Internet Internet 1962: Paul Baran, packet switching 1969: DARPA, - - PowerPoint PPT Presentation

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Internet Internet 1962: Paul Baran, packet switching 1969: DARPA, - - PowerPoint PPT Presentation

May 01, 2023 150 likes •258 views

History Internet Internet 1962: Paul Baran, packet switching 1969: DARPA, 4-node ARPANET 1974: Vint Cerf, Bob Kahn, TCP 1982: TCP/IP ARPANET 1984: DNS 1986: NSFNET Backbone Network, 56kbps 1992 : Tim Berners-Lee,

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Internet Internet

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

History

1962: Paul Baran, packet switching 1969: DARPA, 4-node ARPANET 1974: Vint Cerf, Bob Kahn, TCP 1982: TCP/IP στο ARPANET 1984: DNS 1986: NSFNET Backbone Network, 56kbps 1992: Tim Berners-Lee, WWW

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Development of the internet

NSFNET δίκτυο κορµού ∆ίκτυα τοπικής εµβέλειας ∆ίκτυα πελατών Χρήστες Network service providers (US) MCI, NETCOM SPRINT, 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 and Services

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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

  • r UDP

server B client server A server C

100 101

ports applications server C client

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Applications

Use the client – server model FTP: Listens to port 21, 2 TCP connections SMTP: simple mail transfer protocol

  • Receives: message + addresses of receivers

Telnet: Simulates direct terminal connection

RTP: real-time transfer protocol

  • audio+video transmission with small dealy
  • Transmitter: Codes, Compresses
  • Receiver: Stores, decodes

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Electronic mail

user agent (Alice) (MS Outlook) user agent (Jane) (Netscape) mail server hermes.aueb.gr 25 mail server xxx.ntua.gr 25 SMTP mail to jane@ntua.gr from alice@aueb.gr SMTP http POP3 IMAP http POP3: port 110, memory less IMAP: memory http: only a browser is required to send and receive Send an email message Access the mail server for messages

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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
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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

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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>

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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 request

FIN ack ack FIN

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How http functions

Web page = consists of different objects (base html file + JPEG, GIF,Java ap.) Base html file F A B Get F F client server Get A A Get B B

TCP

Get F F Get B B Get A A Http1.1

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Http mesages

GET /users/courcou/index.html HTTP/1.1 Host: www.aueb.gr Connection: close User-agent: Mozilla/4.0 Accept-language:gr POST /yahoo.com/search HTTP/1.1 arg1?arg2?arg3 HTTP/1.1 200 OK Connection: close Date:… Server:Apache Last-modified: Mon, 12 May 1999 02:23:26 Content-length: 23232 Content-type: text/html data…………………… ……………………….. 301 Moved Permanently 304 Not modified since 400 Bad Request 401 Authorization required 404 Not Found HTTP REQUEST message HTTP RESPONSE message Πείραµα: telnet www.aueb.gr 80 GET /users/courcou/index.html HTTP/1.0 request line (one line) header lines entity body

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http request message

Two types of http messages: request and response

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http request message

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http response message

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http response status codes

In the first line of a response message

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Authentication

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Cookies

Keep “state”

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Conditional GET

Client-side caching

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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 server location and name of program Key=value pairs

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Creating Dynamic Content

Common 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 server Written 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

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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

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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

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Name and addresses (2)

root name server local

name server dns.aueb.gr

requesting host high.aueb.gr authoritative name server dns.berkeley.edu authoritative name server dns.cs.berkeley.edu cyber.cs.berkeley.edu 1 2 3 4 5 6 7 8 root name server requesting host dias.aueb.gr 1 2 3 4 5 6 7 8 iterative query recursive queries

Internet value chain

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The Internet value chain (2)

user Applications and content (ASP) Server farm Backbone Access ISP Bit pipes

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The Internet value chain

  • 1. I nfrastructure service level: simple services

used by other levels

  • bit pipes, equipment, call-center services, billing
  • 2. I nternet services level:
  • Connectivity services: transport services (IP data,

streaming,…), connection with applications (data centers) and with users

data center, IP backbone, access, end-user IP network, distribution

  • I nformation services: content services: applications,

telecommunication services to end-users, e-commerce

Application Service Provider (ASP), Content Provider (CP), Electronic Marketplace Provider (EMP), Communication Service Provider, Internet Retailer

  • End-user level

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The Internet value chain (3)

Internet Service Layer

Financial Service Provider Connectivity Provider Information Provider End-User Billing Service Provider Network Component Service Provider

Infrastructure Layer

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More slides

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Architecture

F T P

T E L N E T R L O G I N

S M T P D N S

...

H T T P R T P T F T P

TCP UDP IP LAN link

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File Transfer Protocol

ftp client ftp server Local file system Remote file system TCP control connection port 21 TCP data connection port 20 (one per file) Control: user id, list, chdir, put, get, ...