[clug] VOIP advice

Bernard Duggan bernard at guarana.org
Wed Oct 1 21:31:06 GMT 2008

Woo!  Finally a subject I have a chance of knowing more than other
people about :)

Andrew Janke wrote:
>> You need plenty of bandwidth.
> Perhaps, I think this is more a function of how "close" you are to
> your provider...  But that could be just pontificating on my part.
> (see below)
Even the most bandwidth hungry prototol, G.711, only uses 64kbits of
data.  Add UDP and RTSP overhead, and you're still looking at a
"requirement" no more than about 100kbits in each direction.  If you're
using G.729, that drops lower.  Distance to your provider will only
affect latency.  The most important thing is a "good" link - low
latency, minimal packet loss and consistently sufficient bandwith -
between you and the provider's SIP gateway.  The only time you'll
actually need "lots" of bandwidth is if you're doing something else at
the same time (you know, downloading anything) and even with a fat pipe
that can still cause you problems without....
>> You need a modem with QOS.
>   $_ =~ s/need/should\ have/
Should /definitely/ have unless you want to turn off all your downloads
every time you make/take a call.  I run two voip phones here at home -
one that's QoS'd and one that isn't (only because I've been too lazy to
set it up).  Even on my ADSL2+ connection syncing at 5Mbits the latter
will break up significantly if I have a download running during a call.
>> However, the quality of the provider seems to be very important.
Very true.  iiNet had serious drop-out problems 2 and a half years back
when I started with them, and a lot of people (myself included) were on
the verge of giving up on them.  They're quite good now though - nary a
dropout for over a year.



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