What really counts is packet loss. If a service is obsubscribed a million to one, but there is no packet loss, users will not see a problem. If however a service is oversubscribed 6:1 and there is packet loss the subscribers will experience terrible performance.
Not entirely true. The idea with the contention ratios
(or the oversubscribing as you mentioned) is that in theory not all the users will be using the BW at the same... In theory this works, but its not always the case.
Lets say we have a 10 Mbit/s Line, shared in a 10:1 ratio.
Now if all the users are on at the same time, that would allow each user to have 1 Mbit/s available to them, But then comes in the idea of "when are all of them online at the same time?". The customers are still paying for it, but how do you make it cheaper for the customer.. Increase the Ratios, drop your price by 25% and get more customers on the same line. Customers are happy because its cheaper and you end up getting more money off the same line
In order to maximise profit it would be better to use a ratio of 20:1 and if by chance all these users are on at the same time, they will only get 0.5 Mbit/s available to them and it will be put down to a technical fault or even blamed on the line on the other end
(dont we all know that story to well.)
Push that ratio up even more to say 50:1 on the same line.. and you are greatly increasing the chances of more people being on the same line. In effect slowing each user down drastically to 0.2 Mbit/s..However the SP is still paying for the same amount of BW, but now making much more money out it.
Each situation needs to be monitored and checked. Ratios of 20:1 might work perfect for a 10Mbit/s line in an area like Rosebank, given all are on 1 Mbit lines and the line usage is at say 50% - 75%. But in an area like Poffadder you could push that up to 50:1 or 100:1 where your usage is around 10%
You will find in environments where hard SLAs are provided, oversubscription is never mentioned. For instance, providers of MPLS networks quote metrics like packet loss, round trip delay and jitter (which is only relevant for voice and video but no data services).
I might be mistaken here, but in these situations the customer is given a Guaranteed min line speed. IE: the ratios are set in such a way that even if all the users of the line are on at the same time, the shared BW will be at your minumim.
I still firmly believe that if we were to find out what the Ratios are that telkom use, we would find them grossly out of spec, indicating huge profits at our expense, and also explaining why people in certain areas battle with slow speeds. If ICASA would force a minimum required line speed, then we can forget about the ratios since Telkom would in effect have to pull in line with this to make it work.
Of course.. Then we would all move over to Latency and Packet loss due to bad maintanence from the service provider
