Transcript Cos 125 day2

COS 125
DAY 2
Agenda
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Questions from last Class??
Review
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Today’s topics
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ISOC presentation on Internet History
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
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Due Monday, Jan 24
Circuit Switching
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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
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Wasteful
Circuit Switching
Packet Switching
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TCP/IP (and the Internet) uses Packet
Switched networks
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Large files are broken in smaller packets
Each packets finds its way across Internet
DEMO
Allows for Multiplexing
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More efficient
Causes problems for data that requires specific
timing
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Audio, Video
Packet Switching
Original Message
Packet
Switch
Computer X
A
Packet
B
1. Break message into
Smaller packets
(also known as frames)
C
Switching
Decision
D
2. Route packets individually;
Packet switches along the way
Make decisions about the packet
E
Computer Y
F
TCP/IP
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Two protocols that are part of the
Networking Stack
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Transmission Control Protocol
Computer to Computer
 Breaks down Files into Packets and reassemble
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Internet Protocol
Internet Device to Internet Device
 Ensures packets are delivered to right
destination
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TCP/IP Stack
Connecting to Internet
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Two ways
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LANS
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Direct connection
Just like in this lab
24/7/365
Modems
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Cable
DSL
Telephone
Use two different protocols
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SLIP or PPP
Internet Software Structure
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Client/Server
Clients (PC’s) ask for stuff
 Servers (large computers) deliver stuff
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In case of WWW
Uses HTTP
 Browsers (Internet explorer) is the client
 Web Server (www.umfk.maine.edu) is the
server
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Client/Server Architecture
Usually, Two Types of Stations
Clients and Servers
Server
Client PC
Service
Network
Clients
Receive
Services
Servers
Provide
Services
Internet Address and Domains
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The Heart of the Internet is DNS
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Domain Name System
Translate names to addresses
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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
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www.umfk.maine.edu
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Computer.subdomain.minordomain.majordomain
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Major Domains
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Minor domains
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Maine, yahoo, nasa
Sub domains (could have more than one)
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edu, com, net, org mil
Umfk
Computer names
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www, tgauvin, nb11
Domain name organization
Name servers
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DNS Names Server covert names to IP
address
 No ONE name server could know all names
and all addresses
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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
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Every computer connected to the
Internet MUST have an IP address
xxx.xxx.xxx.xxx
 0.0.0.0 <> 255.255.255.255
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If the address for a computer never
changes then it is static
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Else it is dynamic
Why use Dynamic Addressing
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There is not enough address to go around
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4.2 billion possibilities
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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
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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
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Another port
Routing Table for a router
network
10.2.1.56
10.2.0.0
10.3.0.0
10.1.0.0
10.5.0.0
10.6.0.0
0.0.0.0
Next Hop
10.3.4.56
10.3.2.1
Deliver directly
10.3.1.1
Deliver directly
10.5.6.1
10.3.2.1
Routing
Routing
For next week
Read HITW Chaps 7-13 (page 85)
 Assignment # 1
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Due next Monday, January 24, 2004 at
beginning of class