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.