Effect of IP profile and how do individual ISP's use it

There has been a lot of problems recently with the Plusnet mirror of the IP profile not updating and I wondered if the experts here can provide some clarification as to the actual need or otherwise of an IP profile (LLU don't seem to need it) and why no other ISP's (with the exception of A&A I believe) seem to use it in traffic control.
A succinct explanation of just how the IP profile works at an individual user level would be appreciated.

http://www.robertos.me.uk/html/bt_ip_profiles.html

I've not updated it for FTTC/FTTP, but the principle is the same. On any BT Wholesale connection BTW apply it. Some ISPs, as listed in my write-up, and probably some others as well, hold a copy set at or a fraction below the BTW version, to buffer stuff themselves before it gets to your exchange. Thus preventing excessive packet loss which could result if it came direct from source and through them to the exchange, then hit the BTW limiter on your line.

Thanks Robert but can you explain why the LLU suppliers don't seem to have the excessive packet loss problem

No real idea. But don't forget we don't know what systems they have in place internally.

Neither do the BTW ISPs that don't hold copies seem to have a problem.

On FTTC the profile is 90-odd percent of the sync. That's the sort of thing I have to put on the page.

In reply to a post by Oldjim:

Thanks Robert but can you explain why the LLU suppliers don't seem to have the excessive packet loss problem

It's probably to do with the ATM network that the IPStream stuff runs over, there is very little buffering in it, so any packets dropped at the LL means extra traffic over the ATM network for retries.

Once on LLU it's all more IP based which means that the TCP tuning should control the connection better, this means that in theory you don't have as much need to limit the speed.

However, have a look for the term "buffer bloat" and the nasty effects it can have in a network. Too much buffering insulates the ends of a connection from each other and defeats the TCP throughput mechanisms.

The only ATM in BT Wholesale WBC/WBMC (21CN) ADSLx connections is from the exchange to the premises. ATM is also used between those two points on LLU.

In reply to a post by RobertoS:

The only ATM in BT Wholesale WBC/WBMC (21CN) ADSLx connections is from the exchange to the premises. ATM is also used between those two points on LLU.

Are *ALL* exchanges now served by WBMC ? I know of northern scotland where 8mbps IPstream services is all you can still get. (I assume these are on the legacy ATM 'colossus' network).

I was trying to avoid that one , as not very relevant to the particular statement I was querying.

It's difficult, as IPStream is I believe pretty well dead. The issue is confused by IPSC (IPStream Connect), which is used to replace it in non-WBC exchanges.

Basically IPStream requires ISPs to have the old BT Centrals. IPSC starts of at the user end like IPStream but can be delivered from the BRAS to the ISPs through their new MSILs on WBC.

Quite how much of the BT ATM cloud is avoided by this I don't know, but I can't imagine many, if any, ISPs are still running Centrals. I'm not even sure support for them hasn't been withdrawn, or is imminent.

Not seen the notice of withdrawal of IPStream Centrals yet

20% of UK has no WBC at the exchange yet.

In reply to a post by RobertoS:

Quite how much of the BT ATM cloud is avoided by this I don't know, but I can't imagine many, if any, ISPs are still running Centrals. I'm not even sure support for them hasn't been withdrawn, or is imminent.

I assume that BTw has interface so that IPstream only areas and customers can be served by ISPs with only MSIL's as that seems the solution. Obviously ISPs only want to connect to BTw appropriately and not in duplication due to cost - so they will want a service that solves that problem.

BT's WBC rollout is slow and where is the 21CN for voice that was supposed to be complete by now? Anyone remember the "Switched ON" website of 2000/2001 ?