TCP/IP (Transmission Control Protocol / Internet Protocol) : The Protocol That Made the Internet Possible. By Albert Kalim (lecture materials quoted by permission from Dr. Debby Keen, last updated on April 27, 2005). For more information, please visit http://www.cs.uky.edu/~akali2

What is a protocol? Set of rules that tell computers how to talk to each other how to error check, how fast to send, how much to send, how to indicate done talking, start talking. For example: A telephone conversation: how do you know someone wants to talk to you on the phone - it rings then what do you do? pick it up and say something then what? be quiet and listen for response then what? talk and be quiet by turns then what? say goodbye and hang up. Every computer on the Internet knows how to speak TCP/IP.

Packets Every piece of data, even short email, must be broken up into pieces and set off from source computer to destination computer. Does it go there directly, through one continuous wire? No, it jumps from computer to computer to computer... through backbone, big wires, small ones. Routing - not all packets go through same machines - one of the original reasons for having the Internet - "self-healing" - if a machine breaks down, gets turned off, gets too busy, then routers work around to less traveled routes.

Packets (continued) All packets are numbered and labeled so they can get put back together when they get to the other end. Every packet must have an originating address label and a destination address label IP numbers. For example, 255.225.225.255 (0-255 are valid values) are the "address labels" - unique for each machine on the Net. Has to be unique, otherwise how would packets get delivered to right place?

Problems with IP Numbers There are not enough IP numbers to go around! (just like not enough phone numbers in the 606 area code a few years ago - that's why we have 859 as area code now). A short term solution: -Dynamic versus static IP numbers: Your ISP assigns your machine a number when you log in, use as long as you're on, then someone else gets it when you log off - and you may or may not get it again tomorrow when you're logged on -> stretches the supply. A long term solution - Internet 2 - bigger IP numbers.

Domain IP numbers are ugly! hard to remember! Solution: Domain names -Easy to remember names that must be translated into the IP numbers - they are STILL there, just behind the scenes.

Domain Names Top-level domain names In the 1980s, seven domain names (.com, .edu, .gov, .int, .mil, .net, and .org) were created. Domain names may be registered in three of these (.com, .net, and .org)  without restriction; the other four have limited purposes. New ones proposed .pro = professional .biz .name etc.

Domain Name Servers Every ISP has to have domain name servers - machines with databases of domain names and corresponding IP numbers  kept up-to -date daily or even more quickly does translation back and forth between names and numbers.

Registrars Who controls the domain name database? -Used to be Network Solutions - computer company in Virginia. -Agreed to act as "registrar" - you sent in your $50 and your domain name and if noone else had it, you got it for a year or two, keep it registered and it's yours. -Network Solutions kept master domain name database, sent copies of it to other machines on the Net, who copied it, etc.  Could take a week or more before your registration was spread around the world, so you could use your domain name. Now there are many companies around the world acting as registrars, run by ICANN organization.

Cybersquatting Early on Network Solutions was not careful about WHO registered a domain name - first come, first served- somebody registered Hertz - who was not affiliated with Hertz! Lawsuits followed, trademark infringement, etc. But these days the ICANN, registrars are somewhat more careful but still, if you're starting a business, one of the first things you want to do is register your domain name.