Computer Networks

Tutorial #4

1. What is your preferred electronic mail address at Bendigo? In general, what is the format of an Internet email address?

2. What is the general format of an RFC822 electronic mail message?

3. The DATA operation in the SMTP protocol uses a "." on a line by itself to indicate the end of the mail message. What do you think happens if this occurs in the message?

4. The SMTP protocol, like the FTP protocol, uses a 3-digit code in all communications from the server. 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?

5. Here's some header fields from a recently-received email message. What systems did this message traverse before it was finally delivered?

   From pscott@redgum.bendigo.latrobe.edu.au  Fri Mar 21 10:03:10 1997
   Received: from hakea.cs.ntu.edu.au (root@hakea.cs.ntu.edu.au [138.80.116.6])
           by ironbark.bendigo.latrobe.edu.au (8.8.5/8.8.5) with ESMTP id KAA01295        for ; Fri, 21 Mar 1997 10:03:07+1100 (EST)
   Received: from redgum.bendigo.latrobe.edu.au (pscott@redgum.bendigo.latrobe.edu.
   au [149.144.21.3])
           by hakea.cs.ntu.edu.au (8.8.5/8.8.5) with ESMTP id IAA11909
           for ; Fri, 21 Mar 1997 08:33:03 +0930 (CST)
   Received: (from pscott@localhost)
             by redgum.bendigo.latrobe.edu.au (8.8.5/8.8.4)
             id KAA30777 for pscott@it.ntu.edu.au; Fri, 21 Mar 1997 10:03:01 +1100(EST)
   From: Phil Scott 
   Message-Id: <199703202303.KAA30777@redgum.bendigo.latrobe.edu.au>
   Subject: Test message
   To: pscott@it.ntu.edu.au
   Date: Fri, 21 Mar 1997 10:03:01 +1100 (EST)
   

6. What is MIME? Explain briefly how MIME works to send a file (eg, a GIF image) as an email message. What is a MIME Multipart message?

7. What is the Post Office Protocol (POP) used for?

8. Thinking question: The SMTP protocol relies (as do virtually all Internet application protocols) on TCP reliable transport. Now TCP only operates in an end-to-end manner, that is, only the two systems at each end are involved. Why then do mail messages sometimes take several "hops" before they are delivered, such as in the above example? NB: Just understanding the question is sufficient here...