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All About Networking • Devices • Packet Transfer • Hardware • Software • Wiring/Cabling • Protocols • And much much more!

What is a Network?

What is a Network? Lots and Lots of wire. To get information from one machine to another we must connect a wire between them. One machine talks while the other listens, and vice-versa.

Sharing the wire. Instead of running a wire from every machine to all the other machines we share a single wire amongst them. One machine talks while all the others listen.

Taking turns. All machines agree to only use the wire for a short burst of information (a packet) and then let someone else have a chance. This agreement on how to pass information on the wire is called a protocol.

Collision. If two machines start to talk on the wire at the same time, no one can understand what they said. We call it a collision.

Collision (cont.) Both machines can tell that they interrupted each other so they “back off” for a small amount of time and try again.

Too much information! Lets say we have ten machines sharing a wire and they can talk for 1/100th of a second for each packet. If everyone is talking then they can say something every 1/10th of a second. Not a problem.

Too much information (cont.) But what happens when you have 1000 machines on a wire? They can only talk every 10 seconds! Not good!

Too much information! (cont) To keep down the amount of talking on a wire we separate wires with routers. The router listens to all the packets on one wire and passes on only the packets destined for someone on the other wire. Router

Routers Routers are used to connect two or more networks together to logically form a bigger network. Internet Cloud

How far away is it? When a packet of information goes from one network to another it “hops” through the router. We use hops to tell distance. http://www.monitis.com/traceroute/ C A B

What is in a packet? TCP/IP Protocol: • DESTINATION IP ADDRESS • ORIGINATING IP ADDRESS • HOP COUNT • SIZE • CHECKSUM • DATA

So what is the Internet?

So what is the Internet? A network of millions of networks with billions of devices. Nobody really knows!

IP Address. Each device on a network has a unique address to tell it apart from all the other machines. For the TCP/IP protocol the address is four numbers separated by periods (130.86.90.1). Even coke machines and coffee pots can have addresses! http://whatismyipaddress.com/ Do 255 activity. Have them calculate how many bits in the TCP/IP address.

Domain Name Service The phonebook of TCP/IP. We like to use names instead of numbers. The DNS keeps a record of host names and numbers. Let's use Mxtoolbox.com/DNSLookup.aspx to try a few examples. URL: Let’s compare to your postal address. www.csus.edu 130.86.9.189 Domain Name Server Do some reverse lookups of favorite web pages. Talk about URL and parse it out.

How it works LOGICALLY We have looked at how things interconnect at a physical level. Wires, routers, packets. Once everything is connected physically we can setup networks into a logical space to make things easy to use. No matter where in the world a machine is connected, we can talk to it.

HOST or CLIENT Any machine connected to a network, from simple desktop machines to giant mainframes with thousands of users. Marvin Minsky.

SERVER. A host that provides a network service. Services can be e-mail systems, document archives, web sites. A program runs on a server to allow CLIENTS to connect and make requests. You might create a web site on your computer but you transfer it to a server and people access it from the server! This is important because we have to understand the difference between WHERE we create and WHERE our server exists!

So what is the World Wide Web?

So what is the World Wide Web? A specific protocol allowing communication via text, images, video, audio, etc. The World Wide Web is NOT the Internet. Imagine the Internet is just infrastructure to allow all forms of transportation. The WWW is just a specific type of transportation, like the rail system. Text, images, sound, etc. are just hitching a ride on the trains on the railway. Let’s take a break and then learn some HTML or Hypertext Markup Language.

What is a Web Site? 26

What is a Web Page? 27

What is a Homepage? 28