1. COMS 161 Introduction to Computing
Title: Local Area Networks
Date: October 6, 2004
Lecture Number: 18

2. Announcements This material is from chapter 17 in the book
A pirate was talking to a "land-lubber" in a bar. The land-lubber noticed  that, like any self-respecting pirate, this guy had a peg leg,
a hook in place of one of his hands and a patch over one eye. The land-lubber just had to find out how the pirate got in such bad shape.
He asked the pirate, "How did you loose your leg?" The pirate responded, "I lost me leg in a battle off the coast of Jamaica!" His new
acquaintance was still curious so he asked, "What about you hand. Did you loose it at the same time?"
"No," answered the pirate. "I lost it to the sharks off the Florida Keys." Finally, the land-lubber asked,
"I notice you also have an eye patch. How did you loose your eye? The pirate answered,
"I was sleeping on a beach when a seagull flew over and crapped right in me eye." The land-lubber asked,
"How could a little seagull crap make you loose your eye?" The pirate  snapped,
"It was the day after I got me hook!"

3. Review
LANs
Topology
History of the Internet

4. Outline
Internet protocols
Network layers
TCP/IP

5. Internet Growth and the Web
Year
Internet Nodes1
Web Servers2
2004
240,000,000
48,000,000
2002
162,129,000
33,083,000
2000
93,048,000
18,170,000
1998
36,739,000
4,279,000
1996
12,881,000
300,000
1994
3,212,000
3,000
1992
992,000 50
1990
313,000
1988
56,000
1986
5,089
1984
1,024
1982
235
1971 18
Sources: (1) (2)

6. How the Internet Works
Protocol is a set of rules conventions and agreements for the orderly exchange of information
Permits the transfer of information
Hundreds of millions of machines
Made by dozens of manufacturers
Located in hundreds of countries
Referred to as network protocols
Internet Society maintains the viability of the network

7. How the Internet Works Protocols set up as a multilayered hierarchy
Each layer addresses one task the communication
Allows one layer to change without requiring other layers to change
Five layers to the internet protocol hierarchy
Also called TCP/IP (the two most important protocols)
Layer
Name
Examples 5
Application
http, smtp, ftp 4
Transport
TCP, UDP 3
Network IP 2b
Logical Link Control
PPP, Ethernet Data Link Layer 2a
Medium Access Control
Ethernet Data Link Layer 1
Physical
Modem, DSL, Cable Modem

8. How the Internet Works Physical Layer Protocols
Rules for exchange of binary digits across a physical communication channel
Fiber optic
Copper cable (twisted pair)
Wireless channel
Bit pipe
Bits at one end can be read and understood at the other end
11011…

9. How the Internet Works Data Link Layer
Bits emerging from the bit pipe may NOT be a perfect replication of the bits that entered the pipe
No such thing as an error-free channel
Weather, interference, aging components
Error detection
How do we know an error occured?
Correction
How do we fix the bit

10. How the Internet Works Network and transport layers
Transmission Control Protocol (TCP)
Internet Protocol (IP)
TCP/IP are two internet protocols
Open Standards (protocols)
Not owned by a company
Internet Architecture Board (IAB)
Internet Engineering Task Force (IETF)
Allow cross network communication

11. How the Internet Works TCP protocol
Internet messages are broken into packets
Contain all information necessary to travel independently from network to network towards its destination
Different packets can take different routes
Destination machine assembles packets into the original message

12. How the Internet Works
TCP protocol

13. How the Internet Works DATAGRAM IP address Domain name servers provide
A TCP packets
IP address
a number that signifies the address of an Internet host
Domain names are pseudonyms for IP addresses
Domain name servers provide
IP numbers for URLs
addresses