La Trobe University, Bendigo

Department of Information Technology

INT21CN: Computer Networks

Assignment 2, 2003

Your task in this assignment is to investigate and report on one only of the following topics in relation to Internet application-level protocols. Each of the topics has a "theory" section, where you must briefly report on the requested aspect of the protocol under investigation, and a "practical" section where you have to demonstrate the operation of the specified aspects of the given application protocol. You may, if you wish, combine your "theory" and "practical" sections -- for example, by describing in turn each of the requested aspects of the protocol and then illustrating it with an example.

Note also that additional topics might appear on this page as they are suggested to me. It could be worth checking back regularly if you don't like any of those given below.

NB: Students using MS-Windows systems might find these telnet hints useful.

HTTP Cache Control features
Theory
In lecture 7, some HTTP/1.1 cache-management features were discussed. Your "theory" task for this question is to consult the appropriate RFC (and/or other references) and discover more about these features than was presented in the the lecture. You should document at least some of the additional (not discussed in lectures) cache-management headers and briefly describe their function.
Practical
Use a utility such as telnet, or the Unix libwww GET command to obtain a selection of Web pages along with their HTTP response headers -- you may, in fact, prefer to use the HTTP "HEAD" method, since the protocol response headers will be the same, and they're what you're mostly interested in. If you're within La Trobe, you will have to obtain pages via the university's proxy server at port 8080. Document the HTTP/1.1 cache-control headers which are present in the responses for each of the pages that you fetch. Be sure to obtain pages from a variety of sites to ensure that you observe a range of cache-control header types.

Web-based Email Systems
Theory
Many students use Web-based email services (eg Hotmail, Yahoo Mail, etc). This question asks you to discover how such services handle attachments. You should explain how the contents of a data file are transferred from your desktop machine to the Web-based email server when you're sending an attachment, and how they are downloaded to your desktop machine when you receive an attachment. It's obvious that these transfers are implemented using HTTP, but in the lectures we didn't explain exactly how -- which request methods are used, and which MIMEtypes are involved. Your task is to explain the mechanisms involved.
Practical
It's difficult (impossible?) to demonstrate the "file upload" function using a commandline utility, however it may be possible to use telnet or the Unix libwww GET command to demonstrate the "file download" operation -- although not from a mail server. To do this, you will need to discover an Internet file download site which uses the same download technology as the Web-based email servers -- this may not be easy! Then you should be able to isolate the URL of a downloadable file, and fetch it using one of the aforementioned utilities. The interesting aspect of this is, of course, to document the relevant response headers present in the download.

USENET (Newsgroups)
Theory
Investigate (briefly!) the Network News Transfer Protocol (NNTP) in the usenet "news" system. NNTP is the basis of usenet and has many interesting features. You should restrict yourself to the features which relate to simply reading and posting articles: descripion of the entire usenet system's operation is too big a task.
Practical
Use telnet to connect to port 119 on a nearby news server -- within La Trobe,news.latrobe.edu.au is available. If you have commercial Internet access at home or work, your ISP will probably have informed you of the name of your news server when you signed up. It's often something like: news.ISP-NAME.com.au -- substitute your own ISP's name in the obvious place.. Most NNTP servers support a "HELP" command so you can easily discover what features they offer. Use the protocol to learn what newsgroups are carried on the news server, to obtain a list of article headers, and to deliver an article. If you're really keen, try using the protocol to post an article to one of the "test" newsgroups (eg, latrobe.test).

POP
Theory
Investigate the POP3 protocol. What is it used for? What other alternatives are available to achieve the same purpose? How does it handle authentication?
Practical
Use telnet to connect to a POP server. If you're on a La Trobe campus, you can probably use students.latrobe.edu.au. Exercise some of the protocol features mentioned in the "theory" section.

FTP
Theory
Investigate FTP. Find out the answers to mysteries like: "What is FTP used for?", "What is the PORT command used for?" "What is the difference between text and image (binary) modes?", "What is the difference between active and passive mode?"
Practical
See what FTP control protocol messages you can send (and receive) using telnet. Explain why you can't fully debug an "active-mode" FTP session using telnet alone. For maximum possible marks, demonstrate a "passive-mode" FTP file transfer (or directory listing) using passive mode and telnet.

Other
Any other appropriate application protocol-related topic with the explicit prior approval of the lecturer.

You should expect to write a maximum of about 1500 words on the topic of your choice. The practical section must include (at least) sufficient pasted-in headers and/or other text to indicate "liveness": that it, to show that it was actually you who performed these operations. Typical important headers might include, for example, dates, times and client IP address information.

You can submit your assignment in either traditional hard copy (paper) form, or as an email attachment of MIME type text/html sent to cnsubmit@ironbark.bendigo.latrobe.edu.au. Your choice of submission format will not affect the mark gained for your assignment. Submissions must, as usual, adhere to the requirements of the La Trobe University, Bendigo Assignment Guide.

This assignment carries 15% of your mark for Computer Networks.

Due Date:9th May, 2003 (end of week 9)

Lecturer: Phil Scott, 5444 7277, p.scott@latrobe.edu.au.


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