Computer Networks
Tutorial #4
- What is your preferred electronic mail address at Bendigo? In
general, what is the format of an Internet email address?
- In his book Computer Networks 3/e,
P646, Tanenbaum quotes a study by Perry and Adam (1992) which reported
that "Some companies have estimated that email has improved their
productivity by as much as 30 percent." Give some reasons why
such a spectacular increase could occur from the use of email in a
business environment.
- What is the general format of an RFC822 electronic mail message?
- The SMTP protocol, in common with many other Internet application
protocols, uses a 3-digit code in all communications from the server to
the client. From the example given in the lecture, can you generalise
about the significance of the first digit of this code? What about the
second digit?
- Many[1] students prefer to use an
external Web-based email service such as
Hotmail or
Yahoo Mail instead of the
University-supplied email. In the diagram in
slide 1 of the lecture, how does
the right-hand side of the diagram change when a mail message is read
using (eg) Hotmail instead of a POP
client as shown there?[2]
- What is MIME? Explain briefly how MIME works to send a file (eg, a
GIF image) as an attachment to an email message.
- The MIME Type of an email attachment provides a hint to the "user
agent" software as to how to handle the data in the attachment. What do
you think the user agent software should be expected to do with
attachments of the following types
text/plain
text/html
audio/basic
application/octet-stream
?
- What is the Post Office Protocol (POP) used for? Why is it
important that POP uses authentication, whereas SMTP
does not? What sorts of commands do you think POP would implement?
- A file which has been encoded using Base64 is bigger than the
unencoded data. How much bigger, on average, would you expect it to
be?
- Deep thinking question: In today's lecture, the slides which
discussed RFC821 (SMTP) and RFC822 both referred to email addresses. In
SMTP, the
MAIL FROM:
and
RCPT TO:
protocol messages both specify
email addresses --- these are called envelope
addresses. The header of the RFC822 message which is being
delivered also contains From:
and
To:
lines -- these are header
addresses. The interesting question to contemplate is: "what
happens if the To:
header address and
the RCPT TO:
envelope address are
different" in an SMTP delivery operation? Where does
the mail get delivered?
[1] Only Australian-enrolled students of La
Trobe University automatically get a University-supplied email address.
Services such as Hotmail are the only
option for most overseas-enrolled students.
[2] Note, however, that many Web-based
email services have POP facilities and therefore can be used to read
mail from the University POP servers. Whether this is a good idea is for
the individual to decide.
See Prac #4 for the practical exercises
accompanying this tutorial.
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Copyright © 2000 by
Philip Scott,
La Trobe University.