In reply to a post by MrSaffron:

Providers only use The fixed rate products if you order that explicitly ie. As rare as 5 numbers on national lottery

That's true. I just wanted to add that I have the option to go 2Mbps down and 1mbps up on my TT line I have with A&A

I have about 30 profiles from 256k both ways right up to max speed. It's mind blowing

It doesn't actually happen at the exchange. It happens at the other end of the BT Wholesale system, where they pass it over to the individual ISPs.

The ISP rents MSILs at that/those point(s), and they pay by the maximum Mbps that their MSILs can handle. There isn't a direct clash between ISPs in the way ukhardy described - though his method was a very good way of illustrating the effect.

ISPs basically look at their number of customers, and working on the basis that although a high percentage may be connected at any given time the traffic for each comes in bursts.

Let's take two extremes. Think sending and receiving emails, or clicking on a link to a page on a site. They expect say only 1 in 20 people to click a new page link at the same time.

If we assume all 20 are connected at 8Mbps, the therefore need only to provide 400kbps each (total 8Mbps) at the handover point. Most of the time it will work fine.

The problem (at the other extreme) comes when 15 of the 20 want to watch live Wimbledon, or snooker at the moment, and the other five are streaming Netflix.

The more expensive the ISP, in overall cost of the service and bundles, the more simultaneous handover capacity per customer they budget for.

A reasonable summary, backhaul is the middle bit of the network between the exchange and the Internet, as capacity on IPStream Max exchanges costs more generally, tendency is for cheaper providers to not spend the money needed and concentrate on areas where they can get more bang for their buck.

So the ADSL connection would be the same, but experience in day to day use might vary. Of course until you try you cannot be sure, but with a 2 year contract that's a big gamble.

As you have probably gleaned from all the previous answers it does, in the end, come down to: the lower the cost, the lower the quality/support/speed - the have to limit what they can provide.

If an ISP charges more, they have more money to spend on back-haul and links, support - both location and times, and willingness to resolve issues &c

I use a business quality service and certainly pay a lot more than most - do I see congestion, very, very, very occasionally. Do I get outages? Yes, however they are rapidly fixed. Support, 24hr UK based &c &c.

That is a different thing, the TT profiles on your AA line are not about changing products, but about controlling the DLM for the specific product you are using.

In reply to a post by asker:

I think you are saying that due to "back haul" (whatever that is) and other issues, the cheaper ISPs would not be providing the same product - and even though it is still ADSL Max, it would be slower.

"ADSL Max" on refers to the bit on your phone line from the exchange to your house. It doesn't help determine how well your chosen ISP gets the information from the exchange to the internet.

I get what your saying. Thanks for the clarification

it's still cool to go back to 2mbps/512k for nostalgia reasons

In reply to a post by RobertoS:

It doesn't actually happen at the exchange. It happens at the other end of the BT Wholesale system, where they pass it over to the individual ISPs.

The ISP rents MSILs at that/those point(s), and they pay by the maximum Mbps that their MSILs can handle. There isn't a direct clash between ISPs in the way ukhardy described - though his method was a very good way of illustrating the effect.

ISPs basically look at their number of customers, and working on the basis that although a high percentage may be connected at any given time the traffic for each comes in bursts.

Let's take two extremes. Think sending and receiving emails, or clicking on a link to a page on a site. They expect say only 1 in 20 people to click a new page link at the same time.

If we assume all 20 are connected at 8Mbps, the therefore need only to provide 400kbps each (total 8Mbps) at the handover point. Most of the time it will work fine.

The problem (at the other extreme) comes when 15 of the 20 want to watch live Wimbledon, or snooker at the moment, and the other five are streaming Netflix.

The more expensive the ISP, in overall cost of the service and bundles, the more simultaneous handover capacity per customer they budget for.

Is this the same issue as "Contention Ratio"? I presume it is more complex than that, otherwise it would be simple matter to ask a potential ISP what contention ratio they could offer?

In reply to a post by asker:

Is this the same issue as "Contention Ratio"? I presume it is more complex than that, otherwise it would be simple matter to ask a potential ISP what contention ratio they could offer?

They won't quote a contention ratio, they just cram loads of people into a small pipe and let them fight it out. Ask any user who has experience of Sky or TalkTalk over BT Wholesale.

In a way, yes. But much more complicated.

Contention ratios as we used to understand them (20:1 and 50:1) were effectively scrapped when ADSL Max came on the scene. They basically applied to the merging of several fixed-sync lines at some point in the system.

The contention has in general now moved to these MSILs I mentioned earlier, where it is a more complicated calculation involving user profiling, expected normal and unusual peak demands, the profit margin required and the customer satisfaction levels needed. The detail I don't know, but a few years ago they were talking in terms of low hundreds of mbps per customer.

Now that unlimited usage and loads of streaming are expected they must be provisioning rather a lot more than that, but there are still millions who only browse, shop and email. They use very little.