[rtcweb] NAT behavior heuristics

["Dan Wing" <[e-mail]>]

In today's RTCWEB meeting I said that NAT heuristics do not work reliably,
especially if a NAT is busy (high CPU or lots of ports consumed), but there
are other situations with a NAT that cause heuristics to be inaccurate.  The
IETF document regarding this is http://tools.ietf.org/html/rfc5780, and be
sure to read its Applicability Statement in Section 1,
http://tools.ietf.org/html/rfc5780#section-1.

An explicit protocol, such Port Control Protocol (PCP, draft-ietf-pcp-base)
is the only reliable way to communicate with a NAT and reduce application
keepalive traffic.  Several of us have noticed the need to document exactly
how PCP can be reliably used to reduce UDP keepalive traffic.  We will write
down those details before the next IETF, probably in an Internet Draft.

-d