[grc] How much bandwidth to run a VPN?

[al davis]

On Mon, 26 Dec 2016 18:05:28 -0800
shhhhh via grc <grc at maillist.peak.org> wrote:

> How much bandwidth do we need to run a VPN as our STL? We are also
> building a microwave STL but it's taking longer than we planned-- of
> course! And yes, both ends will be on the same network. 

VPN doesn't give any clue about bandwidth needed.

To do your STL, the bandwidth you need depends of the data rate of your
stream.

An uncompressed stream at 44 KHz needs about 1.5 mbits/sec,
officially.  If your actual usage is close to the channel capacity, you
will occasionally get dropouts, so I recommend a capacity of around
twice what you really expect to use.  That would be about 3 mbit/sec
for uncompressed.  This is more than the usual home internet gives you.

You can use less than that if you use data compression, such as MP3,
Ogg-Vorbis, AAC, or Opus.  Whatever you use, figure that your UP-link
speed needs to be twice what you actually use.  So, for a 300k MP3,
figure you need 600k to avoid dropouts.  A Barix will do this.  If your
net is less than that, you can use a lower rate, but the lower rate
will have worse sound quality.

It's up to you to decide what quality/bandwidth tradeoff works for
you.  In general, the higher the rate the better, and for a given rate
Opus tends to sound best, with Ogg or AAC not quite as good as Opus, and
MP3 worse.  For MP3, I would figure 256k minimum.  For Ogg, figure
around 75k minimum.  AAC needs a similar rate to Ogg.

At low rates, as they degrade, Ogg degradation tends to sound "analog",
AAC degradation (and more so MP3) tends to sound more synthetic.
Which is better or worse is a matter of opinion.

Conclusion ..  the ordinary consumer internet will get your signal
through with the right algorithms.  You need to decide what quality is
good enough.

With so much stuff coming in as mp3, the STL is probably not the weak
link most of the time.