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Chapter 4:Networking and the Internet
Computer Science: An OverviewTenth Edition
by J. Glenn Brookshear
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Chapter 4: Networking and the Internet
• 4.1 Network Fundamentals• 4.2 The Internet• 4.3 The World Wide Web
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Network Classifications
• Scope– Local area network (LAN)– Metropolitan area (MAN)– Wide area network (WAN)
• Ownership– Closed versus open Internet is an open network
• Topology (configuration-physical layout of network)– Bus (Ethernet)– Star (Wireless networks with central Access
Point)
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Figure 4.1 Network topologies
Access point (Server)
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Protocols• The set of rules by which activities are conducted
• Example: Protocols which controls rights to transmit messages
– CSMA/CD (Carrier Sense, Multiple Access with Collision Detection)
• Used in Ethernet• Silent bus provides right to introduce new message
– CSMA/CA (Carrier Sense, Multiple Access with Collision Avoidance)
• Used in WiFi• Hidden terminal problem
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Figure 4.2 Communication over a bus network
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Figure 4.3 The hidden terminal problem
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Connecting Networks
• Repeater– Extends a network– Simply transmits messages with some form of
amplification
• Bridge: – Connects two compatible networks– Transmits message ony when that message is
destined for a computer on the other side
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Connecting Networks
• Switch: – A bridge with multiple connections
– Connect several compatible networks
– Minimizes traffic load
• Repeater, bridge and switch are used to construct a single large network (same protocol)
• Router: Connects two incompatible networks resulting in a network of networks called an internet
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Figure 4.4 Building a large bus network from smaller ones
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Figure 4.5 Routers connecting two WiFi networks and an Ethernet network to form an internet
Wi Fi = Wireless Fidelity
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Inter-process Communication• The communication between computers
within a network • Methods of process communication
– Client-server model• One server, many clients• Server must execute continuously• Client initiates communication
– Peer-to-peer (P2P) model• Two processes communicating as equals• Peer processes can be short-lived
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Figure 4.6 The client/server model compared to the peer-to-peer model
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Distributed Systems
• Systems with parts that run on different computers
• eg. global information retrieval systems, companywide accounting and inventory systems, computer games.
• Infrastructure can be provided by standardized toolkits• Example: Enterprise Java Beans from Sun Microsystems• Example: .NET framework from Microsoft
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The Internet
• The Internet: An internet that spans the world (a worldwide collection of connected networks )
– Original goal was to develop a means of connecting networks that would not be disrupted by local disasters (early 1960s).
– Today it has shifted from an academic research project to a commercial undertaking.
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Internet Architecture
• Internet Service Provider (ISP): Organization which constructs and maintains internet.
– Tier-1 : Consist high-speed, high capacity, international WANs (The backbone of Internet)
– Tier-2 : More regional ISPs
– Access ISP: Provides connectivity to the Internet• Traditional telephone (dial up connection)• Cable connections• DSL• Wireless
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Figure 4.7 Internet Composition
End systems= hosts
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Internet Addressing
• IP (Internet Protocol) address:
– The unique address of a computer in internet
– Pattern of 32 or 128 bits often represented in dotted decimal notation
– 17.12.25 = 00010001 00001100 00011001
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Internet Addressing
• Mnemonic address:– Domain names– Top-Level Domains (edu, com, gov, org etc.)– Country-codeTop-Level Domains (tr, au, ca, etc.)
• Domain name system (DNS)– Name server : Translates mnemonic names to IP
address– DNS lookup : The process of translation
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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.
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Traditional Internet Applications
• Electronic Mail (email)
– Domain mail server collects incoming mail and transmits outing mail
– SMTP: The protocol used to transfer between mail servers as well as to send a new message from it’s author’s local machine to author’s mail server (transfers ASCII text messages MIME: non ASCII)
– Mail server delivers collected incoming mail to clients via POP3(Post Office Protocol Version 3) or IMAP (Internet Mail Access Protocol)
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Traditional Internet Applications
• File Transfer Protocol (FTP)
• Telnet : A distant user may contact the telnet server and gain access to the applications and utilities on the computer that a local user has)
• SSH : Secured Shell = Secured Telnet
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More Recent Applications
• Voice Over IP (VoIP) peer to peerSkype
• Internet Radio– Unicast (One sender sending messages to
one receiver)– N-unicast (A single sender involved with
multiple unicasts)– Multicast (A single sender with multiple clients)
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World Wide Web
• The World Wide Web, also known as the Web or WWW:
– Contains billions of documents– Is a portion of the Internet– Uses the Internet as a means to transport
information– Is a separate entity from the Internet
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World Wide Web
4-25
• The Web contains the information.
• The Internet transports information to and from users.
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World Wide Web
• Hypertext : Text file which contains tags to communicate with browser and which contains links to other documents
• Hyperlinks or links are words and images that bring other documents into view when clicked
• HTTP: Hyper Text Transfer Protocol
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World Wide Web
• A Web page is a document that may include text, graphics, sound, animation, and video.
• A Web site is a collection of Web pages.
• A Web browser is a program that displays Web pages and linked items (gets documents from Web server)
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Figure 4.8 A typical URLThe identification of an Internet resource’s type and location is performed through its Uniform Resource Locator (URL).
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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 = . . . >
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Figure 4.9 A simple Web page
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Figure 4.9 A simple Web page (continued)
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Figure 4.10 An enhanced simple Web page
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Figure 4.10 An enhanced simple Web page (continued)
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Extensible Markup Language (XML)
• XML: A language for constructing markup languages similar to HTML
– A descendant of SGML– Opens door to a World Wide Semantic Web
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Using XML : EXAMPLE
<?xml version="1.0"?>
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
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Using XML: EXAMPLE<PARTS>
<TITLE>Computer Parts</TITLE>
<PART>
<ITEM>Motherboard</ITEM>
<MANUFACTURER>ASUS</MANUFACTURER>
<MODEL>P3B-F</MODEL>
<COST> 123.00</COST>
</PART>
<PART>
<ITEM>Sound Card</ITEM>
<MANUFACTURER>Creative Labs</MANUFACTURER>
<MODEL>Sound Blaster Live</MODEL>
<COST> 80.00</COST>
</PART>
</PARTS>
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Client Side & Server Side Activities
• Client-side activities
– Examples: java applets, javascript, Macromedia Flash
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Client Side & Server Side Activities
• Server-side activities– Common Gateway Interface (CGI) : A set of
standards by which clients could request execution of programs stored in server
– Servlets: Java programs (class) that generate web content dynamically depending on the content of a request from a client
– PHP (Hypertext Processor ) A widely used, general-purpose scripting language that was originally designed for web development to produce dynamic web pages