Lantronix ETS Reference Manual - 2.7.2 Telnet
TCP/IP
Concepts
2-8
2.7.2 Telnet
Telnet is an industry-standard network protocol. Networks that support Telnet can (and do) stretch for
thousands of miles and contain thousands of hosts. The theory behind Telnet is that a user anywhere on the
network can access a foreign host and start a terminal session. The user does not have to worry about what
kind of computer or operating system he is dealing with, and the remote host does not need to know the type
of terminal the user is using. Telnet accomplishes this compatibility with the virtual terminal: any Telnet
connection looks the same from both sides of the network. Figure 2-3 illustrates this concept.
Figure 2-3: ETS Network Telnet Example
2.7.2.1 Telnet Connections
All terminals on the network can access all hosts, but do not need to know (nor can they know) the host’s
exact hardware type. Theoretically, terminal 4 in the example above could establish a Telnet session with
host Phred, and would see the same type of session as it would with a direct terminal connection to terminal
5. Phred, the CPU, will also treat terminal 4 as if it were directly connected.
A Telnet connection begins with both parties in the connection assuming that the other terminal is “dumb,”
that it knows little about characters, fonts, cursor movement, and so on. The two sides negotiate options to
determine the capabilities of the other. For example, a terminal might support full cursor-control characters.
Once the connection is established, the terminal and host may agree to support the extra characters. This all
happens transparently to the user, who sees only a login screen and none of the negotiation process.
By default, Telnet connects to a pre-set port number to access a remote host’s Telnet server. The ETS allows
the specification of a port number other than the default to be used for the connection. For example, if a host
is set up to listen to Telnet requests on port number 1034, that port number can be specified in the Telnet
command entered into the ETS.
Note:
The Telnet command is explained in the Command Reference chapter.