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

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-2 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 4-3 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)

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-4 Figure 4.1 Network topologies

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-5 Figure 4.1 Network topologies (continued)

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-6 Protocols Token Ring Protocol –Sample applet: /index.htmlhttp://whale.hit.bme.hu/~remopp/DES/SimpleApplet /index.html CSMA/CD

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-7 Protocols Token Ring Protocol –developed by IBM in 1970’s. –Consists of a set of nodes connected in a ring –Data flows in a particular direction only –Data received from up neighbour forwarded to down neighbour –Token –access to the shared ring a special sequence of bits circulates around the ring Each node receives and forwards token Frame makes its way back to sender –frame removed by sender –sender reinsert token. As token circulates around ring, each station gets a chance to transmit

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-8 Protocols CSMA/CD –used in Ethernet –slient bus provides right to introduce new message

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-9 Connecting Networks Repeater: Extends a network Hub: A hub is the simplest of these devices. Any data packet coming from one port is sent to all other ports. It has more ports than repeater. Bridge: Connects two compatible networks Switch: Connect several compatible networks Router: Connects two incompatible networks resulting in a network of networks called an internet

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-10 Repeater A repeater is specific hardware designed to overcome signal attenuation, it usually has only two ports and is designed to pure boost or amplify a signal.

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-11 Hub Hub A hub is the simplest of these devices. Any data packet coming from one port is sent to all other ports. It is then up to the receiving computer to decide if the packet is for it. Imagine packets going through a hub as messages going into a mailing list. The mail is sent out to everyone and it is up to the receiving party to decide if it is of interest. The biggest problem with hubs is their simplicity. Since every packet is sent out to every computer on the network, there is a lot of wasted transmission. This means that the network can easily become bogged down. Hubs are typically used on small networks where the amount of data going across the network is never very high.

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-12 Bridge Bridge A bridge goes one step up on a hub in that it looks at the destination of the packet before sending. If the destination address is not on the other side of the bridge it will not transmit the data. A bridge only has one incoming and one outgoing port. To build on the analogy above, the bridge is allowed to decide if the message should continue on. It reads the address and decides if there is a on the other side. If there isn’t, the message will not be transmitted. Bridges are typically used to separate parts of a network that do not need to communicate regularly, but still need to be connected.

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-13 Switch Switch A switch steps up on a bridge in that it has multiple ports. When a packet comes through a switch it is read to determine which computer to send the data to. This leads to increased efficiency in that packets are not going to computers that do not require them. Now the analogy has multiple people able to send to multiple users. The switch can decide where to send the mail based on the address. Most large networks use switches rather than hubs to connect computers within the same subnet.

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-14 Router Router A router is similar in a switch in that it forwards packets based on address. But, instead of the MAC address that a switch uses, a router can use the IP address. This allows the network to go across different protocols. The most common home use for routers is to share a broadband internet connection. The router has a public IP address and that address is shared with the network. When data comes through the router it is forwarded to the correct computer. This comparison to gets a little off base. This would be similar to the router being able to receive a packet as and sending it to the user as a fax.

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-15 Figure 4.4 Building a large bus network from smaller ones

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-16 Inter-process Communication Client-server –One server, many clients –Server must execute continuously –Client initiates communication Peer-to-peer (P2P) –Two processes communicating as equals –Peer processes can be short-lived

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-17 Figure 4.6 The client/server model compared to the peer-to-peer model

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-18 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

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-19 The Internet and Internet Addressing The Internet: An internet that spans the world A collection of domains IP address: pattern of 32 or 128 bits often represented in dotted decimal notation Mnemonic address: –Domain names –Top-Level Domains Domain name system (DNS) –Name servers –DNS lookup Internet Corporation for Assigned Names & Numbers (ICANN) –Allocates IP addresses to Internet Service Provides who then assign those addresses within their regions. –Oversees the registration of domains and domain names.

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-20 Internet Architecture

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-21 Internet Architecture Internet Service Provider (ISP) –Tier-1 –Tier-2 Access ISP: Provides connectivity to the Internet –Traditional telephone (dial up connection) –Cable connections –DSL –Wireless

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-22 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 File Transfer Protocol (FTP) Telnet and SSH

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-23 World Wide Web Hypertext and HTTP Browser gets documents from Web server Documents identified by URLs

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-24 Figure 4.8 A typical URL

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-25 Hypertext Document Format 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 © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-26 Figure 4.9 A simple Web page

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-27 Figure 4.9 A simple Web page (continued)

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-28 Another Example This text is bold This text is strong This text is big This text is emphasized This text is italic This text is small This is subscript and superscript

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-29 Figure 4.12 Package-shipping example

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-30 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 4-31 Figure 4.14 Following a message through the Internet

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-32 TCP/IP Protocol Suite Transport Layer –TCP –UDP Network Layer –IP (IPv4 and IPv6)

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 4-33 Security Attacks –Malware (viruses, worms, Trojan horses, spyware, phishing software) –Denial of service –Spam Protection –Firewalls –Spam filters –Proxy Servers –Antivirus software