Computer Networks

Tutorial #3

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

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

  3. The TELNET NVT defines a standard "end-of-line" convention whereby lines of text are delimited using the two character ASCII control code sequence <CR><LF> (in English: Carriage Return followed by Line Feed). Why do you suppose the designers of the protocol adopted this two character sequence instead of just a single character <CR>, or a <LF>, or something else entirely?

  4. The Network Virtual Terminal approach used by TELNET protocol 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 is to perform terminal emulation. What is meant by terminal emulation?

  5. The notion of how the NVT is used in Telnet leads on to a (moderately) serious philosophical discussion about how to map the requirements of different kinds of computer systems to one another when you need to perform some kind of Networked Computing function. Start by comparing the TELNET NVT approach to terminal emulation, and extend the discussion to the more general case.

  6. 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?

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

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

  9. 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.

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

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

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

Practical Exercises

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