# DIGITAL TCP/IP Services for OpenVMS
Concepts and Planning

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broadcast: A delivery system where a copy of a packet is sent simultaneously to many hosts; can be implemented with hardware (for example, as in Ethernet) or with software (for example, as in Cypress). See also multicast.

broadcast address: The address that designates all entities within a domain (for example, network, Internet).

broadcast addressing: A type of multicast addressing in which all nodes receive a message simultaneously.

broadcast circuit: A circuit on which multiple nodes are connected. A message can be transmitted to multiple receivers, and all nodes are adjacent.

broadcast end node adjacency: An end node connected to the same broadcast circuit as the local node. See also adjacency.

broadcast router adjacency: An intermediate system (router) connected to the same broadcast circuit as the local node. See also adjacency.

broadcast mask: A mask used to interpret the IP address as a broadcast address.

broadcast storm: An incorrect packet broadcast on a network that causes most hosts to respond all at once, typically with wrong answers that start the process over again.

brouter: A bridge/router: device that forwards messages between networks at both network and data link levels.

BSD: See Berkeley Software Distribution.

Bulletin Board System (BBS): A message database where people can log in and leave broadcast messages for others grouped (typically) into topic groups.

buffer: A device or an area of memory used for temporary storage when transmitting data from one device to another. Compensates for a difference in rate of data flow or in time of occurrence of events. Used on routing nodes to temporarily store data that is to be forwarded from one node to another.

buffering level: The number of buffers provided at one time by the network software to handle data. Level can be single or multiple. Single buffering tends to be less efficient than multibuffering but uses less memory on the local system. Multibuffering provides better performance, and a network can send or process several buffers of data in quick succession.

bus: (1) A LAN topology in which all nodes connect to a single transmission medium. All nodes are equal, and all nodes hear all transmissions on the medium. Bus topologies are reliable because failure of a node does not affect the ability of other nodes to transmit and receive. (2) A flat, flexible cable consisting of many transmission lines or wires used to interconnect computer system components to provide communication paths for addresses, data, and control information.

cache: A portion of a computer's RAM reserved to act as a temporary memory for items read from a disk. These items become instantly available to the user.

cache server: A BIND server that has no authority for any zone; acquires information in the process of resolving clients' queries and stores it in its cache. See also BIND server, forwarder server, primary server, and secondary server.

canonical name: The main or official name for a host; other names for the same host are aliases.

catenet: The network in which hosts are connected to networks with varying characteristics, and the networks are interconnected by gateways.

centralized management: A form of network management that manages from a single point in the network.

CFS: See container file system.

CFSRTL: See container file system RTL.

channel: The data path between two or more stations, including the communications control capability of the associated stations.

checksum: A computed value based on the contents of a packet. The value is sent with the packet when it is transmitted. The receiving host computes a new value based on the received data. If the originating and receiving values are the same, the receiver has a high degree of confidence that the data was received correctly.

circuit: A logical (virtual) link that provides a communications connection between adjacent nodes.

class name: The name of an entity class. For example, node is the global entity class.

client: A computer system or process that requests a service of another computer service or process.

client/server relationship: A model of interaction used in distributed processing products when a client process sends a request and waits for the results from a server process.

clock: The combined hardware interrupt timer and software register that maintain system time. In many systems, the hardware timer sends interrupts to the operating system; at each interrupt, the operating system adds an increment to a software register that contains the time value.

cluster alias: An optional node name and address used by some or all nodes in an OpenVMS cluster, allowing these nodes to be reachable on the network with the same address.

collision: The condition in which two data packets are transmitted over a medium at the same time, making both unintelligible.

common address notation: The common way of expressing an Internet address. The 32-bit address uses four fields that are separated by periods; each field ranges from 0 to 255.

communications link: The physical medium connecting two systems.

communications server: A special-purpose standalone system dedicated to managing communications activities for other computer systems.

concatenation: The process of joining two or more items together, as when input files are appended to a new output file.

configuration database: The UCX database with SMTP, SNMP, and TIME specifications.

congestion: The condition in which a network or part of a network is overloaded and has insufficient communication resources for the volume of traffic.

connection: A logical communication path between two processes.

connection-oriented: The model of interconnection that consists of three phases: establish connection, transfer data, and release connection. TCP is a connection-oriented protocol.

connectionless: The model of interconnection in which communication takes place without first establishing a connection. UDP, IP, and IPX are connectionless protocols.

connectivity: The degree to which network nodes are interconnected. Full connectivity means all nodes have links to every other node.

container file: A data file on a DIGITAL UNIX NFS server with a UNIX directory structure and UNIX file attributes for a local, logical UNIX-style file system. Each UNIX regular file is stored as a separate data file using. The directory data files in the container file contain the UNIX file names and a pointer to the corresponding OpenVMS Files-11 data file.

container file system (CFS): A logical UNIX-style file system that resides on a Files-11 formatted disk and is represented as a set of Files-11 files. See also container file.

container file system RTL (CFSRTL): The OpenVMS Run-Time Library (RTL) that is used by the NFS server to process files in the UNIX-style container file system.

contention: The condition when two or more stations attempt to use the same channel at the same time.

contention control: The scheme of access control used by many networks. Control is distributed among the nodes of the network. Any node wanting to transmit can do so, accessing the network on a first-come, first-served basis. However, it is possible that two nodes are in contention, or start transmitting at the same time, in which case a collision occurs. Each node must then back off and retransmit after waiting a random period of time.

control cluster: A group of small (256-byte) buffers dynamically allocated from nonpaged pool memory; stores information related to device sockets, internal control structures, IP addresses, Internet routes, and Internet packet headers.

counters: The performance and error statistics kept for an entity by network management, such as lines and nodes.

CRC: See cyclic redundancy check.

cyclic redundancy check (CRC): An error detection scheme whereby a number is derived from a set of data before it is transmitted. Once transmitted, the receiving node recalculates the number and compares it to the value originally transmitted. If the numbers are different, some type of transmission error has occurred.

daemon: A process that executes in the background waiting for some event to occur.

data cluster: A group of large (1792-byte) buffers that store data in the system space; transmit and receive operations service user processes by moving data to and from data clusters.

data encryption key (DEK): Used for encryption of message text and (with certain choices among a set of alternative algorithms) for computation of message integrity check (MIC) quantities.

Data Encryption Standard (DES): A type of encryption scheme approved by the U.S. National Bureau of Standards.

data link: A logical connection between two systems on the same circuit on which data integrity is maintained.

Data Link layer: The layer in a network model that handles communication between physical hosts.

data octet: See octet.

data overrun: The data blocks received that arrived too quickly to be processed by the receiver and were, therefore, lost.

datagram: A self-contained package of data carrying enough information to be routed from source to destination without reliance on earlier exchanges between source and destination or the transporting network.

datagram fragment: The result of fragmenting a datagram. Fragments carry a portion of data from the larger original and a copy of the original datagram header. The header fragmentation fields are adjusted to indicate the fragment's relative position within the original datagram.

datagram service: The mode of delivery for a datagram which is delivered in such a way that the receiver can determine the boundaries of the datagram as it was entered by the source.

DCE: See Distributed Computing Environment.

DCL: See Digital Command Language.

decision: The routing process that determines the path, or route, along which a data packet travels to reach its destination; forwards packets on the lowest-cost path even if that one does not have the fewest hops. The path that the data takes through the network is transparent to users.

decoding: The process by which the transfer syntax representation of a data value is transformed into the local representation of that value.

default route: The route used to direct any data addressed to network host addresses for which no explicit route is specified.

delete access: The access right that grants users the ability to remove data from the domain.

DEK: See data encryption key.

DES: See Data Encryption Standard.

destination address: The IP address that specifies where a datagram is to be sent; contains the network and host identifiers.

destination port: A 2-octet value in the TCP and UDP header field that identifies the destination upper-level protocol for a packet's data.

device driver: The software associated with each physical device; serves as the interface between the operating system and the device controller.

device socket: The extension of the pseudodevice, used for communications; consists of the Internet pseudodevice and the socket. See also pseudodevice.

dialogue: The sequence of message exchanges between open systems that represents a single association and the set of underlying connections.

dialup: A temporary (as opposed to dedicated) network connection established through a telephone line with a modem.

Digital Command Language (DCL): The command interface of the OpenVMS operating system.

DIGITAL TCP/IP Services for OpenVMS: The Digital Equipment Corporation software product implemented on OpenVMS as an ancillary control process (ACP) and a network device driver (BG driver) with executive-level components and user applications that use TCP/IP protocols. Also called UCX.

Distributed Computing Environment (DCE): An architecture of standard programming interfaces, conventions, and server functions (for example, naming, distributed file system, remote procedure call) for transparently distributing applications across networks of heterogeneous computers.

distributed database: A collection of several different data repositories that look like a single database to the user. The Domain Name Service (DNS) is a distributed database.

distributed management: A form of network management in which network managers and management software are dispersed across many systems.

distributed processing: The technology that enables the distribution throughout the network of computing power and storage facilities to user work areas, such as offices, laboratories, or machines on factory floors.

distributed system: A collection of computer systems, tied together by communications networks for the purpose of sharing resources; end users do not need to be aware of the physical location of the shared resources.

DNS: See Domain Name Service.

domain: An organizational unit with administrative responsibility for naming networks or hosts. An internet domain name consists of a sequence of names (labels) separated by periods (dots); for example, tundra.mpk.ca.us.

Domain Name Service (DNS): A distributed database system that allows TCP/IP applications to resolve a host name into a correct IP address.

dot address: See dotted decimal notation.

dotted decimal notation: The syntactic representation for a 32-bit integer that consists of four 8-bit numbers written in base 10 with periods (dots) separating them; used to represent IP addresses in the Internet, as in: 192.67.67.20. Many Internet application programs accept dotted decimal notation in place of destination machine names.

downline loading: Transferring a copy of a system image from a load host node to a target node. Some systems, such as DEC WANrouter systems and DECserver terminal servers, automatically request a downline load of their image upon startup and reboot.

drift: The change in a clock's time rate over a specified period.

dynamic adaptive routing: The automatic rerouting of traffic based on a sensing and analysis of current actual network conditions; not including cases of routing decisions taken on predefined information.

EGP: See External Gateway Protocol.

elective protocol: The classification in Internet standards for optional protocols.

electronic mail: The service whereby a computer user can exchange messages with other computer users (or groups of users) by means of a communications network; one of the most popular uses of the Internet.

email: See electronic mail.

encapsulation: A technique used by layered protocols in which a layer adds header information to the protocol data unit (PDU) from the layer below. As an example, in Internet terminology, a packet would contain a header from the physical layer, followed by a header from the Network layer (IP), followed by a header from the Transport layer (TCP), followed by the application protocol data.

encryption: A process of encoding information so the meaning of its content is no longer immediately obvious to anyone who obtains a copy of it.

end node: See end system.

end system: A nonrouting system; can receive data packets addressed to it and send data packets to other systems on the same subnet but cannot relay, route, or forward data packets to other systems.

entity: An individual, manageable piece of a network; has attributes that describe it, a name that identifies it, and an interface that supports management operations.

entity class: A collection of entities that share the same properties and have the same parent entity; each member of the class has a unique identifier within the class. Entity classes have class names.

entity group: An architecturally defined collection of entities. The entities in the group must have a common top entity and must all be of the same class.

entity hierarchy: A logical hierarchical tree structures of manageable entities in which child entities are below their parent entities. Children can be accessed only through their parents' agent.

entity identifier: An attribute that specifically identifies an entity. See also attribute group.

entity name: A label associated with some entities used to identify or locate them for management purposes.

entity type: The subgrouping of an entity that determines its relationship to other entities.

Ethernet: A baseband network medium. Commonly used to connect a local area network.

event: A measurable network- or system-specific occurrence for which a logging component maintains a record.

experimental protocol: The classification in Internet standards for protocols that are developed as part of an ongoing research project not related to an operational service offering; not intended for operational use.

export database: The UCX database with directory names that can be mounted from remote NFS clients.

exported file: A file in an exported directory or a subdirectory of an exported directory. See also exporting.

exporting: Identifying a directory on an NFS server that can be remotely mounted by NFS clients.

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

External Gateway Protocol (EGP): The protocol that distributes routing information to the gateways that interconnect networks.

FDDI: See Fiber Distributed Data Interface.

fetch/store operation: The operation of two commands that allow a system manager to fetch a value from a data item or to store a value into a data item.

Fiber Distributed Data Interface (FDDI): The high-speed (100 mb/s) networking standard based on fiber optics, established by the American National Standards Institute (ANSI); uses 1300 nanometer light wavelength. FDDI networks are limited to approximately 200 km in length, with repeaters every 2 km or less.

file: A uniquely named collection of information with shared managerial and structural properties.

file attribute: The characteristic of a file, such as its size or creation date. The values of some file attributes may change during the lifetime of a file.

file data: The 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 server: The host whose principal purpose is to store files and provide network access to them.

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

file system: A method for recording, cataloging, and accessing files on a volume.

File Transfer Protocol (FTP): The protocol and software that permit a user on one host to access and transfer files to and from another host over a network. See also Trivial File Transport Protocol.

Files-11 ODS level 2 structure: The set of rules that govern the organization of the OpenVMS file system, external to the files themselves.

Finger utility: The utility that provides information about users on local and remote systems.

flow control: (1) The function of a receiving entity to limit the amount or rate of data that is sent by a transmitting entity. (2) The control of the rate at which hosts or gateways inject packets into a network or Internet, usually to avoid congestion. Flow control mechanisms can be implemented at various levels and allow communicating layers to match their data transfer and receive rates. Simplistic schemes, like ICMP source quench, simply ask the sender to cease transmission until congestion ends. More complex schemes vary the transmission rate continuously.

forwarder server: The name server that processes recursive requests that a slave server cannot resolve locally; has access to the Internet. See also BIND server, cache server, primary server, secondary server, and slave server.

FQDN: See fully qualified domain name.

fragment: A piece of a packet that results from a router dividing an IP datagram into smaller pieces for transmission across a network that cannot handle the original datagram size. Fragments use the same format as datagrams; fields in the IP header declare whether a datagram is a fragment and, if so, where the data in the fragment occurred in the original datagram. IP software at the receiving end must reassemble the fragments. See also maximum transmission unit.

fragmentation: The IP process of breaking up packets into smaller packets for transmission; allows a packet originating in a network that allows a large packet size to traverse a network that limits packets to a smaller size. The destination host reassembles the fragments. See also maximum transmission unit.

frame: A Data Link layer packet that contains the header and trailer information required by the physical medium

FTP: See File Transfer Protocol.

full-duplex circuit: A 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.

fully qualified domain name (FQDN): The full site name of a system such as warren.enet.dec.com, rather than just its host name ---warren.

function code: A parameter in a $QIO system service call that defines the specific function of that $QIO.

gateway: A communications device or program that passes data between networks having similar functions but dissimilar implementations. The term "router" is now used in place of the original definition of "gateway."

gateway client: Another term for an access system.

GID: See group identification.

gigabit: One billion bits

gigabyte: One billion bytes

group identification (GID): The identification code for a group of UNIX users.

half-duplex circuit: A 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: The exchange of connection information between two communicating entities; takes place to enable the successful completion of a connection. Used, for example, in establishing a TCP connection between client and server applications.

hardware address: The address that identifies the connection device between the network controller of a host and the network cable. See also address.

hard link: A mechanism that allows you to assign more than one name to a file. Both the new name and the file being linked must be in the same file system. See link.

header: The portion of a packet that preceeds the actual data and contains control information such as source and destination address and error checking.

heterogeneous network: A network consisting of different network protocols or different operating system software, such as OpenVMS and UNIX.

hierarchical routing: Routing based on domains. Interdomain routers are responsible only for getting data to the right domain and intradomain routers take responsibility for routing within the domain.

hop count: The number of connections between two hosts, based on the number of different routers needed to traverse the distance between the two hosts.

hop: A term used in routing. Number of hosts separating a source and final destination (including the final destination) on a network.

host: A computer system that acts as a source or destination of network messages sometimes called "node."

host address: The part of an IP address that identifies which host on the network is being addressed.

hosts database: The UCX database that is created by default; allows users to use host names; contains host names, IP addresses of the hosts, and any alias names for the hosts.

host name: The name given to a network host. See also fully qualified domain name and alias.

Host-to-Host Communication layer: Also called Transport layer. The second-highest level in the Internet architecture model; provides end-to-end communication services, including mechanisms such as end-to-end reliability and network control. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) reside in this layer.

IAB: See Internet Architecture Board.

IBM TN3270: The TELNET options that allow TELNET users to connect to hosts that support 3270 model terminals.

ICMP: See Internet Control Message Protocol.

IGP: See Interior Gateway Protocol.

imported file: A file within a local NFS server that has been copied or linked to a remote NFS client.

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