DSL statistic lowest acceptable for VoIP

Hi,
I'm new on this forum and hope to get some comments on a professional issue. I'm thinking of putting some quality guarantee towards my VoIP subscribers, estimating the DSL line to either recommend the user to buy VoIP or not, or, lower the price where the DSL line is not showing acceptable values.

So for that I need to use DSL statistic data, and draw a line where the data is ok, or not. So the question is, how to best do this according to data from the Line like:
Sync downstream Sync upstream Max downstream Max upstream SNR Downstream SNR upwnstream Error Seconds Interleave downstream Interleave upstream

Anyone?

Best ulret

Welcome to Voipuser Ulret

Skype used to tell us in the early days that it worked over a 56k dial-up connection. (Not sure if that is still the case with the latest derivation and mercifully I haven't had to revert to dial-up for quite a few years now).

Dependent on what quality you are expecting its possible to get at least some kind of VOIP connection on more or less any DSL no matter how poor. (Lots of experimentation with the data compression may be required).

DSL line capability is dependent on contention and other factors that are very much outside the control of the end user. These change with the time of day/local user profiles. This makes it very difficult to do a clean statement on what will work and provide any quality guarantee - too many factors outside your control unless of course you are the ISP !

I used voip for a number of years via dialup and not even all that fast. The calls were generally acceptable and a lot cheaper that calling by PSTN phone!. If the subscribers have DSL then the considerations are probably about the reliability of the line and what else is happening on the network to use up the available bandwidth. Lots of users fail to recognise that a voip phone call needs bandwidth and a bittorrent download running in competition to the voip will mess up the voip call.
With my ADSL (1.2 mb/s down and 500 kb/s up) it is possible to make several good voip calls at the same time but other activities on the same network can make any call impossible. My solution was to reserve bandwidth for voip through the network server which worked perfectly. You will need to consider how you will be able to "impose" quality of service (Qos) restrictions on your users.