Is there a high-level overview of Linux code for programmers online?

Is there a high-level overview of Linux code for programmers online (any common distro with a leaning toward a Ubuntu-based one)? I'd like to do some reading from my browser (under MS Windows). For example, the first thing I want to understand is where the network stack files are-specifically the code that assembles IP packets for transmission and disassembles IP packets after receiving them-and where they hook into the rest of the OS? Another example: What does the kernel code handle vs. what does it not handle but is still necessary for a minimal Linux install.