at:
http://people.freebsd.org/~julian/layer2b.pdf
I'm going to do one for RELENG_4 by add in the bits added,
and then, the big task..
one for -current
BTW there is also one for the variant of 4.10 I am using at work..
http://people.freebsd.org/~julian/layer2c.pdf
but it's probably not of general interest.