[p2p-sip] NATs and P2P

[philip_matthews at magma.ca (Philip Matthews)]

[I guess all this traffic on the mailing list will teach me not to go  
on vacation
just before an IETF meeting!]

As I catch up on all the messages about NATs over the past two weeks,
it seems to me that many people are thinking only of the "Public P2P  
Service Provider"
use-case as described in the use-cases document. In other words, a Skype
competitor.

However, the use-cases document that David Bryan and his co-authors  
wrote
identified a number of other use-cases and it seems to me that these  
have somewhat
different NAT traversal requirements.

In particular, in some of these other use-cases, it seems to me that  
we CANNOT assume
there are peers with public IP addresses.

For example, consider the "Presence using Multimedia Consumer  
Electronics Devices"
use-case (section 3.1.3) -- essentially a P2P network of multimedia  
consumer electronics devices
that need presence information. Who is going to pay the extra money  
to give their digital camera (or those
neat 770 tablets that Nokia is demoing here in Dallas?) a public IPv4  
address?? On the contrary,
devices like this are almost certainly going to have private IP  
addresses -- it is very common today for
wireless internet providers to place a big NAT in front of their  
entire network and give private addresses
to all their customers.

Or consider the "IP PBX" use-case -- a IP PBX system for a company  
with a number of small branches
scattered throughout the world. Each branch is going to have a NAT in  
front of its network, and all
the phones in that branch are going to have private IP addresses.  
None of the phones are going to
have public IP addresses.

It is handling the NAT traversal issues for use-cases like these that  
Eric Cooper and I wrote our
internet-draft on NAT Traversal for P2P:
       http://www.ietf.org/internet-drafts/draft-matthews-p2psip-nats- 
and-overlays-00.txt

- Philip