This is meant to be a conceptual discussion of how networks work. It is intended for the neophyte and it to be used as a spring board for other conversations. 1) What is a network? For the sake of this document a network is two or more computers that can talk to each other. 2) How do computers talk to each other. There are many many many ways to have computers talk to each other. Most of them boil down to glorified version of the children's toy of a telephone made of two cups and a string. For this document we will focus on these methods: a) Modem - The modem itself is a device inside the computer. You can plug a phone line into the modem. Much like the toy telephone, a modem is a "cup", the phone line is the string. The phone system is also like the string. Here's an example: Plugged into a computer is a modem, plugged into the modem is the phone wire, the phone wire connects to the phone system, and on the other end of the phone system is a phone cable that plugs into another modem, plugged into another computer. With a setup like that the two computers can talk. b) Ethernet - Ethernet is many things, but when people say "Ethernet" they usually mean "Ethernet cable". The physical medium a computer can communicate with another computer. What's important to focus on is that Ethernet is just the cable connecting computers. This is the string in the child's toy telephone. Just like the modem has the phone system, Ethernet has a complicated string part too. It is the Internet. The Internet acts like "string" for Ethernet. Here's an example: Plugged into a computer is an Ethernet card, plugged into the card is Ethernet. The Ethernet connects to the Internet, and on the other end of the Internet are many cables that plug into other Ethernet cards, each plugged into another computer. c) DSL and cable modem DSL and cable are both part of the "string" they take Ethernet from your computer and send it to the Internet. DSL uses phone company technology and cables, and cable modem uses cable company technology and cables. 3) What's the difference between the two? The astute reader will have noticed that a computer connected to a modem can only talk to one other computer. Just like making a phone call, (conference calls excluded) it is a one to one relationship. With Ethernet one computer can talk to many other computers at the same time. The other difference is that Ethernet has much higher bandwidth and lower latencies. 4) What is bandwidth and latency? Latency is the amount of time it takes a computer to contact one computer and get a response. Bandwidth is how much data you can jam down the pipe. Here's an example: A boy fetches water. The amount of time it takes him to go to the well and back is latency, The amount of water he brings back is bandwidth. For some real world numbers on bandwidth. A modem's best bandwidth AFAIK is about 90KB/sec. Ethernet gets 11264 KB/sec. I don't have latency numbers right now. So modem boy goes to the river and brings back one bucket. Ethernet boy brings back 125 buckets in less time. 5) What is the Internet... really? There are many different ideas of the Internet. You can view it as a business, or as a way of life, or as a porn delivery system. At it's core though the Internet is just a bunch of computers connected together. 6) What do I need to connect to the Internet? As of now, you don't need much. You need a computer, a connection (modem, or Ethernet) and an IP address. 7) Whoa! What the hell is an IP address? An Internet Protocol Address or IP Address is best explained with an analogy. In the world today, every house has an address. The address should be unique. This way the postal mailman can find all the right destination for sent mail. All mail should have a return address so the receiver can find the sender. Think of every computer as a house. A house usually has one address. When one computer wants to talk to another it needs that computer's address. It also needs its own address. Once it has both it sends its message. In computer jargon a message between computers is often called a packet. IP addresses are four dotted decimals. None higher than 255. None lower than one. Here is an example: 172.30.24.254 8) I just type www.yahoo.com to find the yahoo computer. What is this IP address stuff? These dotted numbers are a pain to remember. And sometimes people want to move their program from one computer to another, but not force people to switch their address. So there is a system called Domain Name Service, or DNS. This service is in charge of mapping names to IP addresses. Every time you try to use a name instead of an IP address (which is almost all the time) the computer asks a special computer on the Internet called a Domain Server if it knows the IP. If it does the computer uses the IP to connect. Like magic! Right now www.yahoo.com is really 66.218.71.89. If you went to your web browser and typed http://66.218.71.89, you should get to yahoo.com. 9) So I shelled out the money, I got a computer. I got an Internet connection how do I get my IP? Just like houses IP addresses are given out by one organization. This way we prevent duplicates which would break the whole system. Organizations purchase, borrow, or steal blocks of IP addresses on the net. They then allocate the IP addresses as they see fit. When you join an Internet Service Provider, DSL, modem-based or cable service they give you an IP address. 10) How do ISP's manage their IP addresses? Their are two types of IP addresses. Static and Dynamic. Static: This is easy. The ISP tells you your IP. You type it into your computer, and you computer has that address forever. Dynamic: This is harder to understand but easier to manage. Let's say a ISP has 500 users but only 200 of them ever log on at once. Instead of buying 500 IP addresses they only need 200. You can configure your computer to handle this. When it boots, your computer will ask the network "Does anyone have an IP address for me?" The ISP can setup up computers to say "Yes I do! This is one that is not used now. Take 55.44.33.22". Every time you boot your computer you get a new IP. 11) Which is better static or dynamic? It depends what you want. If you are just browsing the net and not offering any services (like a website). Dynamic is cool. It might be preferred too since hackers would find it hard to find your computer twice. The address keeps switching. If you want a website you need static. Otherwise no one would know how to find your machine. It's address would keep changing. 12) Isn't dynamic IP addresses just DHCP? Dynamic Host Configuration Protocol, or DHCP, is often confused with dynamic IP addresses. This is because they are closely related. If your computer is configured for DHCP it will boot and ask "Any DHCP computers got any info for me?" This way it can find more than its IP, it can also obtain DNS servers, and all other information it needs to talk to the Internet. In shorter words: DHCP computers can be plugged into any network with DHCP servers and immediately talk to the Internet with NO WORK from the user. 13) What's a hub or a router or a switch? Kinda off topic but I will tell you. +--------------------------------------+ | Hub | +--------------------------------------+ | | | | | | | | | [ computer A ] [ computer B ] [ computer C ] Above is a Hub. It connects three computers. Instead of plugging them into each other you can put a hub in between them. Then each computer can talk to the other two. On a hub nothing is secret. If Computer A sends a message to Computer B, Computer C sees it too. Computer C probably checks the address, sees the message is for B and ignores it to no ill effect. +--------------------------------------+ | Router/Switch | +--------------------------------------+ | | | | | | | | | [ computer A ] [ computer B ] [ computer C ] With a router or switch the traffic is tightly controlled. Messages from A to B only go to B. We can also play some cool games with this control. 14) What is NAT? Network Address Translation is a cool trick. It is designed to save on IP addresses. Let's say your ISP gives you one IP address for the whole house. But you have two computers. Can they SHARE that IP address? Yeah! Internet | | +--------------------------------------+ | 192.34.56.98 | +--------------------------------------+ | | | | | | | | | [ 1.1.1.1 ] [ 2.2.2.2 ] [ 3.3.3.3 ] So here we have three boxes talking to a router. It has the IP address 192.34.56.98. The computers in the house are given the IP addresses listed above. The magic of using NAT is that the Internet sees all the messages coming from all three computers as having the same IP address, and when messages come back from the Internet the router knows which one goes to which computer. 15) Can I do NAT with DHCP? Doubly yes! If your ISP only gives out dynamic IP addresses, you can configure your router to find out its address when it turns on from the ISP's network. You can also set up your router as a DHCP server. So when the other computers in the house get turned on the router tells them their address to be used inside the home network. 16) How does a firewall work? There are many ways to implement a firewall but the logical idea is shown below. Internet | | +------------+ | Firewall | +------------+ | | +--------------------------------------+ | 192.34.56.98 | +--------------------------------------+ | | | | | | | | | [ 1.1.1.1 ] [ 2.2.2.2 ] [ 3.3.3.3 ] Network security is a BIIIIG topic. I am going to just touch on it here with what I believe is a standard way to use a firewall. Computers are very playful. Most are ready to accept almost any type of packet. Getting the computer itself to stop accepting packets is difficult. So one good way is to stop the packets at the source. A firewall will let packets go out to the Internet, but prevent any packets that have not been asked for. It is a good way to keep hackers out. 17) Wireless? Is it hard? Nahhhhh... Nothing is hard. Officially the first commerical version is called 802.11b. This is the number given to the protocol by IEEE. All the 802s are different ways of sending packets through different physical mediums. For those curious, Ethernet is 802.3. There is one that uses carrier pigeons. So just like Ethernet, you get a card that fits into your computer. Except there is no plug for a cable. Through magic the card talks to a Wireless Access Point, or WAP. This is just a box that can hear wireless and speak Ethernet. It is a bridge between the wireless traffic and the Ethernet traffic. There is also a wirelless version that came about after 802.11b called 802.11a. It was an attempt at getting 802.11b to work faster. It worked alright but it got pushed aside by a newer version of wireless called 802.11g. 802.11g acts much like 802.11b, except it has higher performance. Unfortunately it cannot work over distances as long as 802.11b. 802.11b is often called a "B network" and 802.11g is often called a "G network". While G is 5 times faster than B, it doesn't make that much of a difference if you are just surfing the net. 18) How do modems work? They work just like NAT. When your computer connects via modem, it dials a number connected to your ISP's computer's modem. This computer works like a router. It is connected to the Internet. It gives your computer an IP address for internal use, and lets you surf then et using its IP address.