internet mba 2006 - aueb.gr · Internet Basic concepts and directions in telecommunications C....

InternetInternet

Basic concepts - 2Basic concepts and directions in telecommunications C. Courcoubetis

History

1962: Paul Baran, packet switching1969: DARPA, 4-node ARPANET1974: Vint Cerf, Bob Kahn, TCP1982: TCP/IP στο ARPANET1984: DNS1986: NSFNET Backbone Network, 56kbps

1992: Tim Berners-Lee, WWW


Development of the internet

NSFNET δίκτυο κορµού

∆ίκτυα τοπικής εµβέλειας

∆ίκτυα πελατών

Χρήστες

Network serviceproviders (US)MCI, NETCOMSPRINT, PSI

ANS, Uunet, Verio

NAPs(Network Access Points)

ISPs

∆ίκτυα πελατών

Χρήστες

Internet: 1990

Internet: 2000+

2000: >75 public NAPs, 100M computers, 3M domains

AT&T, BBN

EBONE, Qwest,...

Internet

Architecture andServices


Client-server service model

Server: application that listens to a specific network address (N,p)• p: same for identical services

Client: “light” application, runs locally, connects for short time to a server using TCP or UDP

server Bclient

server A server C

100 101ports

applications

server C

clientBasic concepts - 6Basic concepts and directions in telecommunications C. Courcoubetis

Applications

Use the client – server modelFTP: Listens to port 21, 2 TCP connectionsSMTP: simple mail transfer protocol• Receives: message + addresses of receiversTelnet: Simulates direct terminal connectionRTP: real-time transfer protocol• audio+video transmission with small dealy• Transmitter: Codes, Compresses• Receiver: Stores, decodes


Electronic mail

user agent (Alice)(MS Outlook)

user agent (Jane)(Netscape)

mail serverhermes.aueb.gr 25

mail serverxxx.ntua.gr 25

SMTP

mail to [email protected] from [email protected]

SMTPhttp

POP3IMAPhttp

POP3: port 110, memory lessIMAP: memoryhttp: only a browser is requiredto send and receive

Send an email message Access the mail server for messages


WWW

HTTP: hypertext transfer protocol• Uses TCP for transmission of files (port 80)• web browser: client, remote machine: server• 1. “click” go to my home page

<A HREF=“http://www.aueb.gr/users/courcou”>• 2. Opens a connection with the server (3-way

handshake), Send the file’s address• 3. server: Asks for the password, authentication, Sends

the file and terminates his connection• 4. browser: Terminates his connection


WWW (2)

HTML: hypertext marking language• The browsers understand html

example: • My personal web page, • HTML code

URL: uniform resource locator• “identity” of network places

− www.aueb.gr/users/courcou− Access protocol, Network address− host name, path


HTML

<HTML><HEAD>

<TITLE> Origins of the Internet</TITLE></HEAD>

<BODY BGCOLOUR = “white” TEXT = “darkblue”><P>The history of the Internet begins at the height of the cold war....

...see <A HREF = http://www.aueb.gr/fileF.html> map F <\A> for details....................................................................a nuclear attack?</P>

<P>Communication networks of the day were.............................................................................................................................................<IMG SRC = http://www.ntua.gr/pictures/stars.gif > ................................................................................................................</P>

</BODY></HTML>


Management of TCP connections

3 way handshake model

client server SYN: (SYN=1, seq=client_isn)

SYN

SYN.ack

ack data

SYN.ack: (SYN=1, seq=server_isn, ack= client_isn+1)

ack: (SYN=0, seq=client_isn+1, ack= server_isn+1)

m

http requestFIN

ack

ack

FIN


How http functions

Web page = consists of different objects (base html file + JPEG, GIF,Java ap.)

Base html file F A

B

Get FF

client server

Get AA

Get B

B

TCP

Get FF

Get BB

Get AAHttp1.1


Http mesages

GET /users/courcou/index.html HTTP/1.1Host: www.aueb.grConnection: closeUser-agent: Mozilla/4.0Accept-language:gr

POST /yahoo.com/search HTTP/1.1

arg1?arg2?arg3

HTTP/1.1 200 OKConnection: closeDate:…Server:ApacheLast-modified: Mon, 12 May 1999 02:23:26Content-length: 23232Content-type: text/htmldata……………………………………………..

301 Moved Permanently304 Not modified since400 Bad Request401 Authorization required404 Not Found

HTTP REQUEST message HTTP RESPONSE message

Πείραµα:telnet www.aueb.gr 80GET /users/courcou/index.html HTTP/1.0

request line (one line)

head

er li

nes

entity body


http request message

Two types of http messages: request and response


http request message


http response message


http response status codes

In the first line of a response message


Authentication


Cookies

Keep “state”


Conditional GET

Client-side caching


Dynamic Content

A request is generated by the browser (as an

HTTP request) and contains several things

(concept of the request string):

• server + program + form data http://www.anyserver.com/cgi-bin/results.cgi?name=Sony&cat=TV

web serverlocation and

name of program Key=value pairs


Creating Dynamic ContentCommon Gateway Interface (CGI)

A set of standard methods and routines used to write a stand-alone software program that knows how to receive requests from a Web Server and returns data to the serverWritten in a wide variety of programming languages (Perl, Visual Basic etc.)Problem: Create a process for each CGI program

Web Server

Common Gateway Interface

Process 1-Runtime Environment

- Environment Variables-Program

Process 2-Runtime Environment

- Environment Variables-Program

Internet

Names and addresses


IP addresses• 4 numbers separated by fullstops• example: 128.171.17.13• Official server addresses / hosts• Official Name: ΙΡ address

246.38.17.145

128.171.17.13


From names to addresses

Basic Problem: Computer Name -> Network address• Corresponding example: Telephone catalogue

Name on the internet: Hierarchical Structure• domains: .com, .edu, .gov, .int, .mil, …, .gr, ,.fr, .be, ...• Sub-domains: berkeley.edu, aueb.gr, forth.gr, …• Sub-sub-dmains: ics.forth.gr, thetis.ics.forth.gr, ...

• Every (sub) domain has a responsible name server (DNS)− Each DNS knows the addresses of the sub-domain DNS’s


Name and addresses (2)root name server

localnameserverdns.aueb.gr

requestinghosthigh.aueb.gr

authoritativename serverdns.berkeley.edu

authoritativename serverdns.cs.berkeley.edu

cyber.cs.berkeley.edu

1

23

4 5

67

8

root name server

requestinghostdias.aueb.gr

1

23

4

5 67

8

iterative query

recursive queries

Internet value chain


The Internet value chain (2)

user Applicationsand content

(ASP)

Server farm

Backbone

Access

ISP

Bit pipes


The Internet value chain

1. Infrastructure service level: simple services used by other levels• bit pipes, equipment, call-center services, billing

2. Internet services level: • Connectivity services: transport services (IP data,

streaming,…), connection with applications (data centers) and with usersdata center, IP backbone, access, end-user IP network, distribution

• Information services: content services: applications,telecommunication services to end-users, e-commerceApplication Service Provider (ASP), Content Provider (CP), Electronic

Marketplace Provider (EMP), Communication Service Provider, Internet Retailer

• End-user levelBasic concepts - 30Basic concepts and directions in telecommunications C. Courcoubetis

The Internet value chain (3)

Internet Service Layer

FinancialService Provider

Connectivity ProviderInformation Provider

End-User

BillingService Provider

Network ComponentService Provider

Infrastructure Layer


More slides


Architecture

FTP

TELNET

RLOGIN

SMTP

DNS

...

HTTP

RTP

TFTP

TCP UDPIP

LAN link


File Transfer Protocol

ftp client ftp server

Local file system Remote file system

TCP control connectionport 21

TCP data connectionport 20

(one per file)

Control: user id, list, chdir, put, get, ...

internet mba 2006 - aueb.gr · Internet Basic concepts and directions in telecommunications C....

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