HP OpenVMS Systems Documentation

In DECnet-Plus, the OSI NSAP standard defines the syntax of a network address. See also network service access point.

node name: Alphanumeric identification associated with a node address of a system in a one-to-one mapping.

node name synonym: See node synonym.

node synonym: DECnet Phase IV-compatible node name (six characters or less) that maps to a DECnet-Plus-style name for the same node. For example, XYZ_CORP:.sales.west_coast.ElanaCole might map to ElanaC.

node synonym directory: Required DECdns directory called .DNA_NodeSynonym that stores node synonyms. Created by the decnet_register by default during DECnet-Plus configuration.

nonadjacent nodes: Nodes without direct lines between them; can communicate only if intermediate systems forward the data along the path between the source and the destination.

nonbroadcast circuit: Circuit other than a broadcast circuit. For example, a multipoint DDCMP circuit is not a broadcast circuit because a packet cannot be received by more than one node.

nonbroadcast subnetwork: Subnetwork, or area, made up of one of these kinds of connections: multipoint links, permanent point-to-point links, or dynamically established data links.

nonrouting node: End system.

nontransparent task: Form of device-dependent I/O that uses system services to perform network-specific functions; can initiate and complete a logical link connection, exchange messages between two tasks, and terminate the communication process. Application that has direct access to network-specific information and operations, such as optional user data on connects and disconnects and interrupt messages, to monitor the communications process; can receive and process multiple inbound connection requests.

Example: a nontransparent task on a DECnet-Plus for OpenVMS system can create and use an OpenVMS mailbox to receive information that is not available to a transparent task with transparent communication.

normal data: User information sent under normal circumstances over the transport normal data service.

Data that is normally exchanged during communication, as distinct from expedited data sent over a connection. Contrast with expedited data.

normal mode: HDLC operational mode used over half-duplex links. Contrast with balanced mode.

normalization: Estimation of the change in a counter value over a specified time period.

NSAP: See network service access point.

NSAP address: Address of the network service access point. See also network service access point.

NSAP selector: See transport selector.

NSCTS: See namespace creation timestamp.

NSP: See Network Services Protocol.

null modem: Simple form of modem connection where only the data interchange circuits, and not the modem control circuits, are used.

Null Protocol: Protocol used in the Network layer of a LAN in place of the Internet Protocol (IP); used when the routing functions of IP are not required, for example, when the communicating hosts are on the same LAN.

null qualifier: Qualifier that a VAX FTAM facility accepts for the sake of compatibility but ignores when executing a command involving any remote files.

object class: Attribute of an object that reflects the purpose of that object within an application. The object class can be specific to one application or shared among a group of applications. An application interprets and uses an object's class-specific attributes based on the object's class.

object entry: Entry defining a physical resource (such as a node, disk, or application) stored in DECdns.

object identifier: Standard, unique name for an informational object such as a specific piece of information, a definition, or a specification. See also ASN.1.

OIW (OSI Implementors Workshop): North American regional forum at which OSI implementation agreements are decided; equivalent to EWOS in Europe and AOW in the Pacific. (Also called NIST OIW and the NIST Workshop.)

opaque full name: Internal representation of a DECdns full name, beginning with the namespace creation timestamp (NSCTS); stored in binary format.

opaque simple name: Internal representation of a DECdns simple name; stored in binary format.

open network: Network made up of open systems. See also Open Systems Interconnection.

open system: System with communications software that implements the OSI standards for open networking. See also Open Systems Interconnection.

Open Systems Interconnection (OSI): Set of international networking standards developed by the International Organization for Standardization (ISO). OSI standards are based on ISO's seven-layer model for communications and an associated set of communications protocols and services.

ISO is also developing a suite of protocols like the TCP/IP suite named TP4/IP. See also International Organization for Standardization.

operational mode: In High-level Data Link Control (HDLC), the particular operational state or protocol being used.

originating packet: Packet from the local node's Transport layer.

origination: Beginning point of communications on a circuit.

OSI: See Open Systems Interconnection.

OSI Applications Kernel Software (OSAK software): Open System Application Kernel (OSAK) is DIGITAL's implementation of the OSI upper layers. It provides OSI session, presentation and application services. These services are used by OSI applications such as FTAM, VT, X.400, and X.500. In addition, by using the OSAK programming interfaces, which provide access to OSI session, presentation and application layers, users can develop applications which layer on DIGITAL's implementation of the OSI stack.

OSI Reference Model: See ISO Reference Model for Open Systems Interconnection.

OSI network address: See network service access point.

OSI presentation address: Address used to locate an OSI application entity; consists of an OSI network address and up to three selectors, one each for use by the transport, session, and presentation entities. See also p-address.

OSI Reference Model: See ISO Reference Model for Open Systems Interconnection.

OSI Transport address: See transport service access point.

OSI Transport filter: Filter used by the Transport layer for incoming calls using CONS over the X.25 network.

OSI transport template: Template defined in the X25 Access module; used by the Transport layer for outgoing calls using CONS over the X.25 network.

outbound connection: Task's transport connection request for a logical link connection to another node.

out-of-order packet caching: Taking packets of a user data message that have been received out of order (as a result of the routing process called path splitting) and reassembling them into their proper order; must be supported by destination nodes that receive data packets that have been forwarded over different paths. Also called out-of-order packet reassembly. See also path splitting.

packet: Defined as:

• Routing --- Unit of data routed from a source node to a destination node. A message may be sent as several packets.
• X.25 --- Unit of data switched through a PSDN; normally a user data field has a header carrying destination and other information.

packet assembler/disassembler (PAD): Device at a PSDN node that allows access from an asynchronous terminal, such as a DIGITAL VT series terminal. The terminal connects to the PAD, which formats the data sent from the terminal into packets (is assembled). Data sent to the terminal in packet format is disassembled by the PAD before transmission to the terminal.

packet fragmentation: See fragmentation.

packet level: X.25 protocol level; defines the procedure for the formatting of packets and for packet exchange. Also known as Level 3.

packet looping: Condition in which a packet revisits a node. See also aged packet.

packet mode DTE: DTE that can handle data in packet form and can assemble/disassemble packets, for example, a computer.

packet size: Amount of data in a packet.

packet switching: Method of transmitting messages, using data packets that occupy a channel only for the duration of transmission of the packet. Each packet sent can take different routes to its destination and packets from different users can be interleaved across the network connection during transmission. Long messages are subdivided into short packets (blocks of fixed length), which are then routed to their destination using addressing information carried by the packets.

packet switching data network (PSDN): Refers to both public and private packet switching networks. For public networks, also means the set of equipment and interconnecting links that provide a public packet switching service to subscribers within a particular country.

packet switching exchange (PSE): Equipment in a PSDN that is responsible for accepting and routing packets and ensuring their correct arrival.

packet switching network: Computer network that uses packet switching.

PAD parameter profile: X.25 --- List of PAD parameter settings. See also packet assembler/disassembler.

p-address (presentation address): Specifies service access points (SAPs) for the service providers of all the upper layers to be accessed. For the FTAM software, a p-address always contains presentation, session, and transport selectors. It also must have an NSAP. Within a p-address, each selector is terminated on its right by a delimiter (.). The sequence of selectors and delimiters for an FTAM p-address is: psap. ssap. tsap.nsap.

See also OSI presentation address.

parent directory: Directory that has one or more levels of directories beneath it in a DECdns namespace. A directory is the parent of any directory immediately beneath it in the hierarchy.

parent entity: Entity that has created another entity (the child entity). Higher-level entity that forwards directives to its child entities as defined by the management access relationship.

partial support: Level of support in which FTAM software supports a constant value, such as No value available, in the virtual filestore, because the attribute lacks direct mapping to either a UFS attribute on a DECnet-Plus for DIGITAL UNIX system or an RMS attribute on a DECnet-Plus for OpenVMS system.

path: Physical lines between source nodes and destination nodes; can comprise a sequence of connected nodes. The path that the data takes through the network is transparent to users.

path cost: The sum of the circuit costs along a path between two nodes.

path length: Total distance (the number of circuits) between a source node and a destination node, measured in hops. Each line between systems, including routing nodes and end nodes, equals one hop. See also network diameter.

path splitting: Routing process that splits the transmission load destined for a node over several paths of equal path cost. Paths are less likely to become congested, resulting in improved use of network resources. A destination node receiving data that has been split over several paths must support out-of-order packet caching. See also out-of-order packet caching.

PCI: See protocol control information.

PDU: See protocol data unit.

peer entities: Corresponding entities at the same layer on different open systems.

permanent virtual circuit (PVC): Permanent, logical association between two DTEs that is analogous to a leased line. Transmission of packets on a PVC needs no call setup or call clearing by the DTE; packets are routed directly by the network from one DTE to the other. Supported in DECnet-Plus for DECnet Phase IV compatibility.

phase: Discrete period of protocol exchanges having a specific purpose that involves a single FTAM function. Phases occur sequentially and cannot overlap. Often two phases within one regime are paired, so that after the initial phase occurs, the other must eventually follow. Examples: the selection and deselection phases.

Phase IV area: See DECnet Phase IV area.

Phase IV end node: See DECnet Phase IV end node.

Phase IV level 1 router: See DECnet Phase IV level 1 router.

Phase IV level 2 router: See DECnet Phase IV level 2 router.

physical address: Unique address of each physical connection of a node to the physical media.

physical connection: Physical layer communications path between two systems.

physical connectivity: Physical layer connectivity that is a result of nodes being attached to each other via active lines and nodes.

Physical layer: Bottom layer (Layer 1) in the OSI Reference Model; connects systems to the physical communications media.

Physical level: X.25 protocol level that defines the characteristics of the physical link between the user's equipment and the PSDN equipment. Also known as level 1.

physical media: Any means in the physical world for transferring signals between OSI systems; considered to be outside the OSI Reference Model and, therefore, sometimes referred to as "Layer 0." The physical connector to the media can be considered as defining the bottom interface of the Physical layer, that is, the bottom of the OSI Reference Model.

plug-in: User-configurable portion of the director.

point-to-point circuit: Circuit that connects only two nodes. A point-to-point configuration requires a separate physical connection between each pair of nodes. Point-to-point systems communicate directly with other systems. (DECnet-Plus supports point-to-point and broadcast connections.) Contrast with multipoint circuit.

point-to-point line: Line that connects two systems by using a single circuit.

polling: Scheme for how the tributaries on a multipoint circuit gain access to the communications path.

Tributaries cannot access the path until polled by the control station, usually on a sequential basis. A tributary waits its turn to access the communications path. Tributaries always send data to the control station, which forwards the data to other tributaries, if necessary.

portal mode: Mode of the DEC X25gateway system that allows systems running X.25 software, both DIGITAL systems and multivendor systems, to communicate over PSDNs and over DECnet-Plus networks.

POSI (Promoting Conference for OSI): Consortium of executives from the six major Japanese computer manufacturers and Nippon Telephone and Telegraph; sets policies and commits resources to promote OSI.

positional file transfer: NIST implementation profile that requires an FTAM implementation to be able to transfer files with an unstructured or sequential flat constraint set, that is, files with an FTAM-1, FTAM-2, or FTAM-3 document type. Also known as NBS profile T2 and SPAG profile A112. See also simple file transfer.

Postal, Telegraph and Telephone Authority (PTT): Country's national communications provider, generally European.

presentation address: See p-address.

presentation connection: Link established by the OSI Presentation layer between two users of the presentation service.

presentation context: Association of an abstract syntax with a transfer syntax.

Presentation layer: Layer 6 in the OSI Reference Model; coordinates the conversion of data and data formats to meet the needs of the individual application processes; provides the proper means of transferring information while preserving its meaning.

Presentation service: OSI service provided by the Presentation layer, as defined in International Standard ISO 8822.

primitive: See service primitive.

primitive name: Name that denotes a single, unique object.

principal: Individual user, or group of users, for which access rights to DECdns names can be assigned and checked. A principal name is part of an access control entry (ACE). See also access control entry.

private line: See dedicated line.

Private Management Domain (PRMD): X.400 message handling system private mail system. Example: NASAmail. See also Administration Management Domain.

profile: Defined as:

• Virtual Terminal --- Specific set of predefined values that both systems in the Virtual Terminal association use to translate information by means of local mapping. Each profile has a unique name, which a Virtual Terminal initiator supplies to a Virtual Terminal responder when negotiating an association.
• X.25 --- File that defines the default values for the call parameters of outgoing calls.

Promoting Conference for OSI: See POSI.

protocol: Defined as:

• General data processing --- Set of rules and procedures.
• Data communications --- Set of rules and procedures that defines message exchange between communicating processes; defines the format and contents of messages.

protocol control information (PCI): Encoded specifications about services and their parameters; added by an OSI entity to the service data unit (SDU) passed down from the layer above, all together forming a PDU.

protocol data unit (PDU): Data units (messages or blocks of data) passed between peer entities on different open systems. The information is made up of protocol control information (PCI) from the current layer and, possibly, user data from the layer above. OSI terminology for packet.

protocol ID: Five-byte field in the header of a Subnetwork Access Protocol (SNAP) frame on a LAN, used to identify the Data Link layer client at the destination system receiving this frame.

protocol machine: Set of data structures and routines that implements a specific protocol and controls the progress of a communication between peer entities.

protocol overhead: Part of communications data or processing not directly consumed by the users but necessary to successfully bring about the transfer of user information. Also called control data.

protocol sequence: Ordered list of protocol identifiers.

protocol transparency: Degree to which users of underlying protocols are aware of the specifics of those protocols.

protocol type: Two-byte field in the header of an Ethernet frame, used to identify the Data Link layer client at the destination system receiving this frame.

proxy login: Procedure that permits a remote user to access a specific account at the local node, without supplying the user name and password.

PSDN: See packet switching data network.

PSTN: See public switched telephone network.

PTT: See Postal, Telegraph and Telephone Authority.

public data network: PSDN administered by a public service provider.

public switched telephone network (PSTN): Public packet switching data network.

PVC: See permanent virtual circuit.

RARE (Reseaux Associes pour la Recherche Europeenne): European association of research networks.

RD: See redirect packet.

reachable address: Address prefix in a reachable-address table, for example, an address prefix that maps a destination NSAP address to a destination DTE address/DTE class pair for an outgoing call into an X.25 subnetwork.

reachable-address table: Table on a DECnet-Plus intermediate system that lists address prefixes that are reachable over a circuit; manually-entered routing information that allows packets to be forwarded to subnetworks that do not participate in DECnet-Plus routing, such as DECnet Phase IV subnetworks, X.25 subnetworks, and multivendors' systems.

reachable node: Node to which the local node has a usable communications path.

read access: Access right that grants the ability to view DECdns data.

read-only replica: Copy of a DECdns directory in which applications cannot make changes. Although applications can look up information (read) from it, they cannot create, modify, or delete entries in a read-only replica. Read-only replicas become consistent with other, modifiable replicas of the same directory during skulks and routine propagation of updates.

real file: FTAM-named collection of user data and its attributes that resides in a real filestore.

real filestore: Organized collection of files on a real FTAM system that includes their attributes, such as file names. Each virtual file reference maps to a real file in the real filestore.

reassembly: Routing process of reconstructing a complete data message from received fragments. See also fragmentation.

receive: Routing process that handles incoming messages that have been sent to the router.

receiver: FTAM entity that reads, or receives all or part of a file's contents, during the file-data transfer regime. During an association, an FTAM entity can alternate between sending and receiving data in any order.

Record Management Services (RMS): On DECnet-Plus for OpenVMS systems, set of file-management procedures called by programs to process files and records within files. Used by FTAM software.

redirect NPDU: Network PDU issued by an intermediate system to a source node when it forwards a data network PDU onto the same circuit from which it was received; includes the Data Link layer address to which the network PDU was forwarded. This indicates to the sender of the original data network PDU that it should send subsequent data network PDUs destined for the same NSAP address directly to that address, as the destination can be reached either directly or by a better route.

redirect packet (RD): Redirect packet as defined by ISO 9542.

Reference Model: See ISO Reference Model for Open Systems Interconnection.

regime: Period during which communicating FTAM entities share a standard state that permits a distinct set of FTAM services, such as those associated with data transfer, that are constrained by the current values of activity attributes.

relative time: Discrete time interval that is usually added to or subtracted from an absolute time; used by DECdts software.

Reliable Transfer Service Element (RTSE): Lightweight OSI application service used above X.25 networks to handshake application PDUs across the session service and TP0. (Not needed with TP4.)

remote application address: Address for outgoing FTAM communications that contains a p-address and that accesses a remote responder. On DECnet-Plus for DIGITAL UNIX systems, also contains an application-entity (AE) title. On DECnet-Plus for OpenVMS systems, optionally contains other information, for example, an AE-title.

remote DTE: DTE in a network other than the one at which the user is located.

remote node: Node in the network other than the local node.

Remote Operations Service Element (ROSE) protocol: Lightweight remote procedure call (RPC) protocol, used in these OSI application protocols: message handling, directory, and network management. Transaction-based protocol (as opposed to standard file transfer protocols). See also remote procedure call.

remote procedure call (RPC): Easy and popular paradigm for implementing the client/server model of distributed computing. A request is sent to a remote system to execute a designated procedure, using specified arguments, and the result is returned to the caller. The OSI RPC protocol is Remote Operations Service Element (ROSE).

remote task: Task either executing at a remote host or originating there.

repeater: Bidirectional device that amplifies or resynchronizes signals into standard voltages, currents, and timing; propagates electrical signals from one Ethernet to another without making routing decisions or providing packet filtering; Physical layer intermediate system. See also bridge and router.

repertoire: Virtual Terminal --- Set of representations of symbols, such as numeric, graphic and control characters. Each profile has a specific repertoire associated with it.

replica: Copy of a DECdns directory. The first instance of a directory in the namespace is the master replica. When DECdns managers make copies of the master replica to store in other clearinghouses, all of the copies, including the master replica, become part of the directory's replica set. Replicas other than the master are read-only replicas.

replica set: Set of all copies of a directory. Information about a directory's replica set is contained in an attribute of directories and child pointers called DECdns$Replicas. The attribute contains the type of each replica master, secondary, read-only and the clearinghouse where it is located. When skulking a directory, DECdns refers to the directory's replica set to ensure that it finds all copies of that directory. During a lookup, DECdns may refer to the replica set in a child pointer when trying to locate a directory that does not exist in the local clearinghouse.

requester: Peer entity that requests a service.