few more details about what we'll be studying what we will cover in conceptual termsthe internet can roughly be thought of as being composed of multiple functional layerslow-level networking layers mechanisms such as the tcp/ip transport mechanismwhich deal with transferring bytes between machinesbut don' care what they mean sockets the programmer' interface to the networkwhich runs on top of physical networking layers like tcp/ip and supports flexible client/server models in both ipc and networked modes higher-level protocols structured internet communication schemes such as ftp and emailwhich run on top of sockets and define message formats and standard addresses server-side web scripting application models such as cgiwhich define the structure of communication between web browsers and web serversalso run on top of socketsand support the notion of web-based programs higher-level frameworks and tools third-party systems such as djangoapp enginejythonand pyjamaswhich leverage sockets and communication protocolstoobut address specific techniques or larger problem domains this book covers the middle three tiers in this list--socketsthe internet protocols that run on themand the cgi model of web-based conversations what we learn here will also apply to more specific toolkits in the last tier abovebecause they are all ultimately based upon the same internet and web fundamentals more specificallyin this and the next our main focus is on programming the second and third layerssockets and higher-level internet protocols we'll start this at the bottomlearning about the socket model of network programming sockets aren' strictly tied to internet scriptingas we saw in ' ipc examplesbut they are presented in full here because this is one of their primary roles as we'll seemost of what happens on the internet happens through socketswhether you notice or not after introducing socketsthe next two make their way up to python' clientside interfaces to higher-level protocols--things like email and ftp transferswhich run on top of sockets it turns out that lot can be done with python on the client aloneand and will sample the flavor of python client-side scripting finallythe last two in this part of the book then move on to present server-side "tune inlog onand drop out