Getting Started with Zfone. What is Zfone?
<<<...Here are the known issues in this version of Zfone.
Some VoIP clients attempt to traverse NAT routers by sending RTP voice and video packets through TCP instead of UDP. This protocol tunneling violates the IETF standards for VoIP, which require that RTP media packets be sent over UDP. Zfone assumes that RTP will be found only in UDP packets, and thus will not detect RTP sent through TCP. In that case, Zfone's GUI displays the "Idle" status during a call, and does not engage the ZRTP protocol. Sometimes the packets are going through a media relay which converts them to UDP for the other party, whose Zfone client can therefore see the media stream, but searches in vain for the idled ZRTP peer and displays the "NOT Secure / No ZRTP Peer" status. If this happens, here are a couple of workarounds: 1) The best solution is to move one of the parties' computers (in particular, the one that displays IDLE) off their local network to an external IP address, thereby simplifying the NAT traversal problem. Even better, move both computers to external IP addresses. 2) Or it might help to switch one of the parties (especially the IDLE one) to a different VoIP client. Often the VoIP client software decides to straighten up and follow the standards when talking to a VoIP client from another vendor. Any form of protocol tunneling will subvert Zfone's RTP detection mechanism. In fact, most protocol tunneling is done to defeat various packet filtering mechanisms, such as firewalls. This does not indicate a problem with the ZRTP protocol. It's related to trying to run the ZRTP protocol as a packet filter in the IP stack, as Zfone does. It's a problem that would go away completely if the ZRTP protocol were integrated inside a VoIP client, for example by using our Zfone SDK. We are working on improvements in Zfone's SIP/RTP detection logic. Max OS X users may find that Zfone interferes with their ability to turn their OS X built-in firewall on or off...