T - Z

T1S1 ANSI T1 Subcommittee
TB Transparent Bridging
TC Transaction Capabilities
TC Transmission Convergence. One of the two PHY sublayers that is responsible for adapting the ATM cells into a stream of bits to be carried over the physical medium (see also PM).
TCAP Transaction Capabilities Applications Part
TCI Test Cell Input
TCO Test Cell Output
TCP Transmission Control Protocol
TCP Transmission Control Protocol. A standardized transport protocol developed for interconnecting IP-based networks. Operating on top of IP (combined known as TCP/IP), it is responsible for multiplexing sessions, error recovery, end-to-end reliable delivery and flow control.
TCP/IP A protocol platform, known also as the Internet protocol suite, that combines both TCP and IP. Widely used applications, such as Telnet, FTP and SMTP interface to TCP/IP.
TCS Transmission Convergence Sublayer. Same as TC.
TDJ Transfer Delay Jitter. See CDV.
TDM Time-Division Multiplexing. A technique for splitting the total bandwidth (link capacity) into several channels to allow bit streams to be combined (multiplexed). The bandwidth allocation is done by dividing the time axis into fixed-length slots and a particular channel can then transmit only during a specific time slot.
TE Terminal Equipment
TLV Type / Length / Value
TM Traffic Management. Means for providing connection admission (CAC), congestion and flow control (i.e. UPC, traffic shaping).
TM SWG Traffic Management Sub-Working Group
TMP Test Management Protocol
TNS Transit Network Selection
TPCC Third Party Call Control
TS Traffic Shaping
TS Time Stamp
TS Transport Stream
TS Time Slot
TSAP Transport Service Access Point
UBR Unspecified Bit Rate. One of the best effort service types (the other one is ABR). Realistically, no traffic parameters are specified by the source, so, no actual quality commitment is made by the network management.
UDP User Datagram Protocol. A connectionless transport protocol without any guarantee of packet sequence or delivery. It functions directly on top of IP.
UME UNI Management Entity. Software at the UNIs for providing the ILMI functions.
UNI User-Network Interface. The interface - defined as a set of protocols and traffic characteristics (i.e. cell structure) - between the CPE (user) and the ATM network (ATM switch). The ATM Forum specifications refer to two standards being developed, one between a user and a public ATM network, called public UNI and one between a user and a private ATM network called P-UNI.
UPC Usage Parameter Control. A form of traffic control that checks and enforces user's conformance with the traffic contract and the QoS parameters. Commonly known as traffic policing, it is performed at the UNI level.
UT Upper Tester
UTOPIA Uiversal Test & Operation Physical Interface. An interface to provide connectivity at the PHY level among ATM entities.
UTP Unshielded Twisted Pair. A twisted pair (copper) wire without any protective sheathing, used for short distances wiring (i.e. building). There are two categories specified by the ATM Forum for cell transmission : 3 ( CAT-3) and 5 ( CAT-5 ).
VBR Variable Bit Rate
VBR-RT Variable Bit Rate - Real Time. One of the service types for transmitting traffic that depends on timing information and control and which is characterized by the average and peak cell rates. It is suitable for carrying traffic such as packetized (compressed) video and audio.
VBR-NRT Variable Bit Rate - Non-Real Time. One of the service types for transmitting traffic where timing information is not critical and which is characterized by the average and peak cell rates. It is well-suited for long data packets transfers.
VC Virtual Channel. A term to describe unidirectional flow of ATM cells between connecting (switching or end-user) points that share a common identifier number ( VCI ).

Virtual Connection. A connection established between end-users (source and destination), where packets are forwarded along the same path and bandwidth is not permanently allocated until it is used.

Virtual Circuit. A connection set-up across the network between a source and a destination where a fixed route is chosen for the entire session and bandwidth is dynamically allocated (see also datagram).
VCC Virtual Channel Connection. Defined as a concatenation of virtual channel links.
VCI Virtual Circuit Identifier
VCI Virtual Connection Identifier
VCI Virtual Channel Identifier. A 16-bit value in the ATM cell header that provides a unique identifier for the virtual channel (VC) that carries that particular cell.
VLAN Virtual LAN. A networking environment where users on physically independent LANs are interconnected in such a way that it appears as if they are on the same LAN workgroup (see also LANE ).
VP Virtual Path. A term to describe a set of virtual channels (VCs) grouped together, between crosspoints (i.e. switches).
VP/VC Virtual Path, Virtual Circuit
VPC Virtual Path Connection. Defined as a concatenation of VP links.
VPCI/VCI Virtual Path Connection Identifier/Virtual Channel Identifier
VPI Virtual Path Identifier. A 8-bit value in the cell header that identifies the VP - and accordingly the virtual channel the cell belongs to.
VS Virtual Scheduling
WAN Wide Area Network. A network that covers long-haul areas and usually utilizes public telephone circuits.
X.25 One of the first - CCITT standardized - public (data) packet switching network protocols. Originally designed to operate over unreliable communications links, it supported both virtual circuit ( VC ) and datagram services.
XNS Xerox Network Systems
XTP eXpress Transport Protocol