T.120
ITU standard that describes data conferencing. H.323 provides for the capability to establish T.120 data sessions inside an existing H.323 session.
T.30
Describes the overall procedure for establishing and managing communication between two fax machines.
T.38
Defines procedures for real-time Group 3 facsimile communication over IP networks.
T1
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.
T3
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.
TACACS
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
tag switching
High-performance, packet-forwarding technology that integrates network layer (Layer 3) routing and data link layer (Layer 2) switching and provides scalable, high-speed switching in the network core. Tag switching is based on the concept of label swapping, in which packets or cells are assigned short, fixed-length labels that tell switching nodes how data should be forwarded.
TCP
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.
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.
TDM
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.
TDMA
time division multiplex access. Type of multiplexing where two or more channels of information are transmitted over the same link by allocating a different time interval (“slot” or “slice”) for the transmission of each channel, that is, the channels take turns to use the link. Some kind of periodic synchronizing signal or distinguishing identifier usually is required so that the receiver can tell which channel is which. See also TDM.
TE
terminal equipment. Any ISDN-compatible device that can be attached to the network, such as a telephone, a fax, or a computer.
Telnet
Standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system. Telnet is defined in RFC 854.
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.
TFTP
Trivial File Transfer Protocol. Simplified version of FTP that allows files to be transferred from one computer to another over a network, usually without the use of client authentication (for example, username and password).
traceroute
Program available on many systems that traces the path a packet takes to a destination. It is used mostly to debug routing problems between hosts. A traceroute protocol is also defined in RFC 1393.
traffic engineering
Techniques and processes that cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods were used.
traffic engineering tunnel
A label-switched tunnel that is used for traffic engineering. Such a tunnel is set up through means other than normal Layer 3 routing; it is used to direct traffic over a path different from the one that Layer 3 routing could cause the tunnel to take.
transform
The list of operations done on a dataflow to provide data authentication, data confidentiality, and data compression. For example, one transform is the ESP protocol with the HMAC-MD5 authentication algorithm; another transform is the AH protocol with the 56-bit DES encryption algorithm and the ESP protocol with the
HMAC-SHA authentication algorithm.
Transport Layer Security Protocol
TLS
the successor of SSL is an official Internet Protocol (RFC 2246)
trap
Message sent by an SNMP agent to an NMS, a console, or a terminal to indicate the occurrence of a significant event, such as a specifically defined condition or a threshold that was reached.
Trojan horse
Computer program that appears to have a useful function but also has a hidden and potentially malicious function that evades security mechanisms, sometimes by exploiting legitimate authorizations of a system entity that invokes the program.
trunk
1. Physical and logical connection between two switches across which network traffic travels. A backbone is composed of a number of trunks.
2. In telephony, a phone line between two COs or between a CO and a PBX.
trusted certificate
Certificate upon which a certificate user relies as being valid without the need for validation testing; especially a public-key certificate that is used to provide the first public key in a certification path.
trusted key
Public key upon which a user relies; especially a public key that can be used as the first public key in a certification path.
tunnel
Secure communication path between two peers, such as two routers.
tunneling
Architecture that is designed to provide the services necessary to implement any standard point-to-point encapsulation scheme. See also encapsulation.
twisted pair
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.
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