On Oct 31, 2008, at 1:05 PM, William Herrin wrote:
On Fri, Oct 31, 2008 at 11:51 AM, Scott Brim <[EMAIL PROTECTED]>
wrote:
On 10/30/08 5:34 PM, William Herrin allegedly wrote:
If you asked an audience of system administrators whether Vonage and
Skype would be impacted by fracturing the end-to-end principle with
carrier grade NAT, I'm not sure how many would correctly identify
that
Skype would be impacted but Vonage would not. I think most would
incorrectly believe that all VoIP systems would be hurt, not just
the
ones structured in a peer to peer design.
OK I'm one of them. I thought Skype had STUN-like servers in order
to
deal with NATs. CGNs will affect all such servers but it will affect
them equally. No?
Hi Scott,
Skype's primary mode of operation tries to fool the NATs on each side
into opening the port that the other side will use. Both clients
briefly communicate with a server to determine what the external UDP
source address and port is likely to be. Then the clients switch
communication to each other and hope the ports match. Behind a small
NAT with relatively little simultaneous UDP traffic, this works out
pretty well.
This sounds very much like H.460, which is wide deployment with
devices such as the
Polycom V2IU and, from my experience, works quite well even in heavily
firewalled corporate environments.
Regards
Marshall
They finally added some servers to relay calls, yes, but they're the
last-ditch fallback and I believe they're only available to paying
members though I could have that wrong. Having to provide a lot of
these relay servers and the bandwidth that goes with them would
severely disrupt Skype's business model.
With Vonage, as I understand it, the phones talk to the Vonage
servers, not directly to the other Vonage phone. Their main problem is
keeping the translation alive without wasting too much bandwidth and
dealing with the few NATs that don't implement a generic UDP
translation due to port filtering or what have you. Unless there are
so many Vonage phones behind the NAT that the NAT runs out of sockets
to talk to Vonage, they really aren't affected by the size of the
network behind the NAT.
Regards,
Bill Herrin
--
William D. Herrin ................ [EMAIL PROTECTED] [EMAIL PROTECTED]
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004
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