TAC
Technical Assistance Center - Cisco ¨

TAPI
Telephony Application Program Interface

TB
Terra Bytes

TC
Transmission Control

TCO
Total Cost of Ownership


TCP
Transmission Control Protocol 
Layer 4 of the OSI model - error check control sequences rfc 793 

- Layer 4 of the OSI model - error check control sequences. 
- The major transport protocol in the Internet suite of protocols providing reliable, connection-oriented, full-duplex streams. TCP is both an OSI transport layer 4 protocol that regulates source-to-destination communication over virtual circuits and the portion of the TCP/IP protocol suite that governs the exchange of sequential data.

TCP/IP
Transmission Control Protocol / Internet Protocol

TD
Transmitted Data -RS-232-C standard hardware signal to send data from one device to another; also called Tx or Txd.

TDD
Time Division Duplex - TDMA

TDM
Time Division Multiplexing 
- A method of transmission which relies on providing bandwidth based on fixed time slots or channels, also called circuit switching.
- A device that performs circuit switching. It converts analog signals to digital signals and integrates video, voice, and data applications.

TE1
Terminal Equipment 1
ISDN-compatible devices, such as a router with an ISDN/BRI module.

TE2
Terminal Equipment 2
Non ISDN-compatible devices, such as analog phones and PCs.

TEI
Terminal Endpoint Identifier

TELCO
Telephone Company

TELNET
Telecommunications Network Protocol
RFC 854. It allows users of one host to log in to a remote host and interact as normal terminal users of that host.

TERMINATOR
An electrical impedance attached to the open end of a transmission line to eliminate reflections. Electrical circuitry at the end of a cable designed to match impedance for the purpose of preventing the reflection of electrical signals when they reach the end of the cable.

Threshold
A limit value associated with a specific parameter or attribute of device or network performance.

TN3270
Delivery of a 3270 data stream via Telnet, provided as part of the TCP/IP protocol suite.

TOS
Type Of Service

TP
Transport Protocol - ISO

TPON
Telephony Passive Optical Network

TR
Token-Ring 
The concept of passing a token message to grant the right to access the physical network media is not unique to the 802.5 standards. Our convention, when referring to token passing rings, is to hyphenate the words "Token" and "Ring" to specifically refer to the IBM/802.5 implementation of token passing. 
The ring in 802.5 is a physical, circular, interconnected ring of stations. Each station has a separate transmitter and receiver port. The transmitter port on one station is connected to the receiver port on the next station. The term "Upstream Neighbor" is used to refer to the transmitting station and that station transmits to its "Downstream Neighbor". A Downstream station receives bits on the cable attached to its Nearest Upstream Neighbor station. This station repeats bits to the next station.

IEEE 802.5 for IP 

Transmitter-receiver
An internal or external device for receiving and transmitting data; for example, an IEEE 802.3 medium attachment unit (MAU), through which Ethernet stations attach to the network cabling medium and which provides circuitry to convert signals between a form suitable for the network and a form suitable for the station.

Transparent Bridging
A system-level concept where the bridges perform MAC address learning and look-ups to determine whether or not a packet on a LAN must be forwarded to another segment. The bridging function is transparent to the end station because the end station does not need to know if the device it is addressing is on the same physical segment. All Ethernet bridges are transparent.

TRUNK
Aggregation of multiple telecom lines or VLAN to increase a bandwidth.

TSAP
Transport Service Access Point

TSI
Transmitting Subscriber Information / or Time Slot Interchanger
A frame that can be sent by the caller with the caller telephone number that can be used to screens calls.

TSSI
Time Slot Sequence Integrity

TST
Transparent Spanning Tree

TUNELLING
A mechanism of forwarding traffic from remote users to a corporate network through an existing public IP network. Data is encapsulated within an IP datagram and then decapsulated at the other end point of the tunnel.

TUP
Telephone User Part

TWAIN
Technology Without An Interesting Format

TWB
Thermo Balanced Writing - load balanced temperature writing. Used to moderate the writing on the laser - Philips ¨

TX
Transit Exchange

T1
1.544-Mbit/s transmission system
ISDN service which provides 31 channels B at 64 K-bits and 1 D channel.