cisco Certified Network Associate. Cisco Discovery Protocol Abbreviated CDP. A proprietary Cisco protocol that runs on all hardware made by Cisco, including routers, switches, access servers, and bridges. CDP is both protocol- and mediaindependent. A router running CDP can advertise its existence to other routers and can discover a directly connected neighbor’s port and hostname information, as well as hardware model number and system capabilities. Cisco Extended Bus Abbreviated Cx- Bus. The extended bus used in routers from Cisco Systems, Inc. See also ciscoBus; switch processor Cisco Systems, Inc. The world’s leading manufacturer of routers and internetworking hardware and software products. More than 80 percent of the backbone routers currently in use on the Internet were made by Cisco, and its Internetwork Operating System (IOS) is quickly becoming an industry standard that other vendors are incorporating into their own products. For more information on Cisco, see www.cisco.com . CiscoView Device management software for Cisco networking devices. Cisco- View provides troubleshooting and device monitoring functions and can be used in conjunction with Simple Network Management Protocol (SNMP) products. See also Simple Network Management Protocol. Ciscoworks A set of management applications from Cisco Systems, Inc., designed for use with Cisco routers. CISSP See Certified Information Systems Security Professional. CIX See Commercial Internet Exchange. CJD See Certified Java Developer. CJP See Certified Java Programmer. cladding The transparent material, usually glass, that surrounds the core of an optical fiber. Cladding has a lower refractive index than the core and so prevents the light signal from spreading out due to modal dispersion, by reflecting the signal back into the central core. This helps to maintain the signal strength over long distances. See also dispersion. Class A certification An FCC certification for computer equipment, including mainframe computers and minicomputers   Classless Inter-Domain Routing destined for industrial, commercial, or office use, rather than for personal use at home. The Class A commercial certification is less restrictive than the Class B certification for residential use, because it assumes that most residential areas are more than 30 feet from any commercial computer equipment. See also Class B certification. Class A network In the IP addressing scheme, a very large network. The high-order bit in a Class A network is always zero, leaving 7 bits available to define 127 networks. The remaining 24 bits of the address allow each Class A network to hold as many as 16,777,216 hosts. Examples of Class A networks include General Electric, IBM, Hewlett-Packard, Apple Computer, Xerox, Digital Equipment Corporation, and MIT. All the Class A networks are in use, and no more are available. See also address classes; IP address. Class B certification An FCC certification for computer equipment, including PCs, laptops, and portables destined for use in the home rather than in a commercial setting. Class B levels of radio frequency interference (RFI) must be low enough so that they do not interfere with radio or television reception when there is more than one wall and 30 feet separating the computer from the receiver. Class B certification is more restrictive than the commercial Class A certification. See also Class A certification. Class B network In the IP addressing scheme, a medium-sized network. The 2 highorder bits are always 10, and the remaining bits are used to define 16,384 networks, each with as many as 65,535 hosts attached. Examples of Class B networks include Microsoft and Exxon. All Class B networks are in use, and no more are available. See also address classes; IP address. Class C network In the IP addressing scheme, a smaller network. The 3 high-order bits are always 110, and the remaining bits are used to define 2,097,152 networks, but each network can have a maximum of only 254 hosts. Class C networks are still available. See also address classes; IP address. Class D network In the IP addressing scheme, a special multicast address that cannot be used for networks. The 4 high-order bits are always 1110, and the remaining 28 bits allow access to more than 268 million possible addresses. See also address classes; IP address. Class E network In the IP addressing scheme, a special address reserved for experimental purposes. The first 4 bits in the address are always 1111. See also address classes; IP address. classes In Novell Directory Services, an object can be defined as an instance of an object class. Classes include User, Group, Printer, Print Server, Computer, and so on. Classless Inter-Domain Routing Abbreviated CIDR, pronounced “cider.” An interim solution to the problem that the Internet is running out of addresses.   cleartext Blocks of Class C addresses are assigned to a site based on the number of addresses that site requires, to prevent wasted addresses. Also, the Class C address space is divided into four major areas—Europe, North America, Central and South America, and Asia and the Pacific—and each zone is assigned 32 million addresses. CIDR networks are often described as “slash x ” networks; the x represents the number of bits in the IP address range controlled by the granting authority. For example, a Class C network in CIDR terms becomes a slash 24 network. See also address classes; IP address. cleartext Text that has not been encrypted in any way and that can be intercepted and read easily while in transit; usually applied to an unencrypted password. See also plaintext. clear text authentication An authentication method that encodes user name and password information according to a freely available 64-bit encoding utility. See also challenge-response authentication; encryption. Clear to Send Abbreviated CTS. A hardware signal defined by the RS-232-C standard that indicates that the transmission can proceed. See also RS-232-C; Request to Send. CLEC See Competitive Local Exchange Carrier. client A device or application that uses the services provided by a server. A client may be a PC or a workstation on a network using services provided from the network file server, or it may be that part of an application program that runs on the workstation supported by additional software running on the server. One of the most familiar clients is the Web browser. See also client/server architecture; DOS client; Macintosh client; OS/2 client; Unix client; Windows client. client application In OLE, the application that starts a server application to manipulate linked or embedded information. client pull A mechanism used on the Internet whereby a client application, usually a Web browser, initiates a request for services from a Web site. See also server push. Client Services for NetWare A software package included with Microsoft Windows 2000 that connects a Windows 2000 client to a Novell NetWare file server. client/server architecture A computing architecture that distributes processing between clients and servers on the network. In the past, traditional computing has relied on a hierarchical architecture based on nonprogrammable dumb terminals connected to a mainframe computer. In this scheme, the database was on the same computer that was running the application. A client/ server approach replaces this structure by dividing the application into two separate parts: a front-end client and a back-end   clock server, usually referred to as a client and a server . The client component provides the user with the power to run the data-entry part of the application, and this part of the client is usually optimized for user interaction with the system. The server component, which can be either local or remote, provides the data management, administration, and system security features and manages information sharing with the rest of the network. In other words, clients request information from the servers, and the servers store data and programs and provide network services to clients. Client/server architecture can sustain several levels of organizational complexity, including the following: _ Stand-alone (non-networked) client applications, such as local word processors _ Applications that run on the client but request data from the server, such as spreadsheets _ Programs that use server capabilities to share information among network users, such as electronic mail systems _ Programs in which the physical search of records takes place on the server, while a much smaller program running on the client handles all user-interface functions, such as database applications Client/server computing lightens the processing load for the client PCs, but increases the load on the server. For this reason, server computers tend to have larger and faster hard-disk drives and much more memory installed than conventional file servers. The server may also be a minicomputer or a mainframe computer. Typically, a client/server approach reduces network traffic, because relatively small amounts of data are moved over the network. This is in sharp contrast to the typical network, in which entire files are constantly being transmitted between the workstation and the file server. Database applications were some of the first to embrace the client/server concept, particularly those using Structured Query Language (SQL). SQL has grown into an industry standard database language; it is relatively easy to implement, it is robust and powerful, and it is easy for users to learn. See also network computer; thin client. client-side caching See offline files. Clipper chip A low-cost encryption device backed by the U.S. federal government. The chip would allow businesses to transmit encoded messages, but at the same time, allow certain government agencies to intercept and decode the messages if criminal activities were suspected. Needless to say, this proposal has generated a lot of intense discussion, particularly from civil rights groups concerned with an individual’s right to privacy and other ethical issues; other potential users want access to the best available encryption systems, not just those put forward by the government. CLNP See Connectionless Network Protocol. clock An electronic circuit that generates regularly spaced timing pulses at speeds up   clock-multiplying to millions of cycles per second. These pulses are used to synchronize the flow of information through the computer’s internal communications channels. See also clock speed. clock-multiplying A mechanism used by some Intel processors that allows the chip to process data and instructions internally at a speed different from that used by the rest of the system. clock speed The internal speed of a computer or processor, normally expressed in megahertz (MHz). Also known as clock rate. The faster the clock speed, the faster the computer will perform a specific operation (assuming the other components in the system, such as disk drives, can keep up with the increased speed). The Intel 8088 processor used in the original IBM PC had a clock speed of 4.77MHz— painfully slow when compared with speeds used by current processors, which can run at clock speeds of several hundred MHz. clone Hardware that is identical in function to an original. For example, an IBM clone is a PC that uses an Intel (or similar) microprocessor and functions in the same way as the IBM PC standard. A Macintosh clone functions in the same way as a computer manufactured by Apple Computer, Inc. Although most clones do perform as intended, small internal differences can cause problems in some cases. It can be difficult to ensure consistency of components and level of operation when using a number of clones purchased over a long period of time. See also Advanced Micro Devices, Inc.; Cyrix. closed architecture A design that does not allow for easy, user-supplied additions. This term is often used to describe some of the early Macintosh computers, which did not allow easy expansion of the system with add-in cards. Closed architecture can also refer to a computer design whose specifications are not published or generally available, making it impossible for third-party companies to provide products that work with the computer. See also open architecture. CLP See Cell Loss Priority; Certified Lotus Professional. CLS See Certified Lotus Specialist. CLTP See Connectionless Transport Protocol. cluster controller An IBM or IBM-compatible device located between a group of 3270 terminals and the mainframe computer. The cluster controller communicates between the computer and the terminals using SDLC (Synchronous Data Link Control) or a bisynchronous communications protocol. clustering A fault-tolerant technology designed to keep server availability at a very high level. Clustering groups servers and other network resources into a single system; if one of the servers in the cluster fails, the other servers can take over the workload. Clustering software also adds a load-balancing feature to make sure that processing is   codec distributed in such as way as to optimize system throughput. CLV See constant linear velocity. CMIP See Common Management Information Protocol. CMIS See Common Management Information Services. CMOS See Complementary Metal- Oxide Semiconductor. CNA See Certified Novell Administrator. CNE See Certified Novell Engineer. CNEPA See Certified Novell Engineer Professional Association. CNI See Certified Novell Instructor. CNP See Certified Network Professional. coax See coaxial cable. coaxial cable Abbreviated coax, pronounced “co-ax.” A high-capacity cable used in networking that contains a solid inner copper conductor surrounded by plastic insulation, and an outer braided copper or foil shield. Coaxial cable is used for broadband and baseband communications networks (and for cable television), because the cable is usually free from external interference and permits high transmission rates over long distances. See also fiber-optic cable; RG-58; RG-59; RG-62; thick Ethernet; thin Ethernet. COAXIAL CABLE codec codec 1. Acronym for coder/decoder, pronounced “coe-deck.” A device that converts analog signals (such as voice or video) into a digital bit stream suitable for transmission and then converts those digital signals back into analog signals at the receiving end.   Code Division Multiple Access 2. Acronym for compression/decompression, pronounced “coe-deck.” An overall term to describe the hardware and software used in processing animation, digital video, and stereo-quality audio. See also lossless compression; lossy compression. Code Division Multiple Access Abbreviated CDMA, also known as spread spectrum. A digital cellular standard approved by the Telecommunications Industry Association (TIA) in 1993 and known as IS-95. CDMA combines both data and voice into a single wireless network and can provide users with digital voice services, voice mail, text messaging, and caller ID. CDMA also increases system capacity up to 10 times that of analog systems. See also Advanced Mobile Phone Service; Cellular Digital Packet Data; wireless communications. cold boot The computer startup process that begins when you turn on power to the computer. You are doing a cold boot when you first turn on your computer. A cold boot might also be necessary if a program or the operating system crashes and freezes entirely. If your keyboard is operational, a warm boot may suffice. See also boot; warm boot. collaboration software A set of network- based applications that let users share information quickly and easily. See also whiteboard. collision In networking or communications, an attempt by two nodes to send a message on the same channel at exactly the same moment. See also Carrier Sense Multiple Access/ Collision Detection; token-ring network. colon The symbol used after the protocol name in a URL. See also Uniform Resource Locator. COM See Common Object Model; Component Object Model. COM 1–4 See COM port. command interpreter See command processor. command line Any interface between the user and the command processor that allows you to enter commands from the keyboard for execution by the operating system. See also graphical user interface; shell; text mode. command-line argument A parameter that alters the default mode of a command. In many operating systems, a commandline argument is one or more letters or numbers preceded by the / (slash) character. In Unix, a command-line argument may be called an option or a flag and is usually a single character preceded by a hyphen (as in -r). With some commands, you can group several switches. Sometimes called a command-line switch. See also command line. command processor The part of the operating system that displays the command prompt on the screen, interprets and   Common Hardware Reference Platform executes all the commands and filenames that you enter, and displays error messages when appropriate. Also called the command interpreter. The command processor also contains the system environment. command prompt A symbol (character or group of characters) on the screen that lets you know that the operating system is available and ready to receive input. Commercial Internet Exchange Abbreviated CIX, pronounced “kicks.” A connection point between ISPs. A location where top-tier ISPs maintain the routers used to route packets between their respective network segments. Common Application Environment Abbreviated CAE. A set of standards, developed by X/Open for application development, including standards for the operating system, compilers, software development tools, data management, networking, and the graphical user interface. common carrier A communications company, such as AT&T or MCI, that provides data and voice telecommunication services to the general public. See also Postal Telephone and Telegraph. Common Desktop Environment Abbreviated CDE. A set of specifications developed by the Common Open Software Environment (COSE) that defines an API for a common Unix graphical user interface. The specifications cover the interoperability of applications across different hardware platforms, multimedia and networking operations, as well as objectoriented technology and system administration issues. Common Gateway Interface Abbreviated CGI. A standard way that programs can interface with Web servers and allow them to run applications such as search engines and to access databases and other back-end applications. CGI defines the field specifics and control tags to be placed in an HTML document, the environment variables where the Web server places information for use by scripts, and the flow of information between client Web browser, the server, and the Web server scripts. CGI is platform-independent. See also HyperText Markup Language; script; Web server. Common Internet File System Abbreviated CIFS. A file system supported by Microsoft, DEC, Data General, SCO, and others, which allows users and organizations to run file systems over the Internet. CIFS is an extension to Microsoft’s Server Message Blocks (SMB) file-sharing protocol and allows users to share files over the Internet in the same way that they share files using networking services on Windows clients. See also WebNFS. Common Hardware Reference Platform Abbreviated CHRP. An open hardware architecture, based on the Power- PC and originally defined by IBM, that ensures compatibility between systems made by different manufacturers.   Common Management Information Protocol Common Management Information Protocol Abbreviated CMIP. The Open Systems Interconnection (OSI) management information protocol for network monitoring and control information, designated ISO 9596. CMIP includes fault management, configuration management, performance management, and security and accounting management. It is not widely available. See also Common Management Information Services; Simple Network Management Protocol. Common Management Information Services Abbreviated CMIS. The Open Systems Interconnect (OSI) standard functions for network monitoring and control. See also Common Management Information Protocol. Common name In Novell Directory Services, every object has a name that is unique within its context in the directory structure. This name is known as the Common name when it refers to users, nodes, or servers. See also Distinguished Name. Common Object Model Abbreviated COM. A specification from Microsoft and DEC to provide cross-platform interoperability across non-Windows platforms. COM was developed to allow networks using Microsoft’s OLE technology to communicate with networks using DEC’s Object- Broker technology. Common Object Request Broker Architecture Abbreviated CORBA. A standard from the Object Management Group (OMG), whose members include Sun Microsystems, Hewlett-Packard, DEC, and IBM, that enables communications between distributed object-oriented applications, regardless of the language they are written in and the hardware platform on which they run. CORBA uses Object Request Brokers to set up communications between objects and to invoke methods on behalf of these objects. CORBA competes with Microsoft’s Distributed Component Object Model (DCOM) and ActiveX technology. See also Distributed Component Object Model. Common Open Software Environment Abbreviated COSE, pronounced “cosy.” An industry group consisting of almost 100 members, organized to develop a standard graphical user interface for Unix, known as the Common Desktop Environment, or CDE. Original members included Sun Microsystems, Hewlett-Packard, IBM, SCO, and the UNIX Systems Group. Common Programming Interface for Communications Abbreviated CPI-C. A cross-platform API from IBM that interfaces to the Advanced Program-to-Program Communications (APPC) environment. CPI-C is designed to support a common environment for application execution across several IBM operating systems, including MVS, VS, OS/400, and OS/2-based systems.   Compact Disc-Interactive See also Advanced Peer-to-Peer Networking; Advanced Program-to-Program Communications; Advanced Interactive Executive; Multiple Virtual Storage. common share In Microsoft Windows 2000, system elements automatically shared by default when the operating system is installed or upgraded. Many common shares are also hidden shares. See also default shares; hidden share; share; sharing. communications/modem server In a network, a server equipped with a bank of modems, which can be shared by users for outgoing calls. See also access server. communications parameters Any of several settings required to allow computers to communicate successfully. In asynchronous transmissions, commonly used in modem communications, the settings for baud rate, number of data bits, number of stop bits, and parity parameters must all be correct. communications protocol 1. A standard way of communicating between computers or between computers and terminals. Communications protocols vary in complexity, ranging from Xmodem, a simple file-transfer protocol used to transfer files from one PC to another, to the seven-layer OSI Reference Model used as the theoretical basis for many large, complex computer networks. 2. A hardware interface standard, such as RS-232-C. communications satellite A satellite in geostationary orbit, acting as a microwave relay station. The satellite receives signals from a groundstation, amplifies them, and retransmits them on a different frequency to another groundstation. See also downlink; propagation delay; uplink. compact disc Abbreviated CD. A nonmagnetic, polished, optical disc used to store large amounts of digital information. A CD can store approximately 650MB of information, equivalent to more than 1700 lowdensity floppy disks. This storage capacity translates into approximately 300,000 pages of text or 72 minutes of music, all on a single 4.72-inch disc. Digital information is stored on the compact disc as a series of microscopic pits and smooth areas that have different reflective properties. A beam of laser light shines on the disc so that the reflections can be detected and converted into digital data. See also CD-Recordable; CD ReWritable; CD-ROM Extended Architecture; Compact Disc-Interactive; Compact Disc—Read- Only Memory; digital video disc. Compact Disc-Interactive Abbreviated CD-I. A hardware and software standard disc format for data, text, audio, still video images, and animated graphics. The standard also defines methods of encoding and decoding compressed data, as well as displaying data. See also compact disc; Compact Disc— Read-Only Memory.   Compact Disc—Read-Only Memory Compact Disc—Read-Only Memory Abbreviated CD-ROM. A high-capacity, optical storage device that uses the same technology used to make ordinary music discs to store large amounts of information. A single 4.72-inch disc can hold up to 650MB. CD-ROMs are important components of multimedia applications. They are also used to store encyclopedias, dictionaries, and other large reference works, as well as libraries of fonts and clip art for desktop publishing. CD-ROMs have replaced floppy disks as the distribution mechanism for software packages, including network operating systems and large applications; you can load the whole package from a single compact disc, and you can load an operating system from a set of discs. A CD-ROM uses the constant linear velocity data encoding scheme to store information in a single, spiral track, divided into many equal-length segments. To read data, the CD-ROM disk drive must increase the rotational speed as the read head gets closer to the center of the disk and must decrease as the head moves back out. See also CD-Recordable; Compact Disc-Interactive; constant angular velocity; High Sierra specification. Compaq Computer Corporation One of the world’s largest computer manufacturers, Compaq recently acquired the Digital Equipment Corporation (DEC), which boosted the company into the top three along with IBM and Hewlett-Packard. By acquiring DEC, Compaq gained a world-wide service and support structure, as well as access to DEC’s highly regarded hardware and software products. Compaq also shook up the computer industry when it introduced the first PC that cost less than $1,000. For more information about Compaq, see www.compaq.com . compatibility The extent to which a given piece of hardware or software conforms to an accepted standard, regardless of the original manufacturer. In hardware, compatibility is often expressed in terms of widely accepted models —this designation implies that the device will perform in the same way as the standard device. In software, compatibility is usually described as the ability to read data file formats created by another vendor’s software or the ability to work together and share data. See also plug-compatible. Competitive Local Exchange Carrier Abbreviated CLEC. A term coined from the Telecommunications Act of 1996 to describe the deregulated, competitive phone companies that will be able to offer local exchange service as well as long distance and international services, Internet access, and cable and video on-demand services. See also Incumbent Local Exchange Carrier; Local Exchange Carrier. compiler A program that converts a set of program language source code statements into a machine-readable form suitable for execution by a computer.   compressed file Most compilers do much more than this, however; they translate the entire program into machine language, while at the same time, they check your source code syntax for errors and then post error messages or warnings as appropriate. See also just-in-time compiler. Complementary Metal-Oxide Semiconductor Abbreviated CMOS, pronounced “See-moss.” A type of integrated circuit used in processors and for memory. Because CMOS devices operate at very high speeds and use little power, they generate little heat. In the PC, batterybacked CMOS memory is used to store operating parameters, such as the hard disk type, when the computer is switched off. complex instruction set computing Abbreviated CISC, pronounced “sisk.” A processor that can recognize and execute more than 100 different assembly-language, or low-level, instructions. CISC processors can be powerful, but the instructions take a high number of clock cycles to execute. This complexity is in contrast to the simplicity of reduced instruction set computing (RISC) processors, in which the number of available instructions has been cut to a minimum. RISC processors are common in workstations and can be designed to run up to 70 percent faster than CISC processors. See also assembly language; reduced instruction set computing. Component Object Model Abbreviated COM. A specification from Microsoft that defines how objects interact in the Windows environment. COM components can be written in any programming language and can be added to or removed from a program without requiring recompilation. COM is the foundation of the Object Linking and Embedding (OLE) and ActiveX specifications. See also ActiveX; Common Object Request Broker Architecture; Distributed Component Object Model. COM port In MS-DOS and Microsoft Windows, the device name used to denote a serial communications port. In versions of MS-DOS after 3.3, four COM ports are supported: COM1, COM2, COM3, and COM4. Earlier versions support only COM1 and COM2. compound document A document file that consists of information created by two or more applications, for example, a database document embedded within a wordprocessing document. Object Linking and Embedding (OLE) can link and embed documents and can be used to start the appropriate application program. See also Object Linking and Embedding. compressed file A file that has been processed by a special utility so that it occupies as little hard-disk space as possible. When the file is needed, the same program decompresses the file back into its original form so that it can be read by the computer. Popular compression techniques include schemes that replace commonly occurring sequences of characters by tokens that take up less space. Some utilities use Huffman   Compression Control Protocol coding to shrink a file, and others use adaptive Lempel-Ziv coding. See also data compression; file compression; PKZip; WinZip; ZIP file. Compression Control Protocol Abbreviated CCP. A protocol used with Pointto- Point Protocol (PPP) to configure, enable, and disable data compression algorithms at both ends of the point-to-point connection. CCP can support different compression algorithms in each direction of the connection. See also Point-to-Point Protocol. CompuServe Abbreviated CIS. A major provider of online services including e-mail, file downloading, forums on a variety of topics, chat rooms, and Internet access, as well as commercial services offered to a large number of business users. In 1998, Compu- Serve was bought by America Online. For more information on CompuServe, see www.compuserve.com . computation bound A condition in which the speed of operation of the processor actually limits the speed of program execution. The processor is limited by the number of arithmetic operations it can perform. See also input/output bound. computer account In Microsoft Windows 2000, an object in the Security Accounts Manager that describes a specific computer within a network domain. A computer account is added for each node added to the domain. Computer Associates International Abbreviated CAI. A leading supplier of enterprise applications and services to the corporate world, including defense contractors and Fortune 500 companies. CAI’s rapid expansion in recent years has been due to an aggressive acquisitions policy that has led to the incorporation of Legent and Cheyenne Software and to a joint venture with Fujitsu that created the object-oriented database Jasmine. CAI currently enjoys success with Unicenter TNG, a collection of applications and tools used to manage enterprise computing. For more information on CAI, see www.cai.com. Computer Emergency Response Team Abbreviated CERT. Founded in 1988 at Carnegie-Mellon University, CERT works with the Internet community to increase awareness of security issues; it conducts research into improving existing systems and provides 24-hour technical assistance service for responding to security incidents. Computer Management In Microsoft Windows 2000, the administrative tool used to manage a local or remote computer. Computer Management is a Microsoft Management Console (MMC) snap-in and replaces several Windows NT administrative tools, including Server Manager, User Manager for Domains, and Disk Administrator. See also Active Directory; Microsoft Management Console; snap-in.   concurrent license computer name 1. In Microsoft Windows NT, a name of up to 15 uppercase letters that identifies a specific computer to the other computers on the network. The computer name is created during installation and must be unique within the workgroup or domain; you can change the computer name using the Network applet in Control Panel. 2. In NetBIOS, a name of up to 15 characters that uniquely identifies a workstation to computers and users. Once a computer is named, NetBIOS can establish sessions between computers and use those links to exchange data between systems. These exchanges can be either NetBIOS requests or Server Message Block (SMB) data. Network applications use NetBIOS names to locate resources, although the Windows Sockets API is now more commonly used. See also NetBIOS; WinSock. Computer object In NetWare Directory Services, a leaf object representing a computer on the network. The Computer object’s properties can contain information such as the computer’s physical serial number and the name of the person to whom the computer is currently assigned. See also leaf object; Novell Directory Services. Computer Systems Research Group Abbreviated CSRG. The University of California, Berkeley, group responsible for the development of the Berkeley Software Distribution (BSD). CSRG was home to some remarkable programmers over the years and introduced into Unix many of the fundamental features we take for granted. The last BSD release, 4.4BSD, was made during 1993, and the group was disbanded shortly afterward. concentrator A repeater or hub that joins communications channels from several network nodes. Concentrators are not just simple wire-concentration centers, but also provide bridging, routing, and other management functions. concurrent When two or more programs (processes) have access to the processor at the same time and must share the system resources, they are said to be “running concurrently.” Because a computer can perform operations so quickly, the processes seem to be occurring at the same time, although actually they are not. See also multiprocessing; task; task switching; thread. concurrent license A software license that allows more than one person at a company to share an application over a network, providing that, at any given time, only one person is using it. Different versions of concurrent licensing allow a fixed number of people in an office to share one copy of an application and allow the application to be used on both desktop and portable PCs, rather than run only from the file server. See also application metering.   CONFIG.SYS CONFIG.SYS In MS-DOS and OS/2, a special text file containing settings that control the way the operating system works. In MS-DOS, the CONFIG.SYS file may contain 10 to 20 lines of entries. In OS/2, it is likely to contain between 70 and 100 lines of configuration information. CONFIG.SYS must be in the root directory of the default boot disk, normally drive C, and is read once as the system starts running. configuration The process of establishing your own preferred setup for an application, expansion board, computer system, or network. Most current software can establish a configuration for you automatically, although you may need to adjust that configuration to get the best results. See also Desktop Management Interface; Plug and Play. configuration file A file, created by an application or an operating system, containing configuration information specific to your own computing environment. Application configuration files may have a filename extension of CFG or SET; Windows configuration files use the INI filename extension. If you accidentally erase an application’s configuration file, the program will return to using its default settings. Although the program will continue to function, its configuration settings may not be suitable for your system. See also AUTOEXEC.BAT; CONFIG.SYS; NET.CFG. configuration management A term covering a wide range of network administration tasks, often performed by the network administrator, including: _ Maintaining a hardware database containing details of routers, bridges, and connections so that changes in the network can be made quickly in the event of a failure _ Adding and removing workstations and users to the network as needed _ Adding and configuring new servers and cabling systems as the network expands See also Desktop Management Interface. configuration register A 16-bit, userconfigurable value that determines how a Cisco router functions during router initialization. You can configure information in hardware by using jumpers and in software by specifying a hexadecimal number in configuration commands. congestion An excessive amount of traffic on the network, causing messages to be blocked for long periods of time and adversely affecting network performance. You may see a very slow response from a server, or you may see an error message telling you that no ports are available at the present time for the service or host you are requesting. See also Ethernet meltdown. connectionless A protocol in which the source and destination addresses are included inside each packet so that a direct connection between sender and receiver or an established session between nodes is not required for communications. In a connectionless service, data packets may not reach their destination in the same order in which   connection speed they were sent. UDP is a connectionless transport service. See also connection-oriented; User Datagram Protocol. Connectionless Network Protocol Abbreviated CLNP. An Open Systems Interconnect (OSI) protocol that provides the OSI Connectionless Network Service for the delivery of data. It uses datagrams that include addressing information to route network messages. CLNP is used for LANs rather than WANs. CLNP is the OSI equivalent of IP (Internet Protocol). See also Connection-Oriented Network Service. Connectionless Transport Protocol Abbreviated CLTP. An Open Systems Interconnect (OSI) protocol that provides end-to-end transport data addressing and error correction, but does not guarantee delivery or provide any flow control. CLTP is the OSI equivalent of UDP. See also Connection-Oriented Network Service; User Datagram Protocol. Connection Admission Control Abbreviated CAC. An Asynchronous Transfer Mode (ATM) function that determines whether a virtual circuit connection request will be accepted. See also Asynchronous Transfer Mode. connection number A number assigned to a workstation that attaches to a server; it may be a different number each time the workstation attaches. Connection numbers are also assigned to print servers, as well as other applications and processes that use the server connections. connection-oriented A term used to describe a communications model that goes through three well-defined stages: establishing the connection, transferring the data, and releasing the connection. Analogous to a voice telephone call. In a connectionoriented service, data packets always reach their destination in the same order in which they were sent. TCP is a connection-oriented transport service. See also connectionless; Transmission Control Protocol. Connection-Oriented Network Service Abbreviated CONS. A data transmission service in which data is only transmitted once a connection has been established. Asynchronous Transfer Mode (ATM) is a connection-oriented service. See also Connectionless Network Protocol; Connectionless Transport Protocol. connection speed The speed of a data communications circuit. Some circuits are symmetrical and can maintain the same speed in both directions; others are asymmetrical and use a faster speed in one direction, usually the downstream side. Table C.1 compares the connection speeds available for several technologies. See also Asymmetric Digital Subscriber Line; cable modem; High-Bit-Rate Digital Subscriber Line; Integrated Services Digital Network; modem; Single-Line Digital Subscriber Line; Very-High-Bit-Rate Digital Subscriber Line.   connectivity connectivity The degree to which any given computer or application can cooperate with other network components purchased from other vendors, in a network environment in which resources are shared. connect time The period of time during which a user is logged on to the network. ConnectView An application with a graphical user interface used to manage NetWare Connect and Novell Internet Access Server (NIAS) communication servers. CONS See Connection-Oriented Network Service. cons See console. Conseil Européen pour la Researche Nucléaire Abbreviated CERN. The European Laboratory for Particle Physics located in Geneva, Switzerland, where Tim Berners-Lee and associates created the communications protocols that led to the World Wide Web. For more information on CERN, see www.cern.ch. console Sometimes abbreviated cons. The monitor and keyboard from which the server or host computer activity can be monitored. Certain operating system commands and utilities must be executed from the console TABLE C.1 CONNECTION SPEEDS constant angular velocity Abbreviated CAV. An unchanging speed of rotation. Hard disks use a CAV encoding scheme. The constant rate of rotation means that sectors on the disk are at the maximum density along the inside track of the disk. As the read/write heads move outward, the sectors must spread out to cover the increased track circumference, and therefore the datatransfer rate falls off. See also constant linear velocity. Constant Bit Rate Abbreviated CBR. A type of Asynchronous Transfer Mode (ATM) service reserved for voice or video or other data that must be transmitted at a constant rate and are intolerant of data loss. See also Asynchronous Transfer Mode; Available Bit Rate; Unspecified Bit Rate; Variable Bit Rate. constant linear velocity Abbreviated CLV. A changing speed of rotation. CDROM disk drives use a CLV encoding scheme to make sure that the data density remains constant. Information on a compact disc is stored in a single, spiral track, divided into many equal-length segments. To read the data, the CD-ROM disk drive must increase the rotational speed as the read head gets closer to the center of the disc and decrease as the head moves back out. See also constant angular velocity. Consultative Committee for International Telephony and Telegraphy Abbreviated CCITT. An organization based in Geneva that develops worldwide data communications standards. Three main sets of standards have been established: _ CCITT Groups 1–4 standards apply to facsimile transmissions. _ CCITT V series of standards apply to modems and error detection and correction methods. _ CCITT X series standards apply to LANs. Recommendations are published every four years. In 1993, after a reorganization, the name was changed to International Telecommunication Union (ITU), and even though ITU now creates recommendations and standards, you will still hear the CCITT standards mentioned. See also International Telecommunication Union. container One of the Java programming language classes that can contain graphical user interface components. Components in a container usually appear within the boundaries of that container. For example, the classes Dialog , Frame , and Window are all containers. See also Java. container administrator In Novell Directory Services, an administrator who is granted rights to a container object and all the objects that the container holds. A container administrator can be exclusive, indicating that no other administrator is allowed access to that container. See also container object; leaf object.   container object container object In Novell Directory Services, an object that can contain other objects and that is used to represent a logical or physical organizational element within a company, such as a department or a division. The Tree, Country, Organization, and Organizational Unit objects are all container objects. See also container administrator; Country object; leaf object; Organization object; Organizational Unit object; Tree object. container security equivalence See implied security equivalence. contention The competition between transmitting nodes for access to communications lines or network resources. The first device to gain access to a channel takes control of the channel. In the event of a collision, when two nodes attempt to transmit at the same time, some arbitration scheme must be invoked. See also Carrier Sense Multiple Access/ Collision Detection; token passing. context In Novell Directory Services, an object’s location within the Directory tree. The context is the full path to the container object in which the object is placed. If an object is moved from one container to another, it has changed contexts. See also container object; leaf object. context switching Switching from one program to another without ending the first program. Context switching allows you to operate several programs at the same time; but it differs from true multitasking in that when you are using one program, all the other programs loaded onto your system must halt. control character A nonprinting character with a special meaning. Control characters, such as Carriage Return, Line Feed, Bell, or Escape, perform a specific operation on a terminal, printer, or communications line. They are grouped together as the first 32 characters in the ASCII character set; see Appendix C for details. You can type a control character from the keyboard by pressing and holding the Ctrl key while you simultaneously press another key. For example, if you press and hold the Ctrl key and then press C, you generate Ctrl+C, also known as Break. Control character sequences are often used inside application programs as menu command shortcuts. See also American Standard Code for Information Interchange; Extended Binary Coded Decimal Interchange Code; Unicode. control code A sequence of one or more characters used for hardware control; also known as setup strings or escape sequences. Control codes are used with printers, modems, and displays. Printer control codes often begin with an escape character, followed by one or more characters that the printer interprets as commands it must perform rather than as text it must print. Control Panel In Microsoft Windows, a special system folder that contains applets used to look at or change configuration information. Each applet manages a single task such as adding or removing a program   cooperative multitasking from your system, setting up a connection to the Internet, or changing display settings. See also Network and Dial-up Connections. Controlled Access Unit Abbreviated CAU. An intelligent Multistation Access Unit (MAU) or multiport wiring hub for a token-ring network that allows ports to be switched on and off. controllerless modem A modem that shifts all the protocol management, error detection and correction, and data compression onto software running on the system’s CPU. This allows the modem manufacturer to make a much cheaper modem that does not require the memory or processing power of a traditional modem. Also known as a soft modem. control set That portion of the Microsoft Windows Registry that contains information required to boot the operating system and restore the last known good configuration. conventional memory The amount of memory accessible by MS-DOS in PCs using an Intel processor operating in real mode; normally the first 640KB. The designers of the original IBM PC made 640KB available to the operating system and applications and reserved the remaining space for internal system use, the BIOS, and video buffers. Although 640KB may not seem like much memory space now, it was ten times the amount of memory available in other leading personal computers available at the time. Since then, applications have increased in size to the point that 640KB is inadequate. See also expanded memory; extended memory; high memory area; memory management; protected mode. convergence The synchronization process that a network must go through immediately after a routing change takes place on the network. Convergence time is the time required to update all the routers on the network with routing information changes. See also routing table. convergence sublayer Abbreviated CS. One of two sublayers that make up the ATM Adaptation Layer; the other being the segmentation and reassembly sublayer (SAR). The convergence sublayer is the upper layer that provides the interface for the various ATM services, pads the cells, and adds headers and trailers before passing the cell to the SAR. See also ATM Adaptation Layer; segmentation and reassembly sublayer. cookie 1. A block of data sent from a server to a client in response to a request by the client. 2. On the World Wide Web, a block of data stored by the server on the system running the browser or client software, which can be retrieved by the server during a future session. A cookie contains information that can identify the user for administrative reasons or to prepare a custom Web page. cooperative multitasking A form of multitasking in which all running applications must work together to share system resources.   Copper Distributed Data Interface The operating system supports cooperative multitasking by maintaining a list of the active applications and the order in which they execute. When control is transferred to an application, the other applications cannot run until that application returns control back to the operating system once again. A cooperative multitasking system differs from a preemptive multitasking system, in which the operating system executes each application in turn for a specific period of time (depending on priority) before switching to the next application, regardless of whether the applications themselves return control to the operating system. See also context switching; time-slice multitasking. Copper Distributed Data Interface Abbreviated CDDI. A version of the FDDI standard designed to run on shielded and unshielded twisted-pair cable rather than on fiber-optic cable. CDDI is capable of 100Mbps data transfer rates. See also Fiber Distributed Data Interface. coprocessor A secondary processor used to speed up operations by taking over a specific part of the main processor’s work. The most common type of coprocessor is the math, or floating-point, coprocessor, which is designed to manage arithmetic calculations many times faster than does the main processor. copy left The copyright or General Public License of the Free Software Foundation (FSF), which states that any of the software developed using free software from the FSF must be distributed to others without charge. See also open source software. CORBA See Common Object Request Broker Architecture. COSE See Common Open Software Environment. counter log In Microsoft Windows 2000, a System Monitor log used to monitor data from local or remote computers about hardware use and system service activity. See also alert log; System Monitor; trace log. Country object In Novell Directory Services, a container object placed directly under the Root object in the Directory tree that defines the country for a specific part of your network. Country object names are defined by the International Organization for Standardization (ISO) and follow a standard naming convention. You must specify the Country object if you want to connect to external networks using X.500 directory services. CPDA See Certified PowerBuilder Developer Associate. CPDP See Certified PowerBuilder Developer Professional. CPE See customer-premises equipment. CPI-C See Common Programming Interface for Communications. cps See characters per second.   Ctrl+Alt+Del CPTS See Certified Performance and Tuning Specialist. CPU See central processing unit. cracker An unauthorized person who breaks into a computer system planning to do harm or damage or with criminal intent. The popular press often portrays crackers as people with exceptional talent for eluding detection, and some of them are, but most of them use a set of well-worn tricks to exploit common security weaknesses in the systems they target. See also attack; hacker; intruder. crash An unexpected program halt, sometimes due to a hardware failure but most often due to a software error, from which there is no recovery. You usually need to reboot the computer to recover after a crash. See also blue screen of death. CRC See cyclical redundancy check. critical error An error in a program that forces the program to stop until the user corrects the error condition. Examples of this kind of error are attempts to write to a floppy disk when there is no disk in the drive or to print to a printer that has run out of paper. crosstalk In communications, any interference from a physically adjacent channel that corrupts the signal and causes transmission errors. See also far-end crosstalk; near-end crosstalk. Cryptography API Abbreviated CAPI. An API first introduced in Microsoft Windows NT 4 that provides encryption and decryption functions for application developers. CS See convergence sublayer. CSE See Certified Solutions Expert. C shell In Unix, a popular command interpreter; pronounced “sea shell.” Developed at the University of California at Berkeley as part of the BSD development as an alternative to the Bourne shell. In addition to the features found in the Bourne shell, the C shell adds integer arithmetic, a history mechanism that can recall past commands in whole or in part, aliasing of frequently used commands, job control, and a built-in set of operators based on the C programming language used for writing shell scripts. See also Bash; Bourne shell; Korn shell; Linux; Unix shell. CSMA/CD See Carrier Sense Multiple Access/Collision Detection. CSRG See Computer Systems Research Group. CSU See Channel Service Unit. Ctrl+Alt+Del A three-key combination used to reset the machine and reload the operating system. By pressing Ctrl+Alt+Del, you initiate a warm boot, which restarts the computer without going through the power- on self tests (POSTs) normally run when the computer goes through a cold boot. In Windows 98 and 2000, the sequence opens a dialog box from which you can either end a task or shut down the   Ctrl+Break computer. Sometimes called the threefinger salute. See also warm boot. Ctrl+Break See Ctrl+C. Ctrl+C 1. A key combination recognized by Unix, MS-DOS, and other operating systems as a user-initiated interruption. Pressing Ctrl+C stops a batch file, macro, or command (for example, a directory listing, a search, or a sort). 2. A keyboard shortcut recognized by many programs as the instruction to copy the selected item. Ctrl key A key on the keyboard that, when pressed at the same time as another key, generates a nonprinting control character. On some keyboards, this key is labeled Control rather than Ctrl, but it produces the same function. CTS See Clear to Send. CUE See Certified Unicenter Engineer. current directory In many operating systems, the directory that will be searched first for any file you request, and the directory in which any new files will be stored (unless you specifically designate another directory). The current directory is not the same as the default directory, which is the directory that an application uses unless you specify another. See also dot; dot dot; period and doubleperiod directories. current drive In many operating systems, the disk drive that is being used for reading and writing files. The current drive is not the same as the default drive, which is the drive that an application uses unless you specify another. See also drive mapping. cursor A special character displayed on a monitor to indicate where the next character will appear when it is typed. In text or character mode, the cursor is usually a blinking rectangle or underline. In a graphical user interface, the mouse cursor can take many shapes, depending on the current operation and its screen location. cursor-movement keys The keys on the keyboard that move the cursor; also called cursor-control keys. These keys include the four labeled with arrows and the Home, Pg Up, End, and Pg Dn keys. On full-size keyboards, cursor-movement keys are often found on the numeric keypad; laptops and notebooks often have separate cursor-movement keys. CU-SeeMe A popular videoconferencing and videophone product that works over the Internet. CU-SeeMe was originally developed at Cornell University and is available free for the PC and the Macintosh. An enhanced commercial version that adds an electronic chalkboard is available from White Pine Software. The software is designed for personal use and for use in instruction and in business communications. See also White Pine Software.   Cyrix Customer Information Control System Abbreviated CICS. An IBMmainframe client/server program that manages transaction processing in IBM’s VM and MVS operating systems and that is scalable to thousands of users. It also provides password security, transaction logging for backup and recovery, and an activity log that can be used to analyze session performance, as well as facilities for creating, using, and maintaining databases. customer-premises equipment Abbreviated CPE. Communications equipment, either leased or owned, used at a customer site. cut through A technique used by some Ethernet hardware to speed up packet forwarding. Only the first few bytes of the packet are examined before it is forwarded or filtered. This process is much faster than looking at the whole packet, but it does allow some bad packets to be forwarded. See also store-and-forward. cut-through switching A type of switching used on a Token Ring network in which data is forwarded as soon as the first 20 or 30 bytes in a data frame have been read. After the header information has been read, the connection is established between input and output ports, and the transmission begins immediately. Sometimes known as onthe- fly switching. See also store-and-forward. CxBus See Cisco Extended Bus. cyclical redundancy check Abbreviated CRC. A complex calculation method used to check the accuracy of a digital transmission over a communications link or to ensure the integrity of a file stored on a hard disk. The sending computer uses one of several formulas to calculate a value from the information contained in the data, and this value is appended to the message block before it is sent. The receiving computer performs the same calculation on the same data and compares this number with the received CRC. If the two CRCs do not match, indicating a transmission error, the receiving computer asks the sending computer to retransmit the data. This procedure is known as a redundancy check because each transmission includes extra or redundant error-checking values as well as the data itself. As a security check, a CRC may be used to compare the current size of an executable file against the original size to determine if the file has been tampered with or changed in some way. See also checksum; Kermit; Xmodem; Ymodem; Zmodem. Cyrix A designer of microprocessors, including clones of popular Intel chips such as the 6x86MX and the MII (pronounced Mtwo). Cyrix was bought by National Semiconductor in 1998. For more information about Cyrix, see www.cyrix.com. See also Advanced Micro Devices, Inc.; Pentium; Pentium II; Pentium III.   DACL D Content Type Subtype Description Text Plain Unformatted text. Rich Text Formatted text. Multipart Mixed Multiple parts of different types. Alternative Multiple parts containing the same data in different formats. Digest Message digest with multiple parts all in the same format.   Minimum Cell Rate Content Type Subtype Description   MIPS