How to understand network protocols?

Question

I work in web development, but I don\'t have a great understanding of network protocols. I recall hearing an analogy that TCP, HTTP, and SSL can be thought of as a series of

Answer 1

There's a reason you'll often hear of TCP/IP implementations called a "stack". Part of the concept is that you have a low-level protocol (Ethernet, PPP, what-have-you), slightly higher-level protocols built on top of it (IP), and so on. It's quite similar to the OSI model, and can be described in terms of that model, though TCP/IP breaks up the layers just a bit differently. Anyway, programs generally send data using one of the upper-level protocols, and let the TCP/IP stack handle the details of getting the data from point A to point B.

TCP sits on top of IP and lets you think of the data flowing in and out as a pair of streams (one in, one out) rather than getting raw IP packets and having to figure out what to do with them. (Big BIG benefit: it simplifies multiplexing. Without TCP or UDP or the like, IP would be near useless -- only one program could normally communicate with the network at a given time.)

SSL sits on top of TCP, and lets you send data over the stream that TCP provides without having to get involved in the ugly details of encrypting and decrypting data, verifying certificates, etc.

HTTP sits on top of TCP (or SSL, in the case of HTTPS), and provides a way for a client and server to pass entire requests and responses, along with metadata describing them.