Last week, there were some new I-Ds on p2p-sip.
The draft analyzes various issues with NAT in the context of P2P-SIP and presents some important conclusions: (1) partial mesh of peers is more suited than ring or full mesh connections, for example; (2) connections can remain mostly static for maintenance of p2p; (3) structured p2p is more suited because of bounded connection count; (4) symmetric P2P (such as Kademlia?) is more suited because the connections across NAT are bidirectional; and (5) use of superpeers where all peers behind a common NAT can elect a small number of superpeers which handle connections across the NAT. The basic idea is to understand the NAT limitations such as number of pinholes allowed and timeout, and apply these for a deployable architecture.
The basic idea is to use the SIP-using-P2P architecture. There is some overlap with my 'external DHT' technical report. Some points of contentions are: the draft proposes P2P lookup first, and then fall back to DNS (RFC3263) which has a negative effect on performance since P2P lookup is slower. The format of the record can reuse the SIP Contact header instead of specifying individual terms such as TCP80, UDP5060, etc. The login server is clearly undesirable. But the draft is a good starting point. We will need more maturity in areas of security, authentication, and data format.
It proposes to use telephone numbers instead of email like user@domain format because one can validate that the number owner actually owns the telephone. The main problem is that phone numbers are too rigid and tied to physical port or line, thus we cannot have identifiers for virtual users or devices, e.g., sip:email@example.com belongs to an electric X10 controlled lamp in our lab. Secondly, phone numbers are hard to remember, thus needs address book. Thus it doesn't make much difference whether we use phone number or email as long as we know the remote's public key. The main problem to be solved is the distribution of public key in p2p. A certificate-based approach can be used instead.
It tries to list various requirements for NAT traversal in P2P-SIP. Not much new value. Ignores some of the existing NAT traversal schemes such as ICE.
In conclusion, there are still a lot of open issues in P2P-SIP, most notably in security, authentication and NAT/firewall traversal. Any solution for P2P-SIP must reuse the SIP's NAT traversal schemes such as ICE. There is a new version of best practices draft for NAT traversal in SIP.