Computer Science An Overview Networks PDF

1 Computer Science An Overview 13th Edition Chapter 4 Networks Operating Systems Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved  What Will We Study? 2...

1 Computer Science An Overview 13th Edition Chapter 4 Networks Operating Systems Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved  What Will We Study? 2 3 ‫أ‬ ‫ب‬ 1 Programs ‫ت‬ Algorithms 10001110111 10001110111 4 5 Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 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 Simple Client Server 4.6 Security Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 4.1 Network Fundamentals Network Software allows users to exchange information and share resources – Content – Software – Data storage facilities Network software has evolved into a network-wide operating system Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Network Classifications Scope – Personal Area Network (short-range) – Local Area Network (building/campus) – Metropolitan Area Network (community) – Wide Area Network (greater distances) Ownership – Closed versus open Topology (configuration) – Bus (Ethernet) – Star (Wireless networks with central Access Point) Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.1 Two popular network topologies (1 of 2) Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.1 Two popular network topologies (2 of 2) Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Protocols Rules by which activities are conducted on a network – Example: Coordinating the transmission of messages between computers ▪ Need to avoid all machines transmitting at the same time Allows vendors to build products that are compatible with products from other vendors Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Protocols for Transmitting Messages CSMA/Collision Detection – Carrier Sense, Multiple Access with Collision Detection (CSMA/CD) – used in Ethernet – both machines stop and wait for a independent, random time CSMA/Collision Avoidance – Carrier Sense, Multiple Access with Collision Avoidance (CSMA/CA) – used in WiFi, where not all machines can hear each other (hidden terminal problem) – give advantage to the machine that has already been waiting Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.2 Communication over a bus network Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.3 The hidden terminal problem Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Combining Networks Repeater: passes all messages across two busses Bridge: passes only messages that are destined for computers on the other bus Switch: acts like a bridge, but with connections to multiple busses Router: Connects two incompatible networks resulting in a network of networks called an internet Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.4 Building a large bus network from smaller ones Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.5 Routers connecting two WiFi networks and an Ethernet network to form an internet Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Methods of Process Communication Client-server – Many clients, one server (executing continuously) – Clients make requests of other processes – Server satisfies requests made by clients Peer-to-peer (P2P) – Two processes communicating as equals – Processes execute on a temporary basis Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.6 The client/server model compared to the peer-to-peer model Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Distributed Systems Systems units that execute as processes on different computers – Cluster computing ▪ Independent computers work closely together instead of a single, much larger machine – Grid computing ▪ Millions of home PCs (not connected to each other) work on a complex problem – Cloud computing ▪ Provide services, hide the details Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 4.2 The Internet The Internet is an internet that spans the world – Original goal was to link a variety of networks into a connected system unaffected by local disasters – Today, it is a commercial undertaking that links a worldwide combination of PANs, LANs, MANs, and WANs involving millions of computers Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Internet Architecture Internet Service Provider (ISP) – Tier-1 (Internet backbone) – Tier-2 Access or Tier-3 ISP: Provides connectivity to the Internet – Hot spot (wireless) – Telephone lines – Cellular – Cable/Satellite systems Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.7 Internet Composition Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Internet Addressing IP address: pattern of 32 or 128 bits often represented in dotted decimal notation Mnemonic address: – Domain names (mu.edu) – Top-Level Domains ▪.org,.gov,.com,.mil,.net,.au,.ca,.biz, …. Domain name system (DNS) – Name servers – DNS lookup Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Internet Corporation for Assigned Names & Numbers (ICANN) Allocates blocks of IP addresses to ISPs who then assign those addresses within their regions. Oversees the registration of domains and domain names. Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Early Internet Applications Network News Transfer Protocol (NNTP) File Transfer Protocol (FTP) Telnet and Secure Shell (SSH) Hypertext Transfer Protocol (HTTP) Electronic Mail (email) – Domain mail server collects incoming mail and transmits outing mail – Mail server delivers collected incoming mail to clients via POP3 or IMAP Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved SMTP Simple Mail Transfer Protocol 220 mail.tardis.edu SMTP Sendmail Gallifrey-1.0; Fri, 23 Aug 2413 14:34:10 HELO mail.skaro.gov 250 mail.tardis.edu Hello mail.skaro.gov, pleased to meet you MAIL From: [email protected] 250 2.1.0 [email protected]... Sender ok RCPT To: [email protected] 250 2.1.5 [email protected]... Recipient ok DATA 354 Enter mail, end with "." on a line by itself Subject: Extermination. EXTERMINATE! Regards, Dalek. 250 2.0.0 r7NJYAEl028071 Message accepted for delivery QUIT 221 2.0.0 mail.tardis.edu closing connection Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved More Recent Applications Voice Over IP (VoIP) Internet Multimedia Streaming – N-unicast – Multicast – On-demand streaming – Content delivery networks (CDNs) Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 4.3 World Wide Web Hypertext combines internet technology with concept of linked-documents – Embeds hyperlinks to other documents Browsers present materials to the user Webservers provide access to documents Documents are identified by URLs and transferred using HTTP Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Who Invented the Web? What is the World Wide Web? A network of documents each with a unique URL (Uniform Resource Locator) A URL is the address of a web page on the World Wide Web. It was invented by Tim Berners-Lee. It is used to tell a web browser, where to find a web page. You can think of this like the address of a specific individual on earth. It specifies the country, the city, the street and the house number. 0-27 Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Tim Berners Lee An English CS and MIT professor. The father of the World Wide Web. He combined the Internet and the concept of hypertext to create the Web. Invented in 1989 during his work at (CERN) in Switzerland. On April 30, 1993, it was decided the World Wide Web would be free to everyone. In 1994 Tim Berners-Lee founded the World Wide Web Consortium, known as W3C as a Web standards organization 0-28 Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Hypertext and Hyperlinks Hypertext documents include hyperlinks that connect them to other documents 0-29 Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.8 A typical URL Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved URL Example Protocol Resource Server contains Path identifies identifies the specifies the the domain name the location of means of filename of the of the web server. the document. access. resource. http:// www.learnthenet.com/ english/ html/ 13wworks.htm Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Hypertext Markup Language (HTML) Encoded as text file Contains tags to communicate with browser – Appearance ▪ to start a level one heading ▪ to start a new paragraph – Links to other documents and content ▪ – Insert images ▪ Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.9 A simple webpage Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.9 A simple webpage (continued) Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.10 An enhanced simple webpage Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.10 An enhanced simple Web page (continued) Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Client Side Versus Server Side Client-side activities (browser) – Javascript – Java applets – Macromedia Flash Server-side activities (webserver) – Common Gateway Interface (CGI) – Servlets – JavaServer Pages (JSP) / Active Server Pages (ASP) – PHP Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 4.4 Internet Protocols Control how messages are transferred over the Internet This software must reside on every computer in the Internet Accomplished by a multi-level hierarchy Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.12 Package-shipping example Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 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 © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.13 The Internet software layers Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.14 Following a message through the Internet Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved TCP/IP Protocol Suite Transport Layer – Transmission Control Protocol (TCP) – User Datagram Protocol (UDP) Network Layer – Internet Protocol (IP) ▪ IPv4 ▪ IPv6 Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.15 Choosing between TCP and UDP Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 4.5 Simple Client Server Program Socket: an abstraction for processes at the application layer to connect to the network via the transport layer – Needs to know ▪ Source Address name (localhost) ▪ Source Port number(1023…65535) ▪ Destination Address ▪ Destination Port number Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Client Script in Python import socket Sock = socket.socket() Server_address Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Server Script in Python Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved 4.6 Cybersecurity Forms of Attack – Malware (viruses, worms, Trojan horses, spyware, phishing software) – Denial of service (DoS) – Spam (common medium for delivering malware) Protection and Cures – Firewalls – Spam filters – Proxy Servers – Antivirus software Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Cryptography HTTPS for secure Internet access Public-key Encryption (asymmetric) – Public key: Used to encrypt messages – Private key: Used to decrypt messages Certificate Authorities – Trusted to maintain lists of public keys – Provide Certificates to clients containing a party’s name and its public key Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Figure 4.16 Public key encryption Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Legal Approaches to Network Security Computer Fraud and Abuse Act Electronic Communication Privacy Act USA PATRIOT Act Communications Assistance for Law Enforcement Act Anticybersquatting Consumer Protection Act Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved Copyright This work is protected by United States copyright laws and is provided solely for the use of instructions in teaching their courses and assessing student learning. dissemination or sale of any part of this work (including on the World Wide Web) will destroy the integrity of the work and is not permit- ted. The work and materials from it should never be made available to students except by instructors using the accompanying text in their classes. All recipients of this work are expected to abide by these restrictions and to honor the intended pedagogical purposes and the needs of other instructors who rely on these materials. Copyright © 2015, 2012, 2009 Pearson Education, Inc. All Rights Reserved