The Protocol Stack

I said earlier that the Internet is not a single protocol. Rather, it's a suite of protocols. In this one HTTP request, several protocols get used. You can think of it as a stack of protocols. In the example of the World Wide Web, the stack would be this:

HTTP

TCP

IP

At the bottom of the stack is the Internet Protocol, and this handles all the low-level activity involved in finding other computers on the network and getting them routed there. The actual format of the data sent and how the two machines communicate after they are connected is handled by the Transmission Control Protocol (TCP). It has the rather narrow scope of breaking the data into packets, sending the packets to the other machine, and making sure they all arrive where they are supposed to, in the correct order. Finally, at the top of the stack is the Hypertext Transfer Protocol, which takes all those packets that have been sent and responds based on the content of those packets.

This particular stack of protocols is not the only stack that is used on the Internet. You can take a step back and look at this from a higher level of abstraction and think of each row as a layer that performs a generic function (OSI stuff). If I were to do that, this is where each item in the stack corresponds to the OSI layers.

REALbasic provides several networking classes that work on different aspects of the layer. The following hierarchy shows the class hierarchy and what part of the suite of Internet protocols the class works with.