INT21CN Computer Networks

Tutorial #5

1. Before coming to the tutorial, use your browser to "view source" for this tute sheet. Can you understand the HTML markups used? If you don't, ask for it to be explained in the tutorial

2. Show^[1] the <A> tag that is needed to make the string "ACM" be a hyperlink to http://www.acm.org.

3. In the lecture, the statement was made that the various versions of HTTP are backwards compatible. What does this mean?

4. (Slightly tricky question) In HTTP/0.9, there was no way to specify the content type in objects returned from the server. How did the browser know whether it was receiving a Web page (in HTML), a GIF image, a sound sample or whatever?

5. In HTTP/1.0 the GET request (and other types as well, but we didn't elaborate in the lecture) is terminated by two newlines. Why are two necessary? Wouldn't one newline be sufficient, as in HTTP/0.9?

6. The response from HTTP/1.0 and HTTP/1.1 servers is "MIME-like".
   1. What does this mean?
   2. What is the MIME type for ordinary Web pages in HTTP/1.0?
   3. Why is the "Content-length: " header required in HTTP/1.0?
   4. Why isn't an SMTP-style MIME "Content-encoding: " header required in HTTP/1.0 as it is for some MIME email attachments?

7. A Web browser sends the following request to a Web server:

   GET /Fig1.gif HTTP/1.0<newline><newline>
   

   Presuming the file specified actually exists and is readable, what would the server return? Explain in some detail.

8. What is the HTTP/1.0 HEAD request method used for?

9. A client (ie, browser) can optionally include a GET request method header of the form "If-Modified-Since: "
   1. Why is this used, and what is it called?
   2. Why is the date/time specified in GMT (UTC) instead of local time?
   3. This header takes a date/time value. Is there an Internet standard format for this value? Hint: look at section 3.3 of RFC1945

10. The HTTP/1.0 specification permits a GET request method to include a "Referer: " header in the request. Why is this considered to be a potential privacy issue? Discuss, and comment (if you can) on implications for Web browser design.

11. Research: The Web Accessibility Initiative is a project of the World Wide Web consortium. Find out what you can about this initiative, and its relevance to good design of Web pages.