Ref: 99980050
Title: Glossary of Networking Terms
Date: 8/31/90

Copyright 3Com Corporation, 1991.  All rights reserved.

Access Method       Way to determine which workstation or PC will
                    be the next to use the LAN.  A set of rules
                    used by network software and hardware that
                    direct traffic over the network.  Examples of
                    access methods are token passing and
                    collision detection.

Address             A set of numbers identifying the location of
                    a node on the network.  Each node must have a
                    unique address on that network.

Audit Trail         A function of a network management system
                    that provides a list of information about
                    connections and disconnections and reasong
                    for these disconnections and excessive errors
                    on the network.

Baseband            An electrical signaling technique used to
                    transmit information.  Baseband signaling
                    uses unmodulated signals.  The carrier is
                    present only when data is being transmitted.
                    The entire frequency range of the channel is
                    used during this tranmission.

Broadband           An electrical signaling technique used to
                    transmit information.  Broadband signaling
                    involves modulation of the signal before
                    transmission.  Broadband networks typically
                    divide the total bandwidth of the
                    communication's channel into multiple
                    subchannels, so different types of
                    information can be transmitted simultaneously
                    using different frequencies.  Broadband
                    signaling is used when mixing multiple types
                    of information such as video, voice, and
                    data.

CCITT               The initials for the French International
                    Telegraph and Telephone Consultative
                    Committee.  This organization defines
                    standards or recommendations (e.g., X.25) for
                    international networking.

Coaxial Cable       A physical tranmission medium with two
                    conductors.  The center conductor carries the
                    information signals.  The outer conductor
                    (electrostatic shielding) acts as a ground.

Collision           (See CSMA/CD)
Detection

Communications      A hardware and software device that allows
Server              devices such as terminals, host computers, or
                    printers to access a network without having
                    to implement the communications protocol in
                    the device itself.  The communications server
                    communicates with the device using standard
                    protocols built into the device.

Connection          A communications path between two devices
                    that allows the exchange of information.
                    Other terms used to refer to a connection are
                    session or circuit.

CRC                 Abbreviation for Cyclical Redundancy Check.
                    This is a method of detecting errors in a
                    message by performing a mathematical
                    calculation on the bits in the message and
                    then sending the results of the calculation
                    along with the message.  The receiving
                    network station performs the same calculation
                    on the message data as it receives it and
                    then checks the results against those
                    transmitted at the end of the message.  If
                    the results do not match, the receiving end
                    asks the sending end to send the entire
                    message again.

CSMA/CD             Abbreviation for Carrier Sense Multiple
                    Access with Collision Detection.  It is an
                    access method that allows many nodes to share
                    a single channel of a communications medium.
                    If more than one signal is transmitted at the
                    same time, the signals collide and are
                    retransmitted at a later randomly calculated
                    time.

Datagram            A transmission method in which sections or a
                    message are transmitted in scattered order
                    and the correct order is reestablished by the
                    receiving workstation.

DECnet              Digital Equipment Corporation's proprietary
                    communications protocol.

Ethernet            A local area network that utilizes baseband
                    signaling at 10 Mbps.  The development of the
                    Ethernet specification was a joint effort by
                    Xerox, DEC and Intel and is the predominant
                    local area network standard.

FDDI                Abbreviation for Fiber Distributed Data
                    Interface.  FDDI is an emerging standard for
                    a 100 Mbps fiber-optic LAN.  It uses a
                    "counter-rotating" token ring topology.  It
                    is compatible with the standards for the
                    Physical layer or the ISO model.

Flow Control        The hardware or software mechanisms employed
                    in data communications to turn off
                    tranmission when the receiving workstation is
                    unable to store the data it is receiving.

Frame               A group of bits sent over a communications
                    channel, usually containing its own control
                    information, including address and error
                    detection.  The exact size and format of a
                    frame depends on the protocol used.

HDLC                Abbreviation for High-level Data Link
                    Control, which is the ISO procedure for data
                    link control.  HDLC uses a specific series of
                    bits rather than control characters for
                    transmitting and receiving data.

High-Level          A protocol that allows network users to carry
Protocol            out functions at a higher level than merely
                    transporting streams or blocks of data; for
                    example, reliably transmitting data,
                    formatting data, establishing a connection,
                    transferring a file.

IEEE 802.2          A Data Link layer standard used with the IEEE
                    802.3, 802.4, and 802.5 standards.

IEEE 802.3          A Physical layer standard specifying a LAN
                    with a CSMA/CD access method on a bus
                    topology.  Ethernet following the 802.3
                    standard.

IEEE 802.4          A Physical layer standard specifying a LAN
                    with a token passing access method on a bus
                    topology.  Used with Manufacturing Automation
                    Protocol (MAP) LANs.

IEEE 802.5          A Physical layer standard specifying a LAN
                    with a token passing access method on a ring
                    topology.  Used with IBM's token ring
                    hardware.

ISO                 Abbreviation for International Standards
                    Organization.  (See also ISO Model)

ISO Model           ISO has developed the Reference Model for
                    Open Systems Interconnection, which divides a
                    complex set of communications functions into
                    self-contained modules.

LAN                 Abbreviation for Local Area Network.  A LAN
                    is a communications network that provides
                    high-speed data transmission over a small
                    geographic area.

LLC                 Abbreviation for Logical Link Control.  Upper
                    sublayer of the Data Link layer of the ISO
                    model.

MAC                 Abbreviation for Media Access Control.  The
                    lower sublayer of the Data Link layer of the
                    ISO model.  The MAC layer supports medium-
                    dependent functions.

Network             The overseeing and maintaining of a network.
Management          The duties performed by a network management
                    system include installing and configuring the
                    network, maintaining an operation log,
                    monitoring network performance, and
                    statistics.

Network             Geography of a network or a set of networks.
Topology

Node                Point in a network where service is provided,
                    service is used, or communications channels
                    are interconnected.  Sometimes used
                    interchangeably with station.

Packet              A block of data handled by a network in a
                    well-defined format.

Packet              The internal operations of a communications
Switching           network that uses software to dynamically
                    route packets from a source to a destination.
                    Packet switching allows the sharing of a
                    single communications channel among several
                    connections.

PAD                 The abbreviation for Packet Assembler and
                    Disassembler.  A PAD is a device that allows
                    asynchronous terminals to have access to a
                    Public Data Network.

PDN                 A network that provides data transmission
                    services to the public.  Typically, a Public
                    Data Network uses packet switching
                    technology.

Protocol            A strictly defined procedure and message
                    format that allows two or more systems to
                    communicate over a physical transmission
                    medium.  Due to the complexity of
                    comunications between systems and the need
                    for different communications requirements,
                    protocols are divided into layers.  Each
                    layer of a protocol performs a specific
                    function, such as routing, end-to-end
                    reliability, and connection.

SNA                 Abbreviation for Systems Network
                    Architecture.  The network architecture
                    developed by IBM.

Subnet              A portion of a network that is partitioned by
                    a router.

T-1 Carrier         A digital transmission system developed by
                    AT&T that sends information at 1.544 megabits
                    per second.  T-1 links can transmit voice or
                    data.

TCP/IP              Abbreviation of Transmission Control Protocol/
                    Internet Protocol.  A set of de-facto
                    networking standards commonly used over
                    Ethernet or X.25 networks.  It was originally
                    developed by the U.S. Government and is now
                    supported by many equipment manufacturers.
                    It defines high-level protocols such as
                    Telnet (terminal connection), FTP (file
                    transfer), and SMTP (electronic mail).

Thin Ethernet       A ligher (0.2" diameter, black coating)
                    variation of Ethernet cable that saves cable
                    and installation costs, but is restricted in
                    effective distance.  This type of cabling is
                    specified under the IEEE 802.3 10Base2
                    standard.

Token Ring          A technology developed by IBM whereby a token
                    is used to direct traffic on the network.
                    There is only one token on the ring (the
                    network) at a time.  It is either free or
                    busy.  A node must wait for a free token to
                    tranmit data; it marks the token as busy,
                    then transmits a frame of data onto the
                    ring.  Data collisions cannot occur as only
                    one node can transmit at any one time.

Twisted Pair        A form of wiring commonly used for telephone
                    installations.  Standard networks such as
                    Ethernet can operate over such wiring.  This
                    method is economical, but poses distant
                    limitations unlike coaxial cable.

VAX                 A trademark name for a family of computers
                    manufactured by Digital Equipment
                    Corporation.

Virtual Circuit     A facility in a packet switching network in
                    which packets passing between a pair of
                    devices are kept in sequence.  This is a
                    "virtual circuit" because it appears there is
                    an actual point-to-point connection.

WAN                 Abbreviation for Wide Area Network.  A data
                    communications network designed to serve an
                    area of hundreds or thousands of miles.  A
                    WAN can be public or private.

X.25                A CCITT standard that defines the standard
                    communications protocol by which mainframes
                    access a public or private packet switching
                    network.  These networks are often referred
                    to as X.25 networks.

XNS                 Abbreviation for Xerox Network Systems.  A
                    protocol family specifically designed to run
                    on Ethernet.  It contains the Internetwork
                    Datagram Protocol (level 3) and the Sequenced
                    Packet Protocol (level 4).

