Networking and the Internet

Transcription

1 Introduction to Computer and Program Design Lesson 7 Networking and the Internet James C.C. Cheng Department of Computer Science National Chiao Tung University

2 Reference book l Computer Science: An Overview, 11ed J. Glenn Brookshear Publish by Pearson 2

3 Network Classifications l Scope 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 Closed versus open l Topology (configuration) Bus (Ethernet, a LAN technique) Star (Wireless networks with central Access Point) 3

4 Topology (configuration) l Bus (Ethernet, a LAN technique) Hub l Star (Wireless networks with central Access Point) Access Point, AP 4

5 Protocols l CSMA/CD, Carrier Sense Multiple Access with Collision Detection Used in Ethernet (BUS) Silent bus provides right to introduce new message Not compatible with star networks l CSMA/CA, Carrier Sense Multiple Access with Collision Avoidance Used in WiFi (Star) Hidden terminal problem 5

6 The hidden terminal problem 6

7 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

8 Connecting Networks l Router: Connects two incompatible networks resulting in a network of networks called an internet Forwarding table or routing table Gateway 8

9 Network Devices l Repeater l Wireless AP l Hub l ipshare router l Bridge l switch l router 9

10 Network Cable l Category 5 cable Computer ß à Device 1 8 Computer ß à Computer maximum length: 100 m 10

11 Inter-process Communication l Client-server One server, many clients Server must execute continuously Client initiates communication l Peer-to-peer (P2P) Two processes communicating as equals Peer processes can be shortlived 11

12 Distributed Systems l Systems with parts that run on different computers Infrastructure can be provided by standardized toolkits Example: Enterprise Java Beans from Oracle Example:.NET framework from Microsoft l Cluster computing many independent computers work closely together to provide computation Blade server system Blade server Blade enclosure 12

13 Distributed Systems l Grid computing more loosely coupled than clusters In general, the communication between grid nodes through network. Grid nodes 13

14 Distributed Systems l Cloud computing huge pools of shared computers on the network 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 Application: Online game Online documents Online photo album 14

15 The Internet l An internet that spans the world Original goal was to develop for military purposes (U.S.) l Internet Service Provider (ISP) 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 Intranet: regional and private internet Traditional telephone (dial up connection) Modem, mdulator/demodulator Cable connections DSL, digital subscriber line ADSL: Asymmetric DSL Wireless 15

16 Internet Addressing l IP address pattern of 32 or 128 bits often represented in dotted decimal notation IPv4, 32 bits: ex: (each part is a decimal number ) Some reserved IPs you have to know: Ø 127.x.x.x: Localhost communication ( is the localhost) Ø x.x: Private network Ø x.x: retrieved from a DHCP(Dynamic Host Configuration Protocol) server Ø : broadcast IPv6, 128 bits ex: 2001:0DB8:85A3:08D3:1319:8A2E:0370:7344 (each part is a hexadecimal number) 16

17 Internet Addressing l Mnemonic address: Domain names JamesPC1 Top-Level Domains.edu.tw is a top-level domain.edu: educational institutions.gov: government institutions.org: non-profit organizations.com &.co: commercial l Domain name system (DNS) Name servers DNS lookup n.tw: Taiwan n.cn: China n.jp: Japan n.uk:united Kingdom 17

18 Internet Addressing l Internet Corporation for Assigned Names & Numbers (ICANN) Allocates IP addresses to ISPs who then assign those addresses within their regions. Oversees the registration of domains and domain names. 18

19 Traditional Internet Applications l Electronic Mail ( ) Domain mail server collects incoming mail and transmits outing mail address: account_name@server_domain_name ex: chengchc@cs.nctu.edu.tw 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

20 Traditional Internet Applications l File Transfer Protocol (FTP) FTP server: File provider FTP client: Uploading/downloading files to/from a FTP server l Telnet and Secure Shell(SSH) allow users to access another computers Example: Bulletin Board System, BBS 20

21 More Recent Applications l Voice Over IP (VoIP) voice communication Type 1:P2P model Example: Skype Type 2: VoIP + traditional telephone analog telephone adapters Type 3: Pure VoIP Phone device 21

22 More Recent Applications l Generations of wireless telephones 1G, first generation traditional telephone system 2G, second generation text message 2.5G, GPRS (General Packet Radio Service) 56 kbps -115 kbps 3G, third generation higher data transfer rates (300k-2Mbps), allowing for mobile video calls and other bandwidth-intensive activities 3.5G higher data transfer speeds than 3G (1.8M - 14Mbps) 4G, fourth generation higher data transfer speeds than 3G (100M 1Gbps) fully packet-switched using the IP protocol 22

23 More Recent Applications l Internet Radio N-unicast one sender sending messages to multiple receivers server to send individual messages to each of its clients. Multicast a server transmits a message to multiple clients by means of a single address l Internet TV (online TV) Internet Protocol television (IPTV) video on demand (VOD) 23

24 WWW, World Wide Web l Sir Tim Berners-Lee, CERN, 1990 l Hyperlink l Hypertext CERN: The European Organization for Nuclear Research a reference to data that the reader can directly follow, or that is followed automatically. a text document that contained hyperlinks l Web page l Website A hypertext document on WWW A collection of closely related Web pages 24

25 WWW, World Wide Web l Web browser A software that provides the user interface that allows a user to browse web pages. l Web server A software that contains hypertext documents to be accessed. l HTTP, Hypertext Transfer Protocol Hypertext documents transferred between browsers and Web servers l URL, Uniform Resource Locator a unique address of each web page Format: Protocol://server_address/directory/ /filename EX: Ø Ø dex.html 25

26 HTML, Hypertext Markup Language <html> <head> <title>demonstration page</title> </head> <body> <h1>my Web Page</h1> <p>click <a href=" here </a> for another page. </p> <img src = " </body> </html> 26

27 Extensible Markup Language (XML) l XML: A language for constructing markup languages similar to HTML A descendant of SGML, Standard Generalized Markup Language Opens door to a World Wide Semantic Web <?xml version="1.0" encoding="big5"?> < 課程列表 > < 課程 > < 選課代碼 >1526</ 選課代碼 > < 課程名稱 > 計算機概論與程式設計 </ 課程名稱 > < 授課教師 > 鄭昌杰 </ 授課教師 > </ 課程 > < 課程 > < 選課代碼 >8040</ 選課代碼 > < 課程名稱 > 體育 - 棒球 </ 課程名稱 > < 授課教師 > 王建民 </ 授課教師 > </ 課程 > </ 課程列表 > 27

28 Client Side Versus Server Side l Client-side activities Examples: java applets, javascript, Macromedia Flash l Server-side activities Common Gateway Interface (CGI) Servlets PHP request Client 1 response CGI ASP JSP Client 2 Web Server Client 3 28

29 Package-shipping Prepares package for shipping 29

30 Internet Software Layers l Application: Constructs message with address l Transport: Chops message into packets l Network: Handles routing through the Internet l Link: Handles actual transmission of packets l Packets small segments of a message packet 1 transmission message packet 2 reassembly message packet n 30

31 Following a message through the Internet 31

32 OSI model l Open System Interconnection (OSI) TCP/IP protocal suite Application Transport Network Link 32

33 TCP/IP Application Layer l TCP Port Determining which unit within the application layer should receive an incoming message A port is associated with an IP address of the host, as well as the type of protocol used for communication. ftp://ca.nctu.edu.tw:80 ftp:// :12345 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

34 TCP/IP Transport Layer l Transport Layer Transmission Control Protocol, TCP User Datagram Protocol, UDP 34

35 Security l Attacks Malware (viruses, worms, Trojan horses, spyware, phishing software) Denial of Service attack, DoS attempt to make a computer resource unavailable to its intended users Spam abundance of unwanted messages junk s l Protection Firewalls Spam filters Proxy Servers Antivirus software l Network sniffer Packet analyzer Detect network attacks Filter suspect content Monitor bandwidth utilization 35

36 TCP/IP Network Layer l IP, Internet Protocol forwarding packets routing hop count the number of routers through which data must pass between source and destination. 36

37 Encryption l SSL (Secure Sockets Layer) FTPS(FTP Secure) HTTPS(HTTP Secure) l Public-key Encryption Public key: Used to encrypt messages Private key: Used to decrypt messages l Certificates and Digital Signatures Public key: Used to decrypt signature Private key: Used to encrypt signature 37

38 Public-key encryption 38

39 Certificates and Digital Signatures Document Document Signature + Public key Hash Hash Decrypt Message digest + Private key Message digest Message digest Encrypt Compare Signature = OK! Error! Signing Verification 39