What is the "SDK vs. 'bits on the wire'" debate about?

Question

There appears to be some debate about "the divide is between wanting an SDK and wanting to know the underlying protocol" (see http://www.tbray.org/ongoing/When/199x/1999/08/18/BitsOnTheWire).

I don't really understand what this is referring to, or why they are mutually exclusive.

What is the philosophy of each approach and why do they conflict?

Answer 1

Suppose client C needs to talk to service S provided by vendor V. If all you have is an SDK, then you must install vendor V's SDK software on the client C in order to talk to S. On the other hand, if vendor V documents exactly how to talk to service S down to the bit level, then you can write your own software on client C to talk directly to service S.