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Datornätverk A – lektion 14: Applikationslagret. Kap 24: Sockets Kapitel 25: DNS Kapitel 26: SMTP och FTP Kapitel 27: HTTP och WWW. PART VI. Application Layer. Position of application layer. Chapter 24. Client-Server Model: Socket Interface. Figure 24.2 Client-server relationship.

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Datorn tverk a lektion 14 applikationslagret

Datornätverk A – lektion 14:Applikationslagret

Kap 24: Sockets

Kapitel 25: DNS

Kapitel 26: SMTP och FTP

Kapitel 27: HTTP och WWW


PART VI

Application Layer



Chapter 24

Client-ServerModel:Socket Interface


Figure 24.2Client-server relationship


Figure 24.3Connectionless iterative server


Figure 24.4Connection-oriented concurrent server


Figure 24.6Socket types


Figure 24.7Socket interface for connectionless iterative server


Figure 24.8Socket interface for connection-oriented concurrent server


Chapter 25

DNS = DomainName System


Figure 25.1Domain name space


Domain Name System - DNS

En distribuerad databas som används till att koppla IP-nummer till textbaserade internetadresser.

Ex www.gb.se <-> 195.7.73.37

  • Varje sökning utgår från någon av rootservrarna som håller ordning på toppdomänerna. (.com .edu .se m fl)

  • All information rörande en domän ligger i den ”Name Server” som hanterar domänen.

  • För att lägga upp en ny domän krävs ”tillstånd” från närmast högre


Figure 25.2Domain names and labels


Figure 25.4Domains


Figure 25.5Hierarchy of name servers


Note:

A primary DNS server loads all information from the disk file; the secondary server loads all information from the primary server.


Figure 25.7DNS in the Internet


Table 25.1 Generic domain labels


Table 25.2 New generic domain labels


Figure 25.9Country domains


Figure 25.10Inverse domain


Figure 25.11Recursive resolution


Figure 25.12Iterative resolution


Figure 25.13Query and response messages


Figure 25.14Header format


Note:

DNS can use the services of UDP or TCP, using the well-known port 53.


LAN Tjänster

  • Elektronisk Post via SMTP, POP eller IMAP

  • Konferenssystem via USENET News och NNTP

  • Fildelning via t.ex NFS

  • Filöverföring via t.ex FTP

  • Skrivardelning

  • World Wide Web via HTTP

  • Massutsändningar Mbone - Multicast Backbone


Chapter 26

Internet E-mail


Figure 26.10Email delivery



Figure 26.1Format of an email


Figure 26.2Email address


Figure 26.3User agent



Figure 26.5MIME header


Table 26.1 Data types and subtypes in MIME


Table 26.2 Content-transfer encoding



Table 26.3 Base64 encoding table


Figure 26.7Quoted-printable


Figure 26.8Email client and server


26.2 File Transfer

Connections

Communication

File Transfer

User Interface

Anonymous


Note:

FTP uses the services of TCP. It needs two TCP connections. The well-known port 21 is used for the control connection, and the well-known port 20 is used for the data connection.



Figure 26.13Using the control connection


Figure 26.14Using the data connection


Figure 26.15File transfer


Example 1

  • Figure 26.16 (next slide) shows an example of how a file is stored.

  • The control connection is created, and several control commands and responses are exchanged.

  • Data are transferred record by record.

  • A few commands and responses are exchanged to close the connection.


Figure 26.16Example 1


Table 26.4 List of FTP commands in UNIX


Example 2

We show some of the user interface commands that accomplish the same task as in Example 1. The user input is shown in boldface. As shown below, some of the commands are provided automatically by the interface. The user receives a prompt and provides only the arguments.

$ ftp challenger.atc.fhda.edu

Connected to challenger.atc.fhda.edu

220 Server ready

Name: forouzan

Password: xxxxxxx

ftp > ls /usr/user/report

200 OK

150 Opening ASCII mode

...........

...........

226 transfer complete

ftp > close

221 Goodbye

ftp > quit


Example 3

We show an example of using anonymous FTP. We connect to internic.net, where we assume there are some public data available.

$ ftp internic.net

Connected to internic.net

220 Server ready

Name: anonymous

331 Guest login OK, send "guest" as password

Password: guest

ftp > pwd

257 '/' is current directory

ftp > ls

200 OK

150 Opening ASCII mode

bin

...

ftp > close

221 Goodbye

ftp > quit


Chapter 27

HTTPandWWW


Note:

HTTP uses the services of TCP on well-known port 80.


Figure 27.1HTTP transaction


Figure 27.9Example 1


Example 1

This example retrieves a document. We use the GET method to retrieve an image with the path /usr/bin/image1. The request line shows the method (GET), the URL, and the HTTP version (1.1). The header has two lines that show that the client can accept images in GIF and JPEG format. The request does not have a body. The response message contains the status line and four lines of header. The header lines define the date, server, MIME version, and length of the document. The body of the document follows the header (see Fig. 27.9, next slide).


Figure 27.3Request line



Figure 27.6Status line


Figure 27.7Header format


Figure 27.10Example 2


Example 2

This example retrieves information about a document. We use the HEAD method to retrieve information about an HTML document (see the next section). The request line shows the method (HEAD), URL, and HTTP version (1.1). The header is one line showing that the client can accept the document in any format (wild card). The request does not have a body. The response message contains the status line and five lines of header. The header lines define the date, server, MIME version, type of document, and length of the document (see Fig. 27.10, next slide). Note that the response message does not contain a body.


Note:

HTTP version 1.1 specifies a persistent connection by default.


Figure 27.12Hypertext


Figure 27.11WWW

Hyperlinks


Figure 27.13Browser architecture


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