[asterisk-biz] Experimental/new VoIP rate search engine.

[Alex Balashov]

Nitzan Kon wrote:
> --- On Mon, 1/5/09, Alex Balashov <abalashov at evaristesys.com> wrote:
> 
>> I'd just drop the carrier if I were you.
> 
> That has crossed my mind more than once. ;) Their quality is
> great though other than this problem so I go back and forth
> on this one.
> 
>> 1. Do you have this problem with other carriers?   To the
>> same degree?
> 
> Nope. This happens only with this carrier.
> 
>> 2. What happens when you do proxy the media and use that as
>> your accounting basis;  does your billing reconcile with this
>> carrier almost perfectly?
> 
> We proxy almost all media because most of our users are behind
> NAT so it wouldn't make sense not to do so. 

Well, I hate to open up what seems to be a particularly contentious can 
of worms, but, you actually probably don't need to be proxying media for 
most of these users.  :-)  Just because they're behind NAT doesn't mean 
they can't reach each other.

Here's the canned answer from our VoIP FAQ:

---

"Q: Do I have to use a media proxy with Kamailio/OpenSIPS for a far-end 
NAT traversal solution?"

"A: Not necessarily, although it may be desirable in various cases for 
reasons having to do with accounting or topology hiding.

Use of a media proxy is strictly necessary only in cases where there is 
no logical network-layer reachability between the media endpoints of a 
SIP session. An example would be media passing between a public and a 
private (RFC1918) address space with no NAT on the private side, and a 
SIP proxy that is connected to both; there is no way for the public 
endpoint to address the private endpoint.

NAT-traversal fixups revolve around substituting received IP and port 
information (Layer 3 & 4) in place of that provided by the endpoints 
themselves. If the endpoints can reach each other at the rewritten 
coordinates, there is no reason to proxy the media."

---

Of course, this will break for a certain percentage of users who have 
NAT gateways or UACs that just don't get it.

-- Alex

-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : (+1) (678) 954-0670
Direct : (+1) (678) 954-0671
Mobile : (+1) (678) 237-1775