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The basic means by which the Internet functions is called packet switching italic . Let say you need to send a long message somewhere. There are two main methods doing so electronically. The first older method is via a circuit italic . That is you have a physical between the two ends such that whatever is input at one end is output at the other. For example phones and telegraphs used to work that way. When you made a phone call you pick up your phone. It was ed through a wire to a switchboard italic . When you took your phone off the hook a light woulde on at the switchboard. This would tell the human operator you wanted to make a call. The operator would connect her (the vast majority of operators were women) headset to your wire and ask who you wanted to speak to. Once you told her she would use a device that would send an impulse down the wire to the other person phone making the bell in it ring. She could then plug a wire into each of your circuits making them into a single circuit so you could talk to each other. For a long-distance call multiple operators would be involved. Each would pass the connection on to another operator who would make a new connection to another point along the way until eventually your circuit would be connected to the circuit of someone else telephone potentially hundreds of miles away and you could talk to them. Of course for the entire duration of your conversation all those lines would have to stay connected to each other. Later machines were developed that could route calls automatically. You would dial a number which would send a series of pulses or tones down the line. The automated switchboard (or simply switch) at the other end would receive those pulses then route your call based on them. For example you might dial 1381355533721. The 1 would tell the switchboard that you were going to make a long distance call. The 81 would be the number assigned to an area code italic and the switch would connect you to another switch which handled that area. The 555 would signify an exchange italic a local switch handling a few thousand subscribers and you would be connected to it. Finally the 3721 would be a subscriber number in that exchange and you would be connected to their phone line. Then the proper signals to make the phone on the other end ring would be generated. Still however you needed a continuous connection. Different areas and different exchanges had differing numbers of lines available. If there wasn a line available somewhere along the way you would get a busy signal. There were two different busy signals in the US one signifying that the long-distance connection could not be made and a different one signifying that the long-distance connection had been made but the subscriber line on the other end was already in use. Some areas had what were called party lines where phones in several different homes shared a line. If you picked up your phone in such an area when someone else was using theirs you hear their conversation since your phone was also hooked into the line! This was mostmon in rural areas and became lessmon over time. When my family lived on a farm in the 198s we were on a party line. At times it was quite inconvenient. That leads us to the kind ofmunication the Internet uses packet switching. Many earlyputer networks were a lot like the party line mentioned before all theputers on the network were physically hooked to one line. When oneputer sent data all the others could hear it. So how do you get anymunication done in that case? By dividingmunications up into chunks! Imagine our party line again. Let say the neighborhood has had problems with people hogging the line and so they make an agreement no one gets to use the line for more than five minutes at a time. If you pick up the line and hear someone talking you should hang the phone up for a minute then pick it up and try again. If youre the one one the phone then after five minutes of talking you have to take a one-minute break. That way if someone else is waiting they should pick up the phone before you do and get to talk. This is similar to how earlierputer networks worked. Of course sinceputers are much faster than humans the chunks of time were much smaller. And instead of measuring actual time the designers decided to limit by amounts of data. The data sent at once is called a packet italic and the maximum length of the data the packet size italic . There were some changes though. For example on earlyputer networks privacy wasn much of a concern. So on many networks instead of trying to figure out a way for oneputer to ring another to signal that they wanted to start talking all theputers would listen all the time. Each one was assigned a numeric address and there was a standard pattern to start a packet. When aputer heard the start-of-packet pattern it would listen to see if the next thing was its address. If it was it would listen to the rest of the packet. If it wasn then it would ignore everything until it heard the start-of-packet pattern again. This kind ofmunication created a local network allowing theputers all hooked to the wire to talk. However there were problems with this. First electrical signals fade over distance. If the wire was too longputers at the far ends wouldn be able to hear each other. Second if too manyputers were attached all trying to talk frequently the line would be busy all the time and the time between a particularputer being able to send one packet and the next would be very long. The distance problem could be solved with a repeater italic . This is just a device that has two or more network wires attached to it. When it receives something on one wire it sends it out on the others but it boosts the signal as it does. Of course this would only make the second problem worse since it would let you attach moreputers to a single line. So the next stage was to put anotherputer in the middle. Aputer joining multiple networks could listen to each one and could be programmed to know which addresses were on which network. When it heard a packete in on a line and knew that the destination was on that same line it wouldn pass it on. If it knew the destination was on a different line though it would send that packet out on that italic line. This meant that you no longer had everyone hearing everyone else messages it was like a switchboard joining several party lines. Of course once you could hook multiple networks together like this people started wanting to create even bigger italic networks by ing their networks together. By this time there were several different standards for networking. Some of them worked similarly to the way Ive been describing (though not exactly that way this is simplified). Others worked in other ways though for example in some networks eachputer had two lines it was connected to and messages only came in one line and went out the other. Theputers were ed in a ring so that a message would eventually get around to all theputers with each one that it wasn for just passing it on. In order to up different kinds of networks it was necessary to create a standard they could all follow. People at the ARPA came out with what they called Internet Protocol or IP because it was meant to different networks together. An IP packet could be encapsulated inside another packet that is it would be sent as data inside whatever the local packet was. The receivingputer would see that it was an IP packet and would know it needed to look at the headers to find out about the actual data inside. There have been a lot more technological improvements since then but all modernputer networks and especially the Internet work through this mechanism of packet switchingputer send out data in packets and otherputers look at the packets forwarding them on toward their destination until they finally reach it. With packet switching many messages share the same line by each only using it for a short time. Modern networks are often what called full duplex italic able to both send and receive at the same time (basically bybining separate sending and receiving wires into one cable). With memory in them theputers that handle passing the packets along (called routers italic and switches italic ) can hold a packet while waiting for a chance to send it. Of course ifmunication takes too long the memory might fill up. Thus modern networking protocols have ways to signal that a packet needs to be re-sent. Senders can also automatically re-send packets if they don get a response after too long and modern protocols have ways to mark the order of a packet. In a lot of ways modern packet-switched networks are like a postal system. Imagine each packet as an envelope full of data (with envelopes being a limited size) and the switches and routers as post offices handling the envelope along the way and you won be far off. Different protocols are then different ways of marking your envelope and of formatting the contents. Just as different offices might use different standard forms the protocols provide ways of structuring data that needs to be sent for different purposes.