Ping Open Port (+pop)
=====================

This is a popular name/value pair to send on any Telex that is a request to negotiate/open a direct connection.

The value is a URI specifying the protocol for the direct connection and the IP:PORT to ping open.  For Switches dialing each other they use "th:1.2.3.4:5678" as the value.

(need to explain how to use it to negotiate direct connections, for RTP, tcp-over-udp tunnel, etc)

See NATs for an example how it's used.