*:96 Internet appliction protocols and standards

Exam 11 October 1996 with full score answers

Last update: 2 November 1996 by Jacob Palme E-mail: jpalme@dsv.su.se.
at the Department of Computer and Systems Sciences, Stockholm University/KTH

The following documents can be used during the exam:

(a) All documents whose name begin with "RFC".
(b) All documents whose designation includes "draft-ietf-".
(b) Internet Port Numbers.
(c) IANA directory of registered Media Types.
(d) Ordinary language wordbooks.
(e) Any other document, which in the list of documents for the course are marked exam.

Max score
Cached copies of documents may become out of date and obsolete. What can be done to reduce this problem?

Full score answer:

Most reliable method:

Master server (owner of original) updates mirrors when a document is changed.

Other methods:

  • The master can supply time-to-live
  • Restore all documents older than certain limit
  • Restore depending on how new the document was when loaded
  • Restore automatically in the background
  • Use HTTP feature to check last update and only download if document is changed
  • User pushes reload button
One of the most popular Internet application protocols uses two ports and two channels between client and server. Which protocol is it, and how are the two channels used?

Full score answer:

FTP uses two channels, one control channel to send commands and get reply codes, one data channel to perform the actual data transfer.

A part of a web page looks like this:

If you click on Select beverage", you will see the following:

Which HTML code will produce this result?

Full score answer:

What do you prefer?
<OPTION SELECTED>Select beverage
<OPTION> Coffee
<OPTION> Chocolate
<INPUT NAME="name" TYPE="submit" VALUE="Submit">

Note 1: "SELECTED" not needed, since default is first choice.

Note 2: One student thought it not neat to include a choice "Select beverage" which is not to be used. However, otherwise the "Tea" choice would be default, which might not be desirable. Also, "Select beverage" allows a user to not select any of the beverages.

HTTP has borrowed much from the e-mail protocols. Which are the most important such concepts?
  • HTTP uses similar header and body format as e-mail.
  • HTTP uses the same Media Types as mail.
  • HTTP is specified in ABFN like mail.

The following features are also similar to HTTP and e-mail, but existed before e-mail and can thus not be said to be borrowed from e-mail:

  • Three digit reply codes
  • Textual command encoding
  • Use of TCP as transport protocol

Questions can be answered in Swedish or English