- Digital WAN carrier facility. T1
transmits DS-1-formatted data at 1.544 Mbps through the
telephone-switching network, using AMI or B8ZS coding. Compare with E1.
See also AMI,
B8ZS,
and DS-1.
- Digital WAN carrier facility. T3
transmits DS-3-formatted data at 44.736 Mbps through the telephone
switching network. Compare with E3.
See also DS-3.
- 1.) Terminal Access Controller.
Internet host that accepts terminal connections from dial-up lines.
2.) Technical Assistance Center. Cisco TACs provide technical assistance to partners and end users, and form the hub of Cisco global support.
- Terminal Access
Controller Access Control System.
Authentication protocol, developed by the DDN community, that
provides remote access authentication and related services, such as
event logging. User passwords are administered in a central database
rather than in individual routers, providing an easily scalable
network security solution. See also TACACS+.
- Proprietary Cisco enhancement to
TACACS. Provides additional support for authentication,
authorization, and accounting. See also TACACS.
- ATM cells that have their CLP bit set
to 1. If the network is congested, tagged traffic can be dropped to
ensure delivery of higher-priority traffic. Sometimes called DE
(discard eligible) traffic. See also CLP.
- Transparent Asynchronous
Transmitter/Receiver Interface 4-byte/5-byte.
Encoding scheme used for FDDI LANs as well as for ATM. Supports
speeds of up to 100 Mbps over multimode fiber. TAXI is the chipset
that generates 4B/5B encoding on multimode fiber. See also 4B/5B
local fiber.
T-carrier
- TDM transmission method usually
referring to a line or cable carrying a DS-1 signal.
- Transmission Control
Protocol. Connection-oriented
transport layer protocol that provides reliable full-duplex data
transmission. TCP is part of the TCP/IP protocol stack. See also TCP/IP.
- Transmission Control
Protocol/Internet Protocol. Common
name for the suite of protocols developed by the U.S. DoD in the
1970s to support the construction of worldwide internetworks. TCP
and IP are the two best-known protocols in the suite. See also IP
and TCP.
- Test and control system.
Independently-powered subsystem used to initialize, monitor, and
troubleshoot the hardware on a LightStream 2020 ATM switch. The TCS
consists of a hub residing on the switch card and slaves on NPs and
line cards.
- Trunk coupling unit.
In Token Ring networks, a physical device that enables a station to
connect to the trunk cable.
- Time-division
multiplexing. Technique in which
information from multiple channels can be allocated bandwidth on a
single wire based on preassigned time slots. Bandwidth is allocated
to each channel regardless of whether the station has data to
transmit. Compare with ATDM,
FDM,
and statistical
multiplexing.
- Time domain
reflectometer. Device capable of
sending signals through a network medium to check cable continuity,
length, and other attributes. TDRs are used to find physical layer
network problems.
Technical
Assistance Center
- See TAC.
Technical
Office Protocol
- See TOP.
telco
- Abbreviation for telephone company.
telecommunications
- Term referring to communications
(usually involving computer systems) over the telephone network.
Telecommunications
Industry Association
- See TIA.
telephony
- Science of converting sound to
electrical signals and transmitting it between widely removed
points.
telepole
- Telescoping pole with a hook at one
end. It is used to get cable across a ceiling or attic quickly.
telex
- Teletypewriter service allowing
subscribers to send messages over the PSTN.
- Command used to verify the application
layer software between source and destination stations. This is the
most complete test mechanism available.
- U.S. military standard. Electronic
products adhering to the Tempest specification are designed to
withstand EMP. See also EMP.
- Trans-European Research
and Education Networking Association.
Organization that promotes information and telecommunications
technologies development in Europe. Formed by the merging of EARN
and RARE. See also EARN
and RARE.
- Command used to specify the format of
network masks for the current session.
- SNA cluster controller identification.
Termid is meaningful only for switched lines. Also called Xid.
terminal
- Simple device at which data can be
entered or retrieved from a network. Generally, terminals have a
monitor and a keyboard, but no processor or local disk drive.
Terminal
Access Controller
- See TAC.
Terminal
Access Controller Access System
- See TACACS.
terminal
adapter
- Device used to connect ISDN BRI
connections to existing interfaces such as EIA/TIA-232. Essentially,
an ISDN modem.
terminal
emulation
- Network application in which a
computer runs software that makes it appear to a remote host as a
directly attached terminal.
terminal
server
- Communications processor that connects
asynchronous devices such as terminals, printers, hosts, and modems
to any LAN or WAN that uses TCP/IP, X.25, or LAT protocols. Terminal
servers provide the internetwork intelligence that is not available
in the connected devices.
terminator
- Device that provides electrical
resistance at the end of a transmission line to absorb signals on
the line, thereby keeping them from bouncing back and being received
again by network stations.
test
and control system
- See TCS.
Texas
Higher Education Network
- See THEnet.
- Trivial File Transfer
Protocol. Simplified version of FTP
that allows files to be transferred from one computer to another
over a network.
- Transmission header.
SNA header that is appended to the SNA basic information unit (BIU).
The TH uses one of a number of available SNA header formats. See
also FID0,
FID1,
FID2,
FID3,
and FID4.
THC
over X.25
- Feature providing TCP/IP header
compression over X.25 links, for purposes of link efficiency.
- Texas Higher Education
Network. Regional network comprising
over 60 academic and research institutions in the Texas (United
States), area.
- Term used to define a thinner, less
expensive version of the cable specified in the IEEE 802.3 10BASE2
standard. Compare with Cheapernet.
See also 10BASE2,
Ethernet,
and IEEE
802.3.
throughput
- Rate of information arriving at, and
possibly passing through, a particular point in a network system.
- Telecommunications
Industry Association. Organization
that develops standards relating to telecommunications technologies.
Together, the TIA and the EIA have formalized standards, such as EIA/TIA-232,
for the electrical characteristics of data transmission. See also EIA.
- Token Ring interface
coupler. Controller through which an
FEP connects to a Token Ring.
tie-wraps
- Plastic ties used for holding cables
together or for holding cables in place.
time-division
multiplexing
- See TDM.
time
domain reflectometer
- See TDR.
time
domain reflectometry
- Technique of sending an electrical
signal down a cable and then timing the signal's reflection back
from the end of the cable.
Time
Notify
- See TNotify.
time-out
- Event that occurs when one network
device expects to hear from another network device within a
specified period of time, but does not. The resulting time-out
usually results in a retransmission of information or the dissolving
of the session between the two devices.
Time
To Live
- See TTL.
TN3270
- Terminal emulation software that
allows a terminal to appear to an IBM host as a 3278 Model 2
terminal. The Cisco TN3270 implementation allows users to access an
IBM host without using a special IBM server or a UNIX host acting as
a server.
- Time Notify.
Specifies how often SMT initiates neighbor notification broadcasts.
See also SMT.
- Frame that contains control
information. Possession of the token allows a network device to
transmit data onto the network. See also token
passing.
- LAN architecture using token passing
access over a bus topology. This LAN architecture is the basis for
the IEEE 802.4 LAN specification. See also IEEE
802.4.
- Access method by which network devices
access the physical medium in an orderly fashion based on possession
of a small frame called a token. Contrast with circuit
switching and contention.
See also token.
- Token-passing LAN developed and
supported by IBM. Token Ring runs at 4 or 16 Mbps over a ring
topology. Similar to IEEE 802.5. See also IEEE
802.5, ring
topology, and token
passing.
Token
Ring interface coupler
- See TIC.
Token
Ring Interface Processor
- See TRIP.
- Technical Office
Protocol. OSI-based architecture
developed for office communications.
topology
- Physical arrangement of network nodes
and media within an enterprise networking structure.
- Tool for managing a LightStream 2020
ATM switch that examines a network and displays the status of its
nodes and trunks. The topology map is an HP OpenView-based
application that runs on an NMS.
- Type of service.
Field within an IP datagram that indicates how the datagram should
be handled. See COS
(class of service).
to
switch unit
- See TSU.
total
length
- Field within an IP datagram that
indicates total length of the header + the data.
- Transport Protocol Class
0. OSI connectionless transport
protocol for use over reliable subnetworks. Defined by ISO 8073.
- Transport Protocol Class
4. OSI connection-based transport
protocol. Defined by ISO 8073.
trace
- Command that uses Time-To-Live (TTL)
values to generate messages from each router used along the path.
This is very powerful in its ability to locate failures in the path
from the source to the destination.
traffic
management
- Process used to measure the actual
traffic flow across a given connection and compare it to the total
admissable traffic flow for that connection. Traffic outside of the
agreed upon flow can be tagged (where the CLP bit is set to 1) and
can be discarded en route if congestion develops. Traffic policing
is used in ATM, Frame Relay, and other types of networks. Also know
as admission control, permit processing, rate
enforcement, and UPC (usage parameter control). See also tagged
traffic.
traffic
profile
- Set of COS attribute values assigned
to a given port on a LightStream 2020 ATM switch. The profile
affects numerous parameters for data transmitted from the port
including rate, cell drop eligibility, transmit priority, and
inactivity timer. See also COS.
- Use of queues to limit surges that can
congest a network. Data is buffered and then sent into the network
in regulated amounts to ensure that the traffic will fit within the
promised traffic envelope for the particular connection. Traffic
shaping is used in ATM, Frame Relay, and other types of networks.
Also known as metering, shaping, and smoothing.
- Control information appended to data
when encapsulating the data for network transmission. Compare with header.
transaction
- Result-oriented unit of communication
processing.
- Layer 7 in the SNA
architectural model. Represents user application functions, such as
spreadsheets, word-processing, or electronic mail, by which users
interact with the network. Corresponds roughly with the application
layer of the OSI reference model. See also data
flow control layer, data
link control layer, path
control layer, physical
control layer, presentation
services layer, and transmission
control layer.
transceiver
- See MAU.
transceiver
cable
- See AUI.
Trans-European
Research and Education Networking Association
- See TERENA.
transfer
priority
- See transmit
priority.
transit
bridging
- Bridging that uses encapsulation to
send a frame between two similar networks over a dissimilar network.
- Bridging between networks with
dissimilar MAC sublayer protocols. MAC information is translated
into the format of the destination network at the bridge. Contrast
with encapsulation
bridging.
- Layer 4 in the SNA
architectural model. This layer is responsible for establishing,
maintaining, and terminating SNA sessions, sequencing data messages,
and controlling session level flow. Corresponds to the transport
layer of the OSI model. See also data
flow control layer, data
link control layer, path
control layer, physical
control layer, presentation
services layer, and transaction
services layer.
Transmission
Control Protocol
- See TCP.
Transmission
Control Protocol/Internet Protocol
- See TCP/IP.
transmission
group
- In SNA routing, one or more parallel
communications links treated as one communications facility.
transmission
header
- See TH.
transmission
link
- See link.
- Queuing scheme in which each internal
TOS of a LightStream 2020 ATM switch correlates to a relative
priority in queues in the ATM network. This priority determines
which traffic is serviced first in the case of contention for a
network resource. Also known as forwarding priority and transfer
priority.
TRANSPAC
- Major packet data network run by
France Telecom.
Transparent
Asynchronous Transmitter/Receiver Interface 4-byte/5-byte
- See TAXI
4B/5B.
- Bridging scheme often used in Ethernet
and IEEE 802.3 networks in which bridges pass frames along one hop
at a time based on tables associating end nodes with bridge ports.
Transparent bridging is so named because the presence of bridges is
transparent to network end nodes. Contrast with SRB.
- Layer 4 of the OSI
reference model. This layer is responsible for reliable network
communication between end nodes. The transport layer provides
mechanisms for the establishment, maintenance, and termination of
virtual circuits, transport fault detection and recovery, and
information flow control. Corresponds to the transmission
control layer of the SNA model. See also application
layer, data
link layer, network
layer, physical
layer, presentation
layer, and session
layer.
Transport
Protocol Class 0
- See TP0.
Transport
Protocol Class 4
- See TP4.
- Message sent by an SNMP agent to an
NMS, console, or terminal to indicate the occurrence of a
significant event, such as a specifically defined condition or a
threshold that has been reached. See also alarm
and event.
- LAN topology similar to a bus
topology, except that tree networks can contain branches with
multiple nodes. Transmissions from a station propagate the length of
the medium and are received by all other stations. Compare with bus
topology, ring
topology, and star
topology.
- Token Ring Interface
Processor. High-speed interface
processor on the Cisco 7000 series routers. The TRIP provides two or
four Token Ring ports for interconnection with IEEE 802.5 and IBM
Token Ring media with ports independently set to speeds of either 4
or 16 Mbps.
Trivial
File Transfer Protocol
- See TFTP.
- Physical and logical connection
between two ATM switches across which traffic in an ATM network
travels. An ATM backbone is composed of a number of trunks.
- Line card on a LightStream 2020 ATM
switch that is configured to communicate with other ATM switches.
LightStream 2020 trunk cards offer a variety of interface types.
CLCs, LSCs, and MSCs can operate as trunk cards. See also edge
card.
trunk
coupling unit
- See TCU.
trunk
up-down
- See TUD.
- To switch unit.
Subsystem on each LightStream 2020 ATM switch line card that appends
ATM routing information to outgoing cells and sends the cells to the
switch card.
- Time To Live.
Field in an IP header that indicates how long a packet is considered
valid.
- Architecture that is designed to
provide the services necessary to implement any standard
point-to-point encapsulation scheme. See also encapsulation.
- Trunk up-down.
Protocol used in ATM networks that monitors trunks and detects when
one goes down or comes up. ATM switches send regular test messages
from each trunk port to test trunk line quality. If a trunk misses a
given number of these messages, TUD declares the trunk down. When a
trunk comes back up, TUD recognizes that the trunk is up, declares
the trunk up, and returns it to service. See also trunk.
TUV
- German test agency that certifies
products to European safety standards.
- Relatively low-speed transmission
medium consisting of two insulated wires arranged in a regular
spiral pattern. The wires can be shielded or unshielded. Twisted
pair is common in telephony applications and is increasingly common
in data networks. See also STP
and UTP.
two-way
simultaneous
- See TWS.
- Two-way simultaneous.
Mode that allows a router configured as a primary SDLC station to
achieve better utilization of a full-duplex serial line. When TWS is
enabled in a multidrop environment, the router can poll a secondary
station and receive data from that station while it sends data to or
receives data from a different secondary station on the same serial
line.
TYMNET
- See XStream.
Type
1 operation
- IEEE 802.2 (LLC) connectionless
operation.
Type
2 operation
- IEEE 802.2 (LLC) connection-oriented
operation.
type
of service
- See TOS.