Introduction to Computer and Program Design

Lesson 7

Networking and the Internet James C.C. Cheng Department of Computer Science National Chiao Tung University

Reference book l  Computer Science: An Overview, 11ed u 

J. Glenn Brookshear

u 

Publish by Pearson

2

Network Classifications l  Scope u  u  u 

Local area network (LAN) è a room, a building Metropolitan area (MAN) è a local community Wide area network (WAN) è a greater distance

l  Ownership u 

Closed versus open

l  Topology (configuration) u  u 

Bus (Ethernet, a LAN technique) Star (Wireless networks with central Access Point)

3

Topology (configuration) l  Bus (Ethernet, a LAN technique) u 

Hub

l  Star (Wireless networks with central Access Point) u 

Access Point, AP

4

Protocols l  CSMA/CD, Carrier Sense Multiple Access with Collision Detection u 

Used in Ethernet (BUS)

u 

Silent bus provides right to introduce new message

u 

Not compatible with star networks

l  CSMA/CA, Carrier Sense Multiple Access with Collision Avoidance u 

Used in WiFi (Star)

u 

Hidden terminal problem

5

The hidden terminal problem

6

Connecting Networks l  Repeater: a signal amplifier to extend a network l  Hub: multiport repeater l  Bridge: Connects two compatible networks l  Switch: Connects several compatible networks

7

Connecting Networks l  Router: u 

Connects two incompatible networks resulting in a network of networks called an internet

u 

Forwarding table or routing table

u 

Gateway

8

Network Devices l  Repeater l  Wireless AP

l  Hub l  ipshare ≠ router

l  Bridge

l  router

l  switch

9

Network Cable Computer ßà Device

l  Category 5 cable

1

8

Computer ßà Computer

maximum length: 100 m

10

Inter-process Communication l  Client-server u 

One server, many clients

u 

Server must execute continuously

u 

Client initiates communication

l  Peer-to-peer (P2P) u 

Two processes communicating as equals

u 

Peer processes can be shortlived

11

Distributed Systems l  Systems with parts that run on different computers u 

Infrastructure can be provided by standardized toolkits ¡  Example: Enterprise Java Beans from Oracle ¡  Example: .NET framework from Microsoft

l  Cluster computing u 

many independent computers work closely together to provide computation

u 

Blade server system

Blade enclosure Blade server

12

Distributed Systems l  Grid computing u 

more loosely coupled than clusters

u 

In general, the communication between grid nodes through network.

Grid nodes

13

Distributed Systems l  Cloud computing u 

huge pools of shared computers on the network

u 

Cloud computing provides computation, software, data access, and storage services that do not require end-user knowledge of the physical location and configuration of the system that delivers the services

u 

Application: ¡  Online game ¡  Online documents ¡  Online photo album

14

The Internet l  An internet that spans the world u 

Original goal was to develop for military purposes (U.S.)

l  Internet Service Provider (ISP) u  u 

Tier-1: International ISP; EX: AT&T, HiNet Tier-2: Local ISP; EX: TFN台灣固網

l  Access ISP: Provides connectivity to the Internet u  u 

Intranet: regional and private internet Traditional telephone (dial up connection) ¡  Modem, mdulator/demodulator

u 

Cable connections

u 

DSL, digital subscriber line ¡  ADSL: Asymmetric DSL

u 

Wireless

15

Internet Addressing l  IP address u  u 

pattern of 32 or 128 bits often represented in dotted decimal notation IPv4, 32 bits: ¡  ex: 140.113.243.210 (each part is a decimal number ) ¡  Some reserved IPs you have to know: Ø  127.x.x.x: Localhost communication (127.0.0.1 is the localhost) Ø  192.168.x.x: Private network Ø  169.254.x.x: retrieved from a DHCP(Dynamic Host Configuration Protocol) server Ø  255.255.255.255: broadcast

u 

IPv6, 128 bits ¡  ex: 2001:0DB8:85A3:08D3:1319:8A2E:0370:7344 (each part is a hexadecimal number)

16

Internet Addressing l  Mnemonic address: u 

Domain names ¡  www.nctu.edu.tw ¡  JamesPC1

u 

Top-Level Domains ¡  ¡  ¡  ¡  ¡ 

.edu.tw is a top-level domain .edu: educational institutions .gov: government institutions .org: non-profit organizations .com & .co: commercial

n  n  n  n 

.tw: Taiwan .cn: China .jp: Japan .uk:United Kingdom

l  Domain name system (DNS) u  u 

Name servers DNS lookup

17

Internet Addressing l  Internet Corporation for Assigned Names & Numbers (ICANN) u 

Allocates IP addresses to ISPs who then assign those addresses within their regions.

u 

Oversees the registration of domains and domain names.

18

Traditional Internet Applications l  Electronic Mail (email) u 

Domain mail server collects incoming mail and transmits outing mail

u 

Email address: ¡  account_name@server_domain_name ¡  ex: [email protected]

u 

Mail server delivers collected incoming mail to clients via POP3 or IMAP ¡  SMTP, Simple Mail Transfer Protocol: for ASCII data ¡  MIME, Multipurpose Internet Mail Extensions: for non-ASCII data ¡  POP3, Post Office Protocol ver.3 Ø  User can download mails from a mail server ¡  IMAP, Internet Mail Access Protocol Ø  User can read/modify mails or related materials from different computer ¡  Webmail Ø  User can read/modify mails through a web-browser 19

Traditional Internet Applications l  File Transfer Protocol (FTP) u 

FTP server: File provider

u 

FTP client: Uploading/downloading files to/from a FTP server

l  Telnet and Secure Shell(SSH) u 

allow users to access another computers

u 

Example: Bulletin Board System, BBS

20

More Recent Applications l  Voice Over IP (VoIP) u 

voice communication

u 

Type 1:P2P model ¡  Example: Skype

u 

Type 2: VoIP + traditional telephone ¡  analog telephone adapters

u 

Type 3: Pure VoIP Phone device

21

More Recent Applications l  Generations of wireless telephones u 

1G, first generation ¡  traditional telephone system

u 

2G, second generation ¡  text message

u 

2.5G, GPRS (General Packet Radio Service) ¡  56 kbps -115 kbps

u 

3G, third generation ¡  higher data transfer rates (300k-2Mbps), ¡  allowing for mobile video calls and other bandwidth-intensive activities

u 

3.5G ¡  higher data transfer speeds than 3G (1.8M - 14Mbps)

u 

4G, fourth generation ¡  higher data transfer speeds than 3G (100M – 1Gbps) ¡  fully packet-switched ¡  using the IP protocol

22

More Recent Applications l  Internet Radio u 

N-unicast ¡  one sender sending messages to multiple receivers ¡  server to send individual messages to each of its clients.

u 

Multicast ¡  a server transmits a message to multiple clients by means of a single address

l  Internet TV (online TV) u 

Internet Protocol television (IPTV)

u 

video on demand (VOD)

23

WWW, World Wide Web l  Sir Tim Berners-Lee, CERN, 1990 u 

CERN: The European Organization for Nuclear Research

l  Hyperlink u 

a reference to data that the reader can directly follow, or that is followed automatically.

l  Hypertext u 

a text document that contained hyperlinks

l  Web page u 

A hypertext document on WWW

l  Website u 

A collection of closely related Web pages

24

WWW, World Wide Web l  Web browser u 

A software that provides the user interface that allows a user to browse web pages.

l  Web server u 

A software that contains hypertext documents to be accessed.

l  HTTP, Hypertext Transfer Protocol u 

Hypertext documents transferred between browsers and Web servers

l  URL, Uniform Resource Locator u 

a unique address of each web page

u 

Format: ¡  Protocol://server_address/directory/…/filename ¡  EX: Ø  http://www.nctu.edu.tw/in Ø  dex.html 25

HTML, Hypertext Markup Language demonstration page

My Web Page

Click here for another page.

26

Extensible Markup Language (XML) l  XML: A language for constructing markup languages similar to HTML u 

A descendant of SGML, Standard Generalized Markup Language

u 

Opens door to a World Wide Semantic Web

1526 計算機概論與程式設計 鄭昌杰 8040 體育-棒球 王建民

27

Client Side Versus Server Side l Client-side activities u 

Examples: java applets, javascript, Macromedia Flash

l Server-side activities u 

Common Gateway Interface (CGI)

u 

Servlets

u 

PHP

Client 1

request response

CGI ASP JSP

Client 2

Client 3 Web Server

28

Package-shipping

Prepares package for shipping

29

Internet Software Layers l  l  l  l 

Application: Constructs message with address Transport: Chops message into packets Network: Handles routing through the Internet Link: Handles actual transmission of packets

l  Packets u 

small segments of a message transmission packet 1

message

packet 2 packet n

reassembly

message 30

Following a message through the Internet

31

OSI model l  Open System Interconnection (OSI)

TCP/IP protocal suite

Application

Transport Network

Link

32

TCP/IP Application Layer l  TCP Port u 

Determining which unit within the application layer should receive an incoming message

u 

A port is associated with an IP address of the host, as well as the type of protocol used for communication. ¡  http://www.nctu.edu.tw:80 ¡  ftp://ca.nctu.edu.tw:80 ¡  ftp://140.113.100.99:12345

u 

Port number : 0~65536 (User: 1024 to 49151) ¡  20, 21: FTP ¡  23: Telnet remote login service ¡  25: SMTP ¡  53: DNS ¡  80: HTTP ¡  110: Post Office Protocol (POP) ¡  1863: MSN

33

TCP/IP Transport Layer l  Transport Layer u 

Transmission Control Protocol, TCP

u 

User Datagram Protocol, UDP

34

Security l  Attacks u  u 

Malware (viruses, worms, Trojan horses, spyware, phishing software) Denial of Service attack, DoS ¡  attempt to make a computer resource unavailable to its intended users

u 

Spam ¡  abundance of unwanted messages ¡  junk emails

l  Protection u  u  u  u 

Firewalls Spam filters Proxy Servers Antivirus software

l  Network sniffer u  u  u  u 

Packet analyzer Detect network attacks Filter suspect content Monitor bandwidth utilization

35

TCP/IP Network Layer l  IP, Internet Protocol u 

forwarding packets

u 

routing

u 

hop count ¡  the number of routers through which data must pass between source and destination.

36

Encryption l  SSL (Secure Sockets Layer) u 

FTPS(FTP Secure)

u 

HTTPS(HTTP Secure)

l  Public-key Encryption u 

Public key: Used to encrypt messages

u 

Private key: Used to decrypt messages

l  Certificates and Digital Signatures u 

Public key: Used to decrypt signature

u 

Private key: Used to encrypt signature

37

Public-key encryption

38

Certificates and Digital Signatures Document

Document

Hash Message digest

Signature +

Decrypt

Hash +

Private key

Public key

Message digest

Message digest

Encrypt Compare Signature

Signing

≠ Error!

= OK! Verification

39