COS 125 DAY 2. Agenda Questions from last Class?? Review ISOC presentation on Internet History...
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Transcript of COS 125 DAY 2. Agenda Questions from last Class?? Review ISOC presentation on Internet History...
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
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
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
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
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
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