Mundy

The following post to ANZ-SMB-ITS by Hilton Travis has some really good info about the bandwidth requirements of VOIP on ADSL/SHDSL:

I'm a big believer that our Govt should own the infrastructure, else what are we really paying taxes for? We don't have a system of Government that allows the parties to project further than about 6 years ahead, which is appalling.

That aside, your ADSL connection is a big part of the issue with VoIP - ADSL can transmit *or* receive data (single copper pair) whereas SHDSL can transmit *and* receive data - and with VoIP doing both transmitting and receiving simultaneously, running it over *any* ADSL connection is reducing its quality. So, given the need for (approximately) 64 Kbps per VoIP channel, on a 384 Kbps connection (your stated outbound) then you'll lose about 10% of that with PPPoE overhead, bringing it down to roughly 346 Kbps, meaning that you'll be able to get a maximum of 5 simultaneous calls (assuming there is *no* other Internet traffic activity) before noticing a degraded VoIP quality (not even considering the ADSL half-duplex issues).

Now, to this, add the ADSL vs SHDAL half-duplex issues and also the fact that there *will* be other Internet activity and you can see why on an 8192/384 ADSL connection, VoIP isn't going to be wonderful.

QoS can assist this for outbound traffic and intra-network traffic, but can do nothing for inbound traffic (unless your ISP supports your QoS, which is extremely unlikely (currently, unfortunately)).

Now, add cloud computing to this already seriously compromised VoIP performance and see exactly how much bandwidth you need for decent performance. Next, use a hosted VoIP platform and even internal extension-to-extension calls will need Internet bandwidth, further reducing the quality of the solution.

So, for VoIP, a dedicated 512/512 SHDSL is recommended for up to 7 external/hosted VoIP calls, faster if you need more. And then your 8192/384 ADSL can be used for your Internet and cloud traffic and it may all be usable. :)

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