HP OpenVMS Systems Documentation

Service user that initiates a particular action, such as requesting a service from a peer entity.

request primitive: Primitive issued by a service user to ask for a function and provide parameter values, if necessary.

responder: Defined as:

• OSI --- Peer entity that receives an association request.
• FTAM --- Application process that accepts an incoming request from an initiator to establish an FTAM regime; maps the incoming requests to actions performed on the real filestore.
• Virtual Terminal --- Component that reacts to requests from a remote virtual terminal initiator.

responding host: Host on which a responding OSI application executes.

responding task: Task that receives and processes a request for an OSI transport connection.

response primitive: Primitive issued by a service user to confirm negotiated parameter values that the user accepts and to return attribute values that the initiating user requests.

resynchronization: Process that enables the recovery of user information lost or corrupted during transfer across an association. Sets the association back to the state it was in at a specified point in the transfer.

retransmission: Method of error recovery in which stations receiving messages acknowledge the receipt of correct messages and, on receipt of incorrect messages, either do not acknowledge or acknowledge in the negative. The lack of acknowledgment or receipt of a negative acknowledgment indicates to the sending station that it should transmit the failed message again.

RMS: See record management services.

root directory: Top directory in the DECdns namespace, designated by a dot (.).

ROSE: See Remote Operations Service Element.

round-trip delay: Total time, during communications that implement a protocol with positive acknowledgments, for a message to be transmitted, arrive at its destination, and its corresponding acknowledgment to be sent and subsequently received by the sender of the original message.

route through: Packets not destined for the local node. See also forward.

router: See intermediate system.

routing: Network layer function, implemented in intermediate systems, that determines the path along which data travels to its destination and the movement of that data. See also decision.

routing algorithm: See link state algorithm and routing vector algorithm.

routing domain: Collection of end systems, intermediate systems, and subnetworks that operates according to the same routing algorithm, and in which routers exchange routing information; resides within an administrative domain. Within an administrative domain, the routing domains can be DECnet-Plus routing domains. Can be divided into subdomains, or areas.

routing layer: See Network layer.

routing node: See intermediate system.

routing protocol: See routing vector algorithm and link state algorithm.

routing record: Database entry that associates a subnetwork address of an adjacent system with an NSAP address.

routing vector algorithm: DECnet Phase IV routing algorithm; routers exchange network reachability information with adjacent routers. Contrast with link state algorithm.

RPC: See remote procedure call.

RTSE: See Reliable Transfer Service Element.

SAP: See service access point.

SDU: See service data unit.

security attributes: Attributes that control access to a file on an FTAM system.

Security filter: Entity that defines an access control list (ACL) on an X.25 system that controls who can access a filter.

security information: FTAM initiator identity and, optionally, a filestore password and account. DECnet-Plus users can specify security information as part of the DECnet-Plus for OpenVMS or DECnet-Plus for DIGITAL UNIX file specification. On DECnet-Plus for OpenVMS systems, users can also specify security information with a DCL qualifier.

segmentation: Division of a block of user data into smaller units, known as segments, for transfer across a connection.

selector: Identifier used by an OSI entity to distinguish among multiple service access points (SAPs) at which it provides services to the layer above; format is one of these: ASCII string, hexadecimal string, or null.

semiautomatic management: Type of network management in which a human system manager is not directly involved in a network management decision; rather, management software in a director makes decisions and takes actions on behalf of the system manager.

send routing message flag: Link State algorithm---Flag associated with each link state packet for each circuit on an intermediate system; when set, it indicates that the link state packet needs to be transmitted on that circuit.

send sequence number packet flag: Defined as:

• Link state algorithm --- Flag associated with each link state packet for each circuit on an intermediate system; when set, it indicates that information about the packet needs to be included in a partial sequence number packet transmitted on that circuit.
• Routing vector algorithm --- Flag associated with each circuit on a router; when set, it indicates that a routing vector message needs to be transmitted on that circuit.

sender: FTAM entity that writes (sends) either part of or all of the contents of a file during the file-data transfer regime.

sent packet: Packet passed from the local node's Network layer to its Data Link layer.

sequence number: Routing --- Field carried in link state packets (LSPs) that allows the receiver to determine if the received LSP is newer than the one it has stored in its link state database.

sequence number packet (SNP): Routing: Network protocol data units (PDUs) exchanged between intermediate systems that allow an intermediate system to determine if its link state database is up to date.

server: Component of a distributed application that provides a service, such as a file access or a database query, on behalf of a client.

server entity: Service provider in an asymmetric usage relationship between entities.

service: Task that an application can carry out.

Interface provided by a service element or layer for accessing one or more OSI functions.

service access point (SAP): Point at which an entity provides a service to a user entity in the layer above; interface at which a service provider delivers services to a service user. Named according to the layer providing the services; for example, transport services are provided at a Transport SAP (TSAP) at the top of the Transport layer.

service class: Set of functional units that supports a global function, such as file transfer, for an FTAM association.

service data unit (SDU): Data units (messages or blocks of data) passed between entities in adjacent layers on the same open system. The information is made up of a PDU received by a service provider from a service user.

service definition: International standard that describes the capabilities of a layer or the service it provides. Each layer provides a set of services at its upper boundary. Services are available to the next higher layer or, in the case of Application layer services, to the application processes. This set of services is the user's view of the functions performed by a layer.

service element: Portion of an OSI entity that provides services, such as routing, filtering, or data transmission.

service interface: Boundary at which a layer provides a service to the adjacent higher layer in the network architecture; may vary between implementations.

service parameter: Means by which a service user and a service provider exchange information.

service primitive: Message that carries the values of parameters for a specific service and that constitutes the smallest defined interaction between service users and providers. Service users issue service primitives to request services and to accept service requests from their peers on behalf of their own service users. Service providers use service primitives to pass incoming information to their service users. See also request primitive, indication primitive, response primitive, and confirm primitive.

service provider: Service element or layer that provides a set of services to the layer immediately above.

service specification: International standard that describes the functions and service parameters of every service of a service provider.

service user: Application program, service element, or layer that uses the services of a service provider.

session connection: Link established by the Session layer between two users of the session service.

Session Control: DNA layer that provides functions for system-dependent, process-to-process communication, name-to-address mapping, and protocol selection; works with DECdns software to translate names to addresses (for nodes and application services) and selects the appropriate protocols to be used at each layer; provides the application interface into the other DNA layers. Compare with Session layer.

Session Control application database: Collection of memory-resident Session Control application entities on a system. Each entity stores identifying information about an application; MAIL, CML, and FAL are examples of applications supplied by the DECnet-Plus implementations. The characteristics of user-written applications also are described in Session Control application entities. These Session Control application characteristics include the task name, image file name, and user name.

Session Control layer: See Session Control.

Session layer: Layer 5 in the OSI Reference Model; organizes and structures the interactions between pairs of application processes. Compare with Session Control.

Session service: OSI service provided by the Transport layer, as defined in International Standard ISO 8326.

set host: Feature of DECnet-Plus for OpenVMS software that allows users of one system to log in to other systems. Comparable to Berkeley UNIX rlogin, DECnet-Plus for DIGITAL UNIX software's dlogin, and DECnet-Plus' Virtual Terminal (VT) software.

set-valued attribute: DECdns attribute that contains a set of values, rather than a single value.

SFDP: See short format data packet.

short format data packet (SFDP): Short format protocol header used for data packets on point-to-point subnetworks when communicating with DECnet Phase IV nodes. Contrast with long format data packet.

simple file transfer: NIST FTAM implementation profile that requires the ability to transfer entire files using an unstructured constraint set, that is, files with an FTAM--1 or FTAM--3 document type. Also known as NBS profile T1, SPAG profile A111, and CEN/CENELEC profile ENV 41 204. See also positional file transfer.

simple name: One element in a DECnet-Plus full name that is delineated by dots. The rightmost simple name in a DECnet-Plus full name.

single-valued attribute: Attribute that expresses a single value rather than a set of values. For example, the DNS$CTS attribute expresses the creation timestamp of the DECdns namespace entry with which it is associated. Contrast with attribute set.

sink: Logical repository used to receive logged events. A logging sink can be a file or console located on an end system.

skew: Time difference between two clocks or clock values.

skulk: Process by which DECdns makes the data consistent in all replicas of a particular directory. DECdns collects all changes made to the master replica since the last skulk completed, and applies them to the replica on the server where the skulk started. It then disseminates the changes from the up-to-date replica to all other existing replicas of the directory. A skulk also performs cleanup functions that include removing soft links that have timed out, removing information about deleted directories, and adding information about newly created directories.

SNAP: See Subnetwork Access Protocol.

SNDCF: See subnetwork dependent convergence function.

SNP: See sequence number packet.

soft link: Pointer that provides an alternate name for an object entry or directory in the DECdns namespace.

source service access point (SSAP): One-byte field in an LLC frame on a LAN that identifies the link service access point of the sending Data Link layer client protocol.

source task: Task that initiates a transport connection request in a task-to-task communication environment.

SPAG: See Standards Promotion and Application Group.

spanning tree: Logical arrangement created by bridges in an extended LAN in which all LANs are connected and there are no loops.

splitting: Process of mapping one transport connection to several network connections.

SSAP: See source service access point.

stack: Protocol sequence along with associated address and protocol-specific information. DECnet-Plus systems and applications have multiple stacks, which describe various sets of protocols for communicating with the node. The term tower is often used to mean a stack.

Standards Promotion and Application Group (SPAG): Group of European OSI manufacturers that defines a set of profiles for FTAM implementations for its members and publishes these profiles in Guide to the Use of Standards (GUS).

static routing: Routing using manually entered information; nonadaptive routing. Contrast with adaptive routing.

station: Termination of a communications link of Physical and Data Link layer entities.

status: Network management entity group that contains attributes pertaining to an entity's state. Status attributes may change through direct management commands, such as ENABLE or DISABLE, or by the system itself.

storage attributes: Attributes that deal with the actual storage of a file on a local system, for example, information on accounting and file size.

subaddress: Subaddress that identifies the Internet service provider (particular subscriber line or group of lines) of an X.25 subnetwork; some number of digits of an adjacent system's X.25 subnetwork address; defined by the PSDN provider.

subdomain: See area.

subentity: See child entity.

sublayer: See subnetwork dependent sublayer and subnetwork independent sublayer.

subnetwork: Communications network (within a group of interconnected networks) that is a collection of OSI end systems and intermediate systems in which all systems use a common addressing format and that forms an autonomous whole. Examples: HDLC data link, ISO 8802-3 LAN, and X.25 packet switched network.

Subnetwork Access Protocol (SNAP): Form of LLC frame used on LANs in which multiplexing uses a 5-byte protocol ID field; allows higher layer protocols that are not international standards to be addressed.

subnetwork address: X.25 PSDN DTE or physical address of a system on a local subnetwork.

subnetwork dependent convergence function (SNDCF): Set of functions required to enhance the service provided by a particular subnetwork as defined by the CLNS protocol (ISO 8473).

subnetwork dependent sublayer: Sublayer of the Network layer that interfaces to the Data Link layer; masks the characteristics of the different types of subnetworks from the subnetwork independent sublayer so that they all appear the same to the subnetwork independent layer. Some of its functions are: setting up calls on dynamically established data links (DEDs), clearing calls on dynamically established data links, and determining the reachability of adjacencies.

The Data Link layer protocol is not transparent to the subnetwork-dependent sublayer. The subnetwork dependent sublayer provides protocol transparency to the subnetwork-independent sublayer; that it, it masks the characteristics of the different types of subnetworks.

subnetwork independent sublayer: Sublayer of the Network layer that performs all routing functions required to route data to its destination, for example, establishing and maintaining the routing database on each router, extracting and interpreting the route header in packets, determining the best route for packet forwarding, and performing packet forwarding based on the destination address. See also decision, update, and forward.

subordinate entity: See child entity.

subscriber line: Physical line between a DCE and the local exchange in a public data network.

superior entity: See parent entity.

SVC: See switched virtual circuit.

switched line: Communications link for which the physical path can vary with each use, such as the dial-up telephone network.

switched virtual circuit (SVC): Temporary logical association between two DTEs to a PSDN and analogous to a dial-up line; is set up only when there is data to transmit and is cleared when the data transfer is complete.

Dynamically established data link that supports routing over X.25.

switching: Identifying and connecting independent transmission links to form a temporary, continuous path from the source to the destination. Contrast with dedicated line.

synchronization: Process by which a DECdts entity requests clock values from other systems, computes a new time from these values, and adjusts its system clock to the new time.

synchronization list: List of DECdts servers that a DECdts entity has discovered. The entity sends requests for clock values to the servers on the list.

synchronization points: Markers positioned in data that is being transferred, allowing an application to recover lost or corrupted data.

synchronous disconnect: Disconnect that occurs when a nontransparent task issues a call to terminate I/O operations over a transport connection without deassigning the channel. Thus, the task can use the channel for subsequent I/O operations with the same remote task or a different one.

synchronous link: Communications link using synchronous transmission, in which transmission of a block of data is preceded by a special synchronization sequence. Data is transmitted at a fixed rate with the transmitter and receiver synchronized.

synchronous transmission: Data transmission in which characters are transmitted at a fixed rate. The transmitter and receiver are synchronized, gaining greater efficiency than in asynchronous transmission. Synchronous transmissions send a predetermined group of "sync" characters ahead of a long stream of data. The sync characters enable the communicating devices to synchronize with each other in accordance with time clock at each end. Contrast with asynchronous transmission.

syntax: Descriptive technique used to convey information.

syntax transformation: Transformation of data back and forth between local data and data that is interpretable by other FTAM systems using a presentation context (abstract syntax/transfer syntax pair).

system: Information-processing unit that supports the Data Link, Network, Transport, and Session layers; single, addressable unit, such as a computer, workstation, or peripheral device. Each system has a unique Network layer address. Also called node.

system time: Time value that the operating system maintains according to its reading of the system's hardware clock.

tap: Entry point at which the transceiver connects to an Ethernet cable.

target system: Intended destination of messages.

target task: Task that receives and processes a transport connection request in a task-to-task communication environment.

task: Image running in the context of a process.

task specifier: Information provided to DECnet-Plus software so it can complete a transport connection to a remote task. This information includes the name of the remote node on which the target task runs and the name of the task itself.

task-to-task communication: Communication between two processes using DECnet-Plus or mailboxes. These processes may be on different systems, using different operating systems and languages.

TDF: See time differential factor.

Telnet: Virtual terminal protocol in TCP/IP. See also virtual terminal.

template: Network management --- Named collection of module-specific attributes that can be referenced by a client of the module without knowing their individual significance.

terminal emulator: Program that acts as a transparent interface between two ports, making it appear as though a terminal on the local system is connected directly to a remote system.

terminal server: System that handles terminal operations for host nodes on a LAN; can be used to connect terminal users to nodes on the same LAN and to users on nodes located off the LAN. Offload the terminal connection and I/O responsibilities from host nodes, and reduce the number of direct terminal connections to each host, saving substantial power, packaging, and cabling expense.

terminating packet: Packet whose destination is the local node.

test access: Access right that grants DECdns users the ability to test whether an attribute has a specific value without having read access to the attribute. This right is useful for client application programmers: testing for a specific value in a set is more efficient than reading the whole set of values.

test name: Argument of the test entity directive that identifies the test to be performed.

third-party router: OSI intermediate system that implements ISO ES-IS, but does not have the same implementation of the DECnet-Plus IS-IS protocol as DEC WANrouter systems.

throughput: Measure of how much data is sent, or can be sent, between two points in a specified unit of time; often used in either of two contexts:

• Rated throughput, which refers to the bandwidth or capacity of a component.
• Real throughput, which refers to actual measured throughput.

tick: Clock timer interrupt that causes the operating system to increment the system time.

time differential factor (TDF): Difference between Coordinated Universal Time (UTC) and the time in a particular time zone. Used by DECdts software.

time provider: Hardware device that monitors UTC time and forwards it to a DECdts server.

timestamp: See creation timestamp (CTS) and binary timestamp.

token: Mechanism for determining which side of an association can initiate certain services; the means by which peer entities agree on which of them can call certain services. Token management is the allocation and exchange of tokens between peer entities.

Mechanism for controlling the use of request primitives for token-controlled services by a specific entity.

topology: Logical arrangement of interconnected systems regardless of their physical locations.

tower: Protocol sequence along with associated address and protocol-specific information. DECnet-Plus systems and applications have multiple stacks, which describe various sets of communications protocols. The term tower is often used to mean a stack.

TP: See Transport Protocol.

TP0: OSI Transport Protocol Class 0 (Simple Class); the simplest OSI Transport Protocol, useful only on top of an X.25 network or other network that does not lose or damage data.

TP2: OSI Transport Protocol Class 2 (Simple Class); same as Class 0, but with the added features of multiplexing and optional flow control.

TP4: OSI Transport Protocol Class 4 (Error Detection and Recovery Class); the most powerful OSI Transport protocol, useful on top of any type of network. OSI equivalent to TCP.

TP server: DECdts server system connected to a time provider.

trace: Software function for analysis of messages that pass between peer entities; provided by Common Trace Facility (CTF), for example. See also Common Trace Facility.

traffic: Measurement of data flow, volume, and velocity over a communications link.

transceiver: Transmitter-receiver; physical device required in baseband networks that takes the digital signal from a computer or terminal and imposes it on the baseband medium; connects a host interface to a LAN, such as Ethernet.

transfer syntax: Machine-independent form in which data passes between peer entities.

Set of rules used in the formal specification of data that embodies a specific representation of that data, allowing its transfer between open systems. See also syntax transformation.

transient information: Network management information carried in an operation; is meaningful only while the operation is being performed.

transit packet: Packet arriving from a source node at an intermediate system that is destined for another node. See also route through.

transport address: Identifier that specifies the location of a transport service access point (TSAP). See also transport service access point.

transport connection: Link established by the Transport layer between two users of the transport service.