TA - Terminal Adapter

TAT - Theoretical Arrival Time (used in GCRA definition)

TAXI - Transparent Asynchronous Transmitter/Receiver Interface

Tbps - Terabits per second

TC - Transmission Convergence

TCA - TeleCommunications Association

TCP - Transmission Control Protocol

TCP/IP - Transmission Control Protocol/Internet Protocol

TCR - Tagged Cell Rate

TDM - Time Division Multiplexing

TDMA - Time Division Multiple Access

TDS - Time Division Switching

TFTP - Trivial File Transfer Protocol 

TIA - Telecommunications Industry Association

TIF - Telephone Influence Factor

TIG - Topology Information Group (ATM Forum, PNNI)

TLD - Top-Level Domain

TM - Traffic Management

TS - Traffic Shaping

TUC - Total User Cell count

TUCD - Total User Cell Difference

TUNIC - TCP/UDP over Non-existent IP Connections

UART - Universal Asynchronous Receiver/Transmitter

UBR - Unspecified Bit Rate

UDP - User Datagram Protocol

UME - UNI Management Entity (used in ILMI Definition)

UNI - User-to-Network Interface

UPC - Usage Parameter Control

UPS - Uninterruptable Power Supply

USAC - Universal Service Administrative Company (Fund Administrator)

USF - Universal Service Fund

USTA - United States Telephone Association

USTSA - United States Telecommunications Suppliers Association

UTP - Unshielded Twisted Pair