[Linux-aus] SIP

Russell Stuart russell-linuxaus at stuart.id.au
Thu Jul 4 14:42:47 EST 2013

On Thu, 2013-07-04 at 13:01 +0930, David Newall wrote:
> > http://www.google.com.au/search?q=voip+providers
> What, everybody?  I don't think so.  Can you mention somebody specific?

If you are after a recommendation I don't use VOIP at home, so I can't
really give one.

A couple of points though.  For VOIP to be as reliable as the POTS land
line needs guaranteed bandwidth.  If it is going to share the same
ADSL/Cable connection as the rest of the house, this means you have to
do effective QoS between you and the VOIP server.  Repeating what I said
earlier, if you don't, what you end up with is something like the
reliability Skype provides, but with none of the benefits like video.

VOIP uses around 100Kb/s per channel after IP overheads in both
directions, less if you use an aggressive codec like G729.  In other
words far less than Skype, easily within the capabilities of the average
ADSL/Cable connection - if it is unloaded.  However, if the connection
is loaded eg by an incoming email or some malware probing your IP
address for vulnerabilities, quality will suffer unless your ISP
implements end to end Quality of Service between your modem and the VOIP
server you are using.

If the ISP provides QoS all, they will typically provide it only between
your modem and their VOIP Server.  I understand Internode does this very
well and some others not at all, so beware.  Not doing it at all means
you may as well just use a third party server rather than sticking with
your ISP.

As I said, the NBN gets around this by provided a dedicated channel for
VOIP free when you get a data connection.  On the codec front we should
all be moving to Opus now, but I haven't see any evidence of that.  Opus
at 64Kbs should provide much better quality than a POTS phone.

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