Chapter 4: Networking and the Internet

Transcription

1 Chapter 4: Networking and the Internet Computer Science: An Overview Tenth Edition by J. Glenn Brookshear Presentation files modified by Farn Wang Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

2 Chapter 4: Networking and the Internet 4.1 Network Fundamentals 4.2 The Internet 4.3 The World Wide Web 4.4 Internet Protocols 4.5 Security Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-2

3 Network Classifications Scope Local area network (LAN) Metropolitan area (MAN) Wide area network (WAN) Ownership Closed versus open Topology (configuration) Bus (Ethernet) Star (Wireless networks with central Access Point) Ring (IBM FDDI) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-3

4 Network topologies Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-4

5 Communication over a bus network Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-5

6 Network topologies (continued) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-6

7 Protocols CSMA/CD (Carrier Sense, Multiple Access with Collision Detection) For wired communication. CSMA/CA (Carrier Sense, Multiple Access with Collision Avoidance) for wireless communication Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-7

8 Protocols CSMA/CD (Carrier Sense, Multiple Access with Collision Detection) For wired communication. Used in Ethernet Silent bus provides right to introduce new message Retry after collection detection. CSMA/CA (Carrier Sense, Multiple Access with Collision Avoidance) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-8

9 Ethernet bus arbitration algorithm IEEE Optimistic why pessimistic? Use it and withdraw if bad things happen. Collision detection bad things 51.2 s 2.5km Bus Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

10 Ethernet bus arbitration algorithm IEEE Ethernet bus arbitration algorithm 1. If there is some signals in the bus, then stop and try later. 2. Start sending the message and monitoring the bus. 3. If in 52 s the message is corrupted, then stop and try later. 4. At the 808 th s, complete the message. Bus Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

11 Communication over a bus network through a hub computer computer computer hub computer computer Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-11

12 Protocols CSMA/CD (Carrier Sense, Multiple Access with Collision Detection) CSMA/CA (Carrier Sense, Multiple Access with Collision Avoidance) For wireless communication. Used in WiFi (IEEE ) Hidden terminal problem signal drowning or blocking difficulties in collision detection. Random stream testing before the real frames Significantly reduction in retries. may need ack from AP Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-12

13 The hidden terminal problem May block collision detection. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-13

14 Connecting Networks Repeater: Extends a network Bridge: Connects two compatible networks Switch: Connect several compatible networks Router: Connects two incompatible networks resulting in a network of networks called an internet forwarding table Gateway: connecting a network to Internet Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-14

15 Building a large bus network from smaller ones Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-15

16 Routers connecting two WiFi networks and an Ethernet network to form an internet Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-16

17 Inter-process Communication Client-server Peer-to-peer (P2P) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-17

18 Inter-process Communication Client-server One server, many clients Ideal for fast network access Server must execute continuously Client initiates communication For large-scale organization Win/NT, Linux, NetWare Peer-to-peer (P2P) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-18

19 Inter-process Communication Client-server Peer-to-peer (P2P) Two processes communicating as equals Ideal for sharing resources and applications For families and small offices Peer processes can be short-lived text conversation, interactive games, file sharing could be difficult for copyright enforcing Win 98, Win 95, Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-19

20 The client/server model compared to the peer-to-peer model Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-20

21 Distributed Systems Systems with parts that run on different computers Infrastructure can be provided by standardized toolkits Example: Enterprise Java Beans from Sun Microsystems Example:.NET framework from Microsoft Example: Cloud computing Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-21

22 The Internet The Internet: An internet that spans the world Original goal was to develop a means of connecting networks that would not be disrupted by local disasters. Today it has shifted from an academic research project to a commercial undertaking. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-22

23 Internet Architecture Internet Service Provider (ISP) sometimes means the internet. Access ISP (intranet) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-23

24 Internet Architecture Internet Service Provider (ISP) Tier-1 very high-speed, high-capacity, international WAN Tier-2 regional, less potent Access ISP (intranet): Provides connectivity to the Internet Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-24

25 Internet Architecture Internet Service Provider (ISP) Access ISP (intranet): Provides connectivity to the Internet is essentially an independent internet. is sometimes called intranet. provides connectivity to the Internet AOL, Microsoft, local cable companies, telephone companies,. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-25

26 Internet Architecture Internet Service Provider (ISP) Access ISP (intranet): Provides connectivity to the Internet hosts (end systems) Traditional telephone (dial up connection) Cable connections DSL (digital subscriber line) through modems Dial-up access (old tech) fiber-optic cables Wireless through AP hotspot: the range of an AP Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-26

27 Internet Composition Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-27

28 Internet Addressing IP address: pattern often represented in dotted decimal notation from 32 to 128 bits Mnemonic address: Domain names Top-Level Domains (TLD) edu, com, gov, org, info, net, The dots in Mnemonic addresses are not related to the dots in IP address. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-28

29 Internet Addressing Domain name system (DNS) How to translate Mnemonic names to IP addresses? Name servers basically directories DNS is an Internet-wide directory system. DNS lookup Originally domain names are tied to physical regions Now individuals and small firms can also have domain presences. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-29

30 Internet Corporation for Assigned Names & Numbers (ICANN) Allocates IP address blocks to ISPs who then assign those addresses within their regions. Oversees the registration of domains and domain names. through companies called registrars once registered, the domain organization can extend for identifiers. ntu.edu.tw subdomains for network in the domain ee.ntu.edu.tw Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-30

31 Traditional Internet Applications Electronic Mail ( ) Domain mail server collects incoming mail and transmits outing mail Mail server delivers collected incoming mail to clients via POP3 or IMAP SMTP for text mails MIME for non-ascii mails to SMTP File Transfer Protocol (FTP) Telnet and SSH Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-31

32 More Recent Applications Voice Over IP (VoIP) Internet Radio - webcasting streaming audio N-unicast burden to the sending servers and their immediate neighbors Multicast let the routers decide to send copies to destinations Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-32

33 World Wide Web Hypertext and HTTP Browser gets documents from Web server Documents uniquely identified by URLs Uniform Resource Locator Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-33

34 2013/04/13 stopped here. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-34

35 A typical URL Uniform Resource Locator a subset of the Uniform Resource Identifier (URI) the location of an identified resource the mechanism for retrieving it. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-35

36 Hypertext Document Format Encoded as text file Contains tags to communicate with browser Appearance <h1> to start a level one heading <p> to start a new paragraph Links to other documents and content <a href =... > Insert images <img src =... > Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-36

37 A simple Web page Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-37

38 An enhanced simple Web page Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-38

39 Extensible Markup Language (XML) XML: A language for constructing markup languages similar to HTML A descendant of SGML (Standard Generalized ML) Opens door to a World Wide Semantic Web note HTML does not strictly follow XML. XHTML does. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-39

40 Using XML <staff clef = treble > <key>c minor</key> <time> 2/4 </time> <measure> < rest> egth </rest> <notes> egth G, egth G, egth G </notes></measure> <measure> <notes> hlf E </notes></measure> </staff> Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-40

41 Figure 4.11 The first two bars of Beethoven s Fifth Symphony Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-41

42 WWW - Client Side Versus Server Side Client-side activities Examples: java applets, javascript, Macromedia Flash Server-side activities Common Gateway Interface (CGI) Servlets: a Java class in Java EE conforms to the Java Servlet API, a protocol of Java classes to HTTP requests. PHP (personal home page) a scripting language for webpages Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-42

43 Package-shipping example Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-43

44 Internet Software Layers Application: Constructs message with address Transport: Chops message into packets Network: Handles routing through the Internet Link: Handles actual transmission of packets Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-44

45 The Internet software layers Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-45

46 Following a message through the Internet Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-46

47 TCP/IP Protocol Suite Much more than TCP and IP. Transport Layer built on top of IP networks Users can choose from different versions, e.g.: TCP (Transmission Control Protocol) UDP (User Datagram Protocol) Network Layer IP (IPv4 and IPv6) deals only with packets Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-47

48 TCP (Transmission Control Protocol) connection-oriented. deal with streams high-quality and reliable. enables two hosts to establish a connection and exchange streams of data. guarantees delivery of data guarantees that packets will be delivered in the same order in which they were sent. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-48

49 UDP (User Datagram Protocol) very few error recovery services used primarily for broadcasting messages minimal overhead connectionless Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-49

50 Choosing between TCP and UDP Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-50

51 Security Attacks Malware viruses: inserting itself into programs already in the machine. worms: replicating and forwarding themselves Trojan horses: disguised as useful programs spyware: sniffing to collect private infor. phishing software Denial of service Spam: unwanted junk mails Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-51

52 Security Protection Firewalls: filtering traffic through a point Spam filters: a variation of firewall Proxy Servers: intermediary shielding the clients from suspicious servers. for specific services, elg., FTP, HTTP, telnet, auditing software for sudden change of system behaviors Antivirus software Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-52

53 Encryption FTPS, HTTPS, SSL (secure socket layer) Private-key Encryption Public-key Encryption Public key: Used to encrypt messages Private key: Used to decrypt messages Certificates and Digital Signatures Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-53

54 Private-key encryption key: k affine transformation modulo operand d message m 1 m 2 m n with m i [0,d), Encryption: ((m 1 +k)% d)((m 2 +k)% d) ((m n +k)%d) Decryption: c 1 c 2 c n with c i [0,d), ((c 1 -k)% d)((c 2 -k)% d) ((c n -k)% d) remainder operator Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-54

55 Private-key encryption Example: k = 5 d = 26 Encryption: S (int(s)+5)%26 = T (int(t)+5)%26 = O (int(o)+5)%26 = P (int(p)+5)%26 = X Y T U Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-55

56 Private-key encryption Drawbacks Receivers also must know the private key. No authentication Once the key is known, messages can be forged. Solution: Need a private key for each sender-receiver pair. Needs a lot of keys. Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-56

57 Public-key encryption Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-57

58 Public key encrytion RSA encryption method Ronald Rivest, Adi Shamir, Leonard Adleman 2 large primes p, q (hundreds of bits each) Ancient Chinese: incorrect! n is prime iff 2 n-1 %n = 1%n Fermat s little theorem: Given a%p 0, a p %p=a%p and a p-1 %p = 1%p Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-58

59 Public key encrytion RSA encryption method Ronald Rivest, Adi Shamir, Leonard Adleman 2 large primes p, q (hundreds of bits each) e: relative prime to (p-1)(q-1) Private key: pq Public key: d with gcd(d,e%(p-1)(q-1))=1 Encryption: c = (m e ) % (pq) Decryption: c d =((m e )%(pq)) d =m 1+k(p-1)(q-1) % (pq) = m%(pq) Copyright 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-59