North American Network Operators Group

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Re: hosted PBX/VOIP thru VPN?

  • From: Nathan Ward
  • Date: Wed Nov 12 07:01:27 2008

On 13/11/2008, at 12:39 AM, Aaron Wolfe wrote:

Because the broadband connection was so fast, TCP was able to
repair the impairments without reducing voice quality. "

That works fine if latency+window size is low, so that segments are retransmitted quickly.

You really should also do the math and factor in the latency that comes from doing something like this, assuming you lose a packet. G. 114 recommends an end to end latency of no more than 150ms for voice applications, where over 400ms is unacceptable (between 150 and 400 you should indicate that performance is not ideal).

Finally, some audio codecs work well with fairly high amounts of loss - I'd recommend doing something like that first. iLBC does this really well. G.729 etc. do not - they rely on context, so a single packet lost results in several packets of lost audio (and so, silence). iLBC doesn't rely on context, and quality degrades during packet loss before you get silence.

The i stands for Internet - so no surprise it works great in typical Internet conditions.

Nathan Ward