In a presentation by Dave Thaler he illustrated the negative effects of energy consumption of keep alive messages that have to be sent regularly to keep state at middleboxes (NATs and firewalls) alive.
He concluded that the PCP protocol will solve this issue and asks for market adoption of it.
This reminds me to the work I have done on Next Steps in Signaling (NSIS) NAT & Firewall signaling. The specification can be found here and implementations are available as well, for example from Goettingen University. A paper can be found here.
The NSIS work did not got deployed. Let’s see whether the PCP will do better…