General Computer Science 320201 GenCS I & II Lecture ... - Kwarc

the telnet protocol for remote terminal emulation which we do not discuss here.
telnet is one of the oldest protocols, which uses TCP directly to send text-based messages between
a terminal client (on the local host) and a terminal server (on the remote host). The operation
of a remote terminal is the following: the terminal server on the remote host receives commands
from the terminal client on the local host, executes them on the remote host and sends back the
results to the client on the local host.
A Protocol Example: SMTP over telnet
We call up the telnet service on the Jacobs mail server
telnet exchange.jacobs-university.de 25
it identifies itself (have some patience, it is very busy)
Trying 10.70.0.128...
Connected to exchange.jacobs-university.de.
Escape character is ’^]’.
220 SHUBCAS01.jacobs.jacobs-university.de
Microsoft ESMTP MAIL Service ready at Tue, 3 May 2011 13:51:23 +0200
We introduce ourselves politely (but we lie about our identity)
helo mailhost.domain.tld
It is really very polite.
250 SHUBCAS04.jacobs.jacobs-university.de Hello [10.222.1.5]
We start addressing an e-mail (again, we lie about our identity)
mail from: user@domain.tld
this is acknowledged
250 2.1.0 Sender OK
We set the recipient (the real one, so that we really get the e-mail)
rcpt to: m.kohlhase@jacobs-university.de
this is acknowledged
250 2.1.0 Recipient OK
we tell the mail server that the mail data comes next
data
this is acknowledged
354 Start mail input; end with .
Now we can just type the a-mail, optionally with Subject, date,...
Subject: Test via SMTP
and now the mail body itself
.
And a dot on a line by itself sends the e-mail off
250 2.6.0
[InternalId=965770] Queued mail for delivery
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