TA (Telecommunications Administration) A
body, usually a company, that provides public telecommunications
services.
T1 A committee belonging
to the ANSI whose role is to establish US standards for digital
telephony, particularly ISDN. The committee is in no way responsible
for or involved with the Tl (1.5Mbit/s) circuit standards.
T1 A US and Japanese
standard for high-speed data transmission at 1.544Mbit/s - 24
64Kbit/s channels plus 8Kbit/s' control information are provided.
Also called a DS1.
T3 A US standard for
high-speed data transmission at 44.736Mbit/s, providing the equivalent
bandwidth of 28 T1 circuits. Also called a DS3.
T-Carrier The US standards
for digital transmission lines. The line types are of the form
Tn or TIC, and the corresponding line signal standards of the
form DSn or DSIC.
Tap The connecting
device on cable-based LANs like Ethernet, linking to the main
transmission medium.
TCP (Transmission Control Protocol) The
standard transport level protocol that provides the full duplex,
stream service on which many application protocols depend. TCP
allows a process or one machine to send a stream of data to a
process on another. Software implementing TCP usually resides
in the operating system and uses the IP to transmit information
across the network.
TCP/IP (Transmission Control Protocol/Internet
Protocol) The suite of protocols developed
and used by DAR PA and the US DOD. They build up to Laye r Four
of the ISO OSI model, but there is no direct correspondence layer
for layer. Three main protocols sit above TCP/IP: Telnet, FTP
and SMTP.
TDM (Time Division Multiplexer/Multiplexing)
Multiplexer which apportions the time
available on its Composite link between its channels, interleaving
data from successive channels. The method divides up digital channels
to make maximum use of their bandwidth, by taking input from each
source in turn. TDMs use one of two methods to achieve this, bit
interleaving for synchronous protocols and character interleaving
for asynchronous protocols.
TDMA (Time Division Multiple Access) In
LAN technology, a high-speed, burst mode of operation that can
interconnect LANs. First used as a multiplexing technique on shared
communications satellites.
Teletex ITU-TS standard
for text and message communications intended to replace telex-operating
at 2,400bps, it accommodates upper and lower case characters and
has a well-defined format for transmission and text presentation.
Teletext Method of
transmitting pages of information using broadcast transmission
techniques. Embraces both standard broadcast transmission systems
and in-house/cable systems using this format.
Terminal emulation Software
that allows a PC to mimic the attributes of a dumb terminal normally
attached to a mainframe or mini-computer, giving the user with
access to function keys and control sequences which the host applications
normally use when communicating with one of their own dumb terminals.
The most commonly emulated terminals are Dec's VT100 terminal
and IBM's 3270.
TFTP (Trivial File Transfer Protocol) The
TCP/IP standard protocol for file transfer with minimal capability
and minimal overhead. TFTP depends on the connectionless datagram
delivery service, UDP.
Thin Ethernet An 802.3
LAN that uses smaller than normal diameter coaxial cable; often
used to link PCs together. It runs at the same frequency as Ethernet
but at smaller distances. Colloquially called Cheapernet.
Timeout The expiration
of a pre-defined interval which then triggers some action. For
example, in a 30-second, no activity timeout, disconnection occurs
after 30 seconds of no data activity. Simple eh? Alternatively,
the length or existence of such an interval.
Token Unique information
in a packet header which acknowledges that control of the network
is to be relinquished upon receipt of the packet. An empty packet
containing a token is forwarded by the recipient to the next node.
The token packet passes round the LAN continuously and, as it
goes by, give each workstation the all-clear to transmit data.
Token Bus A LAN with
a bus topology that uses token passing as its access method. The
sequence of nodes is not governed by physical architecture, but
is controlled by software. Arcnet and Map are examples.
Token passing A technique
for restricting access to a network, to a single node at a time.
A token is passed from node to node, granting permission to transmit
data. The sender attaches its message to the token which conveys
it across the LAN to its destination, The message is ignored by
all other nodes, and is acted upon by the addressee, When the
recipient has accepted the message, it releases the token so that
the next node wishing to send can use it.
Token Ring A 4/16Mbit/s
LAN architecture which uses a token passing access method to allow
nodes on the network to transmit data. Defined in IEEE 802.5 with
a ring architecture, a special data packet, called a token, is
passed continuously from node to node (see Token passing, above).
The sequence of nodes is governed by the physical order in which
the nodes appear on the ring. Every node on the ring sees the
data, but only the addressed receiving node will accept it.
Top (Technical and Office Protocols) A
Functional Profile originated by Boeing to separate networking
in a non-shop floor environment. TOP was designed from the outset
to be compliant with the ISO OSI seven-layer model. Development
has beer merged with MAP, and the two functional profiles share
a common integration strategy, and have a single (Map/Top) user
group.
TP-4/IP A term given
to the ISO protocol suite that closely resembles TCP/IP. Transceiver
- A communications device and software capable of transmitting
and receiving (see also MAU). Transmission block - A sequence
of continuous data characters or bytes transmitted as a unit,
over which a coding procedure is usually applied for synchronous
or error control purposes.
Transparent Bridging So
named because the intelligence necessary to make relaying decisions
exists in the bridge itself and is thus "transparent"
to the communicating workstations. It involves frame forwarding,
learning workstation addresses and ensuring no topology loops
exist (in conjunction with the Spanning Tree algorithm).
Transport driver A
network device driver that implements a protocol for communicating
between LAN Manager and one or more media access control drivers.
The transport driver transfers LAN Manager events between computers
on the local area network.
Transport Layer The
Fourth Layer in the OSI model, drawn up by the ISO. The purpose
of the transport layer is to act as an intermediary between the
user and the network. All layers above the transport layer are
network independent.
Tree topology A graphic
description of a network topology where there is only one route
between any two nodes.
Trellis coding An
advanced method of modulation which combines coding of both amplitude
and phase. This gives a greater throughput and lower error rate
for speeds above 9.6Kbit/s.
Trunk in token ring,
a trunk is the cab e running between MSAUs and can be either fiber
or shielded twisted pair cable. STP uses two positive transmit
wires in normal mode, with no crossover, while fiber has one transmit
fiber and one receiver fiber. In normal mode, the second pair
of wires is not used it acts as backup and implements the Wrap
feature.
Twisted Pair Two insulated
copper wires twisted together with the twists or lays varied in
length to reduce potential signal interference between the pairs.
Where cables comprise more than 25 pairs, they are usually bundled
and wrapped in a cable sheath. Twisted pair is the most common
medium for connecting phones, computers and terminals to PABXS.
With the IEEE ratification of 10BaseT for networking 10Mbit/s
Ethernet over UTP telephony wiring, twisted pair has become ubiquitous.
As well as performance at Ethernet rates, it offers cost benefits
to the end user through flexibility - ease of relocation. New
data-grade and even voice-grade UTP methods support l00Mbit/s
transmission, with 155Mbit/s ATM a probability.
Type A Intelligent
Network term describing IN services evoked by, and affecting,
a single user. Most of them can only be invoked during call setup
or teardown.
Type B Intelligent
Network term describing IN services invoked at any point by, and
affecting directly, several users.
