4B/5B
A block encoding scheme used to send Fast Ethernet data. In this signal
encoding scheme, 4 bits of data are turned into 5-bit code symbols for
transmission over the media system.
4D/PAM5 (aka PAM-5)
The encoding scheme used for 1000BASE-T over four twisted-pair links and having high bandwidth utilization. It uses four signalling levels for data and one level for forward error correction.
10BASE-T
10 Mbps Ethernet system based on Manchester signal encoding transmitted
over Category 3 or better twisted-pair cable.
10BASE-FL
Popular 10 Mbps link fiber optic solution which replaces the older FOIRL
implementation utilizing 850 nm fiber optic technology.
100BASE-FX
100 Mbps Fast Ethernet system based on 4B/5B signal encoding transmitted
over fiber optic cable utilizing 1300 nm fiber optic technology.
100BASE-SX
850 nm fiber optic technology that supports auto-negotiation. 100BASE-SX
devices can communicate with 10BASE-FL devices at 10 Mbps and other
100BASE-SX devices at 100 Mbps.
100BASE-TX
100 Mbps Fast Ethernet system based on 4B/5B signal encoding transmitted
over two copper pairs.
100BASE-X
Term used when referring to any Fast Ethernet media system based on
4B/5B block encoding. Includes 100BASE-TX and 100BASE-FX media systems.
1000BASE-T
A standard for 1000 Mbps Ethernet communication over Category 5 UTP.
802.3
The IEEE 802.3 Working Group that develops standards for Ethernet-based LANs.
Analogue Data
Data that are continuous and smooth - not limited to discrete values.
Address Resolution Protocol (ARP)
A TCP/IP protocol for obtaining the physical address (MAC) of a node when the
Internet address is known.
Applet
A computer program for creating an active Web document - usually written in Java.
Application Layer (Layer 7 in the OSI model)
This is the highest OSI layer in which networking application software interfaces
with the human operator and uses underlying protocols to establish host-to-host
connections. Examples include a Web browser, an email application, Telnet and a
building management system application.
Application Programming Interface (API)
Information followed by programmers to write client-server programs.
Asynchronous Transmission
Transfer of data with start/stop bits and a variable time interval between data units.
AUI
Attachment Unit Interface. The 15-pin signal interface defined in the
original Ethernet standard that carries signals between a station and
an outboard transceiver.
Authentication
Verification of the identity of the sender of a message - usually with a
username and a password.
Auto-Negotiation
An Ethernet standard protocol allowing devices at either end of a link
to advertise and negotiate modes of operation such as the speed, half-
or full-duplex operation and full-duplex flow control.
Auto-MDIX (Auto-Crossover)
A protocol allowing two Ethernet devices to negotiate their use of the
Ethernet TX and RX cable pairs so two Ethernet devices can connect whether
using a crossover cable or a straight-through cable.
Backbone
A network that joins smaller networks together.
Bandwidth
The maximum capacity of a network channel. Usually expressed in bits per
second (bps). Ethernet channels have bandwidths of 10, 100, or 1000 Mbps.
Baud
A unit of signalling speed representing the number of discrete signal
events per second and, depending upon the encoding, can differ from
the bit rate.
Best-Effort Delivery
In IP, a transmission mechanism that does not guarantee message delivery.
Bit
A binary digit. The smallest unit of data, either a zero or a one.
Bit Rate
The amount of bits that can be sent per second. Usually described in
units of kbps or Mbps and frequently referred to as the data rate.
Block Encoding
A system in which data bits are encoded as code bits to ensure synchronization
and detection of errors - used in Fast Ethernet and Gigabit Ethernet.
Blocking
The condition in which a switching network is working at its full capacity and
cannot accept more input.
Blocking Port
In STP and RSTP, a switch port that does not forward frames.
Bridge
A device with filtering and forwarding capabilities that connects two or more
networks at the Data link Layer.
Broadcast
A transmission initiated by one station and sent to all stations on the network.
Browser
An application that displays a Web document - typically with the aid of other
Internet services.
Bus
A shared connection for multiple devices over a cable or backplane.
Byte
A unit of digital information - usually 8 bits. Originally, the bits needed
to encode a text character. Historically, it was hardware dependent with no standard size.
The term octet (8 bits) arose due to the ambiguity of the size of a byte.
Cable Modem
A device integrating switch and modem functions to deliver broadband Internet
via coaxial cable to a local network.
Cache
Small, fast memory for holding data that is being processed.
Category 5
Twisted-pair cable with characteristics suitable for all twisted-pair Ethernet media
systems - including 10BASE-T, 100BASE-TX and 1000BASE-T. Category 5 and
Category 5e cable are preferred cable types for structural cabling systems.
Category 5e
An enhanced version of Category 5 cable, developed to improve certain
cable characteristics important to Gigabit Ethernet operation. It is
recommended that all new structured cabling systems be based on Category
5e cable; however, this cable may not be the best for use in industrial
installations because of noise susceptibility.
Channel
A communications pathway.
Checksum
An error detection value derived from the sum of a bit stream.
Circuit Switching
Using a dedicated path to establish an electrical connection between stations.
Cladding
The glass or plastic surrounding the core of an optical fiber.
Client
A computer or application that obtains services from another machine,
called the server.
Client Process
A local program process that requests service from a remote application.
Client-Server Model
The communication model in which a client program requests service from a server.
Collision
The result of having two or more simultaneous transmissions on a common
signal channel such as half-duplex Ethernet or shared Ethernet.
Collision Domain
The set of all stations connected to a network where faithful detection
of a collision can occur. A collision domain terminates at a switch port.
Core
The glass (or, rarely, plastic) centre of an optical fiber.
CRC
Cyclic Redundancy Check. An error-checking technique used to ensure
the fidelity of received data.
Crossover Cable
Twisted-pair patch cable wired so as to route the transmit signals from one
piece of equipment to the receive port of another piece of equipment, and
vice versa. This allows communication between two peer devices. The opposite
of a crossover cable is the straight-through cable.
Crosstalk
Line noise caused by signals from another nearby (usually parallel) line.
CSMA/CD
Carrier Sense Multiple Access/Collision Detect. The medium access control
(MAC) Protocol used in Ethernet.
Datagram
In packet switching, a basic data unit in which delivery is not guaranteed.
Its contains a header (source and destination addresses and a type field)
and data. See User Datagram Protocol (UDP).
Data Link Layer (Layer 2 of the OSI model)
Communicates between the Network and Physical layers using data groups called
frames. Aka just the Link Layer, it is divided into sublayers for
Media Access Control (MAC) and Logical Link Control (LLC)
DCE (Data Communications Equipment)
Any equipment that relays data between Data Terminal Equipment (DTE). DCEs are
not considered end devices or stations.
DHCP
See Dynamic Host Configuration Protocol.
DiffServ (Differentiated Services)
A layer-three QoS method described in RFCs 2474 and 2475. It uses the 8-bit
ToS field in an IP frame.
Digital Data
Data represented by discrete values or conditions.
Digital Subscriber Line (DSL)
A technology using legacy telecommunication networks to achieve high-speed
data delivery.
Dotted-Decimal Notation
An IP address version that is easier for humans to read. Each byte is converted
to a decimal equivalent then separated from its neighbour by a dot.
Download
To transfer data from a remote site to a local one or from a server to a client.
DNS Server
A computer that converts user-friendly names into corresponding IP addresses
that identify computer systems or resources in a network or on the Internet.
DTE
Data Terminal Equipment. Any piece of equipment at which a communication
path begins or ends. A station (computer or host) on the network that is
capable of initiating or receiving data.
Dynamic Host Configuration Protocol (DHCP)
A protocol which allows a server to automatically assign an IP address to
a subscribing device.
Electromagnetic Interference (EMI)
Also called radio frequency interference (RFI). Electromagnetic energy
(usually from an external source) that disturbs the data-handling properties
of the affected equipment. The source may artificial (such as electrical
equipment) or natural (such as radiation from the Sun).
Encapsulation
Placing a lower protocol message into the data field of a higher protocol to
utilize the enhanced transportation capability of the higher protocol.
Encoding
A means of combining clock and data information into a self-synchronizing
stream of signals.
Error Detection
A method that detects errors in received data by examining cyclic redundancy
checks (CRC) or checksum.
Ethernet
A popular LAN technology first standardized by DEC, Intel, and Xerox (or DIX)
and later standardized by the IEEE 802.3 committee. It operates at the
physical and data link layers of the OSI model
Fast Ethernet
A version of Ethernet that operates at 100 Mbps. Although 100 Mbps is
no longer the fastest data rate, this term is still used.
Fast Link Pulse
A link pulse that encodes information used in the Auto-Negotiation Protocol.
Fast link pulses consist of bursts of the normal link pulses used in 10BASE-T.
fiber Optic Cable
A cable with a glass or plastic filament which transmits digital signals
in the form of light pulses at wavelengths of 850 nm (10BASE-FL and
100BASE-SX) or 1300 nm (100BASE-FX).
Fiber Optic Connector Intermateability Standards (FOCIS)
A set of standards of the Telecommunications Industry Association that insures proper
mating of fiber connectors. FOCIS documents are in the series TIA/EIA-604-XX.
Firewall
Security firmware (usually in a router) to safeguard one network from another
- typically separating a local network from the Internet.
Flow Control
The process of controlling data transmission at the sender to avoid
overfilling buffers and loss of data at the receiver.
FOIRL
Fiber Optic Inter-Repeater Link. An early version of fiber optic link
segment. FOIRL was replaced by 10BASE-FL.
Forwarding
The process of moving frames from one port to another in a switching hub.
Frame
The fundamental unit of transmission at the data link layer of the OSI model.
Full-Duplex Operation
A communication method that allows simultaneous transmission and reception of data.
Gateway
A device that exchanges data between two networks that use different communication protocols.
Gigabit Ethernet (aka GbE or 1 GigE)
A version of Ethernet that operates at 1000 Mbps.
Half-Duplex Operation
A communication method in which transmissions and receptions can occur
in either direction but not at the same time.
Host (Node)
A station on a network.
Hub
A DCE with three or more ports at the centre of a star topology network.
Hubs can usually be cascaded with a hub-to-hub connection. Frequently
this name is used to mean repeating hub.
Hypertext
Text that transfers the application focus to other documents via hyperlinks.
Hypertext Markup Language (HTML)
Computer language specifying the content and format of a Web document.
Hypertext Transfer Protocol (HTTP)
An application service for retrieving a Web document.
IEEE
Institute for Electrical & Electronics Engineers. A professional organization
and standards body.
IGMP Snooping
The ability of a switch to observe Internet Group Multicast Protocol
(IGMP) traffic in order to learn IP Multicast group membership for the
purpose of restricting multicast transmissions to only those ports which
have requested them.
See a tutorial on IGMP Snooping
Interface
A means of communicating between components or technologies - involving either
hardware (such as a graphics card) or software (such as a browser) or both.
Internet
Worldwide collection of networks based on the use of TCP/IP network
protocols. The most common example of an Internetwork.
Internet Protocol (IP)
The Network-Layer protocol in the TCP/IP protocol suite that provides
unguaranteed (connectionless) data exchanges across packet switching networks.
Internet Protocol Suite
The collection of protocols that are used for Internet messaging. The two main
protocols are TCP (Transmission Control Protocol) and IP (Internet Protocol).
It is commonly called TCP/IP but includes several more protocols.
Internetwork
A network of networks - connected with devices such as routers and gateways.
Intranet
A private network that uses the TCP/IP protocol suite.
ISP
Internet Service Provider.
Jabber
The act of continuously sending data. A jabbering station is one whose
circuitry or logic has failed, and which has locked up a network channel
with its incessant transmissions.
Java
A programming language used to create interactive Web documents.
LAN (Local Area Network)
A network of limited geographical area, high data-transfer rates and no need
for leased telecommunication lines - unlike Wide Area Networks (WANs) that
typically connect to the Internet.
Late Collision
A failure of the network in which the collision indication arrives too
late in the frame transmission to be automatically dealt with by the
medium access control (MAC) Protocol. The defective frame may not be
detected by all stations requiring that the application layer detect
and retransmit the lost frame, resulting in greatly reduced throughput.
Layer 3 Switch (L-3 Switch)
An unofficial marketing term for a device that can route IP messages within
an organization but lacks full router functionality - such as
a WAN port and firewall that are unneeded for internal routing.
LC (Lucent Connector, aka "Little Connector")
A fiber optic connector which resembles a small SC connector. Both
simplex and duplex form factors are in common use. The duplex connector houses both
transmit and receive channels in the same assembly. Named after Lucent Technologies
which developed it. Standardized in TIA/EIA-604-10 (FOCIS 10).
Link Integrity Test
This test verifies that an Ethernet link is connected correctly and
that signals are being received correctly. This is a helpful aid but
does not guarantee the link is completely functional.
Link Layer
Short for Data Link Layer. This is layer 2 on the OSI model.
Link Pulse
A test pulse sent between transceivers on a 10BASE-T link segment during
periods of no traffic, to test the signal integrity of the link.
Link Segment
A point-to-point segment that connects only two devices and is "capable"
of supporting full-duplex operation. Commonly shortened to just Link.
Local Access
Using a terminal directly connected to a computer or networking device such
as a switch. Since the access does not use a network signal path, greater
communication security is provided.
MAC
Medium Access Control. A Protocol operating at the data link layer used
to manage a station's access to the communication channel.
MAC Address
A unique address assigned to a station interface, identifying that station
on the network. With Ethernet, this is the unique 48-bit station address.
It is also known as the physical address.
Manchester Encoding
Signal encoding method used by all 10 Mbps Ethernet media. Each bit is
converted into a "bit symbol" which is divided into a high half
and a low half. This yields a 20 Mbaud stream although data is only sent at 10 Mbps.
Mask (Subnet Mask)
In a subnetted IP network, the value (common to all subnet hosts) that
determines the subnet prefix value. Each host is then specified with the
value of the rest of the IP address.
MAU
Medium Attachment Unit. The MAU provides the physical and electrical
interface between an Ethernet device and the media system to which it
is connected. It is also known as a transceiver.
MDI
Medium Dependent Interface. The name for the connector used to make
a physical and electrical connection between a transceiver and a media
segment. For example, the RJ-45-style connector is the MDI for 10BASE-T
and 100BASE-TX.
MDI-X
An MDI port on a hub or media converter that implements an internal
crossover function. This means that a "straight-through" patch
cable can be used to connect a station to this port, since the required
signal crossover is performed inside the port instead of in the cable.
Mesh (Topology)
A network configuration in which each device has a dedicated point-to-point
link to every other device.
MIB
Management Information Base. An MIB describes a set of managed objects.
An SNMP management console application can manipulate the objects on
a specific computer if the SNMP service has an extension agent DLL that
supports the MIB. Each managed object in a MIB has a unique identifier.
The identifier includes the object's type (such as counter, string,
gauge or address), the object's access level (such as read, or read/write),
size restrictions and range information.
MII
Medium Independent Interface. Similar to the original AUI function,
but designed to support both 10 and 100 Mbps, an MII provides a 40-pin
connection to outboard transceivers (also called PHY devices). Used
to attach 802.3 interfaces (MACs) to a variety of physical media systems.
Media Converter
A device that converts signals from one media type to that of another.
Modem
A device that converts between digital and analogue signals.
Multicast
A transmission initiated by one station and sent to many stations on
the network.
NAT (Network Address Translation)
A technology allowing private addresses for internal communication and
a Internet addresses for external communication.
Network
A system of connected nodes (hosts) that share data.
Network Layer (Layer 3 in the OSI model)
Provides switching and routing technologies - creating logical paths for
data exchange between nodes. IP is its most common protocol and IP addressing
occurs at this layer.
NIC (Network Interface Card)
Also called an adapter, network interface module, or interface card. The
electronic circuitry that connects a computer (node or host) to a network.
Node (aka Host)
An addressable network device (such as a computer or router) where data enters
and exits a network.
Noise
Unwanted electromagnetic energy that degrades the quality of the signal.
OPC
Originally, OLE for Process Control. A process control communications
standard for accessing process data from multi-vendor systems.
OSI (Open Systems Interconnection)
A seven-layer reference model for networks, developed by the International
Organization for Standardization (ISO). It describes the interlocking
sets of networking hardware and software used to deliver network services.
Although a good model, strict compliance is seldom accomplished.
Overhead
Control bits added to the data.
Packet
A unit of data exchanged at the network layer. This is a much abused
definition and the terms "frame" and "packet" are frequently interchanged.
Packet-Switched Network
A network in which data are exchanged using packets.
Parity
An error-detection method in which an extra bit (the parity bit) is added to
the data so the sum of all 1-bits becomes either odd (used in Odd Parity) or
even (used in Even Parity).
Patch Cable
A twisted-pair or fiber optic jumper cable used to make a connection
between a media segment and a network interface (on a station) or a
network port (on a hub), or to directly connect stations and hub ports
together.
Path
The channel through which a signal travels.
PAUSE
A unique frame sent by full-duplex capable stations to indicate to the
sender to slow down transmissions.
PHY
Physical Layer Device. The name used for a transceiver in Fast Ethernet
and Gigabit Ethernet systems.
Physical Address (MAC address)
The address of a device used at the Data Link layer.
Physical Layer (Layer 1 in the OSI model)
The lowest of the OSI layers, it converts physical impulses - electrical,
light or radio - into network-usable data using data groups called symbols.
Ping (Packet InterNet Groper)
An Internet Control Message Protocol (ICMP) echo request to a specific host
who responds by returning an echo. It is a simple, quick means of determining
if a working signal path exists between the origin and destination devices.
Some machines may not respond if Ping service is disabled or if a firewall
gateway interferes.
Plenum Cable
Cable rated as having adequate fire resistance and satisfactorily low
smoke-producing characteristics for use in plenums (air handling spaces).
Plenums are often located below machine room floors or above suspended
ceilings, requiring the use of plenum-rated cable.
Point-to-Point Topology
A network system composed of point-to-point links. Each point-to-point
link connects two and only two devices-one at each end. Devices could
be DTEs or DCEs, but no more than two can be connected on one link.
Poll
A procedure in which the primary station asks a secondary station if it has
any data to transmit.
Port (Logical)
A number associated with an IP address to identify a TCP or UDP channel endpoint
for an application or process. This allows different activities to use the
same IP address simultaneously. Well-known port numbers are reserved for
common services - such as 21 for FTP or 80 for HTML.
Port (Physical)
A connection point for a cable. Repeater hubs and switching hubs typically
provide multiple ports for connecting Ethernet devices.
Port Forwarding (Port Mapping)
A firewall modification allowing an IP port from one network to be used in
another network.
Port Mirroring
Port Mirroring allows a switch port to monitor packets from any or all
of its ports so that traffic can be analyzed.
See a tutorial on Port Mirroring
Port Security
Prevents a switch port from learning MAC addresses. Thus, frames pass
through only if their destinations are listed in the switch address look-up
table. Static addresses are not affected. This feature is typically used
to limit device access to a network.
PPP (Point-to-Point Protocol)
A Data Link protocol for building a direct connection between two nodes with
the options of authentication, encryption and compression.
PPPoE (Point-to-Point Protocol over Ethernet)
A protocol for encapsulating PPP frames within Ethernet frames. Used mainly
with DSL services. It is described by RFC 2516.
PPTP (Point-to-Point Tunneling Protocol)
A method to achieve a VPN using TCP and a tunnelling protocol. Relying on
PPP for security, no encryption or authentication is specified - but
security is provided by the Windows PPTP stack.
Preamble
The first 7 bytes of an IEEE 802.3 frame - having alternating 1s and 0s
that alert and synchronise the receiver.
Presentation Layer (Layer 6 in the OSI model)
In casual discussion, this function (aka the syntax layer) is seldom distinguished
from the Application Layer. It translates data from machine-oriented to
human-friendly for use at the Application Layer. An example would be the
conversion from and EBCDIC-coded text file to an ASCII-coded file.
Private Network
A network that is isolated from the Internet.
Promiscuous Mode
A mode of operation where a device receives all frames on a network regardless
of their destination address. Typically used by network analyzer tools.
Propagation Delay
The signal transit time through a cable, network segment, or device.
Important in making collision domain calculations.
Protocol
A set of agreed-upon rules and message formats for exchanging information
among devices on a network.
Quality of Service (QoS)
Some switches support QoS (per 802.1p and 802.1Q standards) whereby
tagged measures, or messages received on a certain port can be assigned
one of eight levels of priority. QoS can be important where time-critical
applications can be impaired by data delays.
See a tutorial on Quality of Service (QoS)
RapidRing®
Contemporary Controls' proprietary redundant ring technology which provides
an alternate path in the event of a single break in the ring.
See a tutorial on RapidRing redundancy
Rapid Spanning Tree (RSTP)
Newer version of Spanning Tree Protocol that is backward compatible
while providing a faster recovery time.
RARP (Reverse Address Resolution Protocol)
A TCP/IP protocol for obtaining the Internet address of a node when the
physical (MAC) address is known.
Rate Limiting
The ability of a switch to limit the throughput of particular ports
on the switch. Used to prevent certain ports from consuming all the
bandwidth.
See a tutorial on Rate Limiting
Redundant Cabling
Standby (back-up) cabling designed to carry network traffic if the primary
signal path fails. Since a redundant path creates an unacceptable loop in
Ethernet messaging, the redundant path must be deactivated until needed.
Remote Access
Using a terminal that is not directly connected to a computer or networking device
such as a switch. Since the access uses a network signal path, less communication
security is provided.
Remote Host
A computer accessed by someone at a different computer.
Repeater
A physical layer DCE used to interconnect segments within the same network.
An Ethernet repeater can only link Ethernet segments that are all operating
in half-duplex mode and at the same speed. Some repeaters offer media
conversion as well.
Repeating Hub
A repeater with more than two ports. This name is frequently shortened
to simply "hub".
RJ-45
An 8-pin modular connector used on twisted-pair links.
Route
A path travelled by a packet.
Router
An internetworking device attached to two or more networks (or subnet)
for forwarding packets from one network (or subnet) to another.
SC (Subscriber Connector)
A type of fiber optic connector used in 100BASE-FX fiber optic media systems.
It is designed to be pushed into place and automatically seat itself. It was
standardized in TIA/EIA-604-3 (FOCIS 3).
Segment
A cable made up of one or more cable sections and connections joined
together to produce the equivalence of a continuous cable.
Segmentation
Splitting a message into multiple packets; usually performed at the
transport layer.
Server
A computer or application that provides services to other machines,
called clients.
Session Layer (Layer 5 in the OSI model)
This layer is seldom distinguished from the Application Layer. It coordinates
communication session connections between applications.
Shielded Twisted Pair (STP)
Twisted-pair cable wrapped in a foil or mesh shield that protects against
electromagnetic interference. Its use is controversial because it can impart
greater signal immunity if properly installed, but it can degrade reliability
if improperly installed.
Signal
A electronically encoded message carried from a transmitter to a receiver
through a communications channel where it is decoded for subsequent use.
Signal-to-Noise Ratio (SNR)
Signal strength divided by noise, both in decibels.
Slot Time
A unit of time used in the medium access control (MAC) Protocol for
Ethernet.
SNMP (Simple Network Management Protocol)
The de facto standard for switch management. A familiarity with MIB objects
is necessary to manage a switch with an SNMP management program. SNMP is not
necessarily limited to TCP/IP networks.
See a tutorial on Simple Network Management
Protocol (SNMP)
Socket (Logical)
An IP channel end point - specified by the combination of an IP address
and a port (which serves this particular channel) into a single identity.
Example: 1.2.3.4:80.
Spanning Tree Protocol (STP)
A link management protocol providing path redundancy and preventing
network loops by defining a tree to span all switches in a network.
It forces redundant data paths into a standby (blocked) state. If a path
malfunctions, the topology is reconfigured and the link re-established
by activating the standby path.
ST (Straight Tip)
A type of fiber optic connector used in 10BASE-FL and FOIRL links, but also
in 100BASE-TX links. The male portion has an inner sleeve with a slot cut
into it, and an outer ring with a bayonet latch. The inner sleeve is aligned
with a mating key in the socket and the outer ring is turned to complete the
bayonet latch. It was standardized in TIA/EIA-604-2 (FOCIS 2).
Star Topology
A network topology in which each station on the network is connected
directly to a hub. If multiple hubs are present, the topology is
called a distributed star.
Straight-Through Cable
A cable where connections at both ends are pinned the same way. Used to
interconnect non-peer devices such as a hub to a station.
Station
A unique, addressable device on a network. Sometimes referred to as a node.
Subnet (Subnetwork)
The practice of logically subdividing an IP network is called subnetting. All
hosts on a subnet share identical values in the most-significant bits of their
IP address - creating two fields: a common network or routing prefix and the
rest of the address which uniquely identifies each host.
Switching Hub
A switching hub is another name for a bridge; a DCE that interconnects
network segments at the data link layer. Switching hubs are typically
located in the centre of a star topology, and provide multiple ports
for connections to network stations. Frequently this name is shortened
to switch.
Switched Ethernet
An Ethernet LAN that uses switches (instead of repeating hubs) to direct a
message to its destination.
Table
A collection of address/port associations that allows a switch or router
to pass network traffic to the proper destination.
TCP (Transmission Control Protocol)
A core protocol of the Internet Protocol Suite.
TCP/IP (TCP/IP Suite)
A common casual name for the Internet Protocol Suite and so-named because
its principal protocols are TCP (Transmission Control Protocol) and
IP (Internet Protocol) - although many more protocols are involved.
Terminator
A device to prevent signal reflection at the end of a cable.
TELNET (Terminal Network)
An Application Layer protocol that provides interactive text-oriented
communications using a virtual terminal connection. Useful for remote login.
Throughput
The number of bits passing through a point in one second.
TIA-568A and TIA-568B
Two standards used to define RJ-45 pin connectors and wire colour-coding
schemes.
Topology
The physical layout of a network.
TOS (Type of Service)
A type of priority using the second octet (the TOS field) of the IP frame header.
ToS priority is now largely superseded by DiffServ, but is provided as a
QoS option in managed switches from Contemporary Controls to serve legacy
equipment. This octet has been used inconsistently over the years -
defined differently by five RFCs.
Traffic
Messages on a network.
Transceiver
A combination of the words transmitter and receiver. A transceiver is
the set of electronics that sends and receives signals on a media system.
Transceivers may be internal or external. Sometimes called a MAU.
Transport Layer (Layer 4 in the OSI model)
Ensures reliable data transfer between end systems (hosts) using error
recovery and flow control. TCP is its most common protocol.
Trunking
Two or more ports grouped together as one logical path to increase bandwidth
between a switch and a network node when a single path cannot handle
the traffic. Loops are avoided because specific paths are designated.
Often a single link is designated for flooding broadcasts and packets
of unknown destination. Trunks can provide redundancy to critical devices.
See a tutorial on Trunking redundancy
Twisted-Pair Cable
A multiple-conductor cable whose wires are paired together, twisted, and
enclosed in a single jacket. A Category 5 twisted-pair segment is a cable
with 4 pairs in a single jacket. Each pair consists of two insulated
copper wires that are twisted together. Twisted-pair cable may be shielded
(STP) or unshielded (UTP).
Unicast
A message sent to just one destination.
Unshielded Twisted Pair (UTP)
Twisted-pair cable that lacks a shield. Although shielded cable (STP)
can impart greater signal immunity, if improperly installed STP can
degrade reliability. Consequently, UTP is often preferred over STP.
Upload
To send a local file or data to a remote site or from a client to a server.
URL (Uniform Resource Locator)
A string of characters (address) identifying a document (file) on the World Wide Web.
User Datagram Protocol (UDP)
The IP protocol for simple, connectionless (non-guaranteed) data delivery.
VLAN (Virtual Local Area Network)
A LAN that maps stations on a basis other than location - such as by
department, user type or application. Managing traffic, workstations, and bandwidth
can be easier with a VLAN and improve network efficiency.
See a tutorial on Virtual Local Area Networks
(VLANs)
VPN (virtual Private Network)
A technology that creates a network that is physically public, but virtually private
because it logically includes/excludes specified stations (hosts).
WAN (Wide Area Network)
A network of large geographical area that uses leased telecommunication lines
and has slower data-transfer rates than Local Area Networks (LANs). Typically,
a WAN connects to the Internet.
Web Page
A hypertext document viewable by a Web browser.
Web Server
A computer or device that serves up Web pages. By installing server software
into a computer or device and connecting it to a network, it can become a Web
server. Every Web server has an IP address and possibly a domain name.