ABR "Available Bit Rate"
(ATM term) one of several quality-of-service traffic classes used in ATM.
ABR basically means "use whatever
is available", i.e. don't offer any special quality of service.
ADSL "Asymmetric Digital Subscriber Line"
Remote access method that makes use of a faster channel
for local-to-remote communications than remote-to-local.
ANSI "American National Standards Institute"
A definer of
standards of all kinds, including FDDI.
ANSI X3
ANSI group developing standards for information
processing.
ANSI X3T9
ANSI group within X3 developing standards for I/O
interfaces.
ANSI X3T9.3 Committee
ANSI group within X3T9 standardizing HiPPI.
ANSI X3T9.5 Committee
ANSI group within X3T9 that standardized
FDDI, PMD, SMF-PMD, and is standardizing TP-PMD and LCF-PMD.
AppleTalk
A protocol family developed by Apple Computer to
implement LANs serving Macintoshes.
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 (see SONET & TAXI). 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.
ATM Forum
Non-profit international industry consortium chartered
to accelerate ATM acceptance & interoperability.
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).
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.
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.
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.
Broadcast
A message (e.g. packet or frame) sent to all the nodes
on a network.
Broadcast Address
An address which can be used as the destination of a communication
that indicates the packet/message is a broadcast.
IP has broadcast addresses as does IEEE 802.
Broadcast Domain
That part of a network which receives the same broadcasts.
Bus
A term used for a kind of electronic device in which a number
of elements are wired together with a single wire in such way that
all the elements can use the same wire to transmit information to
other devices on it.
Buses are used internally in computers and used to attach
computers to peripherals.
For the purposes of LANs, bus is a term for a LAN
topology which has the same characteristic: the same
wire is attached to a number of devices which all share that
wire to transmit to other devices on the LAN.
ThickWire and ThinWire Ethernet, Localtalk, and ARCnet are
examples of LAN technologies with a bus topology.
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.
Category 4 Unshielded Twisted Pair
standardization of unshielded
twisted pair cable.
Category 5 Unshielded Twisted Pair
standardization of unshielded
twisted pair cable for data use. TP-PMD requires Category
5 cable rather than Category 3.
Category 6
Name people and organizations often associate with their various
proposals for yet another gradee of twisted pair media.
At the time of this writing, 9/27/96, there is no official "Category 6".
CBR "Constant Bit Rate"
(ATM term) one of several quality-of-service traffic classes used in ATM.
See also "ABR".
CCITT "Consultative Committee for International Telegraph and Telephone"
An international telecommunications standards organization, now subsumed by the ITU.
CDDI "Copper Data Distribution Interface"
Commonly used term
for TP-PMD, but actually a trade name of Crescendo.
Cell
An ATM 53-byte cell. Note: there are various proposals for
how typical packets will be broken into cells and restored.
Cell Switching
a term for ATM-style networks. See "ATM".
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.
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.
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.
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.
Counterrotating Ring
(see Ring, FDDI, Token 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.
CRC "Cyclic Redundancy Check"
An error checking technique: a way in which a frame or packet
can be created in such a way that the receiver can determine
whether an error is likely to have occurred in the transmission.
CSMA/CD "Carrier Sense Multiple Access with Collision Detection"
The method by which nodes on an Ethernet/IEEE 802.3 LAN gain access
to the network, i.e. one of several techniques that have been built
into different LAN technologies to allow multiple nodes to share
the same wires/electronics to send their data.
Cut-Through Switching
A method of switching (bridging) where the beginning of
the packet/frame is being sent on one LAN while the end of it
is still being received from another LAN.
The method allows quicker transmission of the data in the best
case, but defeats some of the error checking that would be
available in standard bridging.
DAS "Dual Attachment Station"
A type of FDDI node that attaches to both rings of a counter-rotating
ring to provide some fallback capability.
The other type is SAS (Single Attachment Station).
Typically, more vital FDDI nodes are DAS, e.g. routers, servers,
links between hubs, and invividual client stations are SAS.
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).
Dialup Modem
Modem used over ordinary dial-up telephone lines
as opposed to private or leased lines.
DS3 UNI
ATM Forum DS3 UNI, 44.236Mbps.
DXI
ATM Forum "Data Exchange Interface".
ELAN "Emulated LAN"
Essentially, a fairly simple kind of VLAN defined in
the ATM Forum's LANE specification.
Unlike many VLAN schemes, the ELAN scheme is agreed upon
by multiple vendors, i.e., the members of the ATM Forum.
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.
Fast Ethernet
A nickname for the 100Mbps version of IEEE 802.3.
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.
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.
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.
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.
Fiber
optical fiber: a very long, narrow, flexible piece of
glass. Used for high-speed communications.
Fibre Channel
an ANSI standard to replace HiPPI. It uses optical
fiber instead of copper cables. Speeds are up to roughly
1Gbps.
Fibre Channel Systems Initiative
Group of vendors trying to
accelerate Fiber Channel acceptance & interoperability. Members
include: HP, IBM, Sun.
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.
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.
Fragment
A portion of a packet/frame.
In Ethernet terminology, Fragment (or "Runt") often means a part
of an Ethernet frame left over from a collision.
In IP terminology, Fragment means a packet which is the result
of splitting a larger packet into smaller ones.
Frame
A term for the unit of data transferred on a LAN; it is something
larger than a cell, i.e. depending on the type of LAN,
hundreds or thousands of bytes long
(any particular type of LAN will have a limit on the frame size,
e.g. Ethernet's 1500 byte/octet limit).
Roughly equivalent to the term packet, but "frame" is a LAN term
whereas "packet" is a term used for higher level protocols such
TCP/IP, IPX, and AppleTalk.
Frame Switching
A term used in contrast to "Cell Switching". Frame
Switching means a switch which forwards entire frames,
e.g. Ethernet or FDDI frames.
FTP
Protocol in the "TCP/IP" family for copying files from
one computer to another. Stands for "File Transfer Protocol".
Full Duplex
A possible property of a data-communications line: that
data can be transferred in both directions, simultaneously.
The alternatives are Half Duplex and Simplex.
Full Duplex Switched Ethernet Consortium
Group of vendors that
are working out the details of FDSE. Cabletron is a member.
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.
GAE
Gigabit Ethernet Alliance.
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".
Gigabit Ethernet
High-speed version of Ethernet (a billion bits per second)
under development by the IEEE.
Gigabit Ethernet Alliance
Group of vendors working together to help drive the standarization
of Ethernet at 1Gbps data rates.
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.
Half Duplex
A possible property of a data-communications line: that data
can be transferred in either direction, but only in one direction
at a time.
If the line is sufficiently high-speed, then to a human, it may appear
that data transfer is simultaneous in both directions if the two
ends quickly take turns transferring.
The alternatives are Half Duplex and Simplex.
Hardware Address
Often used phrase for MAC Layer address or Ethernet address.
HDLC "High-level Data Link Control"
A low-level protocol used on synchronous WAN lines.
HDSL "High-bit-rate Digital Subscriber Line"
Remote access line above basic ISDN speed.
Header
A portion of a message (cell, packet, frame, etc)
at the front with control information such as the destination
address.
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. See Question on SQE/Heartbeat below.
HiPPI
"High Performance Parallel Interface", ANSI draft standard
X3T9.3.
HSSI "High Speed Serial Interface"
A physical layer interface for serial communications between a DTE
(e.g. a router) and a DCE (e.g. a DSU/CSU) that supports up to 52Mbps.
Serves the same purpose as RS-232, but at a higher range of
communication speeds.
Used mostly for DS3 WAN links.
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.
ICMP "Internet Control Message Protocol"
(TCP/IP term) An IP-related protocol used to carry out some
control functions such as "ping".
Documented in RFC792.
IEEE
Institute of Electrical & Electronic Engineers
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.
IEEE 802.1
The IEEE 802 standard for Network Management and
Network Bridging of IEEE 802 networks.
IEEE 802.11
Proposed IEEE 802 group for wireless Ethernet.
IEEE 802.12
Group within IEEE 802 working on 100VG-AnyLAN.
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.
IEEE 802.3
An IEEE standard for LANs--their "improved" version of
Ethernet. See Ethernet.
IEEE 802.3u
The portion of IEEE 802.3 which defines the 100Mbps version,
i.e. Fast Ethernet or 100BASE-T.
IEEE 802.4
An IEEE standard for LANs: Token Bus networks.
Basically, standardizes MAP, a protocol that operates a Token
Bus protocol on broadband.
IEEE 802.5
An IEEE standard for Token-Ring-based LANs. There
are two types: 4Mbps and 16Mbps. See also "Token Ring".
IEEE 802.6
An IEEE standard for Metropolitan Area Networks. Also
known as DQDB.
IEEE 802.7
IEEE 802 technical advisory group on Broadband.
IEEE 802.8
IEEE 802 technical advisory group on FDDI & fiber
optics.
IEEE 802.9
IEEE 802 group on integrated data & voice networks.
IETF "Internet Engineering Task Force"
A group responsible for defining protocols in the TCP/IP family
for use on the Internet.
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.
IP "Internet Protocol"
The basic protocol of TCP/IP and the Internet.
IPX
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.
ISDN "Integrated Services Digital Network"
A recent development in telephone/data communications
that offers the subscriber digitized voice service and/or
64Kbps data service.
LAN Switching
Term for bridging or cut-through switching, usually
referring to a device with more than two ports.
LANE
ATM Forum's method of using an ATM switch or switches to
emulate an Ethernet or Token Ring LAN.
The resulting "Emulated LAN" is called an ELAN, which can
be thought of as a kind of fairly simple VLAN.
Latency
The amount delay in the delivery of data through a network
or network device.
LCF-PMD
FDDI "Low-Cost Fiber" PMD. Less expensive than PMD. I
don't believe it is common nor is it finished as a standard.
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.
MAC "Media Access Control"
A layer within the OSI Data Link Layer.
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.
MII "Media Independent Interface"
An Interface much like the 10Mbps Ethernet "AUI" Interface
only for 100Mbps Ethernet (100BASE-T, etc).
MPOA "Multiprotocol Over ATM"
ATM Forum's method of using an ATM switch or switches
to take the place of routing.
The protocol/method is currently in development.
As its name implies, it is intended to handle more than just
TCP/IP, but TCP/IP support is what is being developed to begin with.
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.
NIC "Network Interface Card"
A term used for the card you put in a PC to allow it to
be attached to a network.
The term and acronym is most often used with respect to
IBM compatibles, and LANs such as Ethernet and Token Ring.
NFS "Network File System"
an IP-based protocol originally
developed by Sun Microsystems which provides file services.
Octet
A networking term which is basically equivalent to the
term "byte", i.e. 8 bits.
OCx
(e.g. OC1, OC3) variants of SONET.
OSI "Open System Interconnect"
A standard put forth by the ISO
for communication between computer equipment and networks.
OSI Reference Model
A model put forth by the ISO for
communication between computer equipment and networks, which
maps out 7 protocol layers.
Top layer: layer number 7: application layer
layer number 6: presentation layer
layer number 5: session layer
layer number 4: transport layer
layer number 3: network layer
layer number 2: data-link layer (e.g. IEEE 802.x)
Bottom layer: layer number 1: physical layer (wire & electricity)
This model explains what each layer does. The model is often
used to explain anyones protocols (not just OSI) to the point
where many people seem to believe that true data-communications
requires these 7 layers.
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.
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.
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.
Relay
One terminology uses the term "relay" as a device that
interconnects LANs, different kinds of relays being repeaters,
bridges, routers, and gateways.
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.
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.
RG numbers (E.g. RG62; sometimes there are qualifiers, e.g. RG 58 A/U)
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". One can't recommend this practice because you
can get yourself in trouble. I think "RG" originally stood
for "Radio Guide", presumably reflecting the fact that the
series of cables was designed to handle radio frequencies. The
IEEE 802.3 10BASE2 specifications define two RG numbered cables
(RG58 A/U and RG58 C/U) as meeting the cable requirements for
thin Ethernet. However, cable vendors may list a range of
cables under these same RG numbers, and some of the cables
listed may not meet the 802.3 specs. You need to check the
cable specifications closely, and beware of relying on the RG
number alone when ordering network cables.
Ring
A classification of network technology (known as its
topology) 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".
RJ numbers ("Regestered Jack" numbers, e.g. RJ11, RJ45)
numbers
applied to types of connectors often used in UTP wiring.
Borrowed from voice telecommunications industry.
Router
A network "relay" that uses a protocol beyond the
data-link protocol to route traffic between LANs and other
network links.
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.
RSVP "Resource Reservation Protocol"
A method being developed by the IETF to assist in providing
quality-of-service characteristics to communications over an
IP network.
The name refers to the fact that it allows the end-stations to
reserve bandwidth on the network.
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.
SDLC "Serial Data Link Control"
A low-level protocol used on synchronous WAN lines.
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.
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".
SMF-PMD
FDDI "Single-Mode Fiber" PMD. Runs further than PMD.
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.
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.
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).
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. See Question on SQE/Heartbeat
below.
Star
A classification of network technology (known as its
topology) defined by a network which consists of
a central element attached to its client computers via
wires leading out from the central element. A LAN that
consists of a number of computers each directly attached
to an ATM switch is a good example of a star-topology LAN.
STP
Shielded Twisted Pair
STS-3c UNI
ATM Forum SONET STS-3c UNI, 155.52Mbps.
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.
Switched FDDI
really the same as FDDI as far as standards
go: acts like a very fast multiport FDDI bridge. Basically the
DEC GigaSwitch.
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 to provide 24 low-speed circuits, or to provide 1
high-speed circuit, or to be divided other ways.
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
specification. The faster one ran at 140Mbps.
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.
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.
Terminal Server
a network device that allows a number of
terminals to attach to a LAN, and do remote logins across the
LAN.
ThickWire
"ThickWire" Ethernet or IEEE 802.3 10BASE5.
ThinWire
ThinWire Ethernet or IEEE 802.3 10BASE2.
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.
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.
Topology
Term used to describe a general characteristic of a
LAN technology which more or less describes the shape of
the necessary wiring.
Three examples are bus, ring, and star.
TP
"Twisted Pair".
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.
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.
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").
Type1
IBM Type 1 STP. The most usual type of Shielded Twisted
Pair in LAN communications.
UNI
ATM Forum "User to Network Interface". See ATM.
UTP (Unshielded Twisted-Pair)
See "Twisted-Pair" and "Shielded Twisted-Pair".
Virtual LAN (VLAN)
A portion of one or more LAN switches which delivers packets
as if it were a physical LAN; actually like a switched LAN.
It is a feature planned or included in numerous LAN switches.
VLAN is a well-known industry buzzword as of 1995 and 1996 and
is not used consistently throughout the industry.
The most primitive VLAN facility that a switch can have allows
the switch to be partitioned into two or more groups of ports (VLANs)
within which communication is possible, but between which communication
is blocked.
More complex is a feature which allows each VLAN to reside on two or more
switches (e.g. some of VLAN A's ports are on switch 1 and some of its
ports are on switch 2; and the same for VLAN B) even though the
two switches are connected through a single physical interface.
The most complex is provision for VLANs that overlap, i.e. port 1
of a switch is on VLAN A and VLAN B, while port 2 is on VLAN A but
not VLAN B, etc.
The term "Virtual Network" is also used.
Virtual Network
See "Virtual LAN".
WAN "Wide Area Network"
A term for state/country/world-wide networks developed to parallel
the term LAN for "Local Area Network".
X.25
Protocol used for inter-computer communications over WANs.
X.400, X.500
OSI protocols for mail and directory services.