C = A high-level programming language for writing systems software. The UNIX operating system was written using the C language. C language reduces source code length, which could possibly reduce object code size. C-48 ==== The contiguous 48 states of the United States; excludes Alaska and Hawaii. Also called CONUS. cable ===== A number of electrical or optical conductors assembled and covered with a sheath. Call Request (CRQ) ================== An X.25 packet requesting to set up a call and containing the calling and called DTE addresses (in addition to other various X.25 fields). called address ============== An address (usually X.121) in packed binary-coded decimal digits (maximum 15) specifying the requested destination of a call. calling address =============== An address (usually X.121) in packed binary-coded decimal digits (maximum 15) specifying the original requestor of a call. carrier ======= An analog signal (at a fixed amplitude and frequency) combined with an information signal in a modulation process producing a signal for transmission. A carrier provides sufficient power so that a signal can be reliably detected at some other point or points. Modulation makes a more powerful signal. The term carrier may refer to this powerful signal either before or (more commonly) after modulation. Also called carrier wave or carrier frequency. Carrier Detect (CD) =================== The state of an EIA signal in a modem that is true when the modem has detected a carrier signal on its receive channel. Carrier Present (CP) ==================== An RS-232-C interface signal. Carrier Sense Multiple Access/Collection Detection (CSMA/CD) ============================================================ A method for handling network access of several stations on a Local Area Network (LAN). Collision Detection (CD) is a refinement of this method whereby a station on a LAN detects and compensates for the undesirable collisions that could mix data when several stations try to transmit simultaneously. CBEMA ===== Computer and Business Manufacturers Association. CBX === Computerized Branch and Exchange. CCIR ==== International Radio Consultive Committee. CCITT ===== Comite Consultatif International de Telephonie et de Telegraphie or International Telegraph and Telephone Consultative Committee. An organization of the United Nations, whose task it is to make technical recommendations about telephone, telegraph, and data communications interfaces. CCSA ==== Common Control Switching Arrangement. A dedicated, switched network leased by a user to handle communication requirements among various locations. CCT === Circuit Characteristic Type. A number that indicates a circuit's throughput class, batch or interactive circuit type, and protocol. For example, CCT 0 identifies the circuit as an auxiliary circuit. CCU === Cluster Control Unit. A device that can control all communications between a number of terminals or other devices and a host computer. In a TYMNET network, the Cluster Controller is connected to terminal interface (TIF) software that communicates across the network to a host interface (HIF). CD == Carrier Detect. The state of an EIA signal in a modem that is true when the modem has detected a carrier signal on its receive channel. CEI === Current Empty Index. CEN === Comite Europeen de Normalisation. CENELEC ======= Comite Europeen de Normalisation Electrotechnique. centralized network =================== A time-sharing system in which channels radiate from a central computer system. CEPT ==== European Conference of Postal and Telecommunication Administration. channel ======= A means of transmittin' information from one point to another point. A space allocated to a user on a link; a means of oneway transmission. Usually implies a specific set of physical resources, especially a range of frequencies on some transmission medium. The transmission medium can be open (radio), or closed (pairs of telephone company wire, coaxial cable, or other types of wiring and cabling). character ========= A basic unit of information defined by a standard alphabet: upper and lowercase symbols, numerals, punctuation marks, special symbols, and nonprinted characters such as spaces and carriage returns, which are used for control purposes. Character Mode Translator (CMT) =============================== A BT North America network-resident protocol conversion software program that allows ASCII character mode terminals to access non-ASCII character mode hosts. Program examples are as follows: CMTI (I refers to IBM) translates ASCII data stream to EBCDIC 3270 data stream. CMTK (K refers to Katakana or Kanji) translates ASCII to Katakana or Kanji. CMTU (U refers to Universal Terminal Systems [UTS]) translates ASCII to UTS applications. Character Mode Translator Operations Manager (COM) ================================================== A subprocess of the CMT slot. COM allows the user to monitor and control certain aspects of the CMT slot. It can be accessed with a standard login. character pair ============== Two continuous bytes of memory. chassis ======= The mechanical structure in the Engine and Turbo Engine cabinets, which house the logic and protocol interface boards. checking ======== A method of verifying the accuracy of data transmitted by using polynomial functions of the data transmitted against the data received. Also called Cyclic Redundancy Check (CRC). checking-echo ============= A method of checking the accuracy of data transmission. The receiver returns the data to the sender for comparison with the original data. Also called loop checking. checkpoint ========== An address in a program that is recorded in the event log. checksum ======== The last 4 bytes of a packet, which are used to check the validity of data. Also used to refer to numbers or strings that confirm the validity of a file. checksum error ============== An error condition on a line, which is detected when a node receives a packet whose checksum fields do not match the checksums calculated for the received packet. When this condition is detected, the packet is discarded or the message BAD ACK or BAD RECN is sent. circuit ======= A complete electrical path. A data path from host-to-host or host-to-terminal. A collection of buffer pairs and channels connecting two ports. circuit board ============= A board to which electronic components such as transistors, resistors, and microprocessors are affixed. Also called printed circuit board or card. Circuit Characteristic Type (CCT) ================================= A number that indicates a circuit's throughput class, batch or interactive circuit type, and protocol. For example, CCT 0 identifies the circuit as an auxiliary circuit. circuit label ============= The ISIS relative port number assigned by the MUX, or the alphanumeric designation of a circuit assigned by the user. Circuit Multiplexer (MUX) ========================= An ISIS slot program that allows users to build and maintain multiple circuits to other tools and applications on their hosts. A MUX also allows its users to communicate with other users with a Talk mode facility. A MUX is accessed over a Boss circuit as a host in an ISIS slot. circuit segment =============== That portion of a circuit existing in a single node. circuit switching ================= A method of communication that establishes an end-to-end connection between two points on a communication network for the life of the session only. The physical route of the circuit can vary from one session to the next or can be different for each session. CIS === Configuration Information System. class ===== A set of hosts or nodes that is part of an origination list used to control access to the network. This list can be used as an exclusive list (barring access) or an inclusive list (allowing access) from these nodes or hosts to the network. Class and Group tables ====================== A database on each Supervisor's disk that contains lists of origination hosts and nodes and destination hosts in a TYMNET network. At login, the Supervisor reads from this database to validate the user's circuit request. The NETVAL program manages this database and forwards this information to each Supervisor. Clear To Send (CTS) =================== A signal sent by the DCE to the DTE notifying the DTE that it can begin to transmit data. Contrast with Request To Send (RTS). client ====== A software program that requests a service. The client is paired with the server; the client is the requestor, the server the provider. See server. clock ===== A device that generates periodic signals used for synchronization. Closed User Group (CUG) ======================= A group that can only receive data from or transmit data to other users within the same group. Cluster Controller (CC) or Cluster Control Unit (CCU) ===================================================== A device that can control all communications between a number of terminals or other devices and a host computer. In a TYMNET network, the Cluster Controller is connected to terminal interface (TIF) software that communicates across the network to a host interface (HIF). Cluster Remote Display Unit (CRDU) ================================== A terminal interface (TIF) that replaces a cluster control unit (CCU) and hardware-dominated loop-line network. Customized service for special application configurations. CMF === Code Management Facility. A node configuration and code generation system that runs as an application program under the UNIX operating system. CMOS ==== Complementary Metal Oxide Semiconductor. CMT === Character Mode Translator. A BT North America network-resident protocol conversion (CMT) software program that allows ASCII character mode terminals to access non-ASCII character mode hosts. Program examples are as follows: CMTI (I refers to IBM) translates ASCII data stream to EBCDIC 3270 data stream. CMTK (K refers to Katakana or Kanji) translates ASCII to Katakana or Kanji. CMTU (U refers to Universal Terminal Systems [UTS]) translates ASCII to UTS applications. coaxial cable ============= Cable that consists of a central metal conductor surrounded by a dielectric material that is in turn wrapped by a second conductor, all of which is encased in an insulating sheath. Also called coax. COBOL ===== Common Business-Oriented Language. A high-level language developed for business data-processing applications. code ==== A group of characters that has a particular meaning. Also, a general term used to refer to the text of computer programs or portions of programs. A system of symbols representing data or instructions in a computer. BT North America source codes are currently written in the following languages: assembly, C, andCPASCAL. BT North America codes currently written in assembly are CONSAT, Node Code, PROBE, SNA, TYMCOM, and X.25. BT North America codes currently written in C are ISOM-68K and Turbo-SCP. BT North America codes currently written in CPASCAL are OnTyme, NETVAL, RAM, and TMCS. Code Management Facility (CMF) ============================== A node configuration and code generation system that runs as an application program under the UNIX operating system. Coder/Decoder (CODEC) ===================== An electronic device used in digital telephone systems to convert analog signals to digital signals or vice versa. COM === Character Mode Translator Operations Manager. A subprocess of the CMT slot. COM allows the user to monitor and control certain aspects of the CMT slot. It can be accessed with a standard login. command ======= A request for an operation to be performed. Any input to a computer or a program that causes it to take some specified action. command circuit =============== A virtual circuit that connects a node to the active Supervisor. Network management messages are transmitted via a command circuit from the Supervisor to the node's Node Code. A command circuit must exist for the node to be in the TYMNET network. command file ============ A system generation file containing a series of commands used to create a NIB file. Common Business-Oriented Language (COBOL) ========================================= A high-level language developed for business data-processing applications. common carrier ============== A legal entity required by law to carry goods or information of any qualified customer at publicly established and regulated rates. An example is AT&T. TYMNET is not a common carrier. Common Control Switching Arrangement (CCSA) =========================================== A dedicated, switched network leased by a user to handle communication requirements among various locations. communications controller ========================= Another term for front-end processor. Compact XL ========== An intermediate-sized node in the Engine family of communications processors. Supports applications requiring a moderate number of interconnections. Provides synchronous and asynchronous communications between dissimilar devices and uses CPU III, MAC III and SIO II boards, with up to five optional I/O cards and a 160-MB hard disk. compatibility ============= The ability of two types of equipment or software using the same protocols to communicate. compiler ======== A computer program that converts source code (programming language) into object code (machine-readable language). See also assembler. complementary buffer ==================== One buffer of a buffer pair, which holds data traveling in the opposite direction on a circuit. compound passthrough circuit ============================ A circuit passing through a Multi-Node Code (MNC) system that enters a node on one Node Code slot and exits on a different Node Code slot. The Turbo Engine uses MNC. Contrast with simple passthrough circuit. computer ======== Any machine that can accept data in a certain form, process the data by problem-solving (perform a mathematical or logical operation on the data) and supply the results of the operation. Also, any machine that can control a process. concentrator ============ A device that multiplexes several low-speed communications lines onto a single high-speed trunk. Concurrent Pascal ================= A version of the high-level PASCAL language, which is structured logically for both synchronous and asynchronous multiple process applications. Concurrent Pascal Compiler (CPASCAL) ==================================== A software program that translates source code written in Concurrent Pascal (CPASCAL) programming language, into object code. This program, which is formatted for Engine loading, produces a code that can run several processes at the same time. See code. conditioning ============ A type of electrical balancing that provides improved electrical characteristics for high-speed data transmissions over a leased-line circuit. For example, equalizing the attenuation distortion between the higher and lower frequencies adjusts the slightly degraded waveform enough for it to become acceptable. configuration ============= A functional arrangement of hardware and software that performs specific node functions. Configuration file ================== A system generation parameter file containing statements that customize slot code. Configurator ============ A planning and analysis tool used to design or reconfigure a TYMNET network. This tool can develop designs based on network performance and point-to-point traffic requirements, designing a network of up to 200 nodes and 4,000 links, and can specify node and neighbor node association. See TYMNET On-line Planning System (TOPS). connect time ============ A measure of system usage by a given user. Also, the length of time it takes a switching system to connect the calling party to the called party. Consolidated TYMSAT (CONSAT) ============================ An asynchronous terminal interface (TIF) code. TYMNET network-resident software that makes it possible for the network to communicate with terminals or personal computers that use asynchronous protocol. constant ratio ============== A code in which the ratio of ones to zeros in each character is constant. See IBM 4 of 8. context switcher ================ A portion of TYM2 Solo Node Code that regulates the execution of independent processes in a node. control code ============ A data item that performs signaling functions between software packages. Usually one byte. Common ASCII control codes are NUL ENQ LF SI DC4 EM RS SOH ACK VT DLE NAK SUB US STX BEL FF DC1 SYN ESC ETX BS CR DC2 ETB FS EOT HT SO DC3 CAN GS Control Table Area (CTA) ======================== A memory segment (segment E) that contains descriptors of a slot's running configuration, such as, which segments are in use, the host numbers assigned to that slot, and the number of ports available to each host in that slot. See slot. See also segment. controller ========== A device that automatically regulates a controlled variable or system. Controlling User Directory (CUD) ================================ A collection of all user validation data (username, password, and network access). Accessed by NETVAL, the CUD is periodically copied to the Master User Directory (MUD) of each Supervisor in the network. CONUS ===== Continental United States; excludes Alaska and Hawaii. conversion boundary =================== A type of interface program that translates one protocol into another protocol. Coordinated Universal Time (UTC) ================================ The mean solar time for the meridian at Greenwich, England, used as a basis for calculating time throughout most of the world. Formerly called Greenwich Mean Time (GMT). GMT became Coordinated Universal Time (UTC) when the atomic clock was moved to Paris, France. In some TYMNET programs, UTC is stored as a 64-bit binary number that represents the time elapsed since January 1, 1974. coprocessor =========== A secondary processor that performs specialized data-processing tasks. core memory =========== An older, slower, and bulkier type of magnetic main memory. The term is often used as a synonym for other types of memory. Its one advantage is that it is nonvolatile when the power is shut off. COS === Corporation for Open Systems. CP == Carrier Present. An RS-232-C interface signal. CPASCAL ======= Concurrent Pascal Compiler. A software program that translates source code written in Concurrent Pascal (CPASCAL) programming language into object code. This program, which is formatted for Engine loading, produces a code that can run several processes at the same time. See PASCAL. CPE === Customer Premise Equipment. Equipment located at a customer site; the equipment might not be owned by the customer. cps === Characters per second or cycles per second. CPU I ===== Central Processing Unit I. A BT North America controller board in the Engine family of communication processors that performs all arithmetic and logical operations. The CPU I is directly cabled to the ROM and I/O board. CPU III ======= Central Processing Unit III. A BT North America controller board in the Engine family of communication processors that performs all arithmetic and logical operations. The CPU III combines the features of the CPU I and the ROM and I/O boards. crash ===== The halting of an execution of computer code, a portion of computer code, or the whole machine due to hardware failure, endless loop, or block. crash options ============= A set of parameters that determines what actions a slot can take following a crash. crash register ============== A description of the contents of registers as they were at the time of a crash. crash table =========== An area of memory that records the slot's crash history. CRC === Cyclic Redundancy Check. An error-detection technique used to check the accuracy of frames transmitted over a data link. A mathematical calculation performed by Node Code to ensure data integrity of the packets transmitted between nodes. CRDU ==== Cluster Remote Display Unit. A terminal interface (TIF) that replaces a cluster control unit (CCU) and hardware-dominated loop-line network. Customized service for special application configurations. crossover cable =============== A cable or double connection that can mate similar cables or equipment. For example, the transmit data signal on the originating end becomes the receiving data signal on the terminating end. Also called a null-modem cable. CRQ === Call Request. An X.25 packet requesting to set up a call and containing the calling and called DTE addresses (in addition to other various X.25 fields). CRT === Cathode Ray Tube. crypto messages =============== Diagnostic messages that are continuously generated by Node Code. The most recent crypto messages are stored in the crypto buffer; a maximum of 256 messages can be stored in the crypto buffer. CSMA/CD ======= Carrier Sense Multiple Access/Collision Detection. A method of handling network access of several stations on a Local Area Network (LAN). Collision Detection (CD) is a refine- ment of this method whereby a station on a LAN detects and compensates for the undesirable collisions that could mix data when several stations try to transmit simultaneously. CSR === Control Status Register. CTA === Control Table Area. A memory segment (segment E) that contains descriptors of a slot's running configuration, such as, which segments are in use, the host numbers are assigned to that slot, and the number of ports are available to each host in that slot. See slot. See also segment. CTS === Clear To Send. A signal sent by the DCE to the DTE notifying the DTE that it can begin to transmit data. Contrast with Request To Send (RTS) CUD === Controlling User Directory. A collection of all user validation data (username, password, and network access). Accessed by NETVAL, the CUD is periodically copied to the Master User Directory (MUD) of each Supervisor in the network. CUG === Closed User Group. A group that can only receive data from or transmit data to other users within the same group. Customer Premise Equipment (CPE) ================================ Equipment located at a customer site; the equipment might not be owned by the customer. Cyclic Redundancy Check (CRC) ============================= An error-detection technique used to check the accuracy of frames transmitted over a data link. A mathematical calculation performed by Node Code to ensure data integrity of the packets transmitted between nodes. Cyclopean Gateway Service (CGS) =============================== A BT North America online electronic library that offers access to thousands of publications.