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

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!"

Review LANs Topology History of the Internet

Outline Internet protocols Network layers TCP/IP

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) www.isc.org/ds; (2) www.netcraft.com/survey

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

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

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…

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

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

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

How the Internet Works TCP protocol

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 e-mail addresses