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COS 125

COS 125. DAY 2. Agenda. Questions from last Class?? Review ISOC presentation on Internet History Today’s topics Circuit versus Packet switching TCP/IP Software Structure of The Internet Internet Addresses and Names How IP Routers work As promised, Assignment #1 is posted to Blackboard

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COS 125

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  1. COS 125 DAY 2

  2. Agenda • Questions from last Class?? • Review • ISOC presentation on Internet History • Today’s topics • Circuit versus Packet switching • TCP/IP • Software Structure of The Internet • Internet Addresses and Names • How IP Routers work • As promised, Assignment #1 is posted to Blackboard • Due Tuesday, Feb 5 @ 2:05 PM

  3. Circuit Switching • This is how Phone Networks operate • For Alice to “talk” to Dean there must a dedicated Connection (wire) from Alice to Dean • If there is no connection path available than circuit is said to be busy • Connection is dedicated for entire length of conversation • Wasteful

  4. Circuit Switching

  5. Packet Switching • TCP/IP (and the Internet) uses Packet Switched networks • Large files are broken in smaller packets • Each packets finds its way across Internet • DEMO • Allows for Multiplexing • More efficient • Causes problems for data that requires specific timing • Audio, Video

  6. Packet Switching 1. Break message into Smaller packets (also known as frames) Original Message Packet Switch A B C Computer X Packet Switching Decision Computer Y F E D 2. Route packets individually; Packet switches along the way Make decisions about the packet

  7. TCP/IP • Two protocols that are part of the Networking Stack • Transmission Control Protocol • Computer to Computer • Breaks down Files into Packets and reassemble • Internet Protocol • Internet Device to Internet Device • Ensures packets are delivered to right destination

  8. TCP/IP Stack

  9. Connecting to Internet • Two ways • LANS • Direct connection • Just like in this lab • 24/7/365 • Modems • Cable • DSL • Telephone • Use two different protocols • SLIP or PPP • Other (Newer) protocols • PPPoE • PPPoA • PPPoEoA • PPTP

  10. Internet Software Structure • Client/Server • Clients (PC’s) ask for stuff • Servers (large computers) deliver stuff • In case of WWW • Uses HTTP • Browsers (Internet explorer) is the client • Web Server (www.umfk.maine.edu) is the server

  11. Client/Server Architecture Usually, Two Types of Stations Clients and Servers Server Client PC Service Network Clients Receive Services Servers Provide Services

  12. Internet Address and Domains • The Heart of the Internet is DNS • Domain Name System • Translate names to addresses • Sort of an automatic phone book • www.umfk.maine.edu -> 130.111.185.92 • Use nslookup at the command prompt (2000, XP, Mac OSX, UNIX) • The name (www.umfk.maine.edu) is a URL or Uniform Resource Locator • 130.111.185.92 is an IP address (like a phone number)

  13. Domain names • www.umfk.maine.edu • Computer.subdomain.minordomain.majordomain • Major Domains • edu, com, net, org mil • Minor domains • Maine, yahoo, nasa • Sub domains (could have more than one) • Umfk • Computer names • www, tgauvin, nb11

  14. Domain name organization

  15. Name servers • DNS Names Server covert names to IP address • No ONE name server could know all names and all addresses • more than 4 billion possibilities • Names <> ip address tables are distributed • Each minor domain is responsible for running its own Name Server(s) • 13 Root Servers (one per major domain) maintain lists of all the name servers responsible of the minor domains

  16. Distributed Name Resolution

  17. Root Servers

  18. Static versus Dynamic IP Addresses • Every computer connected to the Internet MUST have an IP address • xxx.xxx.xxx.xxx • 0.0.0.0 <> 255.255.255.255 • If the address for a computer never changes then it is static • Else it is dynamic

  19. Why use Dynamic Addressing • There is not enough address to go around • 4.2 billion possibilities • Actually only about 3 billion due to allocation schemes • Not all computer are connected 24/7 • If an ISP has only 24 modems that its customers connect to • than why use more than 24 addresses • even though it may have 200 or more customers • Dynamic IP’s became possible with DHCP around 1995

  20. DHCP

  21. How routers work • Traffic cops of the Internet • Ensure all IP packets get to where the are supposed to go • Look at destination IP address of any packet coming into the router on any of its ports (connections) • Looks up ip address in routing table • Decides where to send packet • Another port

  22. Routing Table for a router

  23. Routing

  24. Routing

  25. For next week • Read HITW Chaps 7-13 (page 85) • Assignment # 1 • Due next Tuesday, Feb 5, 2008 at beginning of class

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