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 WebCt Due Monday, Jan 24

3. Circuit Switching This is how Phone Networks operate For Alice to “talk” to Bob there must a dedicated Connection (wire) from Alice to Bob 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 Original Message Computer X Packet Switch A Packet Switching Decision B C Computer Y F E D 1. Break message into Smaller packets (also known as frames) 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

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 serverwww.umfk.maine.edu

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

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 www.umfk.maine.edu Use nslookup at the command prompt (2000, XP, Mac OSX, UNIX) The name (www.umfk.maine.edu) is a URL or Uniform Resource Locatorwww.umfk.maine.edu 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 networkNext Hop 10.2.1.5610.3.4.56 10.2.0.010.3.2.1 10.3.0.0Deliver directly 10.1.0.010.3.1.1 10.5.0.0Deliver directly 10.6.0.010.5.6.1 0.0.0.010.3.2.1

23. Routing

25. For next week Read HITW Chaps 7-13 (page 85) Assignment # 1 Due next Monday, January 24, 2004 at beginning of class