A

AWG

American Wire Gauge, the standard measure for the diameter of a wire. As the numbers increase, the wire diameter decreases. Normal wire for 10BaseT is 22 or 24 AWG. (3)

ATM

Asynchronous Transfer Mode - A method for switching little fixed-size packets (cells) around. Like T1 and DS3, digitized voice was a major consideration in its design, but it can be used for data. It can be run at different speeds over different media including T1 and DS3 as well as 51Mbps, 100Mbps, 155Mbps and 622Mbps standards. The fixed cell size is 53 bytes. Though ATM is really designed for voice and WANs, there are schemes to use it in LANs. ATM is a big buzzword these days but it is still very new. (2)

AUI

Attachment Unit Interface - The Ethernet/IEEE 802.3 term for the interface between a MAU and a station. A special kind of cable known as an AUI Cable can attach a MAU to a station at a distance (up to 50 meters). (2)

B

backbone

A fairly nebulous term for a part of the network that interconnects other parts of the network. For example, a campus might have an FDDI ring that interconnects a number of Ethernets. The FDDI ring could be called the network's backbone. (2)

Bandwidth

The amount of data that can be pushed through a link in unit time. Usually measured in bits or bytes per second.

Baseband

A baseband network is one that provides a single channel for communciations across the physical medium (e.g., cable), so only one device can transmit at a time. Devices on a baseband network, such as Ethernet, are permitted to use all the available bandwidth for transmission, and the signals they transmit do not need to be multiplexed onto a carrier frequency. An analogy is a single phone line such as you usually have to your house: Only one person can talk at a time --if more than one person wants to talk everyone has to take turns. (4)

BNC Connector

Bayonet Neill-Concelman connector - a type of connector used for attaching coax cable to electronic equipment which can be attached or detached quicker than connectors that screw. ThinWire Ethernet (IEEE 802.3 10BASE2) uses BNC connectors. (2)

Bridge

A network "relay" which reads, buffers, and sends data to relay it from one data link to another, but makes the two data links appear as one to levels higher than the data link layer. (2)

Broadband

Simplisticly, it is the opposite of a baseband network. With broadband, the physical cabling is virtually divided into several different channels, each with its own unique carrier frequency, using a technique called "frequency division modulation". These different frequencies are multiplexed onto the network cabling in such a way to allow multiple simultaneous "conversations" to take place. The effect is similar to having several virtual networks traversing a single piece of wire. Network devices "tuned" to one frequency can't hear the "signal" on other frequencies, and vice-versa. Cable-TV is an example of a broadband network: multiple conversations (channels) are transmitted simultaneously over a single cable; you pick which one you want to listen to by selecting one of the frequencies being broadcast. (4)

C

Category 3 Unshielded Twisted Pair

Standardization of unshielded twisted pair cable for voice use. Some data communications standards such as 10BASE-T can utilize it. (2)

Category 4 Unshielded Twisted Pair

Standardization of unshielded twisted pair cable. (2)

Category 5 Unshielded Twisted Pair

Standardization of unshielded twisted pair cable for data use. TP-PMD requires Category 5 cable rather than Category 3. (2)

CDDI

Copper Data Distribution Interface - Commonly used term for TP-PMD, but actually a trade name of Crescendo. (2)

Cell

An ATM 53-byte cell. Note: there are various proposals for how typical packets will be broken into cells and restored. (2)

Cell Switching

A term for ATM-style networks. See ATM. (2)

CMIP

Common Management Information Protocol - An OSI protocol for management of network equipment. Not widely implemented. See SNMP.

CMOT

CMIP over TCP/IP - A protocol consisting of CMIP running under TCP/IP. An alternative to SNMP. (2)

Coaxial Cable

Any of a number of kinds of electrical communications cable designed so one conductor is in the center and the second conductor forms a ring around it. Depending upon who you talk to, someone might have a specific kind of coaxial cable in mind. Some well known kinds are various Cable TV cables, cables used by IBM 327x terminals and ARCNet, and cables used by Ethernet & IEEE 802.3. (2)

Collapsed Backbone

A network backbone that is located in a single room. It might be a single router or multiport bridge, or a small LAN of some sort. A typical collapsed-backbone-style campus LAN might consist of Ethernets in a number of buildings, each with a repeated fiber link into a single room at a central point where a router interconnects them. An example of the opposite would be putting a router in each building and interconnecting them all with a big FDDI ring. (2)

Collision

A condition where two devices detect that the network is idle and end up trying to send packets at exactly the same time. (within 1 round-trip delay) Since only one device can transmit at a time, both devices must back off and attempt to retransmit again. (4)

Concentrator

A device which allows a number of stations to be connected to a LAN. In the case of Ethernet, it is simply a multi-port repeater. In the case of ring networks like Token Ring and FDDI, it acts as a switch which keeps the ring intact even if individual devices are unplugged. (2)

Counterrotating Ring

A method of using two ring networks going in opposite directions to provide redundancy. The network interfaces can change the path of the ring that the data flows around, thereby preserving the ring (thus the operation of the LAN) even if some of the cable is uplugged or cut, or if a device on the ring fails in such a way that it can't transmit data around the ring (see Ring, FDDI, Token Ring). (2)

CRC

Cyclical Redundancy Check - 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 workstation 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 don't match, the receiving end asks the sending end to send again. (4)

Crimper

A plier like device used to attach connectors to the end of cables. (3)

CSMA/CD

CSMA/CD is the media access control mechanism used by Ethernet and 802.3 networks; in other words, it determines how a packet of data is placed on the wire. CSMA/CD stands for "Carrier Sense Multiple Access, with Collision Detection". Before an Ethernet device puts a packet "on the wire", it listens to find if another device is already transmitting. Once the device finds the wire is clear, it starts sending the packet while also listening to hear if another device started sending at the same time (which is called a collision). (4)

D

Data Grading Levels

Ratings for UTP or STP cabling. The higher level cables have better conductors, insulation and more twists per foot. (3)

  Level 1 - Used for up to 1 Megabit Per Second (MPS) 
  Level 2 - Used for up to 4 MPS 
  Level 3 - Used for up to 16 MPS 
  Level 4 - Used for up to 20 MPS 
  Level 5 - Used for 150 ohm data grade applications.  STP only. 

DECNet

Trade name of Digital Equipment Corporation for some of their networking products. It is a kind of network built out of Digital Equipment Corporations own networking protocols (with some standard protocols also used). (2)

Dialup Modem

Modem used over ordinary dial-up telephone lines as opposed to private or leased lines. (2)

E

EMI/RFI

Electro-magnetic Interference / Radio Frequency Interference. The electrical signals in the air that you don't want in your cables. If someone tells you there is no EMI/RFI in their office building, just turn on a radio. (3)

Ethernet

LAN data-link protocol developed by a consortium of vendors; later standardized as IEEE 802.3 with a few modifications. For many applications, users have not adopted all the IEEE 802.3 differences. Ethernet/802.3 now can be run on two types of coaxial cable as well as multi-mode fiber and unshielded twisted-pair. "Raw" rate of data transmission is 10 megabits/second. (2)

F

Fast Ethernet Alliance

Group of vendors working on a 100Mbps version of IEEE 802.3. They intend to submit their proposals for approval by the IEEE for a new set of 802.3 standards called 100BASE-T. (2)

FDDI

Fiber Data Distribution Interface - LAN data-link protocol designed to run on multi-mode fiber. "Raw" rate of data transmission is 100 megabits/second. Developed by the American National Standards Institute. (2)

FDDI-2

Same speed, same fiber, same basic protocol as FDDI. FDDI-2 adds a layer which allows you to allocate fixed bandwidth to applications of your choice, making it more like broadband. FDDI-2 is still rather new. (2)

FDSE

Full Duplex Ethernet: a variant of Switched Ethernet which does not use CSMA/CD, but uses slightly-modified network interface cards to send & receive packets simultaneously. Presumably based on 10BASE-T for most clients, and cannot be based on ThinWire or ThickWire Ethernet. (2)

Fiber

Optical fiber: a very long, narrow, flexible piece of glass. Used for high-speed communications. (2)

Fiber Channel

An ANSI standard to replace HiPPI. It uses optical fiber instead of copper cables. Speeds are up to roughly 1Gbps. (2)

Fiber Channel Systems Initiative

Group of vendors trying to accelerate Fiber Channel acceptance & interoperability. Members include: HP, IBM, Sun. (2)

Firewall Router

A router which blocks traffic according to various criteria for security--for example a router which allows no telnet to any host through one of its interfaces but allows ftp to a list of authorized hosts through the same interface. (2)

FOIRL

Fiber Optic Inter-Repeater Link - a standard for running IEEE 802.3 over fiber, linking two devices (each either a host or a repeater) as a "Link Segment". It has been replaced by 10BASE-FL. (2)

FTP

File Transfer Protocol - Protocol in the TCP/IP family for copying files from one computer to another. (2)

Full Duplex Switched Ethernet Consortium

Group of vendors that are working out the details of FDSE. Cabletron is a member. (2)

Full Duplex Token Ring

IBM scheme to add switching to token-ring hubs that would allow full-duplex linking to individual computers using modified token-ring adaptors. Has the same wiring characteristics as token ring. (2)

G

Gateway

A type of "network relay" that attaches two networks to build a larger network. Modern "narrow" usage is that it is one that translates an entire stack of protocols, e.g., translates TCP/IP-style mail to ISO-style mail. Older usage used it for other types of relays--in particular, in the TCP/IP world, it has been used to refer to what many now insist is a "router". (2)

Gopher

Gopher is a protocol within the TCP/IP suite for delivering text and documents over the Internet. Many organizations use gopher as the platform for their information delivery systems (although the growing popularity of the World Wide Web makes it an attractive alternative). Developed at the University of Minnesota, home of the "Golden Gophers".

GOSIP

Government Open Systems Interconnect Profile - A subset of OSI standards specific to US Government procurements, designed to maximize interoperability in areas where plain OSI standards are ambiguous or allow options. Theoretically, required of all US Government networking procurements since mid-1990. (2)

H

Heartbeat

In Ethernet (Version 2), a test of the collision functionality of the transciever. The term "Heartbeat" is often (wrongly) used interchangeably with "SQE" which is a similar function of IEEE 802.3. (2)

HiPPI

High Performance Parallel Interface - ANSI draft standard X3T9.3. (2)

Hub

A nebulous term, typically applied to a multiport repeater or concentrator consisting of a chassis with slots to be populated by cards, allowing it to be configured with various numbers and combinations of LAN ports. Vendors of networking equipment often also have other types of devices that can be inserted in the slots such as terminal servers, bridges, routers, gateways, etc. (2)

I

ICMP

Internet Control Message Protocol - ICMP is used for diagnostics in the network. The Unix program, ping, uses ICMP messages to detect the status of other hosts in the net. ICMP messages can either be queries (in the case of ping) or error reports, such as when a network is unreachable. (5)

IEEE

Institute of Electrical & Electronic Engineers (2)

IEEE 802

The set of IEEE standards for the definition of LAN protocols. A story goes that a long time ago, IEEE and ANSI decided that IEEE would get the slow protocols and ANSI would get the fast ones, thus IEEE defined the 802 protocols and ANSI defined FDDI. Presumably IEEE saw limited application for FDDI at the time. Also, the IEEE standards-making committees associated with these standards. Also, the group within IEEE that standardizes LAN technologies. (2)

IEEE 802.1

The IEEE 802 standard for Network Management and Network Bridging of IEEE 802 networks. (2)

IEEE 802.11

Proposed IEEE 802 group for wireless Ethernet. (2)

IEEE 802.12

Group within IEEE 802 working on 100VG-AnyLAN. (2)

IEEE 802.2

An IEEE standard for the portion of LAN data-link protocols that is the same for all flavors of IEEE LAN protocols, e.g. 802.3 and 802.5. Sometimes not used. (2)

IEEE 802.3

An IEEE standard for LANs--their "improved" version of Ethernet. See Ethernet. Also, the group within IEEE 802 that standardizes CSMA/CD LANs. (2)

IEEE 802.4

An IEEE standard for LANs: Token Bus networks. Basically, standardizes MAP, a protocol that operates a Token Bus protocol on broadband. (2)

IEEE 802.5

An IEEE standard for Token-Ring-based LANs. There are two types: 4Mbps and 16Mbps. See also Token Ring. (2)

IEEE 802.6

An IEEE standard for Metropolitan Area Networks. Also known as DQDB. (2)

IEEE 802.7

IEEE 802 technical advisory group on Broadband. (2)

IEEE 802.8

IEEE 802 technical advisory group on FDDI & fiber optics. (2)

IEEE 802.9

IEEE 802 group on integrated data & voice networks. (2)

IMAP

Internet Mail Access Protocol - TCP/IP-based protocol similar to POP, but with additional function designed to handle storage of mail on the server rather than the client. There are two versions in common use: IMAP2 and IMAP4. (2)

Impedance

An electrical characteristic that measures opposition to the flow of an alternating current in a wire. Just like resistance is to a direct current flow. AC signals get very upset when cables of different impedances are connected. (3)

IP

Internet Protocol - The lowest layer protocol defined in TCP/IP. This is the base layer on which all other TCP/IP protocols are built. IP is often referred to as TCP/IP as well. (5)

IPX

Internetwork Packet eXchange - Novell's protocol used by Netware. Utilizes part of XNS. A router with IPX routing purports to interconnect LANs so that Novell Netware clients & servers can talk through the router. (2)

J

Jabber

A blanket term for a device that is behaving improperly in terms of electrical signalling on a network. In Ethernet this is Very Bad, because Ethernet uses electrical signal levels to determine whether the network is available for transmission. A jabbering device can cause the entire network to halt because all other devices think it is busy. (4)

Jitter

The effect seen when latency is not a constant. That is, if messages experience different latencies between two points in a network. (5)

K

L

Latency

The amount of time that a message spends in a network going from point A to point B. (5)

Link Beat

Once a second the Hub sends a signal to the workstation. If the workstation does not respond, the hub "segments" that workstation out of the net. This should prevent a bad cable or card from bringing down the whole network. (3)

M

MAC address

The unique hexadecimal serial number assigned to each Ethernet network device to identify it on the network. With Ethernet devices (as with most other network types), this address is permanently set at the time of manufacture, though it can usually be changed through software (though this is generally a Very Bad Thing to do). (4)

MAU

Media Adaptor Unit - an IEEE 802.3 or Ethernet device which attaches a station to the cable. Popularly called a "transceiver". Can be attached by cable to the station or built into the station. (2)

Marshalling

The process of taking arbitrary data (characters, integers, structures) and packing them up for transmission across a network. (5)

MIB

Management Information Base - the set of parameters an SNMP management station can query or set in an SNMP agent (e.g. router). Standard, minimal MIBs have been defined (MIB I, MIB II), and vendors often have custom entries. In theory, any SNMP manager can talk to any SNMP agent with a properly defined MIB. (2)

Multimode fiber

A type of fiber mostly used for shorter, e.g. campus distances. It can carry 100 megabits/second for typical campus distances, the actual maximum speed (given the right electronics) depending upon the actual distance. It is easier to connect to than Single Mode Fiber, but its limit on speed x distance is lower. (2)

N

NDIS

Network Device Independent Specification - a Microsoft/3com spec that allows "stacking" of multiple protocols for a single underlying driver. Essentially it allows a single Ethernet card in a PC (it's not limited to Ethernet) to speak many different network "languages", and usually at the same time. (4)

NEC

National Electric Code - NEC rates the cable for fire resistance and such. If you are going to run your cable above the ceiling in a space used for ventilation (a plenum), then you have to use plenum rated cable. This is a more expensive (Teflon sheath versus PVC) but is required to meet fire codes. (3)

NFS

Network File System - an IP-based protocol originally developed by Sun Microsystems which provides file services. (2)

NIC[1]

Network Information Center - The group at an Internet domain responsible for managing Internet address assignment and DNS registration.

NIC[2]

Network Interface Card.

O

OCx

Variants of SONET (e.g. OC1, OC3). (2)

ODI

Open Datalink Interface - A Novell-developed network card API that provides media and protocol independence. It allows the sharing of a single card by multiple transport layer protocols (e.g., IPX, TCP/IP, AppleTalk) and resolves conflicts. (1)

OSI

Open System Interconnect - A standard put forth by the ISO for communication between computer equipment and networks. (2)

OSI Reference Model

The Open Systems Interconnect (OSI) reference model is the ISO (International Standards Organization) structure for the "ideal" network architecture. This Model outlines seven areas, or layers, for the network. These layers are (from highest to lowest):

   7.) Applications:  Where the  user  applications  software  lies.
       Such  issues as  file  access and transfer,  virtual terminal
       emulation,   interprocess  communication  and  the  like  are
       handled here.

   6.) Presentation:  Differences in data  representation are  dealt
       with at this level.  For example, UNIX-style line endings (CR
       only) might be converted to  MS-DOS style  (CRLF), or EBCIDIC
       to ASCII character sets.

   5.) Session:  Communications between  applications  across a net-
       work  is  controlled  at  the  session  layer.   Testing  for
       out-of-sequence  packets  and handling two-way  communication
       are handled here.

   4.) Transport: Makes sure  the lower three layers are doing their
       job  correctly,  and  provides a  transparent,  logical  data
       stream between the end user  and the network  service s/he is
       using.   This  is the lower layer  that provides  local  user
       services.

   3.) Network: This layer makes certain that a packet sent from one
       device  to another actually gets there in a reasonable period
       of time.  Routing and flow control are performed  here.  This
       is the lowest layer of the OSI model that can remain ignorant
       of the physical network.

   2.) Data Link: This layer deals with getting data packets on  and
       off   the   wire,   error  detection   and   correction   and
       retransmission.  This  layer  is generally  broken  into  two
       sub-layers: The LLC (Logical Link Control) on the upper half,
       which does  the error checking,  and  the MAC (Medium  Access
       Control) on the lower half, which deals with getting the data
       on and off the wire.

   1.) Physical: The nuts and bolts layer.  Here is where the cable,
       connector and signaling specifications are defined. (4)

P

Packet Driver

A packet driver is another method of allowing multiple protocols to access the network interface at the same time. Developed and supported by FTP Software Inc, Clarkson University, BYU and, more recently, Crynwr Software, the packet driver spec (PDS) is used to provide a device independent interface to various TCP/IP applications, and often in combination with concurrent Novell access (IPX/SPX). (4)

PMD

FDDI Physical Layer Medium Dependent part - When "PMD" is used by itself, it may refer to the usual kind of FDDI physical layer that uses multimode fiber. Note that FDDI terminology also uses it as a more generic term, referring to different FDDI PMD's such as TP-PMD and SMF-PMD. (2)

POP

Post Office Protocol - A TCP/IP-based protocol designed to allow client-stations (e.g. micros) to read mail from a server. There are three versions under the name "POP": POP, POP2, and POP3. Latter versions are NOT compatible with earlier versions. (2)

Protocol

The "rules" by which two network elements trade information in order to communicate. Must include rules about a lot of mundane detail as well as rules about how to recover from a lot of unusual communication problems. Thus they can be quite complicated. (2)

Punch (down) Block

A device used in a central closet for managing wires. Available in a 66 or 110 model. The 110 is the new, electrically superior model, but the 66 seems to work fine. Wires are attached with a Punch (down) Tool. Punch Blocks are usually attached to the wall in a wiring closet on a patch panel. (3)

Q

R

Relay

One terminology uses the term relay as a device that interconnects LANs, different kinds of relays being repeaters, bridges, routers, and gateways. (2)

Repeater

In the Ethernet world, a relay that regenerates and cleans up signals, but does no buffering of data packets. It can extend an Ethernet by strengthening signals, but timing limitations on Ethernets still limit their size. (2)

RFC

Request For Comments - The name is a real red herring when it comes to Internet RFCs. Some really are "Requests For Comments" but all Internet protocol documents are stamped with an RFC number that they never shake, so the acronym RFC generally refers to documents that describe protocols in the TCP/IP family. (2)

RG numbers

A shorthand designation for military cable. RG58 & RG62 designate two different types of cable used by the military. Some data-communications equipment was designed to work with a particular military standard, e.g. IBM 3270-type terminals use RG62. In other cases, people use an RG-numbered cable that is close to what they need: for example ThinWire Ethernet & IEEE 802.3 10BASE2 define the type of cable they need and people sometimes substitute flavors of RG58, which are "close". (2)

Ring

A classification of network technology exemplified by Token Ring and FDDI. The interconnected devices are connected one-to-another in the shape of a ring and data flows around it in one direction. See also Counterrotating Ring. (2)

RJ numbers

Numbers applied to types of connectors often used in UTP wiring (E.g. RJ11, RJ45). (2)

Router

A network relay that uses a protocol beyond the data-link protocol to route traffic between LANs and other network links. (2)

Routing Protocol

A protocol sent between routers by which routers exchange information own how to route to various parts of the network. The TCP/IP family of protocols has a bunch, such as RIP, EGP, BGP, OSPF, and dual IS-IS. (2)

RPC

Remote Procedure Call - RPC is a method of making network access to resources transparent to the application programmer by supplying a "stub" routine that is called in the same way as a regular procedure call. The stub actually performs the call across the network to another computer. (5)

S

SDH

Synchronous Digital Hierarchy - Similar to SONET, but used outside North America. Some of the SDH and SONET standards are identical. Standardized by the CCITT. (2)

Satin cable

Four parallel wires (0 twists) used for telephone only. One comes with every modem. Not for network use. (3)

Segment

A piece of network wire bounded by bridges, routers, repeaters, or terminators.

Shielded Twisted Pair

A type of twisted-pair cable with a metallic shield around the twisted conductors. The shield reduces the noise from the cable and reduces the effects of noise on the communications in the cable, but changes the electrical characteristics of the cable so some equipment optimized to non-shielded cable runs worse on shielded cable. (2)

Single Mode fiber

A type of fiber optic cable used for longer distances and higher speeds, e.g. for long-distance telephone lines. See also Multimode Fiber. (2)

SLIP

Serial Line IP - An implementation of IP for use over a serial link (modem). CSLIP is an optimized (compressed) version of SLIP that gives better throughput. (5)

SMF-PMD

FDDI Single-Mode Fiber PMD. Runs further than PMD. (2)

SMTP

Simple Mail Transfer Protocol - the protocol in the TCP/IP family used to transfer electronic mail between computers. It is not oriented towards a client/server system so other protocols (see POP) are often used in that context. However, servers will use SMTP if they need to transfer a message to another server. (2)

SNMP

Simple Network Management Protocol - Originally developed to manage IP based network equipment like routers and bridges, now extended to wiring hubs, workstations, toasters, jukeboxes, etc. SNMP for IPX and AppleTalk under development. Widely implemented. See CMIP. (2)

SONET

Synchronous Optical Network - A set of standard fiber-optic-based serial standards planned for use with ATM in North America. Developed by Bellcore. Different types of SONET run at different speeds (OC1 runs at 51Mbps, OC3 runs at 155Mbps, OC12 runs at about 600Mbps, OC48 runs at over 2Gbps), and use different types of fiber (OC3 has several variants for use with different fibers & different distances; there are versions for both single mode and multimode fiber). (2)

SQE Test

Signal Quality Error Test - an IEEE 802.3 function that tests the transceiver. The term "SQE" is often (wrongly) used interchangeably with "Heartbeat" which is a similar function of Ethernet Version 2. (2)

STP

Shielded Twisted Pair. (2)

Switched Ethernet

Really the same as Ethernet as far as standards go: acts like a very fast multiport Ethernet bridge giving an Ethernet to each station. Presumably based on 10BASE-T for most stations. (2)

Switched FDDI

Really the same as FDDI as far as standards go: acts like a very fast multiport FDDI bridge. Basically the DEC GigaSwitch. (2)

T

T1

A phone-company standard for running 24 digitized voice circuits through one 1.5megabit/second digital channel. Since phone companies run lots of T1, and will run T1 between customer sites, the standard is often used for data communications, either t o provide 24 low-speed circuits, or to provide 1 high-speed circuit, or to be divided other ways. (2)

TAXI

Transparent Asynchronous Transmitter-Receiver Interface - Two ATM UNI specifications developed by Fore. The slower one ran at 100Mbps and borrowed the physical characteristics of FDDI and has been adopted by the ATM Forum as its 100Mbps UNI specifica tion. The faster one ran at 140Mbps. (2)

TCP

Transmission Control Protocol - TCP is a connection oriented protocol that guarantees that messages are delivered in the order in which they were sent and that all messages are delivered. If a TCP connection cannot deliver a message it closes the connection and informs the entity that created it. This protocol is layered on top of IP. (5)

TCP/IP

Transmission Control Protocol/Internet Protocol - literally, two protocols developed for the Defense Data Network to allow their ARPANET to attach to other networks relatively transparently. The name also designates the entire family of protocols built out of IP and TCP. The Internet is based upon TCP/IP. (2)

TDR

Time-Domain Reflectometer - a tool used to detect cable faults. This device operates by sending a brief signal pulse down the cable and looking for its reflection to bounce back. By analyzing the reflected pulse, it is possible to make judgments about the quality of the cable segment. More advanced units can not only detect and identify the nature of the problem, but give a reasonably accurate indication of the problem's location (distance from the point of the test). There is also a device known as an OTDR, which is an Optical Time-Domain Reflectometer for fiber-optic cables. (4)

telnet

A protocol in the TCP/IP family that is used for remote login. The name is also often used as the name of the client program that utilizes the telnet protocol. (2)

Terminal Server

A network device that allows a number of terminals to attach to a LAN, and do remote logins across the LAN. (2)

ThickWire

ThickWire Ethernet or IEEE 802.3 10BASE5. (2)

ThinWire

ThinWire Ethernet or IEEE 802.3 10BASE2. (2)

TN3270

A variant of the TELNET program that allows one to attach to IBM mainframes and use the mainframe as if you had a 3270 or similar terminal. (2)

Token Ring

People often use the term "Token Ring" to designate IEEE 802.5 (see above). In the more general sense of the phrase, a token ring is a type of LAN that has stations wired in a ring, where each station constantly passes a special message (a "token") on to the next. Whoever has the token can send a message. (2)

TP

Twisted Pair (2)

TP-PMD

FDDI Twisted Pair Physical Layer Medium - ANSI specification for FDDI-like service over UTP. Being standardized by ANSI X3T9.5. Was X3T9/93-130 X3T9.5/93-022 TP-PMD/306 Rev 2.0, now there is a Rev 2.1. Uses MLT-3 encoding instead of CDDI's NRZI encoding. (2)

Transceiver

A transceiver allows a station to transmit and receive to/from the common medium. In addition, Ethernet transceivers detect collisions on the medium and provide electrical isolation between stations. 10Base2 and 10Base5 transceivers attach directly to the common bus media, though the former usually use an internal transceiver built-onto the controller circuitry with a "T" connector to access the cable, while the latter use a separate, external transceiver and an AUI (or transceiver) cable to connect to the controller. 10BaseF, 10BaseT and FOIRL also usually use internal transceivers. Having said that, there also also external transceivers for 10Base2, 10BaseF, 10BaseT and FOIRL that can connect externally to the controller's AUI port, either directly or via an AUI cable. (4)

Tunneling

An important concept in the design of many kinds of networks: taking some protocol-family's ability to move packets from user to user, or to open virtual-circuits between users, and use this as if it were a data-link protocol to run another protocol family's upper layers (or even the same protocol family's upper layers). Examples: running TCP/IP over AppleTalk instead of something like Ethernet; running AppleTalk over DECNet instead of something like Localtalk or Ethernet. (2)

Twisted Pair

The type of wire used by the phone company to wire telephones -- at least over distances like between your house and the central office. It has two conductors, which are twisted. The twists are important: they give it electrical characteristics which allow some kinds of communications otherwise not possible. Ordinary telephone cables are not shielded (see Shielded twisted Pair). (2)

Type1

IBM Type 1 STP. The most usual type of Shielded Twisted Pair in LAN communications. (2)

U

UDP

User Datagram Protocol - This is a connectionless protocol built on top of IP. It does not provide any guarantees on the ordering or delivery of messages. This protocol is layered on top of IP. (5)

Usenet

Usenet news is a public e-mail based forum on the Internet consisting of thematically defined "newsgroups" to which a person can subscribe. Usenet differs from other e-mail forums (e.g., listservs) in that mail posted to the group does not come to the subscribers' mailboxes. Instead, you must retrieve the messages in the newsgroup for either online or offline reading.

UTP

Unshielded Twisted-Pair - See Twisted-Pair and Shielded Twisted-Pair. (2)

V

W

Winsock

The Windows Sockets Specification is intended to provide a single API to which application developers can program and multiple network software vendors can conform. Furthermore, in the context of a particular version of Microsoft Windows, it defines a binary interface (ABI) such that an application written to the Windows Sockets API can work with a conformant protocol implementation from any network software vendor. (1)

WWW

World Wide Web - The most recent addition to the Internet world of information delivery systems (e.g., gopher). WWW systems deliver hypertext documents with multimedia contents (e.g., graphical images, sounds, motion pictures) thereby providing a "richer" interface to the Internet.

X

X.400

OSI protocol for mail services. (2)

X.500

OSI protocol for directory services. (2)

Y

Z

Sources:

(1) Free On-line Dictionary of Computing

(2) The BIG-LAN FAQ

(3) 10baseT FAQ

(4) Ethernet FAQ

(5) TCP/IP FAQ

Last revised: 7/13/95

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