*:96 Internet Application Protocols and Standards

Exam 1998-11-21 with suggested replies

No. English text Swedish text Max points


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).

Skriv en ASN.1-specifikation för flygbagage. Varje etikett skall lagra kundens namn, bagagets vikt i kilogram, och en serie av en eller flera på varandra flygningar (två bokstäver för flygbolag, 1-4 siffror för turnumret och 3 bokstäver för nästa flygplats.)



LuggageTag ::= SEQUENCE {
          name VisualString,
          weight Real,
          flights FlightSequence }

FlightSequence ::= SEQUENCE OF SEQUENCE {
              airline VisualString (SIZE (2)),
              flightnumber NumericString (SIZE (1..4))
              airport VisualString (SIZE (3)) }

No. English text Swedish text Max points


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?

E-postprogram i persondatorer brukar vanligen skicka ut utgående brev genom att koppla sig till en närbelägen server, inte genom att koppla sig direkt till en server nära mottagaren inte heller till en brygga för e-post till mottagare som inte kan nås direkt från Internet. Varför?



  1. It is faster for the user to send to only one server, only one copy of the text need be transmitted.
  2. The user need not wait while trying to connect to multiple remote servers.
  3. The message can be queued in a spool area and resent at a later time, if the remote server is temporarily down. This will not work well in a personal computer, since it may not be connected for long periods of time.

Incorrect answers:

Many students answered the question as if it had referred to getting incoming mail, not sending outgoing mail. POP and IMAP are not used for outgoing mail, and SMTP requires a computer to be up all the time only to be able to handle incoming mail.
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What is the difference in the way FTP clients and servers will handle data of ASCII and in IMAGE type.

Hur skiljer sig hanteringen i FTP-klientrar och servrar vid hanteringen av ASCII data och IMAGE-data.



  1. Different computers use different ways of representing lines of text and line breaks. In ASCII mode, the text is converted to a standard format, a sequence of character octets with CRLF between the lines. The receiving computer converts this to the format use at the receiving end.(2)
  2. Different computers store text in different byte sizes, this is in ASCII mode converted to 8-bit bytes before transmission.(2)
  3. In ASCII mode, character set transformation may occur, if the sending and receiving computers use incompatible character sets.(2)
  4. In binary mode, the binary data are mapped on a sequence of octets, which at the receiving end is mapped back to the same binary data as before the transmission.(1)
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A web document at URL http://foo.bar/alpha/beta contains the following code:

Ett webbdokument på URL http://foo.bar/alpha/beta innehåller följande kod:


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

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

Vilket dokument kommer att hämtas via länken i <BODY> ovan.?


The document at "http://foo.bar/delta/exit.html".

  1. Start with the BASE at "http://foo.bar/alpha/gamma"
  2. Ignore "gamma" since only the directory is used
  3. The base directory is thus "http://foo.bar/alpha/"
  4. ".." moves one step up in the path to "http://foo.bar/"
  5. Append "/delta/exit.html" to get "http://foo.bar/delta/exit.html"

Incorrect answers

A common error was to give the reply "http://foo.bar/delta/exit.html". This would have been correct if the <HEAD> had contained the statement <BASE href="http://foo.bar/alpha/gamma/">. But since there is no "/" after "gamma" this is a file name, not a directory, and is stripped before resolution.