Introduction Networks Lecture 15: Internet The Internet and the - - PDF document

▶
introduction
SMART_READER_LITE
LIVE PREVIEW

Introduction Networks Lecture 15: Internet The Internet and the - - PDF document

Feb 01, 2023 600 likes •665 views

Introduction Networks Lecture 15: Internet The Internet and the Web Organisation of networks Peer-2-peer networks Computer Literacy 1 Applications Thursday 27/10/2005 The web File-sharing ARPANET ARPANET

slide-1
SLIDE 1

1

Lecture 15: The Internet and the Web

Computer Literacy 1 Thursday 27/10/2005

Introduction

  • Networks

– Internet – Organisation of networks – Peer-2-peer networks

  • Applications

– The web – File-sharing

ARPANET

  • Aim

– Military communications network – Robust to damage

  • Result

– Packet-switching – All computers equally able to communicate – The internet!

ARPANET University network

  • University LAN

– EdLAN

  • Edinburgh & Stirling MAN

– EaStMAN

  • UK education WAN

– JANET – SuperJANET5

Computers as connectors

  • Different networks can use different

packet-switching methods

  • Bridge

– Connects networks of the same type

  • Gateway

– Connects networks of different type

slide-2
SLIDE 2

2

Computers as connectors

  • Different networks can use different

packet-switching methods

  • Routers & Switches

– Decide path of packets

  • Repeaters

– Boost, resend packets

Intranet and Extranet

  • Intranet

– Network with access restricted to members

  • f an organisation
  • Extranet

– Network outside intranet – Access restricted to authorised users – E.g. business clients

Client-server model

  • Server machine

– Stores data – Or has access to data

  • Client machine

– Runs application – Application requests data from server

  • Server finds data and sends it to the

client

Client-server model: the Web

  • The Web: method of communication

using internet

  • Client is the Web browser
  • Server stores Web pages
  • Communication requires

– Protocol – Addresses – Shared language

slide-3
SLIDE 3

3

The Web

  • 3 standards

– HTTP: data exchange protocol – URL: address – HTML: shared language

  • Browser

– Sends out URL through HTTP – Displays HTML data

  • Server

– Receives URLs through HTTP – Finds pages and sends back

URL: Web page address

  • Protocol method

– Usually http, also https (secure http)

  • Server name

– www.inf.ed.ac.uk

  • Web page file path

– /teaching/courses/cl1

Web Cache

  • Copies of visited Web pages put in a cache
  • Advantages

– Faster – Frees Internet bandwidth

  • Implementation

– HTTP: methods for expressing whether a page can be copied – Cache size limit on your computer

Client-side

  • Client-side Web cache

– On client computer – Or ISP server

  • Example client-side Web application

– Java applets

Server-side

  • Cache on Web server

– Recently visited pages put in cache – Reduces time to retrieve frequently visited pages

  • Speed of Web services not just

connection speed!

  • Example server-side Web application

– CGI scripts

Web proxy

  • Connections to a page are usually direct
  • Web proxy: Mediating connection to the

page

  • Used to manage access

– From a network to the Internet – From outside the network to the intranet

  • Can be a cache: faster access
slide-4
SLIDE 4

4

Cookies

  • Web page stores information on your

computer

  • Used to

– Remember login details – Shopping baskets – Observe your use of web site

  • Security problem?

Peer-to-peer networks

  • Network where each network node is a client

and a server

– No dedicated servers – P2P overlaid on Internet structure

  • Cost

– Use internet infrastructure

  • Reliability

– Not affected by server downtime Bandwidth

P2P Scalability

  • As the number of users and files grow

– Routing becomes time consuming

  • But

– Total bandwidth increases – Not limited by access to servers – Kazaa P2P network “rewards” high bandwidth users: supernodes

P2P Routing

  • Napster

– Centralised file lists – Client server searching – P2P file distribution

  • Gnutella, FastTrack

– Distributed file lists – P2P searching + file distribution

P2P Security

  • Have to be careful what files P2P

software can access

  • P2P software could observe your Web

movements (“spyware”)

  • Freenet, GNUnet, AntsP2P…

– Protect user and file identity – Slower – Safe? For who?

P2P applications

  • Payment schemes (PayPal)

www.paypal.com/html/gartner-020102.html

  • VOIP, e.g. Skype www.skype.com
  • Spam detection razor.sourceforge.net/
  • Distributed computing: GIMPS prime number

search www.mersenne.org/prime

  • Instant Messenger
  • etc
slide-5
SLIDE 5

5

Key Points

  • Network organisation

– Bridges, Gateways, Routers, Repeaters – Client-server model – Peer-2-peer networks

  • Applications

– How organisation affects implementation – Advantages and disadvantages: scalability, speed, security