HP OpenVMS Systems Documentation

event dispatcher (EVD): DECnet-Plus network management software that reports events that occur during network operation on a particular system, between two systems, or across distributed systems.

event filtering: Process of deciding whether to pass an event to its destination, discard it, or subject it to further filtering. Event filtering can be applied to an event both at the event source where it is generated and to the event sink to which it is sent. User-specified.

event logging: See event dispatcher.

event sink: Event dispatching component to which an event is delivered.

event source: Event dispatching component where an event is generated.

event stream: Connection between an event source and an event sink, over which events are delivered.

expedited data: Service that transfers small amounts of data between peer entities without the need for normal token controls.

Small amounts of data that are not subject to the flow control applied to normal data. Contrast with normal data.

extended LAN: Multiple LANs connected with data link relays or bridges.

facility: Service or mode of operation that a PSDN is able to provide for a user upon subscription and/or request, for example, fast select or reverse charging.

FADU: See file-access data unit.

FAL: See file access listener.

FDDI: See Fiber Distributed Data Interface.

Federal Networking Council (FNC): Body responsible for coordinating networking needs among U.S. Federal agencies.

FERPM: See file error recovery protocol machine.

Fiber Distributed Data Interface (FDDI): ANSI standard for a high-speed, general-purpose network using an optical fiber medium for interconnection of computers and peripheral equipment; specifies a 100 mb/s data rate using 1300-nanometer light wavelength and limits networks to approximately 200 km in length, with repeaters every 2 km or less. The access control mechanism uses Token Ring technology and the topology is a dual-attached, counter-rotating Token Ring.

file-access data unit (FADU): Data structure that FTAM file-access services use when accessing file data; either a whole file or a specific subtree comprising one or more nodes and associated file-contents data units such as records.

file access listener (FAL): Image that provides authorized access to the file system of a DECnet-Plus node on behalf of processes executing on any node in the network. FAL communicates with the initiating node by means of the Data Access Protocol (DAP).

file-access structure: Structure that links together a file's file-access data units (FADUs), allowing for their identification, description, and manipulation.

file attribute: Permanent characteristic of a file, such as its file name. The values of some file attributes may change during the lifetime of a file. However, different FTAM users simultaneously accessing a file see the same values for file attributes.

file-contents data unit: Sequence of zero or more file-contents data elements. Each file-contents data element specifies a data type in terms of a specific abstract syntax.

file data: Nonstructural information that is stored within a file and comprises its contents (as opposed to its attributes).

file designation: System-specific information that identifies a file on its storage system.

file error recovery protocol machine (FERPM): FTAM software that implements the FTAM error recovery protocol.

file model: Model of a file-access structure. See also hierarchical file model.

file-open regime: Regime that controls access to the contents of a currently selected file.

file protocol: Communications between FTAM initiators and responders and the operations of file services during an association.

file-selection regime: Regime that associates the initiator with a file and its attributes.

file service: Set of services provided by an FTAM entity for transferring, accessing, and managing remote files.

file-service model: Description of the services, regimes, and activity attributes that support filestore actions.

file specification: System-specific information that identifies a file on its storage system.

filestore: Organized collection of files that includes their attributes, such as file names. See also virtual filestore and real filestore.

filestore actions: Actions performed on files within the virtual filestore, including actions on complete files and their attributes (whole-file actions) and actions for accessing file contents (file-access actions).

filestore password: FTAM parameter whose purpose is to convey a password for authenticating the initiator to the responder. The FTAM responder equates the filestore password to an ULTRIX login password (on a DECnet-Plus for DIGITAL UNIX node) or to a OpenVMS login password (on a DECnet-Plus for OpenVMS node).

File Transfer, Access, and Management: See FTAM protocol.

flag sequence: Series of ones and zeros that indicate the start and end of a frame.

flat file view: Access context for a file that recognizes two levels of nodes: a root node and, optionally, first-level nodes. The root node lacks an associated data unit, but first-level nodes can have an associated file-contents data unit.

flooding: DECnet-Plus routing process that propagates Link State Packets (LSPs) as a result of network changes, for example, node failure. Each new LSP is transmitted on all the circuits of an intermediate system, except the circuit on which it was received.

flow control: Function performed by a receiving entity to limit the amount or rate of data that is sent by a transmitting entity; allows communicating layers to match their data transfer and receive rates in order to ensure that one end of the connection does not send data faster than the other end can process it; keeps traffic within limits acceptable by the end-receiver or any intermediate receiver. At the terminal level, the flow control mechanism must guarantee that the flow of characters will stop if the buffer fills up.

FNC: See Federal Networking Council.

forward: Routing process that transmits, or forwards, data to the destination node or to another routing node. If a packet is addressed to the local node, routing on that node delivers it to the DECnet-Plus Transport layer. If a packet is addressed to a remote node, routing forwards it to the next adjacent node on the best available path.

FPM: See FTAM protocol machine.

fragmentation: Routing process of breaking a large datagram into multiple smaller datagrams for transmission. The reverse process is reassembly. See also maximum transmission unit.

frame: Unit delimited by flags that includes a header; used by the Data Link level to exchange packets and control-and-error information between a DTE and a DCE.

frame checking sequence (FCS): 16-bit, error-check polynomial that checks that the bit content of a frame is the same before and after transmission.

frame level: X.25 protocol level that defines the procedure for transferring packets without errors between a DTE and DCE; also known as level 2.

frame reject frame: See FRMR.

FRMR (frame reject frame): Frame used by the DTE or DCE to report an error that cannot be recovered by the retransmission of the identical frame. Used only by LAPB/LAPBE.

FTAM (File Transfer, Access, and Management): See FTAM protocol.

FTAM-1: Document type for unstructured text files.

FTAM-2: Document type for sequential text files.

FTAM-3: Document type for unstructured binary files.

FTAM application name: Name that corresponds to the FTAM responder on an FTAM system. See also alias.

FTAM element: FTAM-specific service element of the Application layer.

FTAM entity: Entity at the Application layer (application entity) that occurs within an application process and that involves the FTAM, ACSE, and presentation protocol machines, with the rules and procedures of the FTAM protocol machine controlling the operation of the ACSE protocol machine.

FTAM file specification: Unique string of characters that a DECnet-Plus FTAM system uses to select or create a file on another FTAM system in the same network.

FTAM-FTP Gateway: DECnet-Plus for DIGITAL UNIX software that allows DECnet-Plus for DIGITAL UNIX users to perform file operations between OSI and Internet systems; translates both ways between FTAM Protocol and File Transfer Protocol (FTP). The DECnet-Plus for DIGITAL UNIX user issues either FTAM or FTP commands to perform remote file operations.

FTAM protocol: File Transfer, Access, and Management protocol (ISO 8571); ISO protocol at the Application layer that defines the rules for transfer, access, and management of files between multivendor systems on the same OSI network.

FTAM protocol machine (FPM): Software that implements the FTAM file protocol.

FTAM regime: Regime that controls the binding of two FTAM entities to an association.

FTAM standard: FTAM International Standard (ISO 8571), which defines OSI file transfer, access, and management.

FTAM system: Open system with an FTAM implementation that conforms to the OSI FTAM standard.

full-duplex circuit: Circuit designed for transmission in both directions at the same time. Contrast with half-duplex circuit.

full-duplex transmission: Data transmission in both directions at the same time. Contrast with half-duplex transmission.

full name: Complete specification of a name in the namespace, including all parent directories in the path from the root directory to the object, directory, or soft link being named; can also include a namespace name, but not necessary when only one namespace exists in a network.

In a full name, the reserved namespace nicknames LOCAL: and DOMAIN: indicate to DECnet-Plus that the information for the node is contained in the Local namespace (for LOCAL:) and in DNS/BIND (for DOMAIN:.)

full support: Level of support in which a value assigned by FTAM software to an FTAM file attribute corresponds to the value of a file attribute in the real filestore on DECnet-Plus for DIGITAL UNIX nodes (their UFS filestore) and DECnet-Plus for OpenVMS nodes (their RMS filestore).

function code: On a DECnet-Plus for OpenVMS system, parameter to a $QIO system service call that defines the specific function to be performed by that $QIO.

function dispatch table (FDT): Software that identifies the operations supported by an entity and specifies the routines to be called to process them.

functional unit: Logical grouping of services.

Set of low-level communications functions, each of which involves a minimal interaction between a user and a provider of a communications service; when combined in an established order, provide a specific high-level function such as controlling regimes or transferring data. The grouping of specific functions into functional units helps an initiator negotiate the functions required during an association.

gateway: Device or software that enables multivendor communication by converting the functions of one vendor's network into functions recognizable by the other; functions as a language translator, enabling "speakers" of different languages to communicate.

Gateway Access Protocol (GAP): Protocol used between a host DECnet-Plus system and a DECnet-Plus system that is a DTE on a PSDN to provide the X.25 gateway access facility to a user on the host.

gateway client: Access system.

gateway system: Another term for connector system.

GeneralString: String composed of a definable character set that includes format effectors; by default, a GeneralString is an IA5String. DECnet-Plus FTAM software uses a GeneralString as its default to convey strings of characters from the ISO 8859 character set (DEC multinational character set). The ISO 8859 character set is an 8-bit character set containing both graphic characters and control characters.

general topology subnetwork: Nonbroadcast subnetwork.

global entity: Entity that has no parent, for example, the node entity. Entity whose agent can directly receive management requests from a director. All nonglobal entities are child entities of a global entity, and receive management requests through their parent global entity. A global entity class name must be unique among the set of all global entity class names.

global name: Portion of a DECdns entity name that is registered in a DECdns clearinghouse and addresses a parent agent of the target entity.

global network address: See network service access point.

global network addressing: See DECnet-Plus addressing.

global network addressing domain: Addressing domain consisting of all NSAP addresses in the OSI environment.

global server: DECdts server that frequently provides its clock value to courier servers on other LANs, or infrequently provides its clock value to systems that have failed to obtain the specified number of servers locally.

global server directory: DECdns directory where DECdts servers are stored.

global set: All of the global DECdts servers in a network.

GOSIP: See Government OSI Profile.

GOSIP specification: Government OSI procurement document that specifies to computer vendors what requirements their OSI products must meet to qualify for purchase by governmental organizations. Some countries, such as the United States and the United Kingdom, have their own separate GOSIP specifications.

Government OSI Profile (GOSIP): Government procurement specification for OSI protocols.

GraphicString: String of printable characters, that is, without format effectors, taken from the GeneralString character set.

group: Class of object that lets you associate, or manage as a group, a set of names that have something in common; maps a specific name (the group name) into a set of names, denoting the group members. DECdns uses groups internally for access checking. DECdns managers can create groups that assign several users a single set of access rights to DECdns names. Applications that use DECdns can create groups for purposes other than access control.

half-duplex circuit: Circuit designed for transmission in either direction, but only one direction at one time. Contrast with full-duplex circuit.

half-duplex transmission: Data transmission in either direction, but only one direction at a time. Contrast with full-duplex transmission.

handshaking sequence: Exchange of transport connection information between two tasks; takes place to enable the successful completion of a transport connection.

hardware address: For an Ethernet device, the unique Ethernet physical address associated with a particular Ethernet communications controller (usually in read-only memory) by the manufacturer.

HDLC: See High-level Data Link Control Protocol.

header: Control information placed before the data in a frame or a packet, such as source or destination specification, priority, and packet or frame identification.

hierarchical file model: Model of an internal file structure comprising an ordered tree of file-access data units (FADUs) that defines the basic file-access structure used by FTAM software.

hierarchical namespace: DECdns namespace with one or more levels of directories beneath the root directory.

high convergence: Directory convergence setting for which DECdns attempts to propagate an update to all replicas. If the attempt fails (for example, if one of the replicas is unavailable), a skulk is scheduled for within 1 hour. Background skulks occur at least once every 12 hours.

High-level Data Link Control (HDLC) Protocol: ISO, bit-oriented, Data Link layer (OSI layer 2) protocol that operates over synchronous, switched, or nonswitched communications links; supports a broad range of existing subsets, including the subset used in X.25 networks. Similar to LAPB.

hop: Logical distance between two nodes. One hop is the distance from one node to an adjacent node. See also path length.

host: Defined as:

• DECnet-Plus node that provides services for another node. For example, a load host supplies image files for a downline load.
• System running any implementation of the OSI transport protocol.

host-based PAD: Packet assembler/disassembler (PAD) situated at the X.25 host node and not within the PSDN.

host-echo mode: Mode in which the PAD can operate at which time characters typed at the terminal are sent across the PSDN, and echoed across the PSDN.

IA5String: String of characters from the IA5 character set. This 7-bit character set contains both graphic characters (printable) and control characters (nonprintable format effectors).

IDI: See initial domain identifier.

IDP: See initial domain part.

IEEE (Institute of Electrical and Electronic Engineers): Standards body that sponsored, among other things, the 802 series of physical communications protocols, including the 802.3 protocol.

IEEE 802.2: IEEE protocol that defines frame formats for 802.3 LANs.

IEEE 802.3 local area network: LAN using the IEEE 802.3 specification; a CSMA-CD network.

IEEE Project 802: IEEE project set up to develop standards for LANs.

implementation profile: Standard subset of functions and features from the full set of OSI standards. Profiles are designed to specify certain user functions such as simple file transfer.

inaccuracy: Bounded uncertainty of a clock value as compared to a standard reference.

inbound connection: Logical link connection requests that a task receives.

incoming call: Packet sent to a DTE by its DCE when a call request packet has been received through the network from another DTE.

indication primitive: Primitive generated by a service provider to pass an incoming request on to a service user.

initial domain identifier (IDI): Component of the IDP of an NSAP address; value allocated under the addressing authority identified by the authority and format identifier (AFI).

For example, the IDI value is based on CCITT recommendation E.163 and is created from a public switched telephone network (PSTN) number that has been assigned to a company or organization. The parts of this IDI are:

• World zone number
• Country or geographic area number
• Local number

initial domain part (IDP): Part of an NSAP address; identifies the authority that allocated the IDP; consists of an AFI and an initial domain identifier (IDI).

initialization failure: Failure to start a circuit or establish a connection with an adjacency.

initiating host: Host on which an initiating OSI application executes.

initiating task: OSI task that requests a transport connection with another OSI application.

initiator: Defined as:

• OSI --- Peer entity that requests an association.
  Application process that receives requests from system users for application functions and that activates an application entity to start OSI communications.
• Virtual Terminal --- Component that starts the interaction with a remote virtual terminal responder.

initiator identity: FTAM parameter whose usual purpose is to identify the calling user. The FTAM software responder equates the initiator identity (initiator ID) to either a local DIGITAL UNIX or a local OpenVMS user name, depending on the local DECnet-Plus system.

Institute of Electrical and Electronic Engineers: See IEEE.

INTAP (Interoperability Technology Association for Information Processing, Japan): Technical organization with the official charter to develop Japanese OSI profiles and conformance tests.

integrated IS-IS: See integrated routing.

integrated routing: DECnet-Plus routing feature that allows a DECnet-Plus intermediate system to forward DECnet-Plus packets and Internet Protocol (IP) packets.

Allows for DECnet-Plus networks with IP routers, OSI routers, and multiprotocol routers. Each network area can be OSI-only (contain a mix of OSI-only and multiprotocol routers, but forward only OSI packets), IP-only, or multiprotocol.

Integrated Services Digital Network (ISDN): Technology offered by the telephone carriers of the world that combines voice and digital network services in a single medium, making it possible to offer to customers digital data services through a single "wire." The standards that define ISDN are specified by CCITT.

interface: Boundary between two parts of a system across which communication is possible; may be defined through hardware or software. Example: the network management command interface NCL.

interface data unit: Unit of information transferred across the layer n service access point between a layer n+1 entity and a layer n entity in a single interaction.

intermediate system: Routing system that receives data packets from a system on one subnetwork and passes them on to a system on another subnetwork; receives data packets from a source end system, or from the previous intermediate system on the route, and passes them on to the destination end system, or to the next intermediate system on the route.

Intermediate System to Intermediate System Protocol (IS-IS): OSI protocol (ISO 10589) that describes the exchange of routing information between intermediate systems.

Internal Organization of the Network Layer (IONL): OSI standard for the detailed architecture of the Network layer. This architecture partitions the Network layer into subnetworks interconnected by convergence protocols (equivalent to internetworking protocols).

International Consultative Committee for Telegraphy and Telephony: See CCITT.

International Organization for Standardization (ISO): Nonprofit, international organization based in Geneva, Switzerland, whose members develop standards for international, multivendor, open networking. Coordinates national standards bodies, such as the British Standards Institution (BSI) and the American National Standards Institute (ANSI). Along with CCITT, is developing OSI. See also Open Systems Interconnection.

International Standard: Standard approved by ISO. Each standard has a reference number, for example:

• End System to Intermediate System routing (ES-IS): ISO 9542
• Connection-Oriented Network Service (CONS): ISO 8348
• Connectionless-mode Network Service (CLNS): ISO 8348/AD1
• X.25 Packet-Level Protocol (PLP): ISO 8208
• X.25 to provide CONS: ISO 8878

International Telegraph and Telephone Consultative Committee: See CCITT.

Internet: Collection of packet switching networks, interconnected by gateways along with protocols, that allow them to function as a single, large network; refers specifically to the Defense Advanced Projects Research Agency (DARPA) Internet and the TCP/IP protocols it uses.

Internet service: Network layer OpenVMS service that allows communications to span subnetworks that have distinct addressing rules and communication protocols; allows a source system to route messages across subnetworks using one or more intermediate systems to reach a target system.

Internet subaddress: Subaddress that identifies the OpenVMS VAX Internet service provider of an X.25 subnetwork; forms the last two digits of an adjacent system's X.25 subnetwork address.

Interoperability Technology Association for Information Processing, Japan: See INTAP.

interrupt: Defined as:

• DECnet-Plus --- Event (other than an exception or branch, jump, case, or call instruction) that changes the normal flow of instruction execution; generally external to the process executing when the interrupt occurs.
• X.25 --- To send data to a remote DTE by using flow control for control packets rather than for data packets. Interrupt packets are paired; an interrupt packet can be sent only if a previous interrupt has been acknowledged.

Interrupt Confirmation: Packet sent to:

• The local DCE by a DTE that has received an interrupt packet (DTE interrupt confirmation).
• An interrupting DTE by a DCE that has received a DTE interrupt confirmation packet through the network (DCE interrupt confirmation packet).

interrupt message: During nontransparent task-to-task communication, a user-generated message sent outside the normal exchange of data messages. (This usage of the term interrupt is contrary to the normal usage, which means to designate a software or hardware interrupt mechanism.)

interval: Combination of a clock's value and the inaccuracy associated with it; range of values in the clock value minus its inaccuracy, and the clock value plus its inaccuracy used by DECdts.

I/O status block (IOSB): On a DECnet-Plus for OpenVMS system, data structure associated with the $QIO system service; holds information about how the I/O request completes.

IONL: See Internal Organization of the Network Layer.

ISDN: See Integrated Services Digital Network.

IS-IS: See Intermediate System to Intermediate System Protocol.

ISO: See International Organization for Standardization.

ISO Development Environment: See ISODE.