A GLOSSARY OF NETWORKING TERMS
This text
is a shortened version of the Request for Comments No. 1208 by O. Jacobsen
& D. Lynch, Interop, Inc., dated March 1991. Some less important terms from
this RFC have been omitted and several others have been added. (J.L.)
This RFC is a glossary adapted from "The
INTEROP Pocket Glossary of Networking Terms" distributed at Interop '90.
This text provides information for the Internet community. It does not specify
any Internet standard. Distribution of this text is unlimited.
This glossary is adapted from "The INTEROP
Pocket Glossary of Networking Terms" produced to help you understand the
many terms - and in particular the myriad of acronyms - that can be encountered
in networking literature. We also realize that producing this glossary is akin
to shooting at a moving target. The computer and communications industries are
moving very rapidly, and terms and acronyms are born every day. You are invited
to submit words which you think should be included in future editions.
abstract syntax: A description of a data structure
that is independent of machine-oriented structures and encodings.
ACSE: Association Control Service Element. The
method used in OSI for establishing a call between two applications. Checks the
identities and contexts of the application entities, and could apply an
authentication security check.
address mask: A bit mask used to select bits
from an Internet address for subnet addressing. The mask is 32 bits long and
selects the network portion of the Internet address and one or more bits of the
local portion. Sometimes called subnet
mask.
address resolution: A means for mapping Network Layer
addresses onto media-specific addresses. See ARP.
ADMD: Administration Management Domain. An X.400
Message Handling System public service carrier. Examples: MCImail and ATTmail
in the U.S., British Telecom Gold400mail in the U.K. The ADMDs in all countries
worldwide together provide the X.400 backbone. See PRMD.
agent: In the client-server model, the
part of the system that performs information preparation and exchange on behalf
of a client or server application. See NMS,
DUA, MTA.
ANSI: American National Standards Institute. The
U.S. standardization body. ANSI is a member of the International Organization
for Standardization (ISO)
API: Application Program Interface. A set of
calling conventions defining how a service is invoked through a software
package.
Application Layer: The top-most layer in the OSI
Reference Model providing such communication services as electronic mail and
file transfer.
ARP: Address Resolution Protocol. The Internet
protocol used to dynamically map Internet addresses to physical (hardware)
addresses on local area networks. Limited to networks that support hardware
broadcast.
ARPA: Advanced Research Projects Agency. Now called
DARPA, the U.S. government agency that funded the ARPANET.
ARPANET: A packet switched network
developed in the early 1970s. The "grandfather" of today's Internet.
ARPANET was decommissioned in June 1990.
ASN.1: Abstract Syntax Notation One. The
OSI language for describing abstract syntax. See BER.
attribute: The form of information items
provided by the X.500 Directory Service. The directory information base
consists of entries, each containing one or more attributes. Each attribute
consists of a type identifier together with one or more values. Each directory
Read operation can retrieve some or all attributes from a designated entry.
Autonomous System: Internet (TCP/IP) terminology for
a collection of gateways (routers) that fall under one administrative entity
and cooperate using a common Interior Gateway Protocol (IGP). See subnetwork.
backbone: The primary connectivity mechanism
of a hierarchical distributed system. All systems which have connectivity to an
intermediate system on the backbone are assured of connectivity to each other.
This does not prevent systems from setting up private arrangements with each
other to bypass the backbone for reasons of cost, performance, or security.
Bart Simpson â: Internet and OSI cult hero.
baseband: Characteristic of any network
technology that uses a single carrier frequency and requires all stations
attached to the network to participate in every transmission. See broadband.
BER: Basic Encoding Rules. Standard rules for
encoding data units described in ASN.1. Sometimes incorrectly lumped under the
term ASN.1, which properly refers only to the abstract syntax description
language, not the encoding technique.
big-endian: A format for storage or
transmission of binary data in which the most significant bit (or byte) comes
first. The reverse convention is called little-endian.
BITNET: Because It's Time NETwork. An
academic computer network based originally on IBM mainframe systems
interconnected via leased 9600 bps lines. BITNET has recently merged with
CSNET, The Computer+Science Network (another academic computer network) to form
CREN: The Corporation for Research and Educational Networking. See CSNET.
bridge: A device that connects two or more
physical networks and forwards packets between them. Bridges can usually be
made to filter packets, that is, to forward only certain traffic. Related
devices are: repeaters which simply forward electrical signals from one cable
to another, and full-fledged routers which make routing decisions based on
several criteria. In OSI terminology, a bridge is a Data Link Layer
intermediate system. See repeater and
router.
broadband: Characteristic of any network that
multiplexes multiple, independent network carriers onto a single cable. This is
usually done using frequency division multiplexing. Broadband technology allows
several networks to coexist on one single cable; traffic from one network does
not interfere with traffic from another since the "conversations"
happen on different frequencies in the "ether," rather like the
commercial radio system.
broadcast: A packet delivery system where a
copy of a given packet is given to all hosts attached to the network. Example:
Ethernet.
BSD: Berkeley Software Distribution. Term used
when describing different versions of the Berkeley UNIX software, as in
"4.3BSD UNIX."
catenet: A network in which hosts are
connected to networks with varying characteristics, and the networks are
interconnected by gateways (routers). The Internet is an example of a catenet.
See IONL.
CCITT: International Consultative
Committee for Telegraphy and Telephony. A unit of the International
Telecommunications Union (ITU) of the United Nations. An organization with
representatives from the PTTs of the world. CCITT produces technical standards,
known as "Recommendations," for all internationally controlled
aspects of analog and digital communications. See X Recommendations.
CCR: Commitment, Concurrency, and Recovery. An OSI
application service element used to create atomic operations across distributed
systems. Used primarily to implement two-phase commit for transactions and
nonstop operations. client-server model: A common way to describenetwork
services and the model user processes (programs) of those services. Examples
include the name-server/name-resolver paradigm of the DNS and file-
server/file-client relationships such as NFS and diskless hosts.
CLNP: Connectionless Network Protocol. The OSI
protocol for providing the OSI Connectionless Network Service (datagram
service). CLNP is the OSI equivalent to Internet IP, and is sometimes called
ISO IP.
CLTP: Connectionless Transport Protocol. Provides
for end-to-end Transport data addressing (via Transport selector) and error
control (via checksum), but cannot guarantee delivery or provide flow control.
The OSI equivalent of UDP.
CMIP: Common Management Information Protocol. The
OSI network management protocol.
CMOT: CMIP Over TCP. An effort to use the OSI
network management protocol to manage TCP/IP networks.
connectionless: The model of interconnection in
which communication takes place without first establishing a connection.
Sometimes (imprecisely) called datagram. Examples: LANs, Internet IP and OSI
CLNP, UDP, ordinary postcards. connection-oriented: The model of interconnection
in which communication proceeds through three well-defined phases: connection
establishment, data transfer, connection release. Examples: X.25, Internet TCP
and OSI TP4, ordinary telephone calls.
core gateway: Historically, one of a set of
gateways (routers) operated by the Internet Network Operations Center at BBN.
The core gateway system forms a central part of Internet routing in that all
groups must advertise paths to their networks from a core gateway, using the
Exterior Gateway Protocol (EGP). See EGP,
backbone.
COS: Corporation for Open Systems. A vendor and
user group for conformance testing, certification, and promotion of OSI
products.
COSINE: Cooperation for Open Systems
Interconnection Networking in Europe. A program sponsored by the European
Commission, aimed at using OSI to tie together European research networks.
CREN: See BITNET
and CSNET.
CSMA/CD: Carrier Sense Multiple Access with
Collision Detection. The access method used by local area networking
technologies such as Ethernet.
CSNET: Computer+Science Network. A large
computer network, mostly in the U.S. but with international connections. CSNET
sites include universities, research labs, and some commercial companies. Now
merged with BITNET to form CREN. See BITNET.
DARPA: Defense Advanced Research Projects
Agency. The U.S. government agency that funded the ARPANET.
Data Link Layer: The OSI layer that is responsible
for data transfer across a single physical connection, or series of bridged
connections, between two Network entities.
DCA: Defense Communications Agency. The government
agency responsible for the Defense Data Network (DDN).
DCE: Distributed Computing Environment. An
architecture of standard programming interfaces, conventions, and server
functionalities (e.g., naming, distributed file system, remote procedure call)
for distributing applications transparently across networks of heterogeneous
computers. Promoted and controlled by the Open Software Foundation (OSF), a
consortium led by HP, DEC, and IBM. See ONC.
DDN: Defense Data Network. Comprises the MILNET
and several other DoD networks.
DECnet: Digital Equipment Corporation's
proprietary network architecture.
DNS: Domain Name System. The distributed
name/address mechanism used in the Internet.
domain: In the Internet, a part of a
naming hierarchy. Syntactically, an Internet domain name consists of a sequence
of names (labels) separated by periods (dots), e.g.,
"tundra.mpk.ca.us." In OSI, "domain" is generally used as
an administrative partition of a complex distributed system, as in MHS Private
Management Domain (PRMD), and Directory Management Domain (DMD). dotted decimal
notation: The syntactic representation for a 32-bit integer that consists of
four 8-bit numbers written in base 10 wi th periods (dots) separating them.
Used to represent IP addresses in the Internet as in: 192.67.67.20.
DSA: Directory System Agent. The software that
provides the X.500 Directory Service for a portion of the directory information
base. Generally, each DSA is responsible for the directory information for a
single organization or organizational unit.
DUA: Directory User Agent. The software that
accesses the X.500 Directory Service on behalf of the directory user. The
directory user may be a person or another software element.
EARN: European Academic Research Network. A network
using BITNET technology connecting universities and research labs in Europe.
EGP: Exterior Gateway Protocol. A reachability
routing protocol used by gateways in a two-level internet. EGP is used in the
Internet core system. See core gateway.
encapsulation: The technique used by layered
protocols in which a layer adds header information to the protocol data unit
(PDU) from the layer above. 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.
end system: An OSI system which contains
application processes capable of communicating through all seven layers of OSI
protocols. Equivalent to Internet host.
entity: OSI terminology for a layer
protocol machine. An entity within a layer performs the functions of the layer
within a single computer system, accessing the layer entity below and providing
services to the layer entity above at local service access points.
EUnet: European UNIX Network.
EUUG: European UNIX Users Group.
EWOS: European Workshop for Open Systems. The OSI
Implementors Workshop for Europe. See OIW.
FARNET: Federation of American Research
NETworks.
FDDI: Fiber Distributed Data Interface. An emerging
high-speed networking standard. The underlying medium is fiber optics, and the
topology is a dual-attached, counter-rotating Token Ring. FDDI networks can
often be spotted by the orange fiber "cable."
FIPS: Federal Information Processing Standard.
flame: To express strong opinion and/or
criticism of something, usually as a frank inflammatory statement in an
electronic message.
fragmentation: The process in which an IP
datagram is broken into smaller pieces to fit the requirements of a given
physical network. The reverse process is termed reassembly. See MTU.
FTAM: File Transfer, Access, and Management. The
OSI remote file service and protocol.
FTP: File Transfer Protocol. The Internet protocol
(and program) used to transfer files between hosts. See FTAM.
gateway: The original Internet term for
what is now called router or more precisely, IP router. In modern usage, the
terms "gateway" and "application gateway" refer to systems
which do translation from some native format to another. Examples include X.400
to/from RFC 822 electronic mail gateways. See router.
GOSIP: Government OSI Profile. A U.S.
Government procurement specification for OSI protocols.
IAB: Internet Activities Board. The technical body
that oversees the development of the Internet suite of protocols (commonly
referred to as "TCP/IP"). It has two task forces (the IRTF and the
IETF) each charged with investigating a particular area.
ICMP: Internet Control Message Protocol. The
protocol used to handle errors and control messages at the IP layer. ICMP is
actually part of the IP protocol.
IESG: Internet Engineering Steering Group. The
executive committee of the IETF.
IETF: Internet Engineering Task Force. One of the
task forces of the IAB. The IETF is responsible for solving short-term
engineering needs of the Internet. It has over 40 Working Groups.
IGP: Interior Gateway Protocol. The protocol used
to exchange routing information between collaborating routers in the Internet.
RIP and OSPF are examples of IGPs.
IGRP: Internet Gateway Routing Protocol. A
proprietary IGP used by cisco System's routers.
INTAP: Interoperability Technology
Association for Information Processing. The technical organization which has
the official charter to develop Japanese OSI profiles and conformance tests.
intermediate system: An OSI system which is not an end
system, but which serves instead to relay communications between end systems.
See repeater, bridge, and router.
internet: A collection of networks
interconnected by a set of routers which allow them to function as a single,
large virtual network.
Internet: (note the capital "I")
The largest internet in the world consisting of large national backbone nets
(such as MILNET, NSFNET, and CREN) and a myriad of regional and local campus
networks all over the world. The Internet uses the Internet protocol suite. To
be on the Internet you must have IP connectivity, i.e., be able to Telnet
to--or ping--other systems. Networks with only e-mail connectivity are not
actually classified as being on the Internet.
Internet address: A 32-bit address assigned to hosts
using TCP/IP. See dotted decimal notation.
IONL: Internal Organization of the Network Layer.
The OSI standard for the detailed architecture of the Network Layer. Basically,
it partitions the Network layer into subnetworks interconnected by convergence
protocols (equivalent to internetworking protocols), creating what Internet
calls a catenet or internet.
IP: Internet Protocol. The network layer protocol
for the Internet protocol suite.
IP datagram: The fundamental unit of
information passed across the Internet. Contains source and destination
addresses along with data and a number of fields which define such things as
the length of the datagram, the header checksum, and flags to say whether the
datagram can be (or has been) fragmented.
IRTF: Internet Research Task Force. One of the task
forces of the IAB. The group responsible for research and development of the
Internet protocol suite.
ISDN: Integrated Services Digital Network. An
emerging technology which is beginning to be offered by the telephone carriers
of the world. ISDN combines voice and digital network services in a single
medium making it possible to offer customers digital data services as well as
voice connections through a single "wire." The standards that define
ISDN are specified by CCITT. IS-IS: Intermediate system to Intermediate system
protocol. The OSI protocol by which intermediate systems exchange routing info
rmation. ISO: International Organization for Standardization. You knew that,
right? Best known for the 7-layer OSI Reference Model. See OSI.
JANET: Joint Academic Network. A
university network in the U.K.
JUNET: Japan UNIX Network.
KA9Q: A popular implementation of TCP/IP and associated
protocols for amateur packet radio systems.
Kermit: A popular file transfer and
terminal emulation program.
little-endian: A format for storage or
transmission of binary data in which the least significant byte (bit) comes
first. See big-endian.
mail exploder: Part of an electronic mail
delivery system which allows a message to be delivered to a list of addressees.
Mail exploders are used to implement mailing lists. Users send messages to a
single address (e.g., hacks@somehost.edu) and the mail exploder takes care of
delivery to the individual mailboxes in the list.
mail gateway: A machine that connects two or
more electronic mail systems (especially dissimilar mail systems on two
different networks) and transfers messages between them. Sometimes the mapping
and translation can be quite complex, and generally it requires a store-and-forward
scheme whereby the message is received from one system completely before it is
transmitted to the next system after suitable translations.
MHS: Message Handling System. The system of
message user agents, message transfer agents, message stores, and access units
which together provide OSI electronic mail. MHS is specified in the CCITT X.400
series of Recommendations.
MILNET: MILitary NETwork. Originally part
of the ARPANET, MILNET was partitioned in 1984 to make it possible for military
installations to have reliable network service, while the ARPANET continued to
be used for research. See DDN.
MTA: Message Transfer Agent. An OSI application
process used to store and forward messages in the X.400 Message Handling
System. Equivalent to Internet mail agent.
MTU: Maximum Transmission Unit. The largest
possible unit of data that can be sent on a given physical medium. Example: The
MTU of Ethernet is 1500 bytes. See fragmentation.
multicast: A special form of broadcast where
copies of the packet are delivered to only a subset of all possible
destinations. See broadcast.
multi-homed host: A computer connected to more than
one physical data link. The data links may or may not be attached to the same
network.
name resolution: The process of mapping a name into
the corresponding address. See DNS.
NetBIOS: Network Basic Input Output System.
The standard interface to networks on IBM PC and compatible systems.
Network Address: See Internet address or OSI
Network Address.
network byte order: The TCP/IP standard for
transmission of integers that specifies the most significant byte appears first
(big-endian). Sending machines are rquired to translate from the local integer
representation byte to the network byte order, and receiving machines to
translate back.
Network Layer: The OSI layer that is responsible
for routing, switching, and subnetwork access across the entire OSI
environment.
NFS â: Network File System. A distributed file
system developed by Sun Microsystems which allows a set of computers to
cooperatively access each other's files in a transparent manner.
NIC: Network Information Center. Originally there
was only one, located at SRI International and tasked to serve the ARPANET (and
later DDN) community. Today, there are many NICs, operated by local, regional,
and national networks all over the world. Such centers provide user assistance,
document service, training, and much more.
NIST: National Institute of Standards and
Technology. (Formerly NBS). See OIW.
NMS: Network Management Station. The system
responsible for managing a (portion of a) network. The NMS talks to network
management agents, which reside in the managed nodes, via a network management
protocol. See agent.
NOC: Network Operations Center. Any center tasked
with the operational aspects of a production network. These tasks include
monitoring and control, trouble-shooting, user assistance, and so on.
NSAP: Network Service Access Point. The point at
which the OSI Network Service is made available to a Transport entity. The
NSAPs are identified by OSI Network Addresses.
NSF: National Science Foundation. Sponsors of the
NSFNET. NSFNET: National Science Foundation NETwork. A collection of local,
regional, and mid-level networks in the U.S. tied together by a high-speed
backbone. NSFNET provides scientists access to a number of supercomputers
across the country.
OIW: Workshop for Implementors of OSI. Frequently
called NIST OIW or the NIST Workshop, this is the North American regional forum
at which OSI implementation agreements are decided. It is equivalent to EWOS in
Europe and AOW in the Pacific.
ONC ä: Open Network Computing. A
distributed applications architecture promoted and controlled by a consortium
led by Sun Microsystems.
OSI: Open Systems Interconnection. An
international standardization program to facilitate communications among
computers from different manufacturers. See ISO.
OSI Network Address: The address, consisting of up to
20 octets, used to locate an OSI Transport entity. The address is formatted
into an Initial Domain Part which is standardized for each of several
addressing domains, and a Domain Specific Part which is the responsibility of
the addressing authority for that domain.
OSI Presentation Address: The address used to locate an OSI
Application entity. It consists of an OSI Network Address and up to three
selectors, one each for use by the Transport, Session, and Presentation
entities.
OSPF: Open Shortest Path First. A "Proposed
Standard" IGP for the Internet. See IGP.
PCI: Protocol Control Information. The protocol
information added by an OSI entity to the service data unit passed down from
the layer above, all together forming a Protocol Data Unit (PDU).
PDU: Protocol Data Unit. This is OSI terminology
for "packet." A PDU is a data object exchanged by protocol machines
(entities) within a given layer. PDUs consist of both Protocol Control
Information (PCI) and user data.
Physical Layer: The OSI layer that provides the
means to activate and use physical connections for bit transmission. In plain
terms, the Physical Layer provides the procedures for transferring a single bit
across a Physical Media.
Physical Media: Any means in the physical world
for transferring signals between OSI systems. Considered to be outside the OSI
Model, and therefore sometimes referred to as "Layer 0." The physical
connector to the media can be considered as defining the bottom interface of
the Physical Layer, i.e., the bottom of the OSI Reference Model.
ping: Packet internet groper. A program used to
test reachability of destinations by sending them an ICMP echo request and
waiting for a reply. The term is used as a verb: "Ping host X to see if it
is up!"
port: The abstraction used by Internet transport
protocols to distinguish among multiple simultaneous connections to a single
destination host. See selector.
PPP: Point-to-Point Protocol. The successor to
SLIP, PPP provides router-to-router and host-to-network connections over both
synchronous and asynchronous circuits. See SLIP.
Presentation Address: See OSI Presentation Address.
Presentation Layer: The OSI layer that determines how
Application information is represented (i.e., encoded) while in transit between
two end systems.
protocol: A formal description of messages to
be exchanged and rules to be followed for two or more systems to exchange
information.
proxy: The mechanism whereby one system
"fronts for" another system in responding to protocol requests. Proxy
systems are used in network management to avoid having to implement full
protocol stacks in simple devices, such as modems.
proxy ARP: The technique in which one
machine, usually a router, answers 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. Subnetting would normally
be a better solution.
PSN: Packet Switch Node. The modern term used for
nodes in the ARPANET and MILNET. These used to be called IMPs (Interface
Message Processors). PSNs are currently implemented with BBN C30 or C300
minicomputers.
RARE: Reseaux Associes pour la Recherche
Europeenne. European association of research networks.
RARP: Reverse Address Resolution Protocol. The
Internet protocol a diskless host uses to find its Internet address at startup.
RARP maps a physical (hardware) address to an Internet address. See ARP.
repeater: A device which propagates
electrical signals from one cable to another without making routing decisions
or providing packet filtering. In OSI terminology, a repeater is a Physical
Layer intermediate system. See bridge and
router.
RFC: Request For Comments. The document series,
begun in 1969, which describes the Internet suite of protocols and related
experiments. Not all (in fact very few) RFCs describe Internet standards, but
all Internet standards are written up as RFCs.
RFS: Remote File System. A distributed file
system, similar to NFS, developed by AT&T and distributed with their UNIX
System V operating system. See NFS.
RIP: Routing Information Protocol. An Interior
Gateway Protocol (IGP) supplied with Berkeley UNIX.
RIPE: Reseaux IP Europeenne. European continental
TCP/IP network operated by EUnet. See EUnet.
rlogin: A service offered by Berkeley UNIX
which allows users of one machine to log into other UNIX systems (for which
they are authorized) and interact as if their terminals were connected
directly. Similar to Telnet.
ROSE: Remote Operations Service Element. A
lightweight RPC protocol, used in OSI Message Handling, Directory, and Network
Management application protocols.
router: A system responsible for making
decisions about which of several paths network (or Internet) traffic will
follow. To do this it uses a routing protocol to gain information about the
network, and algorithms to choose the best route based on several criteria
known as "routing metrics." In OSI terminology, a router is a Network
Layer intermediate system. See gateway,
bridge and repeater.
RPC: Remote Procedure Call. An easy and popular
paradigm for implementing the client-server model of distributed computing. A
request is sent to a remote system to execute a designated procedure, using
arguments supplied, and the result returned to the caller. There are many
variations and subtleties, resulting in a variety of different RPC protocols.
RTSE: Reliable Transfer Service Element. A
lightweight OSI application service used above X.25 networks to handshake
application PDUs across the Session Service and TP0. Not needed with TP4, and
not recommended for use in the U.S. except when talking to X.400 ADMDs.
SAP: Service Access Point. The point at which the
services of an OSI layer are made available to the next higher layer. The SAP
is named according to the layer providing the services: e.g., Transport
services are provided at a Transport SAP (TSAP) at the top of the Transport
Layer. selector: The identifier used by an OSI entity to distinguish among
multiple SAPs at which it provides services to the layer above. See port. Session Layer: The OSI layer that
provides means for dialogue control between e nd systems.
SGMP: Simple Gateway Management Protocol. The
predecessor to SNMP. See SNMP.
SLIP: Serial Line IP. An Internet protocol used to
run IP over serial lines such as telephone circuits or RS-232 cables
interconnecting two systems. SLIP is now being replaced by PPP. See PPP.
SMDS: Switched Multimegabit Data Service. An
emerging high-speed networking technology to be offered by the telephone
companies in the U.S.
SMI: Structure of Management Information. The
rules used to define the objects that can be accessed via a network management
protocol. See MIB.
SMTP: Simple Mail Transfer Protocol. The Internet
electronic mail protocol. Defined in RFC 821, with associated message format descriptions
in RFC 822.
SNA: Systems Network Architecture. IBM's
proprietary network architecture.
SNMP: Simple Network Management Protocol. The
network management protocol of choice for TCP/IP-based internets.
socket: The abstraction provided by 4BSD
UNIX that allows an application to access the TCP/IP protocols. An application
opens a socket, specifies the service desired (e.g., reliable stream delivery),
binds the socket to a specific destination, and then sends or receives data.
SPAG: Standards Promotion and Application Group. A
group of European OSI manufacturers which chooses option subsets and publishes
these in a "Guide to the Use of Standards" (GUS).
SQL: Structured Query Language. The international
standard language for defining and accessing relational databases.
subnet mask: See address mask.
subnetwork: A collection of OSI end systems
and intermediate systems under the control of a single administrative domain
and utilizing a single network access protocol. Examples: private X.25
networks, collection of bridged LANs.
TCP: Transmission Control Protocol. The major
transport protocol in the Internet suite of protocols providing reliable,
connection- oriented, full-duplex streams. Uses IP for delivery. See TP4.
Telnet: The virtual terminal protocol in
the Internet suite of protocols. Allows users of one host to log into a remote
host and interact as normal terminal users of that host.
three-way-handshake: The process whereby two protocol
entities synchronize during connection establishment.
TP0: OSI Transport Protocol Class 0 (Simple
Class). This is the simplest OSI Transport Protocol, useful only on top of an
X.25 network (or other network that does not lose or damage data).
TP4: OSI Transport Protocol Class 4 (Error
Detection and Recovery Class). This is the most powerful OSI Transport
Protocol, useful on top of any type of network. TP4 is the OSI equivalent to
TCP.
transceiver: Transmitter-receiver. The physical
device that connects a host interface to a local area network, such as
Ethernet. Ethernet transceivers contain electronics that apply signals to the
cable and sense collisions.
Transport Layer: The OSI layer that is responsible
for reliable end- to-end data transfer between end systems.
UDP: User Datagram Protocol. A transport protocol
in the Internet suite of protocols. UDP, like TCP, uses IP for delivery;
however, unlike TCP, UDP provides for exchange of datagrams without
acknowledgements or guaranteed delivery. See CLTP.
UUCP: UNIX to UNIX Copy Program. A protocol used
for communication between consenting UNIX systems.
XDR: eXternal Data Representation. A standard for
machine- independent data structures developed by Sun Microsystems. Similar to
ASN.1.
X/Open: A group of computer manufacturers
that promotes the development of portable applications based on UNIX. They
publish a document called the X/Open Portability Guide.
X Recommendations: The CCITT documents that describe
data communication network standards. Well-known ones include: X.25 Packet
Switching standard, X.400 Message Handling System, and X.500 Directory
Services.
The X Window System ä: A popular window system developed
by MIT and implemented on a number of workstations.
Ole J. Jacobsen Daniel
C. Lynch
Interop, Inc. Interop, Inc.
480 San Antonio Road Suite 100 480 San Antonio Road
Suite 100
Mountain View, CA 94040 Mountain View, CA
94040
EMail: OLE@CSLI.STANFORD.EDU EMail: Lynch@ISI.EDU