La Trobe University, Bendigo

Department of Information Technology

INT21CN: Computer Networks

Assignment 2, 2002

Your task in this assignment is to investigate one only of the following topics in computer network architecture, and submit a report on your findings. Note that all of the topics are about, or related to, application-level protocols in the Internet. Each of the topics has a "theory" section, where you have to look up the information somewhere (presumably on the Web, or in an RFC), and a "practical" section where you have to demonstrate how the particular system under discussion actually operates in practice. You must complete both sections to gain a high mark.

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.

Caching Proxy Servers

Theory

In the lectures, some of the HTTP/1.1 cache-management features were discussed. At many sites (including La Trobe), HTTP access to the "outside" Internet is via a Caching Proxy Server. The software which is used for this at La Trobe (and many other organisations) is called squid. Find out about this software, and discuss briefly how it can be used to implement distributed caching.

Practical

How effective is La Trobe's proxy server? Obtain some typical "hit rate" figures from the proxy and assess their significance. You should also use telnet (as described in the lectures) to GET some external Web pages via the proxy server (NB: port 8080 is used for the proxy function). Can you tell if the page was cached? How? Demonstrate fetching a cached page from the proxy. What other HTTP/1.1 headers are present in the proxy response?

NB: If you're outside the University networks, you won't be able to use its proxy server. In this situation you may be able to connect to your own ISP's proxy, or you may have to choose a different question!

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.

Clock Synchronisation Protocols

Theory

It's more important than it might initially seem to have the internal clocks in Internet-connected systems in reasonably close agreement. Discuss briefly the need for clock synchronisation and describe some protocols which are used for this purpose.

Practical

A suggested in the "theory" section, there are a variety of synchronisation protocols available, with varying accuracies and applicability. Use whatever software tools you consider appropriate to set your desktop system's clock. Comment on the varying "ease-of-use" and accuracy of each.

Other

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

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

Due Date:17th May, 2002

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