Digi X2 User Manual

Page 237

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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.