Router Getting Started Guide

Glossary
GL-12
Cisco IOS XR Getting Started Guide
OL-10957-02
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.
tar
A tar file is a file produced by the UNIX tar program, which packages multiple files in a single file for
distribution as a single unit. Each tar file has a tar filename extension.
target configuration
A “two-stage” configuration of the Cisco IOS XR software running configuration. This allows users to
make changes to the running configuration and accept these changes by entering the
commit command.
task ID
An identifier that determines user access to a given command or series of commands. A user must be
a member of a group with the appropriate task IDs assigned to it to execute the related commands.
Tbps
terabits per second. The amount of data that can be sent in a fixed amount of time. 1 terabit = 2
40
bits,
or 1,099,511,627,776 bits.
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.
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.
terabyte
A unit of computer memory or data storage capacity equal to 1024 gigabytes (2
40
bytes).
Approximately 1 trillion bytes.
TFTP
Trivial File Transfer Protocol. A 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).
Note: some TFTP servers (such as Sun Solaris) may not support file sizes larger that 32 MB.
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.
tunnel
Secure communication path between two peers, such as two routers.
Tx
The transmitter end of a fabric link. All links are unidirectional. See also Rx.
U
UDP
User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is
a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery,
requiring that error processing and retransmission be handled by other protocols. UDP is defined in
RFC 768.
unicast
Message sent to a single network destination.
unicast
transmission
A unicast transmission sends one copy of each packet to each member of the group. This method is
inefficient because the same information must be carried multiple times, requiring extra bandwidth.