Subjects ->
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Lectures ->
Tute #07
INT21CN Computer Networks
Tutorial #7
- This question refers to Web caching.
- Why does a Web browser normally cache downloaded objects (HTML
pages, images, etc). The answer is probably obvious, but
it's worth checking that you do know this.
- What aspects of HTTP are intended to support the correct
operation of caching? Give some examples.
- Why is it necessary, when a Proxy Server is in
use, to specify a full URL in the HTTP request? If a request is
made to, for example, a local server (for which the proxy is not
involved) is the full URL needed?
- Proxy servers can reduce network (download) costs for an
organisation, and make best possible use of the organisation's
link to the Internet, however they are not altogether
successful in practice. Give two reasons why proxy caches are
not able to satisfy the majority of Web requests in The Real
World(tm).
- Some Web browsers seem to (on occasion) cache a little
too aggressively. One common browser, in particular,
will use a cached copy of a Web page even when the user hits
the "Reload" (or "Refresh") button. One way to force a
reload is to append a "
?
" character to an
ordinary (static) URL and then load (or reload) the page. Why
do you think this works?
- Practical question: on your preferred Web browser, is it
possible to configure how often cached objects are checked for
consistency?
- Give some of the reasons why HTTP/1.0 is not a highly regarded
protocol in the Internet technical community. How does HTTP/1.1
address these problems? At least two points required.
- The HTTP/1.1 "
Etag
" header extends the earlier
concept of "Last-modified
" date of an object.
What is the particular advantage of the
"Etag
"?
- Contemplate this: the specification for the original version of
HTTP (0.9) was approximately 6 Kbytes in size. The RFC for HTTP/1.0
(RFC1945) was 134 Kbytes. The RFC for the current version of
HTTP/1.1 (RFC2616) is 412 Kbytes. What conclusions can you draw?
These tutorial exercises accompany
Lecture #7.
See Prac #7 for the practical exercises
accompanying this tutorial.
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Copyright © 2003 by
Philip Scott,
La Trobe University.