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 WebCt Due Monday, Jan 24

Circuit Switching

This is how Phone Networks operateFor 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

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 problems for data that requires specific timing

Audio, Video

Packet Switching

Original Message

Computer X

PacketSwitch

APacket

SwitchingDecision

B

C

Computer Y

FED

1. Break message intoSmaller packets

(also known as frames)

2. Route packets individually;Packet switches along the way

Make decisions about the packet

TCP/IP

Two protocols that are part of the Networking StackTransmission Control Protocol

Computer to ComputerBreaks down Files into Packets and reassemble

Internet Protocol Internet Device to Internet DeviceEnsures packets are delivered to right

destination

TCP/IP Stack

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/ServerClients (PC’s) ask for stuffServers (large computers) deliver stuff

In case of WWW Uses HTTPBrowsers (Internet explorer) is the clientWeb Server (www.umfk.maine.edu) is the

server

Client/Server Architecture

Client PCServer

Network

Service

ClientsReceiveServices

ServersProvideServices

Usually, Two Types of StationsClients and Servers

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)

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

Domain name organization

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

Distributed Name Resolution

Root Servers

Static versus Dynamic IP Addresses

Every computer connected to the Internet MUST have an IP addressxxx.xxx.xxx.xxx0.0.0.0 <> 255.255.255.255

If the address for a computer never changes then it is staticElse it is dynamic

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

DHCP

How routers work

Traffic cops of the InternetEnsure all IP packets get to where the are

supposed to goLook at destination IP address of any

packet coming into the router on any of its ports (connections)

Looks up ip address in routing tableDecides where to send packet

Another port

Routing Table for a router

network Next Hop

10.2.1.56 10.3.4.56

10.2.0.0 10.3.2.1

10.3.0.0 Deliver directly

10.1.0.0 10.3.1.1

10.5.0.0 Deliver directly

10.6.0.0 10.5.6.1

0.0.0.0 10.3.2.1

Routing

Routing

For next week

Read HITW Chaps 7-13 (page 85)Assignment # 1

Due next Monday, January 24, 2004 at beginning of class