Re: [Sipwitch-devel] SIPWitch P2P

[David Sugar]

First, sipwitch makes sure all media paths are direct peer to peer.  There is
no local processing of media.  Each user agent rtp stream is sent directly
to the destination user agent.

Of course, sipwitch can be deployed as a central server on a public ip
address, but it can also be deployed locally and has very low resource usage.
Sipwitch can call other sipwitch (or other sip instances) whether to federate
or contact external services by uri whether locally or on an external sip
server.  Hence, if you run a local sipwitch, say on your desktop, and a local
client (or local clients) connected to it, you can call a remote user in the
same configuration, without requiring an external mediating party, assuming no
other network complexity (such as NAT...).  Each end user has their own
service and routing locally in this scenario.  In that respect, sipwitch
running locally on a desktop (or cell phone) along with a local user agent
would be what most people would like to think of as GFC.  Indeed, there has
been thought about making sipwitch itself also buildable as a kind of
"library" that can be built directly into a stand-alone gfc user agent, as
well as the more normal use as a daemon service.

The mechanics for this are potentially clear and simple in ipv6, assuming a
world where all ipv6 addresses and endpoints are truly reachable.  In ipv4, of
course, this immediately imposes a lot of NAT issues for almost everyone. Some
of them can be resolved by each user doing port forwarding, or, perhaps, for
example running sipwitch on the local gateway, such as potentially on a
linksys with openwrt, where it has direct access to a real public ip address.
This possibility had a lot to do with the design of auto-detecting subnet
layout in sipwitch.

Sipwitch is also experimenting with a (asymetric) l-nat rtp proxy, to kick
port forwarded media ports out to local user agents behind the NAT, but this
code is still experimental and broken.  It also would assume that sipwitch
either is already on a gateway router, or that known a range of ports are
port forwarded to it behind a NAT, neither of which I agree is that easy for
most users to arrange.  In the peer-to-peer scenario we want to achieve,
sipwitch simply mediates all sip services and connections locally for each
user, and local users simply connect through sipwitch to another sipwitch peer
that mediates that destination users sip services locally too.

liang wrote:

> Hi??
> 
>          Mr sugar, somebody doubt that SIPWitch can??t achieve P2P as Skype,
> isn??t it?If is not, How SIPWitch make it? Thanks!!
>