Protocols – Intro to Computer Science


And what we need to make a network work is a Protocol. And what a protocol is, a set of rules that people agree to, that tell you how two entities can talk to each other. So, for the web, the protocol gives rules about how a client and a server talk to each other. The client is the web browser and the server, is the web server. So that might be udacity dot com. The web browser is what you’re running at home. And what the protocol says is, if you want to get the server to do something, the client has to send a message in a particular way. The protocol that we use on the web, is called hypertext transfer proto, protocol. Which is abbreviated as HTTP. When you look in your browser, almost all the URLs that you use start with HTTP. That indicates that the protocol, that you should use to talk to the sever, that you’re requesting a document from, is this protocol, called hyper text transfer protocol. An it’s a very simple protocol. There aren’t, too many messages. There’s actually only two main messages and there is only one, we’ll talk about. That’s the message called GET. The client can send a message to the server, where the message says get, and then the name of that object that you want to get. So that’s all the client does. It sense the message like this, and if you remember the python code for get page. Well, let’s call in some library function that actually does this. That’s sending the get message to the server. The server will get that message. It will do some, run some code on it. It will find a file that was requested. It might run some more code to get the result. Take the web application course to understand more about what the server does, but what matters to the client, and what matters to us in using this, is what happens after that. The server sends back a response, which is the contents of the requested object. So that’s the whole protocol, that’s what’s going on whether you send a web request using your browser, by clicking on a link. Well then the browsers doing a lot of things to figure out what you requested and then its sending a get message to the right web server. That was the server specified by the URL, to know which server it is, and then its getting a response and its doing processing on that response to render it. If you want to understand more about what the web browser is doing, take the programming languages class that focuses on how to build a web browser.

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