Do you Want to Test your Knowledge of
Internet Application Layer Standards?

This document contains a collection of exam questions which have been used in exams in some courses I have been giving at Stockholm University and at the KTH Technical University. You can use these questions to test your knowledge of Internet application layer standards.

The students were allowed to bring copies of the text of all the major RFCs containing the standards, plus a document describing the syntax (but not the semantics) of ASN.1 and the official W3C HTML 4.0 specification. This means that some of the questions in the exams could be seen as a test of the ability to find information in the text of the standards. The students had 45 minutes/question to prepare their responses. The list of reading for the course lists these documents with URLs to retrieve them, where available. Note that all documents in the list of reading were not allowed during the exam, only those marked "exam" in the "validity" column of the table.

To students: Do not push the hyperlink to look up the correct reply immediately. Instead, first try to find the reply yourself. In that way, you will learn how to find information, and that knowledge is what you need to pass the exam!

Jacob Palme. Last revision 30 May, 2008

Table of contents

Questions on basic concepts or questions covering more than one standard

Question 010116-1: Some platforms represent end of line with LF characters, some with CR characters, some with a CRLF sequence of two characters. How is transfer of texts with line breaks handled when using the SMTP, FTP and HTTP standards. Reply.

Question 000522-2: You want to send a person's name, separated into subfields for Surname, Given name, Middle Initial and Generation qualifier (like "Jr"). Show how this is specified using both ASN.1 and XML/DTD. Also show an example of how the name "John F. Kennedy Jr" is sent, and compare how many bytes are sent using the ASN.1/BER and the XML encoding. Reply.

Question 000522-1: If you want to send data from one computer to another, there is a need to mark the end of one data item. How can you, for example, include the "." character in a string, if "." is used to mark the end of the string, or some other character which you use as the end mark. Discuss different methods to handle this problem in protocols based on ABNF, ASN.1 and XML, and their pros and cons. Reply.

Question 961026-1: Cached copies of documents may become out of date and obsolete. What can be done to reduce this problem? Reply.

Question 960920-1: World Wide Web and Usenet News differ in their method of storing and replicating data. Describe the differences, and the pros and cons of the methods used. Reply.

Question 971031-3: Several Internet standards use three-digit reply codes. How are these three-digit reply codes made up? Reply.

Question 980604-2: A client program connects to a server and sends an operation, and gets a result back. What happens then? Is the connection open, so that the client can send more operations? Answer the question for the protocols SMTP, FTP, HTTP, POP and IMAP. What are the pros and cons of keeping the connection open or closing it down after each operation? Reply.

Question 981219-3: By "architecture" is meant the different computer processes, which communicate with each other within a particular application. Describe common architectures for groupware systems. Reply.

Question 990601-2: What are the pros and cons of defining a protocol as a sequence of interactions within a single session (like SMTP) versus one single REQUEST, one single RESPONSE and then disconnectiong (as in HTTP 1.0). Reply.

Question 990918-1: Make a comparison between ASN.1/BER, ABNF and DTD/XML as languages for specificaitons of protocol data. What are the main differences, advantages and restrictions of these methods? Reply.

Question 000211-2: What are the main basic differences between the HTTP and the FTP protocols? Not details but main principles. Reply.

Question 011020-2: A common technique to reduce load on a network is to replicate some information in several places, so that the information needed can be downloaded from a nearby copy. Describe different strategies for managing such replication. Which problems can occur, and how can they be handled? Reply.

Other questions on coding

Question 010831-3: Write a specification, suitable for becoming an IETF standard, of a facility to have a message to a Usenet Newsgroup delivered only to those members of the Newsgroup, who have a certain profession, like medical doctors or salespersons. Reply.

Question 010308-4: Domain names may (when this is written, February 2001) not contain other characters than A-Z, a-z, 0-9, " -" and "." between elements. Upper and lower case characters are indifferent to the meaning of a domain name. Many people want to use national characters in other languages than English, like "é" and "ä", in domain names. Various proposals for modifying the DNS to allow this are being discussed. One group of proposals is using a method which does not require any changes at all in the way the domain name servers work. How can this be achieved? Reply.

Question 990823-4: What are the advantages of encoding text with the UTF-8 encoding of Unicode/ISO 10646 as compared to ISO Latin One (8859) and UTF-16? Reply.

Questions on which standard

Question 961026-2: 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? Reply.

Question 021019-3: Describe an existing example of a standard which allows future extensions, and where client and server can agree on which of a larger set of extensions both support. Reply.

Questions on URIs and URLs

Question 011020-3: A relative URL is evaluated relative to a base. The method which evaluates a relative URL into an absolute URL takes two parameter values as input, one of them is the relative URL, the other is the base. From which different sources can the value of the base be taken? Reply.

Questions on ABNF

Question 020227-1: Write an ABNF specification for Swedish social security numbers (personnummer) of the format like 16 12 01-0924, i.e. two digits, space, two digits, space, dash, four digits. Reply.

Question 010308-1: A search engine accepts queries using Boolean conditions containing the operators AND, OR, NOT, NEAR, and parethesises. Search words can be specified with double apostrophes (") around them to specify exact match, or any word except upper-case AND-OR-NOT-NEAR to specify non-exact match. Example:

Apple OR (orange AND NOT (banana OR "Hans Bergman"))

Question 001114-4: Write a specification of how e-mail standards might be extended to allow the sender to specify, for each body part, whether it is to be shown on a screen or printed on paper or handled in some other way. Reply.

Question 980604-1 Specify, using ABNF, a syntax for the date format shown by the example 1998-06-04T12:34:59+01:00, and where the minutes and seconds are allowed to be omitted, and where the character between date and time is either "T" or "t". Reply.

Question 990601-1: Write an ABNF specification for Swedish social security numbers, written in the format shown by the example 41 02 01-1410. It is an advantage if the syntax shows that a social security number consists of local elements: Date, month and day of birth, a three-digit sequence number and a single check digit in the last character position. Reply.

Question 000211-3: The RFC822 date format will in the future be changed in the following ways:

1. Specify more clearly that one or more LWSP characters are allowed between "Date:" and the value.
2. Exactly one space between the elements in the date-time specification.
3. Only numerical time-zones allowed.
4. A comment inside parenthesis is allowed, but only after the end of the date-time.
5. Four-digit years.

Specify in ABNF format the new format for the "Date:" header. Reply.

Question 020306-4: You have been given the task of specifying a standards extension to the HTTP standard, to allow a HTTP request to indicate the age of the person making the request. Write such a specification in a format which might actually be sent as a proposal to a standards organisation. Reply.

Questions on DTD and XML

Question 010831-2: How can you, using XML, specify a list of abbreviations, and then use these abbreviations instead of the longer text, which they are replacement for? Reply.

Question 000823-1: XML information can sometimes be specified either as attributes or as elements, for example
   <book title="Elektronic Mail"/>
or
   <book><title>Electronic Mail</title></book>
Discuss pros and cons of these alternative methods. Reply.

Question 001114-1: While HTML contains elements to describe the layout of information on a display, XML contains elements to describe the information in a logical way. How, then, can a web browser be instructed how to present and layout the XML information? Reply.

Qustion 000419-2: You are designing a protocol for sending ratings of web pages to a data base. Each submission contains information about the rater (e-mail address, competence), identification of a document through its URI, and a series of values which rates the document according to different scales, such as readability, newsvalue, correctness, suitability-for-minors. Rater-competence can be amateur or expert. Write a DTD for this. Use XML attributes when suitable. Reply.

Question 020522-3: Is there a tool, in XML, to handle references between different objects described in different places of an XML structure? If so, how? Reply.

Question 020306-1: Write an XML DTD for storing an ancestor structure for a person. By an ancestor structure is meant the name and birthdate of the person, and the same information recursively for his or her father and mother, grandfathers and grandmoters, etc., to an unlimited depth. The structure should allow stops at different depth in different branches, when som ancestor is not known any further. Reply.

Questions on CSS

Qustion 000419-3: What is meant by cascading style sheets and where are they used? Reply.

Question 010116-3: How can style sheets in HTML be used to indicate that some, but not all, paragraphs are to be shown with reduced font size. Reply.

Questions on ASN.1

(The reason there are so many questions on ASN.1 is that this collection also contains some of the simpler questions from a previous course where the whole course dealt with only ASN.1, and which is not given any more.)

Question 010221-1:Which of the ASN.1 tags in the example below can be removed, and which tags are needed for the receiving agent to interpret the information sent to it?

Family ::= [APPLICATION 1] SEQUENCE
      father [1] Person OPTIONAL,
     mother [2] Person OPTIONAL,
     children [3] SEQUENCE OF Person OPTIONAL }

Person ::= [APPLICATION 2] CHOICE {
      socialsecuritynumber [1] NumericString,
      phonenumber [2] NumericString,
     name [3] Name }

Name ::= [APPLICATION 3] CHOICE {
      fullname [1] Fullname,
     shortname [2] Shortname }

FullName ::= [APPLICATION 4] SET {
      givenname [1] UniversalString,
     surname [2] UniversalString }

ShortName ::= [APPLICATION 5]
     SET { inititals [1] UniversalString,
     surname [2] UniversalString }                         Reply.

Question 990918-2: A Beziér curve segment is specified by a start point (x0,y0), an end point (x3,y3) and two control points (handles) (x1,y1) and (x2,y2). Several curve segments can be combined in a line, where the end point of each segment is the start point of the next segment. Write an ASN.1 specification to transfer such a line of Beziér curve segments. Reply.

Question 981121-1: Write an ASN.1 specification for an airline luggage tag. The luggage tag stores the name of the customer, the weight of the luggage in kilograms, and a series of one or more succeeding flights (two letters for the airline, 1-4 digits for the flight number, and 3 letters for the next airport). Reply.

Question 980508-1: Specify an ASN.1 data type to indicate for all days of the year, whether each day was a holiday or a working day. Only these two values are allowed. Reply.

Question 970919-1: Write an ASN.1 data type to convey a diet plan for one day. A diet plan consists of 4-6 meals, where each meal consists of a number of food items. Each food item is specified by a weight in grams and an item name as a text string. Reply.

Question 971031-1: 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? Reply.

Question 970607-1: Specify an ASN.1 declaration to transfer date and time without using the built-in ASN.1-types UTCTime or GeneralizedTime. Instead, year, month (1 to 12), day of the month (1 to 31), day of the week (monday to sunday) hour (from 0 to 23) and minute (from 0 to 59) shall be transmitted .Reply.

Question 970607-2: A keyboard has 44 keys, in 4 rows of 11 keys/row. Each of the keys can be pressed or not pressed. It is thus permitted to press many keys at the same time. Specify an ASN.1-declaration for transfering information about which of the keys are pressed. Reply.

Question 970502-1: Specify an ASN.1 data type for a text string, which is only allowed to contain the characters 0-9 and A-F upper case. Reply.

Question 960429-2: The text below is taken from the Internet standard RFC 822:

Question 980820-1: Write an ASN.1 speficication to be used when returning a name from a data base. The data returned will either be a name, as a text string, or an error code. The error code can indicate various error conditions such as "not permitted" or "not found". The recipient must know whether an error code or a useful reply is returned. Reply.

Question 980926-1: IWrite an ASN.1 specification to transfer an image. The image is sometimes in GIF and sometimes in JPEG format, and the choice of format must also be transferred. In addition to the picture, also its name, specified as a text string, shall be transferred. Reply.

Question 990823-1: Write an ASN.1 specification to control a video recorder. The specification should allow the requestor to tell the recorder to rewind the tape, play the tape, and record a certain television channel at a certain time. Reply.

Question 991109-2: Below is a specification of a proposed addition to Internet e-mail. The specification is based on ABNF. Write a specificaction which will convey the same information using ASN.1. You need only translate the syntax (down to "Note:") not the explanatory text which comes after "Note:". Note: Your solution should only transfer the information, not the syntactical form.

Supersedes

Syntax

Supersedes-field = "Supersedes:" " " identifier
                    *(identifier) optional-parameter-list CRLF

optional-parameter-list = *( ";" " " parameter )

parameter = parameter-name [ "=" parameter-value ]

parameter-name = "noshow" / "show" / "repost"
                 private-parameter / future-parameter

Note: There is no comma between multiple values, and that each Message-ID
value is to be surrounded by angle brackets.

Warning: Some software may not work correctly with comments in header
fields, especially comments in other places than at the beginning and
end of the field value.

Warning: This header MUST be spelled "Supersedes" and not
"Supercedes".

Semantics

The Supersedes header identifies previous correspondence, which this
message supersedes. Different messaging agents such as user agents,
mailing list expanders and mailing list archives. A user agent is expected
to handle this field in much the same way as the In-Reply-To and References
header.

Note: The Message-ID of a superseding message MUST be different from
the Message-ID of the superseded message. The Message-ID of the superseded
message is used as value in the "Supersedes:" header, not
in the Message-ID of the superseding message.

Parameters:



noshow In the opinion of the sender, this message makes such
a minor change to the superseded version, that a
recipient, who has already seen the previous verson,
will probably not want to see the new version, unless
the user explicitly asks for it.

show In the opinion of the sender, this message makes such
a large change to the superseded version, that a
recipient, who has already seen the previous version,
will probably want to see the new version, too.
repost This document is a document which is repeatedly, at
regular or irregular intervals, reposted, such as
FAQs or mailing list monthly information.
None of these parameters have values. The "noshow" and the
"show" parameters are mutually exclusive, but both of them
can occur together with the "repost" parameter. 
Reply

Question 011020-1: Write an ASN.1 specification to send a request for one or more theater tickets. The request should contain the name of the theatre (text string), the name of the play (text string), the date and time of the performance, a request for one or more tickets, where each ticket request should indicate whether the customer is a minor (lower price), a seinor (lower price) or an ordinary adult (not minor or senior) and whether this seat are wanted in the stalls or on the balcony. Note that it should be possible to order several tickets in one request, some of which are in the stalls and some on the balcony, and some of which are minors, some seniors and some adults, in all possible combinations. Reply.

Question 020227-2: Write an ASN.1 specification for sending the results of an exam. The results is a list of students, for each student the name and the social security number (personnummer) is specified, a list of question scores, with the score on each question, and a final verdict, which can be U, G or VG for SU students and U, 3, 4 or 5 for KTH students.

Important: The format must allow an unlimited number of students, and an unlimited number of questions in the exam. Reply.

Question 021019-1: Give an ASN.1 specification of a protocol unit for transferring a list of people, and for each person indicating which other person is his/her father and mother. Fathers and mothers outside the listed people need not be specified. The solution must be able to handle two different people with the same name. Reply.

Questions on E-mail and Netnews standards

Question: 010831-1: Why have the standards makers chosen to specify that requests for Delivery Status Notifications are to be sent via SMTP, and not via a header in the mail heading?. Reply.

Question 010221-3: What is required, in order to be allowed to send 8-bit characters unencoded in e-mail according to e-mail standards? Reply.

Question: 010116-4: Specify an SMTP service extension to prevent a message to be routed through MTAs in certain countries, on its way from sender to recipient. Reply.

Question: 010116-2: Usenet News servers keep their data bases up to date by transferring what is new between neighbouring servers. Which mechanisms do they use to avoid downloading the same article twice from two different neighbouring servers? Reply.

Question: 000823-4: Two MIME content-types are "text/html" and "application/postscript". Discuss why HTML has placed under the primary type "text", while Postscript has been placed under the primary type "application". Reply.

Question 000522-3: The SMTP protocol includes many interactions back and forward between the sending and recipient agent. For example, for a multi-recipient message, the recipient addresses are sent one at a time, with an acknowledgement from the recipient before the next recipient name can be sent. What is the disadvantage with this, and how can it be overcome using facilities provided by existing standards? Reply.

Question 000226-3: Does e-mail contain a trace list of the stages of transmission of a message? If yes, how does it work, and what can it be used for? Reply.

Question 000419-1: Describe the functionality of the Multipart/alternative MIME content-type. Reply.

Question 990918-4: Threads are sequences of e-mail messages which directly or indirectly refer to each other. How is this information specified when the messages are transported. Reply.

Question 981121-2: E-mail clients in personal computer usually will connect to a nearby mail server to send e-mail. They do not directly connect to a remote server close to the recipient, or to a server at a bridge to another net, even if the recipient is there. Why? Reply.

Question 980508-3: When the MIME standard was defined, it was carefully designed so that MIME data would not break older mail software. How was this done? Reply.

Question 970919-3: You have received an e-mail message which is unreadable to your e-mail software, and you want to send it to a help desk which can find out what is wong with it. Which MIME structure is suitable for this, and why? Reply.

Question 960920-4: You want to send a collection of e-mail messages in one single e-mail message to one or more recipients. Which media types would be suitable for this. Reply.

Question 971031-4: 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? Reply.

Question 980604-4: In e-mail, the name of the sender and the recipient are often specified both in the SMTP "envelope" and in the RFC822-heading. What is the difference in how this information is meant to be used by e-mail software. Reply.

Question 980820-2: E-mail clients in personal computers mostly use the POP or the IMAP protocols to download incoming mail. Why do they not use SMTP? Reply.

Question 980926-3: Is it possible, in e-mail, to specify that a certain body part is not included, and must be fetched from the net by the recipient? Which construct in the e-mail standards are specially defined for this? Reply.

Question 990303-4: Discuss the handling of error messages, saying that an e-mail message could not be put into the mailbox of the recipient, in the case where the message was sent via a mailing list. Reply.

Question 990601-4: Specify a new (not yet standardized) extension to ESMTP, allowing a request that an e-mail message may not, for security reasons, be transmitted through certain countries. Reply.

Question 990823-2: How are new articles passed from one Usenet news server to another? Describe all the connections and commands that might be used. Discuss problems with the methods described. Reply.

Question 020522-1: Transfer of e-mail is often described as the transfer of envelope and content information. What kind of information is usually said to belong to the envelope, and what kind of information is usually said to belong to the content? Reply.

Question 020306-2: How is it possible to send binary data in e-mail, even though e-mail is based on sending text messages? Reply.

Questions on FTP

Question 010221-2: There are two commonly used data types in FTP today. Which are they and which are the differences between them? Reply.

Question 981121-3: What is the difference in the way FTP clients and servers will handle data of ASCII and in IMAGE type. Reply.

Questions on HTTP

Question 020227-3: Compare pros and cons for different ways, when communicating with users using HTTP/HTML, for the server to ”remember” who the user is and what the user has done in earlier steps of the dialouge between user and server. Reply.

Question 000823-2: Discuss methods in HTTP to select the natural language in which a document is delivered. Reply.

Question 001114-3: If a user asks for a web page at a certain URL, but that page is no longer stored at the indicated URL, the web browser can automatically download the right web page from another URL. How can this be specified using (a) HTTP commands or alternatively (b) using HTML commands. Reply.

Question 000522-4: Suppose you want to provide a service to users, to which the user can connect either anonymously or non-anonymously. You want to use different cookies for these two uses. How can this be achieved? Reply.

Question 991109-1: Before the WWW was invented, Internet users used FTP to download documents from other sites. Today, HTTP is often used instead. What are the advantages with using HTTP instead of FTP for downloading files from public archives? Reply.

Question 991109-3: At the web site http://www.frukt.se, people can buy apples, oranges, and bananas. A customer's basket can contain for example 0.5 kilograms apples and 1.4 kilogram bananas. What command, and with which parameters, can such a web site use to store this information in a cookie in the user's workstation? Reply.

Question 980508-4: How can an HTTP client automatically select in which language a HTML page is to be displayed (provided that the server has the document available in more than one language)? Reply.

Question 961026-4: HTTP has borrowed much from the e-mail protocols. Which are the most important such concepts? Reply.

Question 970919-4: Compare pros and cons of different methods for an HTTP server of knowing what a client has done in recent previous HTTP transactions. Reply.

Question 960920-2: The HTTP 1.0 protocol is built on short connections, transfer of data, and immediate disconnections. This gives problems if you wish to design an application where the computer needs to know what a certain user has done earlier. Describe different methods, provided with HTTP 1.0 and HTTP 1.1, of handling this problem. Also discuss the pros and cons of the methods you describe.Reply.

Question 960920-3: A client program wishes to download a document with URL:

http://dsv.su.se/jpalme/courses.html

Specify which commands, to and through the net, which are performed from the initial connection to the final disconnection. Also specify the parameters to the command. You can use either HTTP version 1.0 or version 1.1 in your reply. Reply.

Question 980926-4: In which ways can an HTTP server have more than one version of a document, and automatically deliver different versions depending on user settings and capabilities. Is the choice of version done by the server or by the client? (Note: I do not mean manual selection, where a user can select between links or with a menu on a web page!) Reply.

Question 011020-4: Write a specification, in a format which might be submitted to a standards organisation, of an extension to HTTP which would allow the requestors to specify their religion, and then get the version of a web page which is appropriate to their religion. It is an advantage if you allow users to specify more than one religion, in order to get a web page adapted to any of these religions. Reply.

Question: 021019-2: Discuss privacy risks emanating from the use of cookies. Reply.

Question 020306-3: What is meant by an HTTP proxy server, and why are they used? Reply.

Questions on HTML

Question 010831-4: A link is contained in an HTML frame. How can you indicate (a) that clicking the link will replace the content of this frame, leaving the other frames unchanged, (b) that clicking the link will replace the whole browser window content. Reply.

Question 010308-3: Some buttons on web pages will change their colour when the user moves the mouse over the button, even if the user does not press the button. How is this achieved? Reply.

Question 010221-4: An Internet search engine wants to measure which of the different links to web documents, listed by the search engine, are most often clicked on by its users. How can it measure this? Reply.

Question 001114-2: It is in HTML possible to specify that a picture is to be placed at the side of text, and the text is to "flow" around the picture, as in this question. How can this be specified? Reply. The rain in Spain stays mainly in the plain. The rain in Spain stays mainly in the plain. The rain in Spain stays mainly in the plain. The rain in Spain stays mainly in the plain.

Question 990818-3:

The directory main has two subdirectories images and text. The images directory contains gif files, the text directory contains html documents using these gif files. How can such an html document refer to one of the images?

Your solution should work independently of the position of the directory main, and not require rewriting of the html code if main with its subdirectories is moved. Reply.

Question 981121-4: A web document at URL http://foo.bar/alpha/beta/epsilon contains the following code:

<HEAD>
<BASE href="http://foo.bar/alpha/gamma">
</HEAD>
<BODY>
<A href="../delta/exit.html" target="solution">exit</A>

Which document will be retrieved through the link in the body above? Reply.

Question 980508-2:

*:96

Internet application protocols and standards

Question 991109-4: Below is shown a small part of a web page. Specify the HTML code to generate this.

Note 1: No graphics (<IMG> tags) are used.

Note 2: The distance between "Go to:" and "All forums" is slightly larger than the distance between row 2 and 3. But I will give 5 points for an otherwise correct answer, even for those who cannot propose how to achieve this without user of an <IMG> tag.

Reply.

Question 000211-4: What is the difference between server-side image maps and client-side image maps? Reply.

Directory systems and DNS

Question 000823-3: Why does LDAP have an attribute MessageID, what is the intended use of this attribute? Reply.

Question 981219-4: Why is the structure of directory systems and naming spaces often hierarchic? What is the advantages and disadvantages with this? Reply.

Question 000419-4: What is meant by a "relative distinguished name"? Reply.

Question 020522-4: Describe the difference between, and the advantages of handling layout of HTML documents using either:

1. Tables
2. CSS (Cascading Style Sheets)
3. Frames

Reply.

PICS - Platform for Internet Content Selection

Question 021019-4: Describe at least two different rating systems that can be specified based on the PICS platform. Reply.