Kevin Schroeder has posted a new book excerpt from his "You Want to Do WHAT with PHP?" book - chapter two dealing with binary protocols.
PHP developers know text really, really well. We can write SQL, we can build HTML, we can work with XML. But computers don't speak in terms of structured text markup, they speak in terms of bytes. And while there are many PHP developers who can speak at the lower level of bytes and bits and such, there are many more that have difficulty there.
His short excerpt (from a very long chapter) talks about working with DNS information and how you can send requests (similar to the unix "host" command) and parse them correctly. Some sample code is provided to make a request for a record on mcpressonline.com and the output it would produce.