Overview
Conventions and Introduction
| Important! | This information is something you should pay close attention to. |
| Warning! | Be Careful! What you're about to do could damage hardware or injure you! |
| Of Note | This is a cool thing to take a look at and think about. |
| Security! | This may create a security hole if not done correctly! |
Word Highlight the Word to the left to see its definition
What is the internet?
In the broadest terms, people like to view the Internet as a cloud, you put your data in one place, it comes out the place you want it to on the other side. In reality the internet is tens of thousands kilometers of fiber optic cable, hundreds of thousands to millions of kilometers of copper wire, and hardware and software connecting them all together in a redundant, fast, and self-sufficient network. But not to worry, it's not that bad: you only have to worry about a very small portion of the network, you can let someone else worry about the rest, and you even get someone to yell at when things go wrong.
A Metaphor for the Internet
| Important! | The information from this section is reused throughout the rest of the course. |
Because the internet feels like smoke and mirrors to a lot of people, a concrete physical metaphor could be very helpful in explaining both the parts of the internet and how it all comes together. The best metaphors to use are: how good old fashion snail mail is transferred around and the network of roads crossing the country. Lets start with your house. Houses have 2 ways to describe them, they have a physical description, "My House has a red brick first floor, white siding on the second floor, a maple to it's left, and a maple in the left side of the front yard." this is a description that is fixed and (fairly) hard to change. On the internet, this would be your computers MAC Address Or you can describe it by the street address assigned to it by your City or County and the US Postal Service, as in 833 Montlieu Avenue, High Point, NC 27262.
Your Local US Postal Service is a set of buildings that route letters and packages between different post offices. Stuff goes into one Post Office and gets routed from that office, to a distribution center. The distribution center then sends it to another major distribution center and so on until it reaches the distribution center that serves the remote Post Office. It is then sent to the remote Post Office and then to the house that it needs to go to.
So, the address of your house is very much like an IP address you'd have assigned to you by who you pay to get on the internet. The streets and surrounding neighborhood you're in could be considered a local area network, where each house has it's own address, and they're all connected. The State and City or County is your ISP, most ISPs have a local branch that's for your region, which could be related to your city/county, the full ISP is the State, and the Internet is a country.
A Working Metaphor for the Internet
- House - (address vs. physical description)
- Local Streets / Neighborhood - LAN
- State, City/County - ISP, local division of ISP
- Country - Internet
- Major Roads (US routes / Bigger State Routes) - Internet Connectivity
- Highways - Internet Backbones
- Post Office - Router (GET Picture of 495/395/95)
- Intersection - Hub
- Highway Intersection (Mixing Bowl) - Switch
What is a home network?
A Home Network is all of the computers and Internet devices that you have in your home including your Internet connection. The purpose of this course.
The OSI model
So, we have an idea of how you go about thinking about the Internet, and we have some information about the difference between Local and Wide Area Networks. What we need to add quickly is a blueprint to how a network thinks about data, this is known as the OSI Model. When you try and do something network related, you start from an application. Applications are considered the top level of the network; below what you see, your application handles making your data so it is easy to transmit over the air or wire and translating that transmittable version back to useable data. The application also sets up a method of maintaining a session between you and the computer with which you are conversing.
So now the computer has the data in a transmittable form, and it needs transmit it. This is where things get a little tricky, we have a bunch of data, and we want to make sure nothing changes in it. We could just create some sort of check setup, where we send a short message with a method of checking the data, but there is a huge problem with this. If we send a really large amount of data (say a freely downloadable video game), and then try and check to see if it came through right; we can find that there is a problem but now we have to ask for the whole thing over, cause we don't know where the problem is. Also we have to wait for the entire file to transfer between the different routers and network devices across the Internet. Our solution is to have a layer below the applications, and above the internet that takes the data and turns it into segments to be sent separately with a bit of data to allow for the data to be confirmed as valid on the other side. This is the layer where TCP and UDP (defined above?) work.
Now that the packets are segmented into smaller pieces, they need to be transmitted. To do this, there is more information that each segment needs for routers to be able to transmit the information. This is where the IP address is added and the Packet Header added to the data segments. So now the data has a destination on its envelope, but it needs an initial hardware destination. Say you're sending mail to your brother (or parents?) across the country; you have an envelope, but you need to have an initial place to send the data to. This is what is encoded into the packet that you're about to send out to allow the switch (if you have one) to decide where to send the packet to get it to the Internet. The Layer where this happens is called the "Data Link Layer". Obviously, below that you need a layer of copper and fiber optic cable between your house and the destination. This is what makes up the lowest layer, or "Physical Layer".
((Graphic of OSI Model))