[nhellman]

Heh, what a coincidence!

Does XSP stand for anything?

[dinartem]

Xbox Security Protocol. We liked to add X to things back then.

[CYR1X]

Since you branded it, did you use it in any other games by chance?

[monocasa]

What they're talking about is the base protocol for all Xbox system link and Xbox live games.

AFAIK, it persists to this day, extended with newer features (and crypto primitives).