
    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.                                             


