User`s guide

Glossary
252
Telnet
A user command and an underlying TCP/IP protocol for accessing remote computers. On the
web, HTTP and FTP protocols allow you to request specific files from remote computers, but
not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user
with whatever privileges you may have been granted to the specific application and data on that
computer.
Transmission Control Protocol (TCP)
A set of rules used along with the Internet Protocol (IP) to send data in the form of message units
between computers over the Internet. While IP handles the actual delivery of the data, TCP
handles keeping track of the individual units of data (called packets) that a message is divided
into for efficient routing through the Internet. For example, when an HTML file is sent to you
from a web server, the TCP program layer in that server divides the file into one or more packets,
numbers the packets, and then forwards them individually to the IP program layer. Although
each packet has the same destination IP address, it may get routed differently through the
network. At the other end (the client program in your computer), TCP reassembles the individual
packets and waits until they have arrived to forward them to you as a single file. TCP is known
as a connection-oriented protocol, which means that a connection is established and maintained
until such time as the message or messages to be exchanged by the application programs at each
end have been exchanged. TCP is responsible for ensuring that a message is divided into the
packets that IP manages and for reassembling the packets back into the complete message at the
other end. In the Open Systems Interconnection (OSI) communication model, TCP is in layer 4,
the Transport Layer.
Transport Layer Security (TLS)
A protocol that ensures privacy between communicating applications and their users on the
Internet. When a server and client communicate, TLS ensures that no third party may eavesdrop
or tamper with any message. TLS is the successor to the Secure Sockets Layer (SSL).
Trivial File Transfer Protocol (TFTP)
An Internet software utility for transferring files that is simpler to use than the File Transfer
Protocol (FTP) but less capable. It is used where user authentication and directory visibility are
not required. TFTP uses the User Datagram Protocol (UDP) rather than the Transmission
Control Protocol (TCP). TFTP is described formally in Request for Comments (RFC) 1350.
TTY port redirection
The process of establishing a connection between the host and networked serial devices by
creating a local TTY port on the host. The TTY port appears and behaves as a local port to the
PC or server. See also RealPort
TXD
Transmit eXchange Data.