COS 125 DAY 2

Agenda Questions from last Class?? Review ISOC presentation on Internet History Today’s topic TCP/IP Software Structure of The Internet Internet Addresses and Names How IP Routers work As promised, Assignment #1 is posted to WebCt Due one week from today

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

TCP/IP Stack

Circuit Switching This is how Phone Network operate For Alice to “talk” to Bob there must a dedicated Connection (wire) from Alice to Bob If there is not connection path available than circuit is said to be busy Connection is dedicated for entire length of conversation Wasteful

Circuit Switching

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 problem for data the requires specific timing Audio, Video

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

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

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 ( is the serverwww.umfk.maine.edu

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

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

Domain names Computer.subdomain.minordomain.majordom ain Major Domains edu, com, net, org mil Minor domains Maine, yahoo, nasa Sub domains (could have more than one) Umfk Computer names www, agauvin, nb11

Domain name organization

Name servers DNS Names Server covert names to IP adress No ONE names 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 resosible of the minor domains

Distributed Name Resolution

Root Servers

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

Why use Dynamic Addressing There is not enough address to go around 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 began posiible with DHCP around 1995

DHCP

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

Routing

For next week Read HITW Chaps 7-13 Assignment # 1 Due next Friday, January 23, 2004 at beginning of class