inetd: A UNIX internet daemon. A server
process listens for client requests for specific services. When
inetd receives a request for a service, it starts the
appropriate server process.
initial sequence number: The first sequence number
used for sending or receiving on a connection.
interface: The boundary between two parts of a system
across which communication is possible; may be defined through hardware
or software.
Interior Gateway Protocol (IGP): The protocol used to
propagate network reachability and routing information within an
autonomous system; RIP is among the most popular.
intermediate system: An OSI system that performs
Internet layer forwarding. A routing system receives data packets from
a system on one subnet and passes them on to a system on another
subnet; it receives data packets from a source end system, or from the
previous intermediate system on the route, and passes them on to the
destination end system, or to the next intermediate system on the route.
internet: A shortened form of internetwork; a network
of networks; interconnected TCP/IP networks that function as one large
virtual network. Differs from the Internet by their lack of
connectivity with the global Internet.
Internet: The worldwide network of networks and
gateways that use the TCP/IP protocol suite and function as one virtual
network; provides universal connectivity and three levels of network
services: unreliable, connectionless packet delivery; reliable,
full-duplex stream delivery; and application level services such as
electronic mail that build on the first two. The Internet connects many
universities, government research labs, military installations, and
private businesses.
Internet architecture: A four-layered communications
model that consists of the following: Application layer, Transport
layer, Internet layer, and Network Interface layer.
Internet Architecture Board (IAB): The technical body
that oversees the development of the Internet suite of protocols
(commonly referred to as "TCP/IP"). It has a research task force and an
engineering task force, each responsible for investigating a particular
area.
Internet Autonomous System: A system that consists of
a set of gateways, each of which can reach any other gateway in the
same system using paths by means of gateways only in that system. The
gateways of a system cooperatively maintain a routing database using an
interior gateway protocol.
Internet Control Message Protocol (ICMP): An extension
to the Internet Protocol; used by gateways to communicate with the
network software in hosts.
Internet header length: An IP header field that
indicates the number of 32-bit words making up the Internet header.
Internet layer: The layer in the TCP/IP network model
where data is transferred between hosts across networks. Also referred
to as Network Interface layer.
Internet number: See IP
address.
Internet Protocol (IP): A connectionless best-effort
packet switching protocol that resides in the Internet layer and has
two major functions: internet addressing and fragmentation of messages.
interoperability: The ability of software and hardware
on multiple machines from multiple vendors to communicate meaningfully.
InterNIC Registration Services: The Internet Network
Information Center; organization that provides the Internet community
with registration, directory, database and information services.
I/O status block (IOSB): A data structure associated
with the $QIO system service. The IOSB holds information about how the
I/O request completes.
IP: See Internet Protocol.
IP address: An address that identifies the connection
between the network controller of a node using TCP/IP and the network
cable. The 32-bit address is composed of two parts: network number and
host number.
IP datagram: The basic unit of information passed
across the Internet; contains source and destination addresses, the
data, and fields that define the length of the datagram, the header
checksum, and flags to say whether the datagram can be (or has been)
fragmented. An IP datagram is to the Internet what a hardware packet is
to a physical network. See also datagram.
IP trailer protocol: A protocol in which the protocol
header follows the data.
KA9Q: A popular implementation of TCP/IP and
associated protocols for amateur radio systems.
Kbps: See Kilobits per
second.
kernel: The software that provides the standard API
for application programs. Generally speaking, the kernel embodies the
policy and structure of an operating system. In a narrower sense, the
kernel provides a programmatic interface to any hardware resources
available. In a UNIX system, the kernel is a program that contains the
device drivers, the memory management routines, the scheduler, and
system calls; always running while the system is operating.
Kilobits per second (Kbps or Kb/s): The measure of
data transmission rate.
LAN: See local area network.
layer: (1) The grouping of related communication
functions that provide a well defined service to a client independently
of the protocols and other means used to provide it. (2) A software
protocol levels that make up network architectures; each layer performs
certain functions for the layers above and below it.
limited use protocol: A classification in Internet
standards for protocols that are for use in limited circumstances;
possibly due to their experimental state, specialized nature, limited
functionality, or historic state.
line printer daemon (LPR/LPD): The UCX remote printing
services for UNIX and OpenVMS client hosts.
line speed: The maximum rate at which data can be
reliably transmitted over a line; varies with the capability of the
modem or hardware device that performs the transmitting.
link: A directory entry referring to a file; one file
may have several links to it.
little endian: The format for storage or transmission
of binary data in which the least significant byte comes first. The
reverse convention is called big endian.
local address: The address of a host within a subnet.
local area network (LAN): A self-contained group of
computers and communications devices (such as modems, routers, servers,
and repeaters) that offers a high-speed, reliable communications
channel. LANs span a limited distance such as a building or group of
buildings, but can be connected to wide area networks (WANs) with
gateways. Contrast with wide area network
(WAN).
local data: Any data stored locally by a system.
local network: A network directly attached to a host
or gateway.
local node: A node at which the user is located.
local subnet: A subnet directly attached to a host or
gateway.
logical connectivity: The ability of nodes to
communicate.
logical link: A temporary connection between processes
on source and destination nodes (or between two processes on the same
node).
Logical Link Control: The upper portion of the Data
Link layer that presents a uniform interface to the user of the data
link service, usually the Internet layer.
loop node: A local node that is associated with a
particular address and is treated as if it were a remote node. All
traffic to the loop node is sent over the associated address; used for
loopback testing.
loopback: A program that sends packets to a remote
host on the Internet and looks for replies; works by means of the
echoing facility provided by the ICMP protocol and is a way to
determine if an Internet host is reachable from your host. See
also packet internet groper.
LPR/LPD: See remote line
printing or line printer daemon.
mail bridge: A mail gateway that forwards electronic
mail between two or more networks while ensuring that the messages it
forwards meet certain administrative criteria; specialized form of mail
gateway that enforces an administrative policy with regard to what mail
it forwards.
mail exchange record (MX record): The Domain Name
Service resource record type indicating which host can handle mail for
a particular domain or host.
mail exchanger (MX): The DIGITAL TCP/IP Services for
OpenVMS implementation of a mail exchanger that allows hosts in a local
network to forward mail to systems that might not be directly connected
to the local network.
mail exploder: The part of an electronic mail delivery
system that allows a message to be delivered to a list of addressees.
Users send messages to one address (e.g., hacks@somehost.edu) and the
mail exploder handles delivery to the individual mailboxes.
mail gateway: A host that connects two or more
electronic mail systems (especially dissimilar mail systems on two
different networks) and transfers messages between them.
mail path: A series of hosts used to direct electronic
mail from one user to another.
Management Information Base (MIB): A database used by
the Simple Network Management Protocol (SNMP) to check network
statistics and configurations. An SNMP management station can query a
MIB or set it in an SNMP agent (for example, router). Standard, minimal
MIBs have been defined (MIB I, MIB II), and vendors often have custom
entries. In theory, any SNMP manager can talk to any SNMP agent with a
properly defined MIB.
Management Information Base II (MIB II): Data that can
be accessed by a network management protocol; for UCX, the
database maintained by a gateway running SNMP.
management station: The workstation of a human network
manager running SNMP.
master file directory (MFD): The root of an OpenVMS
file system on a particular physical device.
master server: The name server that is the authority
for a specific domain space. See also BIND
server.
maximum transmission unit (MTU): The largest possible
unit of data that can be sent on a given physical medium. See
also fragmentation.
MBUFs: See memory buffers.
memory buffers (MBUFs): The portions of memory that
act as queues for data arriving at a port before the process is ready
to claim that data.
message: A message block, or a series of message
blocks, that constitute a logical grouping of information; each is
delimited by communications control characters.
MFD: See master file
directory.
MIB: See Management Information
Base.
MIB II: See Management Information
Base II.
MIME: Multipurpose Mail Extensions; a specification
for the transfer of nontext files with regular Internet e-mail.
mode: A protection placed on a file.
modem (modulator/demodulator): A device that
translates digital signals (electrical impulses) generated by a
computer into analog signals (tones) that can be transmitted over
telephone lines, and vice versa.
mount: An NFS process that makes a remote directory
available to local users.
MTU: See maximum transmission
unit.
multicast: A transmission of network traffic intended
for multiple hosts (but not all connected hosts) within a network or
internet.
multicast address: An address that designates a subset
of nodes that are all listening for packets destined to this address.
multicast addressing: An addressing mode in which a
data packet is targeted to a group of nodes that are of the same type,
for example, all level 1 routers or all level 2 routers.
multihomed host: A host that has two or more hardware
connections to a network; requires multiple IP addresses.
multiplexing: Using a single connection to carry
several data streams and the mechanism for assigning these streams to
that connection.
multipoint circuit: A circuit that connects multiple
systems.
multiprocessing system: A network consisting of
multiple processors.
MX record: See mail exchange
record.
NAK: See negative
acknowledgment.
name resolution: The process of mapping a host name to
its corresponding address. See Domain Name
Service.
namespace: A commonly distributed set of names in
which all names are unique.
negative acknowledgment (NAK): The response to receipt
of a corrupted packet of information. See also
acknowledgment.
network: A group of computer systems that can
communicate with each other; can be composed of computers in a single
building (local area networks or LANs), or computers thousands of miles
apart (wide area networks or WANs). The Internet is a worldwide
collection of computer networks that can intercommunicate.
network address: A unique identifier of a specific
system on a network, usually represented as a number or series of
numbers. See also IP address.
network architecture: The specification of a network's
functions and its parts, together with the ways in which the network is
organized; specifies the layers of different functions in the network,
ranging from data transmission at the lowest levels to user
applications at the highest levels.
network class: A definition of the type of network
addressing scheme being used; high-order bits in the network number
designate the network class of the IP address.
network database: The UCX database that allows users
to refer to networks by name rather than network number; contains
network names, IP addresses for the networks, and any alias names for
the networks.
network delay: The time it takes to get a unit of data
from the source of a transmission to the destination; usually refers to
delay from the network and not by system-dependent application
processing delays at source and destination nodes.
network diameter: The distance (number of hops)
between the two nodes in the network with the greatest reachability
distance. The reachability distance is the path with fewest number of
hops between two nodes.
Network File System (NFS): A protocol developed by Sun
Microsystems that allows a computer system to access files over a
network as if they were on its local disks.
Network Information Service (NIS): A set of services
in the Network File System that propagate information out from masters
to recipients; used for the maintenance of system files on complex
networks.
Network Interface layer: The layer in the TCP/IP
architecture model that provides the mechanism for connecting the hosts
to the networks.
network management: See MIB
II and Simple Network Management Protocol
(SNMP).
network mask: A mask used to determine the subnet in
the IP address; each bit that is turned on (binary one) in the mask is
interpreted as part of the network and subnet address. Synonymous with
subnet mask.
network meltdown: The state of complete network
overload; the network equivalent of thrashing. See also
broadcast storm.
network number: The part of an IP address that
designates the network to which the destination host belongs.
network performance: The description of how a network
performs, as measured against the expectations or requirements of
users, customers, designers, or implementors, or as claimed by sales
and marketing personnel. The criteria for network performance include
parameters such as throughput, response time, and resource utilization.
network status notification: Information about the
state of logical and physical links over which two tasks communicate. A
nontransparent task can use this information to take appropriate action
under conditions such as third-party disconnections and a partner's
exiting before I/O completion.
network task: A nontransparent task that can process
multiple inbound connection requests; that is, it has a declared
network name or object number.
Network Time Protocol (NTP): The protocol that ensures
accurate local timekeeping with reference to radio and atomic clocks
located on the Internet; capable of synchronizing distributed clocks
within milliseconds over long time periods.
NFS: See Network File System.
NFS client: The software that requests remote file
services from an NFS server. Client system users access files that
physically reside on an NFS server system.
NFS server: The software that provides remote file
services to NFS clients.
NFS server (OpenVMS server): A computer system that
offers services to NFS clients within an Internet environment; can be a
single host, a whole OpenVMS cluster system, or members of an OpenVMS
cluster system.
NIS: See Network Information
Service.
nobody: A UNIX convention used when file ownership is
not known; maps to an account with a UID and GID of --2.
node: (1) A system on a network; also referred to as a
host. (2) One member in an OpenVMS cluster system.
node address: The required unique numeric
identification of a specific node in the network.
node name: The alphanumeric identification associated
with the node address for one-to-one mapping.
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.
nontransparent task: A form of device-dependent I/O
that uses system services for 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.
normalization: The estimation of the change in a
counter value over a specified time period.
nslookup: The DIGITAL TCP/IP Services for
OpenVMS utility that allows you to interactively query domain name
servers (BIND servers) and helps you set up and manage the BIND server
software.
NTP: See Network Time
Protocol.
null modem: A simple form of modem connection where
only the data interchange circuits, and not the modem control circuits,
are used.
octet: A single 8-bit unit of data; used in networking
(rather than bytes) because some systems have bytes that are not 8 bits
long.
open network: A network made up of nonproprietary,
interoperable systems.
open system: A nonproprietary, interoperable system
with communications software.
Open System Interconnection (OSI): A suite of
protocols, designed by ISO committees, to be the international standard
of computer network architecture.
OpenVMS cluster: A configuration of OpenVMS processors.
OpenVMS cluster alias: An alias that allows remote
hosts to address the cluster members as one host, as well as any
cluster member individually.
OpenVMS file system: The OpenVMS files and directories
on a mounted OpenVMS volume. These files and directories reside on a
Files-11 On-Disk Structured (ODS-2) disk.
origination: The beginning point of communications on
a circuit.
packet: A unit of data sent across a network.
Packet Internet Groper (PING): A program used to test
reachability of a destination by sending an ICMP echo request and
waiting for a reply. See also loopback.
packet looping: A condition in which a packet revisits
a node. See also aged packet.
packet size: The amount of data in a packet.
packet switching: A communication paradigm in which
packets are individually routed between hosts, with no previously
established communication path.
path: The 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: The 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 name: A unique designation that identifies a
directory or subdirectory. UNIX path names are composed of a series of
fields separated by slashes (/); each field designates a file name that
is uniquely contained in the previous field (directory).
path splitting: The ability to split the transmission
load destined for a single node over several paths of equal path cost.
Any destination node receiving data that has been split over several
paths must support out-of-order packet caching.
PC-NFS Daemon: The server software that handles
authentication and printing requests from personal computer
implementations of NFS.
physical address: A unique address of each physical
connection of a node to the physical medium.
physical connection: The Physical layer communications
path between two systems.
physical connectivity: The Physical layer connectivity
that is a result of nodes being attached to each other via active lines
and nodes.
PING: See Packet Internet
Groper.
point-to-point circuit: A 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. Contrast with
multipoint circuit.
point-to-point line: A line that connects two systems
by using a single circuit.
Point-to-Point Protocol (PPP): A method for
transmitting datagrams over serial point-to-point lines where a line is
established between a remote host (usually over a telephone line) and
another host acting as a gateway to a remote host.
polling: Connecting to another system to check for
things such as mail or news.
POP: See Post Office
Protocol.
port: The end point of a communication link between
two processes.
Portmapper Service: A service that client programs can
use to determine the port number that another service uses. Clients use
the Portmapper Service for NFC, PC-NFS, and RPC applications.
post: To send a message to a mailing list or
newsgroup. Distinguished in context from "mail."
Post Office Protocol (POP): The TCP/IP-based protocol
for client stations to read mail from a server.
PPP: See Point-to-Point
Protocol.
primary server: A BIND name server that maintains the
database for a zone; secondary servers copy their information from
primary servers. See also BIND server,
cache server, forwarder server, and
secondary server.
printcap database: The DIGITAL TCP/IP Services for
OpenVMS database that maps local queues to printers on remote hosts;
specifies local queues for LPD printing from remote hosts.
privileged port: A port in which the remote host has
done some level of checking against the application using the port;
privileged port numbers range from 1 to 1023.
process: The context within a system in which a
specific computing session occurs; provides the context in which an
application executes.
protocol: A set of rules that controls the communications between computers. Also, a set of conventions between communicating processes regarding the format and contents of messages to be exchanged.
Protocols can describe low-level details of machine-to-machine
interfaces, such as the order in which the bits from a byte are set
across a wire, or high-level exchanges between applications programs
such as the way in which two programs transfer a file across the
Internet.
protocol data unit (PDU): The unit of data sent across
a network. Also called a packet.
protocol machine: The set of data structures and
routines that implements a specific protocol and controls the progress
of a communication between peer entities.
protocol overhead: The part of communications data or
processing not directly consumed by the users but necessary to
successfully bring about the transfer of user information.
protocol port: An abstraction that transport protocols
use to distinguish among multiple destinations within a given host
computer. Internet protocols identify ports using small positive
integers. Usually the operating system allows an application program to
specify which port it wants to use. Some ports are reserved for
standard services such as electronic mail.
protocol transparency: The quality in a communications
device or system that allows various higher-level protocols to coexist
on the same wire. The protocols are transparent to the device or system.
protocol sequence: An ordered list of protocol
identifiers.
protocol stack: The set of functions, one at each
layer of the protocol stack, that work together to form a set of
network services; each layer of the protocol stack uses the services of
the module beneath it.
protocol transparency: The degree to which users of
underlying protocols are aware of the specifics of those protocols.
proxy: The mechanism whereby one system acts on behalf
of another system in responding to protocol requests. UCX
uses a proxy mechanism to provide an OpenVMS identity (account) for
each UNIX client by adding the name and identification codes of the
client to a proxy database.
proxy ARP: The technique in which one machine, usually
a router, answers Address Resolution Protocol (ARP) requests intended
for another machine. By "faking" its identity, the router accepts
responsibility for routing packets to the "real" destination. Proxy ARP
allows a site to use a single IP address with two physical networks.
Creating a subnet would normally be a better solution.