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rfc:rfc1208

Network Working Group O. Jacobsen Request for Comments: 1208 D. Lynch

                                                         Interop, Inc.
                                                            March 1991
                   A Glossary of Networking Terms

Status of this Memo

 This RFC is a glossary adapted from "The INTEROP Pocket Glossary of
 Networking Terms" distributed at Interop '90.  This memo provides
 information for the Internet community.  It does not specify an
 Internet standard.  Distribution of this memo is unlimited.

Introduction

 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 at the
 INTEROP Tutorials, Conference, and Exhibition.
 To keep this document reasonably small we have deliberately omitted
 common computer and communications terms such as disk, modem, byte,
 and VLSI.  In addition, the definitions have been kept brief.  We
 recommend that you consult the glossaries found in the major computer
 networking textbooks for more comprehensive definitions.
 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.

Glossary

 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.

Jacobsen & Lynch [Page 1] RFC 1208 INTEROP Pocket Glossary March 1991

 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)
 AOW: Asia and Oceania Workshop.  One of the three regional OSI
 Implementors Workshops, equivalent to OIW and EWOS.
 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.

Jacobsen & Lynch [Page 2] RFC 1208 INTEROP Pocket Glossary March 1991

 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 (R): 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.
 BOC: Bell Operating Company.  More commonly referred to as RBOC for
 Regional Bell Operating Company.  The local telephone company in each
 of the seven U.S. regions.
 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

Jacobsen & Lynch [Page 3] RFC 1208 INTEROP Pocket Glossary March 1991

 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.

Jacobsen & Lynch [Page 4] RFC 1208 INTEROP Pocket Glossary March 1991

 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).

Jacobsen & Lynch [Page 5] RFC 1208 INTEROP Pocket Glossary March 1991

 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 with
 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

Jacobsen & Lynch [Page 6] RFC 1208 INTEROP Pocket Glossary March 1991

 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.
 ES-IS: End system to Intermediate system protocol.  The OSI protocol
 by which end systems announce themselves to intermediate systems.
 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.
 FNC: Federal Networking Council.  The body responsible for
 coordinating networking needs among U.S. Federal agencies.
 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.
 FRICC: Federal Research Internet Coordinating Committee.  Now
 replaced by the FNC.
 FTAM: File Transfer, Access, and Management.  The OSI remote file
 service and protocol.

Jacobsen & Lynch [Page 7] RFC 1208 INTEROP Pocket Glossary March 1991

 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,

Jacobsen & Lynch [Page 8] RFC 1208 INTEROP Pocket Glossary March 1991

 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 information.
 ISO: International Organization for Standardization.  You knew that,
 right? Best known for the 7-layer OSI Reference Model.  See OSI.
 ISODE: ISO Development Environment.  A popular implementation of the
 upper layers of OSI.  Pronounced eye-so-dee-eee.
 JANET: Joint Academic Network.  A university network in the U.K.
 JUNET: Japan UNIX Network.

Jacobsen & Lynch [Page 9] RFC 1208 INTEROP Pocket Glossary March 1991

 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.
 Martian: Humorous term applied to packets that turn up unexpectedly
 on the wrong network because of bogus routing entries.  Also used as
 a name for a packet which has an altogether bogus (non-registered or
 ill-formed) Internet address.
 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.
 MIB: Management Information Base.  A collection of objects that can
 be accessed via a network management protocol.  See SMI.
 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.

Jacobsen & Lynch [Page 10] RFC 1208 INTEROP Pocket Glossary March 1991

 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 Layer: The OSI layer that is responsible for routing,
 switching, and subnetwork access across the entire OSI environment.
 NFS(R): 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

Jacobsen & Lynch [Page 11] RFC 1208 INTEROP Pocket Glossary March 1991

 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(tm): 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

Jacobsen & Lynch [Page 12] RFC 1208 INTEROP Pocket Glossary March 1991

 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.
 POSI: Promoting Conference for OSI.  The OSI "800-pound gorilla" in
 Japan.  Consists of executives from the six major Japanese computer
 manufacturers and Nippon Telephone and Telegraph.  They set policies
 and commit resources to promote OSI.
 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.
 PRMD: Private Management Domain.  An X.400 Message Handling System
 private organization mail system.  Example: NASAmail.  See ADMD.
 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.

Jacobsen & Lynch [Page 13] RFC 1208 INTEROP Pocket Glossary March 1991

 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.
 RBOC: Regional Bell Operating Company.  See BOC.
 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,

Jacobsen & Lynch [Page 14] RFC 1208 INTEROP Pocket Glossary March 1991

 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 end 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.

Jacobsen & Lynch [Page 15] RFC 1208 INTEROP Pocket Glossary March 1991

 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.
 UA: User Agent.  An OSI application process that represents a human
 user or organization in the X.400 Message Handling System.  Creates,
 submits, and takes delivery of messages on the user's behalf.
 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

Jacobsen & Lynch [Page 16] RFC 1208 INTEROP Pocket Glossary March 1991

 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 (TM): A popular window system developed by MIT
 and implemented on a number of workstations.

For More Information

 As indicated in the introduction, this is only a partial list of
 words from the world of interoperability.  Yes, you're right, we
 didn't list "interoperability" because the jury is still out on
 exactly what it means, and we invite you to suggest a definition.
 To learn more about these topics, consult the books, standards
 documents, bibliographies, periodicals, mailing lists, etc. listed in
 "Information Sources" in the December 1989 issue of ConneXions--The
 Interoperability Report.

Security Considerations

 Security issues are not discussed in this memo.

Jacobsen & Lynch [Page 17] RFC 1208 INTEROP Pocket Glossary March 1991

Authors' Addresses

 Ole J. Jacobsen
 Interop, Inc.
 480 San Antonio Road
 Suite 100
 Mountain View, CA 94040
 Phone: (415) 941-3399
 EMail: OLE@CSLI.STANFORD.EDU
 Daniel C. Lynch
 Interop, Inc.
 480 San Antonio Road
 Interop, Inc.
 480 San Antonio Road
 Suite 100
 Mountain View, CA 94040
 Phone: (415) 941-3399
 EMail: Lynch@ISI.EDU

Jacobsen & Lynch [Page 18]

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