*:96 Internet Application Protocols and Standards

Exam 1997-10-31 with correct answers

The following documents are allowed during the exam:

  1. Documents in Compendium 1, which has a yellow front page.
  2. Documents in Compendium 2, which has a yellow front page.
  3. The document with the title Appendix A: ASN.1 syntax (basic items).
  4. Ordinary language dictionaries between English and Swedish.

Note: Compendium 3, 4 and 6 are not allowed during the exam.

Important warning

It is not acceptable to answer an exam question by just a verbatim quote from the allowed documents above. You must show that you understand the question and your answer by using your own words.

Exam in English

You can submit the exam in either Swedish or English. If you want the exam questions in English, you must notify the teacher at least two weeks before the exam.

Special for students who have previously participated in the ASN.1 course

If you have previously participated in, and passed the exam on, the course segment *:73 about ASN.1, then you must skip question 1 in this exam and will then get only 2,5 instead of 3,5 points for this exam (plus 0,5 points for the work task). If you are one of these, you must very clearly mark this on the exam.

Notification of result by e-mail

If you write your e-mail address on the front cover page of the exam, then you will be notified by e-mail if you did not pass the exam.


Question in English

Question in Swedish



The main principle of BER (Basic Encoding Rules) is that data is coded as a nested series of records, where each record has three elements. Which are these three elements and what does each of them signify?

Huvudprincipen i BER (Basic Encoding Rules) är att data kodas som en nästad serie av poster, där varje post består av tre element. Vilka är dessa tre element och vad anger de?


Correct response:

  1. Tag (identification) tells what information is coming,
  2. Length in bytes,
  3. The data itself.

The data itself can be split into subrecords of the same format: Tag, length, data, recursively to any level.


How can a URL reference a certain position within a document? How is the target position for such links marked in the target document?

Hur kan man i en URL ange en referens till en viss plats inuti ett dokument? Hur markeras målpunkten för sådana länkar i måldokumentet?


Correct response:

A URL can and with "#xxxx" where the text after the "#" is the name of the location in the document.

The document itself can contain the markup:
<A NAME="xxxx"></A>
to name a particular place in the document.


Several Internet standards use three-digit reply codes. How are these three-digit reply codes made up?

Flera olika Internet-standarder använder sig av tresiffriga svarskoder. Hur konstrueras dessa sifferkoder?


Correct response:

The first code partitions the reply code space into main topics, in SMTP for example these are:

1yz Positive Preliminary reply
2yz Positive Completion reply
3yz Positive Intermediate reply
4yz Transient Negative Completion reply
5yz Permanent Negative Completion reply

The second code partitions the reply code space within the main topics. This is done in different ways in different protocols, as an example, SMTP uses:

x0z Syntax error
x1z Replies to requests for information
x2z Connection-related replies,
x3z Unspecified as yet.
x4z Unspecified as yet.
x5z Status of the receiving mail system

The third code is used to distinguish between different response codes having the same first and second digit.

Other protocols using similar kinds of response codes are for example FTP and HTTP.


Discussions often consists of a series of messages by different people, which are replies to each other. Which information in (a) e-mail, (b) netnews is used to specify the place of a message in such a chain? In which header fields is this information placed, and how is it made up?

Diskussioner består ofta av en serie av inlägg av olika personer, som svarar på varandra. Vilken information i (a) e-post, (b) netnews används för att markera ett meddelandes plats i en sådan serie? I vilket eller vilka fält står denna information, och hur utformas den?


Correct response:

Every message has a "Message-ID". The reply to a message has an "In-Reply-To" header with the Message-ID of the replied-to message. This following the chain of In-Reply-To headers allows a user to traverse a sequence of replies.

The "References" header is also often used in similar ways as In-Reply-To", but there often all the previous messages in the chain are listed.

Finally, replies often have the same text in the "Subject" header as the replied-to message, except that "Re: " is added at the front. "Re: " is not added more than once for successive replies to replies.

Note about correct results: Often less that what is written above was enough to get full points on a question.