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Glossary: CCNA & General Networking Terms 


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A term for a digital carrier facility used to transmit a DS-1 formatted digital signal at 1.544 megabits per second. [Source: RFC1392]
A term for a digital carrier facility used to transmit a DS-3 formatted digital signal at 44.746 megabits per second. [Source: FYI4]
See: Terminal Access Controller (TAC)
Technical Advisory Unit, a JISC sponsored service, performs regular monitoring of JANET, JISCMail and the National Cache, and advises JISC on technical matters.
A protocol which allows two people on remote computers to communicate in a real-time fashion. See also: Internet Relay Chat. [Source: RFC1392]
See: Transmission Control Protocol
TCP/IP Protocol Suite
Transmission Control Protocol over Internet Protocol. This is a common shorthand which refers to the suite of transport and application protocols which runs over IP. See also: IP, ICMP, TCP, UDP, FTP, Telnet, SMTP, SNMP. [Source: RFC1392]
JISC funded Technology for Disabilities information service.
A public packet switched network using the CCITT X.25 protocols. It should not be confused with Telnet. [Source: RFC1392]
Telnet is the Internet standard protocol for remote terminal connection service. It is defined in STD 8, RFC 854 and extended with options by many other RFCs. [Source: RFC1392]
Trans European Network at 155Mbit/s, now replaced by GÉANT.
See: Trans-European Research and Education Networking Association
Terminal Access Controller (TAC)
A device which was once used to connect terminals to the Internet, usually using dialup modem connections and the TACACS protocol. While the device is no longer in use, TACACS+ is a protocol in current use. [Source: RFC1983]
terminal emulator
A program that allows a computer to emulate a terminal. The workstation thus appears as a terminal to the remote host. [Source: MALAMUD]
terminal server
A device which connects many terminals to a LAN through one network connection. A terminal server can also connect many network users to its asynchronous ports for dial-out capabilities and printer access. See also: Local Area Network. [Source: RFC1392]
A free typesetting system by Donald Knuth.
Three Letter Acronym (TLA)
A tribute to the use of acronyms in the computer field. See also: Extended Four Letter Acronym. [Source: RFC1392]
The process whereby two protocol entities synchronize during connection establishment. [Source: RFC1208]
Time to Live (TTL)
A field in the IP header which indicates how long this packet should be allowed to survive before being discarded. It is primarily used as a hop count. See also: Internet Protocol. [Source: MALAMUD]
See: Three Letter Acronym
A variant of the Telnet program that allows one to attach to IBM mainframes and use the mainframe as if you had a 3270 or similar terminal. [Source: BIG-LAN]
token ring
A token ring is a type of LAN with nodes wired into a ring. Each node constantly passes a control message (token) on to the next; whichever node has the token can send a message. Often, "Token Ring" is used to refer to the IEEE 802.5 token ring standard, which is the most common type of token ring. See also: 802.x, Local Area Network. [Source: RFC1392]
A network topology shows the computers and the links between them. A network layer must stay abreast of the current network topology to be able to route packets to their final destination. [Source: MALAMUD]
OSI Transport Protocol Class 0 (Simple Class). This is the simplest OSI Transport Protocol, useful only on top of an X.25 network (or other network that does not lose or damage data). [Source: RFC1208]
OSI Transport Protocol Class 4 (Error Detection and Recovery Class). This is the most powerful OSI Transport Protocol, useful on top of any type of network. TP4 is the OSI equivalent to TCP. [Source: RFC1208]
A program available on many systems which traces the path a packet takes to a destination. It is mostly used to debug routing problems between hosts. There is also a traceroute protocol defined in RFC 1393. [Source: RFC1983]
Transmitter-receiver. The physical device that connects a host interface to a local area network, such as Ethernet. Ethernet transceivers contain electronics that apply signals to the cable and sense collisions. [Source: RFC1208]
transit network
A transit network passes traffic between networks in addition to carrying traffic for its own hosts. It must have paths to at least two other networks. See also: backbone, stub network. [Source: RFC1392]
Transmission Control Protocol (TCP)
An Internet Standard transport layer protocol defined in RFC 793. It is connection-oriented and stream-oriented, as opposed to UDP. See also: connection-oriented, stream-oriented, User Datagram Protocol. [Source: RFC1392]
Transport Layer
The OSI layer that is responsible for reliable end- to-end data transfer between end systems. [Source: RFC1208]
Transport Layer Security (TLS)
An IETF standard in RFC 2246 for eliciting secure (i.e. encrypted) connections (e.g. to web services) across a public network such as the Internet. Formerly known as Secure Sockets Layer (SSL).
Trojan Horse
A computer program which carries within itself a means to allow the creator of the program access to the system using it. See also: virus, worm. See RFC 1135. [Source: RFC1392]
a network independent version of X29. The dependency of X29 on X25 is removed. See also Green Book.
The MAPS Transport Security Initiative.
Ta-Ta For Now [Source: RFC1392]
See: Time to Live
Tunnelling refers to encapsulation of protocol A within protocol B, such that A treats B as though it were a datalink layer. Tunnelling is used to get data between administrative domains which use a protocol that is not supported by the internet connecting those domains. See also: Administrative Domain. [Source: RFC1392]
Thames Valley Network.
twisted pair
A type of cable in which pairs of conductors are twisted together to produce certain electrical properties. [Source: RFC1392]


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