Computer Networks

Tutorial #3

  1. What is "remote login"? What is the standard protocol which provides remote login on the Internet?

  2. The TELNET protocol defines a Network Virtual Terminal, (NVT) which means that servers and clients don't need to know the details of the actual terminal or host (if any) at the other end of the connection. The alternative to this approach is to perform terminal emulation. What is meant by terminal emulation, and why is the NVT approach considered better?

  3. What are some of the characteristics of the TELNET NVT?

  4. When the telnet program starts up, it informs the user as follows:
    ironbark 27> telnet redgum
    Trying 149.144.21.3...
    Connected to redgum.bendigo.latrobe.edu.au.
    Escape character is '^]'.
    
    What is the "escape character" used for?

  5. The[1] text file for RFC 854 (the TELNET protocol specification) contains exactly 854 lines. Do you think there is cosmic significance in this?

  6. Why do they call it "anonymous" FTP if the server insists on your email address as a password?

  7. The FTP protocol has two different modes of operation: text and binary, or image.
    1. What do you think is the difference between these two modes? What does RFC 959 have to say on the matter?
    2. Explain why a binary mode FTP transfer of a PC (or Macintosh) text file to a Unix system (or vice versa) results in a (slightly) corrupted file.

  8. Why does the control connection in FTP need to use the TELNET NVT specification?

  9. BSD Unix introduced a file transfer utility called rcp, analogous to rlogin. What does this do?

  10. (Optional question) Why[2] is the XDR library needed in NFS? Under what conditions is the XDR scheme inefficient?

  11. (Research question) How does TELNET perfom option negotiation?

Practical Exercises

See separate prac sheet.
[1] From Comer, P418.
[2] From Comer, P432.
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Phil Scott