gen-art-33

- "The AP sends the response…" -> "The AP MUST send the response…".
- "…can directly connect…" -> "MAY directly connect".
- "it can still populate" -> "it MAY still populate".
- Reworded the Ping description with normative language.
- "JP simply sends" -> "JP MUST send".

Closes #164
Merge pull request #71 from deanwillis/gen-art-33

gen-art-33