Transcript TCP/IP: Transmission Control Protocol / Internet Protocol

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 - "selfhealing" - 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.