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Definitions & Terms

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C/C++/C# - C Sharp:

  • C is a structured, procedural programming language that has been widely used both for operating systems and applications and that has had a wide following in the academic community. Many versions of UNIX-based operating systems are written in C. C has been standardized as part of the Portable Operating System Interface (POSIX).
  • With the increasing popularity of object-oriented programming, C is being rapidly replaced as "the" programming language by C++, a superset of the C language that uses an entirely different set of programming concepts, and by Java, a language similar to but simpler than C++, that was designed for use in distributed networks.
  • C++ is an object-oriented programming (OOP) language that is viewed by many as the best language for creating large-scale applications. C++ is a superset of the C language. A related programming language, Java , is based on C++ but optimized for the distribution of program objects in a network such as the Internet. Java is somewhat simpler and easier to learn than C++ and has characteristics that give it other advantages over C++. However, both languages require a considerable amount of study.
  • C# (pronounced "C-sharp") is a new object-oriented programming language from Microsoft, which aims to combine the computing power of C++ with the programming ease of Visual Basic. C# is based on C++ and contains features similar to those of Java. C# is designed to work with Microsoft's .NET platform. Microsoft's aim is to facilitate the exchange of information and services over the Web, and to enable developers to build highly portable applications. C# simplifies programming through its use of Extensible Markup Language (XML) and Simple Object Access Protocol (SOAP) which allow access to a programming object or method without requiring the programmer to write additional code for each step. Because programmers can build on existing code, rather than repeatedly duplicating it, C# is expected to make it faster and less expensive to get new products and services to market.
  • Microsoft is collaborating with ECMA, the international standards body, to create a standard for C#. International Standards Organization (ISO ) recognition for C# would encourage other companies to develop their own versions of the language. Companies that are already using C# include Apex Software, Bunka Orient, Component Source, devSoft, FarPoint Technologies, LEAD Technologies, ProtoView, and Seagate Software.

C2 - Class C2:

  • See Class C2.

Cable Modem:

  • A cable modem is a device that enables you to hook up your PC to a local cable TV line and receive data at about 1.5 Mbps . This data rate far exceeds that of the prevalent 28.8 and 56 Kbps telephone modems and the up to 128 Kbps of Integrated Services Digital Network (ISDN) and is about the data rate available to subscribers of Digital Subscriber Line (DSL) telephone service. A cable modem can be added to or integrated with a set-top box that provides your TV set with channels for Internet access. In most cases, cable modems are furnished as part of the cable access service and are not purchased directly and installed by the subscriber.
  • A cable modem has two connections: one to the cable wall outlet and the other to a PC or to a set-top box for a TV set. Although a cable modem does modulation between analog and digital signals, it is a much more complex device than a telephone modem . It can be an external device or it can be integrated within a computer or set-top box. Typically, the cable modem attaches to a standard 10BASE-T Ethernet card in the computer.
  • All of the cable modems attached to a cable TV company coaxial cable line communicate with a Cable Modem Termination System (CMTS) at the local cable TV company office. All cable modems can receive from and send signals only to the CMTS, but not to other cable modems on the line. Some services have the upstream signals returned by telephone rather than cable, in which case the cable modem is known as a telco-return cable modem.
  • The actual bandwidth for Internet service over a cable TV line is up to 27 Mbps on the download path to the subscriber with about 2.5 Mbps of bandwidth for interactive responses in the other direction. However, since the local provider may not be connected to the Internet on a line faster than a T-carrier system at 1.5 Mpbs, a more likely data rate will be close to 1.5 Mpbs. Leading companies using cable TV to bring the Internet to homes and businesses are @Home and Time-Warner. In addition to the faster data rate, an advantage of cable over telephone Internet access is that it is a continuous connection.

Cable Modem Termination System - CMTS:

  • A cable modem termination system (CMTS) is a component that exchanges digital signals with cable modems on a cable network. A cable modem termination system is located at the local office of a cable television company.
  • A data service is delivered to a subscriber through channels in a coaxial cable or optical fiber cable to a cable modem installed externally or internally to a subscriber's computer or television set. One television channel is used for upstream signals from the cable modem to the CMTS, and another channel is used for downstream signals from the CMTS to the cable modem. When a CMTS receives signals from a cable modem, it converts these signals into Internet Protocol (IP) packets, which are then sent to an IP router for transmission across the Internet. When a CMTS sends signals to a cable modem, it modulates the downstream signals for tranmission across the cable to the cable modem. All cable modems can receive from and send signals to the CMTS but not to other cable modems on the line.

Cache Memory:

  • Pronounced cash, a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching. A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.
  • Some memory caches are built into the architecture of microprocessors. The Intel 80486 microprocessor, for example, contains an 8K memory cache, and the Pentium has a 16K cache. Such internal caches are often called Level 1 (L1) caches. Most modern PCs also come with external cache memory, called Level 2 (L2) caches. These caches sit between the CPU and the DRAM. Like L1 caches, L2 caches are composed of SRAM but they are much larger.
  • When data is found in the cache, it is called a cache hit, and the effectiveness of a cache is judged by its hit rate. Many cache systems use a technique known as smart caching, in which the system can recognize certain types of frequently used data. The strategies for determining which information should be kept in the cache constitute some of the more interesting problems in computer science. Also see Disk Cache


  • CallXML is a language based on the Extensible Markup Language (XML) that lets a company describe a phone-to-Web site application in terms of how the call would be handled at the Web site and how it would interact with the caller based on keyed-in or voice responses. CallXML is similar to other voice markup languages such as VoiceXML and Microsoft's WTE.
  • <a> <img></a> Basically, CallXML is used to describe the user interface of a telephone, VoIP, or multimedia application to a CallXML browser. A CallXML browser then uses that description to control and react to the call itself. According to a Voxeo, a vendor that supports CallXML, the markup language includes:
  • * Media action elements such as "playAudio" and "recordAudio" to describe what to be presented to the user during a call
  • * Call action elements such as "answer", "call" and "hangup" to describe how to control and route the call
  • * Logic action elements such as "assign," "clear" and "goto" to describe how to modify variables and interact with traditional
  • server-side Web logic such as Perl, other CGI languages, PHP or ASP
  • * Event elements such as "onTermDigit," "onHangup" to describe how to react to things the user can do during the call, such as pressing digits or hanging up
  • * Block elements that logically group actions & events together, so that one set of event handling elements can be used for several sequential actions
  • Whereas VoiceXML, another computer telephony language, is used with voice-based applications that provide access to Web content and information, CallXML aims to make it easy for Web developers to create applications that can interact with and control any number or type of calls. VoiceXML 1.0 was created through a collaboration of AT&T, IBM, Lucent Technologies, and Motorola.


  • In programming, canonical means "according to the rules." And non-canonical means "not according to the rules." In the early Christian church, the "canon" was the officially chosen text. In The New Hacker's Dictionary, Eric Raymond tells us that the word meant "reed" in its Greek and Latin origin, and a certain length of reed came to be used as a standard measure. In some knowledge areas, such as music and literature, the "canon" is the body of work that everyone studies. The terms are sometimes used to distinguish whether a programming interface follows a particular standard or precedent or whether it departs from it.

CAPI - Common Application Programming Interface:

  • CAPI (Common Application Programming Interface) is an international standard interface that applications can use to communicate directly with ISDN equipment. Using CAPI, an application program can be written to initiate and terminate phone calls in computers equipped for ISDN. Computer telephony (CTI ) applications can be written for ISDN users. Officially, CAPI is referred to as Common-ISDN-API and is embodied in ETS 300 838 ("Integrated Service Digital Network (SDN); Harmonized Programmable Communication Interface (HPCI) for ISDN." ETS refers to standards from the European Telecommunication Standards Institute (ETSI). The standard is internationalized by recommendation T.200 "Programmable communication interface for terminal equipment connected to ISDN" from the International Telecommunications Union (ITU).
  • CAPI can be compared with the Intel-Microsoft "standard" programming interface, the Telephony Application Program Interface (TAPI). CAPI includes signaling and data exchange protocols not included in TAPI. TAPI services are also provided by CAPI and a TAPI application can be mapped to CAPI functions.
  • Because ISDN is widely used in Germany, the Netherlands, and Scandinavia, users there are accustomed to receiving a CAPI software program or driver along with their ISDN computer card . Not all CAPI driver versions support all functions. CAPI provides functions that are independent from physical signaling protocols that vary among different countries. CAPI supports these protocols: HDLC, HDLC inverted, SDLC, LAPD, X.75, Voice (PCM), Fax group 3 (T.30), V.110/V.120, and compression (V.xx).


  • Cardinal refers to a basic or primary value. Examples of cardinal numbers are 1, 7, 9, and 123. A cardinal rule is a rule that is basic or essential. Cardinal numbers can be contrasted with ordinal numbers.


  • The term cardinality refers to the number of cardinal (basic) members in a SET . Cardinality can be finite (a non-negative integer) or infinite. For example, the cardinality of the set of people in the United States is approximately 270,000,000; the cardinality of the set of integers is denumerably infinite.
  • In tables, the number of rows (or tuples) is called the cardinality. In practice, tables always have positive-integer cardinality. The reason for this is simple: tables with no rows, or with a negative number of rows, cannot exist. In theory, however, tables with denumerably infinite cardinality can exist. An example is a multiplication table of non-negative integers in which entries are implied for all possible values:
  • 0 1 2 3 ..
  • 1 1 2 3 ..
  • 2 2 4 6 ..
  • 3 3 6 9 ..
  • ::::
  • The concept of cardinality is of interest to set theoreticians because it has been used to demonstrate that some infinite sets are larger than others. The cardinality of the set of real numbers is greater than the cardinality of the set of integers, even though both sets are infinite. The cardinality of the set of integers is called aleph-null or aleph-nought; the cardinality of the set of real numbers is called aleph-one.
  • One of the great mysteries of mathematics is contained in the question, "What is the cardinality of the set of points on a geometric line?" Generally it is presumed to be aleph-one; the set of points on a line is thought to correspond one-to-one with the set of real numbers. This is by no means a trivial supposition, and has become known as the Continuum Hypothesis.

Carrier Sense Multiple Access/Collision Detect - CSMA/CD:

  • Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is the protocol for carrier transmission access in Ethernet networks. On Ethernet, any device can try to send a frame at any time. Each device senses whether the line is idle and therefore available to be used. If it is, the device begins to transmit its first frame. If another device has tried to send at the same time, a collision is said to occur and the frames are discarded. Each device then waits a random amount of time and retries until successful in getting its transmission sent. CSMA/CD is specified in the IEEE 802.3 standard.

CAT2/3/4/5/6 - Category 2/3/4/5/6 Cable:

  • The type of cable used for 10BaseT/100BaseT networking. CAT5 is a standard type known industry-wide as "Category 5 Unshielded Twisted Pair Cable", or "CAT5" for short. Inside the jacket of any grade of unshielded twisted pair cable (UTP) are four individual pairs of wires, with the wires of each individual pair twisted around each other in a spiral fashion that helps minimize and cancel out some of the problems that can disrupt data and/or voice communication over the wire, such as crosstalk and interference ("noise") from outside electrical sources, such as motors and flourescent lights. In the 10BaseT/100BaseT ethernet standards, only two of these pairs are actually used, one to transmit data and the other to receive. There are currently some higher-speed networking technologies using UTP cable that require use of all four pairs, and it is likely that other future technologies will as well.
  • The "category" system for UTP was devised a number of years ago to differentiate between the capacity of different grades of UTP to carry network traffic at different speeds. Categories 1 and 2 are obsolete, a brief description of Categories 3, 4 and 5 is as follows:
  • Category 3 (CAT3): essentially "voice grade" (telephone) cable, but capable of handling data traffic at a frequency of up to 15 MHz over a length of up to 100 meters.
  • Category 4 (CAT4): "data grade", capable of handling data and voice traffic at a frequency of up to 20 MHz over a length of up to 100 meters.
  • Category 5 (CAT5): "data grade", capable of handling data and voice traffic at a frequency of up to 100 MHz over a length of up to 100 meters.

CDMA - Code Division Multiple Access:

  • CDMA (code-division multiple access) refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.
  • CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes; this enhances privacy and makes cloning difficult.
  • The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft handoff , which minimizes signal breakup as a handset passes from one cell to another. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes. CDMA is compatible with other cellular technologies; this allows for nationwide Roaming.
  • The original CDMA standard, also known as CDMA One and still common in cellular telephones in the U.S., offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and wideband CDMA deliver data many times faster.

CDSL - Consumer Digital Subscriber Line

  • Consumer Digital Subscriber Line (CDSL) is a version of Digital Subscriber Line (DSL) service, trademarked by Rockwell Corp., that is somewhat slower than Asymmetric DSL (ADSL) - up to 1 Mbps downstream, probably less upstream - and has the advantage that a splitter does not need to be installed at the user's end. Rockwell no longer provides information about CDSL at its Web site and it does not appear to be marketing it.

CFML - ColdFusion Markup Language:

  • See ColdFusion Markup Language.

CGI - Common Gateway Interface:

  • See Common Gateway Interface.

Channel Definition Format:

  • The Channel Definition Format (CDF) is a file format from Microsoft that lets you create a file that defines a Web "channel ," which is a preselected Web site or group of related Web sites. To use the channel, a user needs to have the Microsoft Internet Explorer 4 or later browser . The CDF file identifies the Web page and subpages that the user sees after selecting a channel on the browser. The file may also identify subpages that may be selected from the main channel page. A channel developer for a Web site puts the CDF file on the Web server. A user who clicks on a channel (for example, from the Internet Explorer channel menu bar) is actually specifying the Uniform Resource Locator or Internet file name of the Channel Definition File that defines the channel.
  • The Channel Definition Format is an application of Extensible Markup Langugage (XML ) that Microsoft is proposing as a standard way to describe a Web site channel. In Internet Explorer 5, the channel user implementation has been changed. The Channel Bar that formerly appeared automatically when Windows was started has been removed. Channels are now accessed as a special folder in the Favorites menu.

CHAP - Challenge-Handshake Authentication Protocol:

  • CHAP, or Challenge-Handshake Authentication Protocol, is a more robust and secure method of negotiating communications with another computer or network. A method more secure relative to the PAP or Password Authentication Procedure. A breakdown of how CHAP functions is as follows:
  • 1) Upon establishing a comm link between a calling and responding computing systems, the receiving system following in kind by transmitting a "challenge message" request to the calling host. The calling/requesting system then responds to the "challenge message" request via a "value" to a variable utilizing a unidirectional hash function.
  • 2) The called system then performs a comparison of the received response to the "challenge message" to that of the expected hash value calculated by the called system.
  • 3) Upon agreement of the calculated hash value, between the called and receiving/requested system, authentication is acknowledged and granted. Upon failure, usually resulting in termination of the connection.
  • Note: during any time of the CHAP connection, the called server may perform another "challenge message" request. It's because CHAP performs redundant "challenge message" actives during a comm session that CHAP is shown to be an inherently more secure means of communication compared to PAP. Both CHAP and PAP are defined in RFC1334.


  • A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, it's assumed that the complete transmission was received. Both TCP and UDP communication layers provide a checksum count and verification as one of their services.


  • In a UNIX-based operating system , chmod (change mode) is a command used by a file owner or administrator to change the definition of access permissions to a file or set of files.

CIDR - Classless Inter-Domain Routing:

  • See Classless Inter-Domain Routing.


  • In object-oriented programming, a class is a template definition of the methods and variables in a particular kind of object. Thus, an object is a specific instance of a class; it contains real values instead of variables. The class is one of the defining ideas of object-oriented programming. Among the important ideas about classes are:
  • * A class can have subclasses that can inherit all or some of the characteristics of the class. In relation to each subclass, the class becomes the superclass.
  • * Subclasses can also define their own methods and variables that are not part of their superclass.
  • * The structure of a class and its subclasses is called the class hierarchy.

Class C2:

  • Class C2 is a security rating established by the U.S. National Computer Security Center (NCSC ) and granted to products that pass Department of Defense (DoD) Trusted Computer System Evaluation Criteria (TCSEC) tests. A C2 rating ensures the minimum allowable levels of confidence demanded for government agencies and offices and other organizations that process classified or secure information. TCSEC standards were established in the 1985 DoD document, Department of Defense Trusted Computer System Evaluation Criteria, known unofficially as the "Orange Book" (evaluation criteria for networks, the Trusted Network Interpretation is known as the "Red Book"). NCSC's objectives in publishing the document were: to provide DoD users with a means of ensuring the security of sensitive information; to provide manufacturers with guidelines to be followed; and to provide those involved in acquisitions with criteria for specifications.
  • According to TCSEC, system security is evaluated at one of four broad levels, ranging from class D to class A1, each level building on the previous one, with added security measures at each level and partial level. Class D is defined as Minimum Security; systems evaluated at this level have failed to meet higher level criteria. Class C1 is defined as Discretionary Security Protection; systems evaluated at this level meet security requirements by controlling user access to data. Class C2, defined as Controlled Access Protection adds to C1 requirements additional user accountability features, such as login procedures. Class B1 is defined as Labeled Security Protection; systems evaluated at this level also have a stated policy model, and specifically labeled data. Class B2, defined as Structured Protection, adds to B1 requirements a more explicit and formal security policy. Class B3, defined as Security Domains, adds stringent engineering and monitoring requirements and is highly secure. Class A1 is defined as Verified Design ; systems evaluated at this level are functionally equivalent to B3 systems, but include more formal analysis of function to assure security.

Classless Inter-Domain Routing - CIDR:

  • Classless Inter-Domain Routing (CIDR) is a way to allocate and specify the Internet addresses used in inter-domain router more flexibly than with the original system of Internet Protocol (IP ) address classes. As a result, the number of available Internet addresses has been greatly increased. CIDR is now the routing system used by virtually all gateway hosts on the Internet's backbone network. The Internet's regulating authorities now expect every Internet service provider (ISP) to use it for routing.
  • The original Internet Protocol defines IP address es in four major classes of address structure, Classes A through D. Each of these classes allocates one portion of the 32-bit Internet address format to a network address and the remaining portion to the specific host machines within the network specified by the address. One of the most commonly used classes is (or was) Class B, which allocates space for up to 65,533 host addresses. A company who needed more than 254 host machines but far fewer than the 65,533 host addresses possible would essentially be "wasting" most of the block of addresses allocated. For this reason, the Internet was, until the arrival of CIDR, running out of address space much more quickly than necessary. CIDR effectively solved the problem by providing a new and more flexible way to specify network addresses in routers. (With a new version of the Internet Protocol - IPv6 - a 128-bit address is possible, greatly expanding the number of possible addresses on the Internet. However, it will be some time before IPv6 is in widespread use.)
  • Using CIDR, each IP address has a network prefix that identifies either an aggregation of network gateways or an individual gateway. The length of the network prefix is also specified as part of the IP address and varies depending on the number of bits that are needed (rather than any arbitrary class assignment structure). A destination IP address or route that describes many possible destinations has a shorter prefix and is said to be less specific. A longer prefix describes a destination gateway more specifically. Routers are required to use the most specific or longest network prefix in the routing table when forwarding packets.
  • A CIDR network address looks like this:
  • The "" is the network address itself and the "18" says that the first 18 bits are the network part of the address, leaving the last 14 bits for specific host addresses. CIDR lets one routing table entry represent an aggregation of networks that exist in the forward path that don't need to be specified on that particular gateway, much as the public telephone system uses area codes to channel calls toward a certain part of the network. This aggregation of networks in a single address is sometimes referred to as a supernet.
  • CIDR is supported by The Border Gateway Protocol, the prevailing exterior (interdomain) gateway protocol. (The older exterior or interdomain gateway protocols, Exterior Gateway Protocol and Routing Information Protocol, do not support CIDR.) CIDR is also supported by the OSPF interior or intradomain gateway protocol.

Class of Service - CoS:

  • Class of Service (CoS) is a way of managing traffic in a network by grouping similar types of traffic (for example, e-mail, streaming video, voice, large document file transfer) together and treating each type as a class with its own level of service priority. Unlike Quality of Service (QoS) traffic management, Class of Service technologies do not guarantee a level of service in terms of bandwidth and delivery time; they offer a "best-effort." On the other hand, CoS technology is simpler to manage and more scalable as a network grows in structure and traffic volume. One can think of CoS as "coarsely-grained" traffic control and QoS as "finely-grained" traffic control.
  • There are three main CoS technologies:
  • * 802.1p Layer 2 Tagging
  • * Type of Service (ToS)
  • * Differentiated Services (DiffServ)
  • 802.1p Layer 2 Tagging and ToS make use of three bits in the layer 2 packet header that can be used to specify priority. Since three bits does not allow for much sophistication in managing traffic, a new protocol, Differentiated Services (DS or DiffServ), has been developed in draft form by an IETF Working Group. Differentiated Services uses a different approach to managing packets than simple priority labeling. It uses an indication of how a given packet is to be forwarded, known as the Per Hop Behavior (PHB). The PHB describes a particular service level in terms of bandwidth, queueing theory, and dropping (discarding the packet) decisions. The Differentiated Services protocol exists as a set of related working documents from the Internet Engineering Task Force (IETF).

Clear Channel/Clear 64:

  • See Bipolar 8-zero Substitution.

CMTS - Cable Modem Termination System:

  • See Cable Modem Termination System.

COBOL - Common Business Oriented Language:

  • Common Business Oriented Language (COBOL) was the first widely-used high-level programming language for business applications. Many payroll, accounting, and other business application programs written in COBOL over the past 35 years are still in use and it is possible that there are more existing lines of programming code in COBOL than in any other programming language. While the language has been updated over the years, it is generally perceived as out-of-date and COBOL programs are generally viewed as legacy applications.
  • COBOL was an effort to make a programming language that was like natural English, easy to write and easier to read the code after you'd written it. The earliest versions of the language, COBOL-60 and -61, evolved to the COBOL-85 standard sponsored by the Conference on Data Systems Languages (CODASYL).
  • In years immediately preceding the year 2000 , many COBOL programs required change to accommodate the new century. Programmers with COBOL skills were in demand by major corporations and contractors. A number of companies have updated COBOL and sell development tools that combine COBOL programming with relational databases and the Internet.


  • ColdFusion, developed by Allaire which has recently merged with Macromedia, is a popular and sophisticated set of products for building Web sites and serving pages to users. With ColdFusion, a company can build a content database using input template s and combine these with application programs to create a Web site in which pages are developed dynamically as they are served. ColdFusion consists of ColdFusion Studio, which is used to build a site, and ColdFusion Server, which serves the pages to users. ColdFusion Studio is described as "a complete integrated development environment (IDE)" and ColdFusion Server as "a deployment platform."
  • The most valuable feature for many companies that use ColdFusion is the ability to build Web sites as "piece parts" that can be stored in a database and then reassembled for Web pages, e-mail newsletters, and other uses. ColdFusion provides a visual interface for building Web pages directly or for building the "piece parts." For example, a newspaper with a Web site can have a reporter enter a story, dateline, author, and other information, using a text entry form free of all Web page formatting and structure details or language tag s. (The newspaper uses ColdFusion to design the forms and to define the database.) The content entered by the reporter is later gathered and formatted into a Web page when it is requested. The reporter is free from having to understand HTML and other details. ColdFusion is also a popular tool for building e-commerce sites.
  • ColdFusion has its own page markup language, called ColdFusion Markup Language (CFML). CFML encompasses the Web's Hypertext Markup Language (HTML) and Extensible Markup Language (XML). A just-in-time (JIT) compiler turns the CFML into the pages that get served. Allaire emphasizes that their product set is open and "extensible". Applications can access databases using Microsoft's OLE DB, Open Database Connectivity (ODBC), or driver s that access Oracle and Sybase databases. ColdFusion can be coordinated with distributed applications that use Common Object Request Broker Architecture (CORBA) or Microsoft's Distributed Component Object Model (DCOM) to interact with other network applications.
  • Allaire also says that ColdFusion is scalable, allowing both the size of a database and the number of users that can be served to grow. For large Web sites, multiple ColdFusion servers can be run together as a cluster.

ColdFusion Markup Language - CFML:

  • ColdFusion Markup Language (CFML) is a Web page markup language that allows a Web site developer to create pages with variable information (text or graphics) that is filled in dynamically (on the fly) in response to variables such as user input. Along with the usual Hypertext Markup Language (HTML) tags that determine page layout and appearance, the page creator uses CFML tags to bring in content based on the results of a database query or user input. CMFL is a proprietary language developed for use with ColdFusion, a product from Allaire.
  • CFML tags perform all server-side tasks (such as database queries) by condensing complex processes, that would normally require knowledge of programming languages such as Java or C++, into four basic tags: CFQUERY, which is used to submit a structured query language (SQL) request to the database; CFOUTPUT, which is used to display the result of a query; and CFTABLE or CFCOL, which are used to display a preformatted table containing the results of a set of queries. Files created with CFML are saved as ColdFusion templates and use a ".cfm" extension.


Common Gateway Interface - CGI:

  • The Common Gateway Interface (CGI) is a standard way for a Web server to pass a Web user's request to an application program and to receive data back to forward to the user. When the user requests a Web page (for example, by clicking on a highlighted word or entering a Web site address), the server sends back the requested page. However, when a user fills out a form on a Web page and sends it in, it usually needs to be processed by an application program. The Web server typically passes the form information to a small application program that processes the data and may send back a confirmation message. This method or convention for passing data back and forth between the server and the application is called the common gateway interface (CGI). It is part of the Web's Hypertext Transfer Protocol (HTTP).
  • If you are creating a Web site and want a CGI application to get control, you specify the name of the application in the uniform resource locator (URL ) that you code in an HTML file. This URL can be specified as part of the FORMS tags if you are creating a form. For example, you might code:
  • and the server at "" would pass control to the CGI application called "" to record the entered data and return a confirmation message. (The ".pl" indicates a program written in Perl but other languages could have been used.)
  • The common gateway interface provides a consistent way for data to be passed from the user's request to the application program and back to the user. This means that the person who writes the application program can makes sure it gets used no matter which operating system the server uses (PC, Macintosh, UNIX, OS/390, or others). It's simply a basic way for information to be passed from the Web server about your request to the application program and back again.
  • Because the interface is consistent, a programmer can write a CGI application in a number of different languages. The most popular languages for CGI applications are: C, C++, Java, and Perl. An alternative to a CGI application is Microsoft's Active Server Page (ASP), in which a script embedded in a Web page is executed at the server before the page is sent.

COM - Component Object Model:

  • Component Object Model (COM) is Microsoft's framework for developing and supporting program component objects. It is aimed at providing similar capabilities to those defined in the Common Object Request Broker Architecture (CORBA ), a framework for the interoperation of distributed objects in a network that is supported by other major companies in the computer industry. Whereas Microsoft's Object Linking and Embedding provides services for the compound document that users see on their display, COM provides the underlying services of interface negotiation, life cycle management (determining when an object can be removed from a system), licensing, and event services (putting one object into service as the result of an event that has happened to another object). COM includes COM+, Distributed Component Object Model (DCOM), and ActiveX interfaces and programming tools.

COM+ - Component Object Model+:

  • COM+ is an extension of Component Object Model (COM), Microsoft's strategic building block approach for developing application programs. COM+ is both an object-oriented programming architecture and a set of operating system services. It adds to COM a new set of system services for application components while they are running, such as notifying them of significant events or ensuring they are authorized to run. COM+ is intended to provide a model that makes it relatively easy to create business applications that work well with the Microsoft Microsoft Transaction Server (MTS) in a Windows NT or subsequent system. It is viewed as Microsoft's answer to the Sun Microsystems-IBM-Oracle approach known as Enterprise JavaBeans (EJB).
  • Among the services provided by COM+ are:
  • * An event registry that allows components to publish the possibility of an event and other components to subscribe to be notified when the event takes place. For example, when a sales transaction is completed, it could trigger an event that would allow other programs to be notified for subsequent processing.
  • * The interception of designated system requests for the purpose of ensuring security
  • * The queues of asynchronously received requests for a service
  • How COM+ Works Briefly
  • A "component" is a building block program that is self-describing. This means that it can be run with a mix of other components and each will be able to understand the capabilities and characteristics of the other components. Practically, this means that a new application can be built by reusing components already known to exist and without having to compile the application. It also makes it relatively easy to distribute different components of an application among different computers in a network. Microsoft's Distributed Component Object Model (DCOM) adds interfaces to do this.
  • In addition to its self-description, a component consists of one or more classes that describe objects and the methods or actions that can be performed on an object. A class (or coclass in COM+ terminology) has properties described in an interface (or cointerface). The class and its interface are language-neutral.
  • Associated with the class are one or more methods and fields that are implemented in a specific language such as C++ or Java or a visual programming environment. When you instantiate a class, you create an object (something real that can be executed in the computer). Sometimes the term "class" is also used for the instantiated object (which can be confusing).
  • Using COM, objects (or classes) and their methods and associated data are compiled into binary executable modules, that are, in fact, files with a dynamic link library (DLL) or EXE file name suffix. A module can contain more than one class.

Complex Number:

  • A complex number is a quantity of the form v + iw, where v and w are real numbers, and i represents the unit imaginary numbers equal to the positive square root of -1. The SET C of all complex numbers corresponds one-to-one with the set R R of all ordered pairs of real numbers. The set C also corresponds one-to-one with the points on a geometric plane.
  • The set of complex numbers is two-dimensional, and a coordinate plane is required to illustrate them graphically. This is in contrast to the real numbers, which are one-dimensional, and can be illustrated by a simple number line. The rectangular complex number plane is constructed by arranging the real numbers along the horizontal axis, and the imaginary numbers along the vertical axis. Each point in this plane can be assigned to a unique complex number, and each complex number can be assigned to a unique point in the plane.


  • Compression is the reduction in size of data in order to save space or transmission time. For data transmission, compression can be performed on just the data content or on the entire transmission unit (including header data) depending on a number of factors.
  • Content compression can be as simple as removing all extra space characters, inserting a single repeat character to indicate a string of repeated characters, and substituting smaller bit strings for frequently occurring characters. This kind of compression can reduce a text file to 50% of its original size. Compression is performed by a program that uses a formula or algorithm to determine how to compress or decompress data.
  • Graphic image file formats are usually designed to compress information as much as possible (since these can tend to become very large files). When you send or receive information on the Internet, larger text files, either singly or with others as part of an archive file, may be transmitted in a zip, gzip, or other compressed format. WinZip is a popular Windows program that compresses files when it packages them in an archive.


  • A cookie is information that a Web site puts on your hard disk so that it can remember something about you at a later time. (More technically, it is information for future use that is stored by the server on the client side of a client/server communication.) Typically, a cookie records your preferences when using a particular site. Using the Web's Hypertext Transfer Protocol (HTTP ), each request for a Web page is independent of all other requests. For this reason, the Web page server has no memory of what pages it has sent to a user previously or anything about your previous visits. A cookie is a mechanism that allows the server to store its own information about a user on the user's own computer. You can view the cookies that have been stored on your hard disk (although the content stored in each cookie may not make much sense to you). The location of the cookies depends on the browser. Internet Explorer stores each cookie as a separate file under a Windows subdirectory. Netscape stores all cookies in a single cookies.txt fle. Opera stores them in a single cookies.dat file.
  • Cookies are commonly used to rotate the banner ads that a site sends so that it doesn't keep sending the same ad as it sends you a succession of requested pages. They can also be used to customize pages for you based on your browser type or other information you may have provided the Web site. Web users must agree to let cookies be saved for them, but, in general, it helps Web sites to serve users better.

CORBA - Common Object Request Broker Architecture:

  • Common Object Request Broker Architecture (CORBA) is an architecture and specification for creating, distributing, and managing distributed program object s in a network. It allows programs at different locations and developed by different vendors to communicate in a network through an "interface broker." CORBA was developed by a consortium of vendors through the Object Management Group (OMG), which currently includes over 500 member companies. Both International Organization for Standardization (ISO) and X/Open have sanctioned CORBA as the standard architecture for distributed objects (which are also known as components). CORBA 3 is the latest level.
  • The essential concept in CORBA is the Object Request Broker (ORB). ORB support in a network of clients and servers on different computers means that a client program (which may itself be an object ) can request services from a server program or object without having to understand where the server is in a distributed network or what the interface to the server program looks like. To make requests or return replies between the ORBs, programs use the General Inter-ORB Protocol (GIOP) and, for the Internet, its Internet Inter-ORB Protocol (IIOP). IIOP maps GIOP requests and replies to the Internet's Transmission Control Protocol (TCP) layer in each computer.
  • A notable hold-out from CORBA is Microsoft, which has its own distributed object architecture, the Distributed Component Object Model (DCOM ). However, CORBA and Microsoft have agreed on a gateway approach so that a client object developed with the Component Object Model will be able to communicate with a CORBA server (and vice versa).
  • Distributed Computing Environment (DCE ), a distributed programming architecture that preceded the trend toward object-oriented programming and CORBA, is currently used by a number of large companies. DCE will perhaps continue to exist along with CORBA and there will be "bridges" between the two. More information is available in our definitions of Internet Inter-ORB Protocol and Object Request Broker

CoS - Class of Service:

  • See Class of Service.


  • See Brute Force Cracking


  • A crawler is a program that visits Web sites and reads their pages and other information in order to create entries for a search engine index. The major search engines on the Web all have such a program, which is also known as a "spider" or a "bot." Crawlers are typically programmed to visit sites that have been submitted by their owners as new or updated. Entire sites or specific pages can be selectively visited and indexed. Crawlers apparently gained the name because they crawl through a site a page at a time, following the links to other pages on the site until all pages have been read.
  • The crawler for the AltaVista search engine and its Web site is called Scooter . Scooter adheres to the rules of politeness for Web crawlers that are specified in the Standard for Robot Exclusion (SRE). It asks each server which files should be excluded from being indexed. It does not (or can not) go through firewalls. And it uses a special algorithm for waiting between successive server requests so that it doesn't affect response time for other users.


  • Depending on its usage, crypto can be a short form for cryptography or for encryption . The term is sometimes used to broadly encompass the major aspects and issues of developing and using cryptography technologies.


  • Cryptography is the science of information security. The word is derived from the Greek kryptos, meaning hidden. Cryptography is closely related to the disciplines of cryptology and cryptanalysis . Cryptography includes techniques such as microdots, merging words with images, and other ways to hide information in storage or transit. However, in today's computer-centric world, cryptography is most often associated with scrambling plaintext (ordinary text, sometimes referred to as cleartext) into ciphertext (a process called encryption), then back again (known as decryption). Individuals who practice this field are known as cryptographers.
  • Modern cryptography concerns itself with the following four objectives:
  • 1) Confidentiality (the information cannot be understood by anyone for whom it was unintended)
  • 2) Integrity (the information cannot be altered in storage or transit between sender and intended receiver without the alteration being detected)
  • 3) Non-repudiation (the creator/sender of the information cannot deny at a later stage his or her intentions in the creation or transmission of the information)
  • 4) Authentication (the sender and receiver can confirm each other?s identity and the origin/destination of the information)
  • Procedures and protocol s that meet some or all of the above criteria are known as cryptosystems. Cryptosystems are often thought to refer only to mathematical procedures and computer programs; however, they also include the regulation of human behavior, such as choosing hard-to-guess passwords, logging off unused systems, and not discussing sensitive procedures with outsiders.
  • The origin of cryptography is usually dated from about 2000 BC, with the Egyptian practice of hieroglyphics. These consisted of complex pictograms, the full meaning of which was only known to an elite few. The first known use of a modern cipher was by Julius Caesar (100 BC to 44 BC), who did not trust his messengers when communicating with his governors and officers. For this reason, he created a system in which each character in his messages was replaced by a character three positions ahead of it in the Roman alphabet.
  • In recent times, cryptography has turned into a battleground of some of the world's best mathematicians and computer scientists. The ability to securely store and transfer sensitive information has proved a critical factor in success in war and business.
  • Because governments do not wish certain entities in and out of their countries to have access to ways to receive and send hidden information that may be a threat to national interests, cryptography has been subject to various restrictions in many countries, ranging from limitations of the usage and export of software to the public dissemination of mathematical concepts that could be used to develop cryptosystems. However, the Internet has allowed the spread of powerful programs and, more importantly, the underlying techniques of cryptography, so that today many of the most advanced cryptosystems and ideas are now in the public domain.

C Shell:

  • C shell is the UNIX shell (command execution program, often called a command interpreter) created by Bill Joy at the University of California at Berkeley as an alternative to UNIX's original shell, the Bourne shell. These two UNIX shells, along with the Korn shell, are the three most commonly used shells. The C shell program name is csh, and the shell prompt (the character displayed to indicate readiness for user input) is the % symbol. The C shell was invented for programmers who prefer a syntax similar to that of the C programming language.
  • The other popular member of the C shell family is called tcsh (for Tab C shell) and is an extended version of C shell. Some of tcsh's added features are: enhanced history substitution (which allows you to reuse commands you have already typed), spelling correction, and word completion (which allows you to type the first couple of letters in a word and hit the tab key to have the program complete it).
  • Once considered "bug gy", the C shell has had a number of different versions developed to overcome the flaws in the original program. Most often, only experienced users prefer to use the C shell. C is frequently the default shell at universities and research organizations and is the default on many systems, especially those derived from Berkeley UNIX.

CSMA/CD - Carrier Sense Multiple Access/Collision Detect:

  • See Carrier Sense Multiple Access/Collision Detect.

CSU/DSU - Channel Service Unit/Data Service Unit:

  • A Channel Service Unit/Data Service Unit (CSU/DSU) is a hardware device about the size of an external modem that converts a digital data frame from the communications technology used on a local area network (LAN ) into a frame appropriate to a wide-area network (WAN) and vice versa. For example, if you have a Web business from your own home and have leased a digital line (perhaps a T-1 or fractional T-1 line) to a phone company or a gateway at an Internet service provider, you have a CSU/DSU at your end and the phone company or gateway host has a CSU/DSU at its end.
  • The Channel Service Unit (CSU) receives and transmits signals from and to the WAN line and provides a barrier for electrical interference from either side of the unit. The CSU can also echo loopback signals from the phone company for testing purposes. The Data Service Unit (DSU) manages line control, and converts input and output between RS-232C, RS-449, or V.xx frames from the LAN and the time-division multiplexed (TDM ) DSX frames on the T-1 line. The DSU manages timing errors and signal regeneration. The DSU provides a modem-like interface between the computer as Data Terminal Equipment (DTE) and the CSU.
  • CSU/DSUs are made as separate products or are sometimes part of a T-1 WAN card. A CSU/DSU's Data Terminal Equipment interface is usually compatible with the V.xx and RS-232C or similar serial interface. Manufacturers of separate unit or integrated CSU/DSUs include Adtran, Cisco, and Memotec.
  • The CSU originated at AT&T as an interface to their nonswitched digital data system. The DSU provides an interface to the data terminal equipment (DTE) using a standard (EIA/CCITT) interface. It also provides testing capabilities.


  • According to the U.S. federal law known as the Anti-Cybersquatting Consumer Protection Act, cybersquatting is registering, trafficking in, or using a domain name with bad-faith intent to profit from the goodwill of a trademark belonging to someone else. Commercial domain names (technically, you reserve a second-level domain name) are obtained from one of several registries, companies authorized to ensure that a domain name you want is unique (no one else already has it) and issue it to you if it is. However, these registries make no attempt to determine whether the domain name is one that rightfully ought to go to someone else. The principle is "First come, first served." For this reason, a number of enterprising individuals and companies have applied for and reserved domain names, either new or expired, that they think someone else will want, either now or in the future. Well-known companies or their products, sports figures and other celebrities, political candidates, and others often discover that someone else has already reserved the domain name (for example, "") they would most likely want to use. Although trademark laws may offer some protection, it is often cheaper to buy the domain name from the cybersquatter than it is to sue for its use.
  • Many cybersquatters reserve common English words, reasoning that sooner or later someone will want to use one for their Web site. Examples of words sold by cybersquatters to companies developing significant Web sites include,,, and Cybersquatters may also regularly comb lists of recently expired domain names, hoping to sell back the name to a registrant who inadvertently let their domain name expire. eBay, the auction site, sometimes lists domain names for sale. Several cybersquatter companies offer their wares at their own Web sites.
  • Since there is an initial and yearly fee for owning a domain name, some cybersquatters reserve a long list of names and defer paying for them until forced to - preempting their use by others at no cost to themselves. The registry companies are working on this problem. Meanwhile, the Internet Corporation for Assigned Names and Numbers (ICANN ), which licenses the domain name registrars, is working on a process for resolving domain name disagreements outside of the regular court system.
  • The term derives from squatting, the practice of building some kind of home or dwelling or in some way using someone else's landed property without their permission.


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