And back to the question, does the IP throughput match the sync speed, or does 10% to 13% still need to be allowed for due to the overheads of IP carried over ATM?

I know what interleaving is, but when you say 'reduce your max delays' what do you mean?

Methinks Jonny is proving the old proverb "A little knowledge is a dangerous thing"

Of course, when I said that on Sky "you get what you sync at", I didn't mention overheads, because these are inherent in any system.

Edited by deleted (Sun 27-Jul-08 10:35:29)

FYi on sky BB 8mb LLU Mid - i sync at 8188 and dl at 860-900 kb/s around 7.2-7.6 mb

Sky cover these overheads by giving there users a bit of extra speed so they are not losing out on anything they are getting what they pay for so what exactly is your point.
And another thing when i said sky can lower your max delays what this basically does is improves latency so there is really no need for the extra sync speed if you have got very low ping times.
lower ping times=faster browsing,online gaming,etc,etc

Edited by jonny1310 (Tue 29-Jul-08 04:45:10)

Okay so what you are saying is that Sky can control the depth of interleaving on its LLU products.

As for Sky giving extra speed, you are still losing me. I think what you mean is something like this.
If a line is sold as 2Mbps, it will sync at 2272Kbps (which BT Wholesale do too btw).

Otherwise on the rate adaptive lines if it syncs at 10Mbps, then max IP throughput will be around 9Mbps.

Assuming gaming traffic is low, e.g. 128kbps or less, then sync speed makes no difference, so the comment about no need for extra sync speed is hogwash in terms of lowering latency.

if I a line synchs at 4530kbit on sky you will get that speed, on a ipstream isp you will lose 530kbit as you on a 4000kbit ip profile, I assume this is what he meant by extra speed.

So Sky is not using ATM for the ADSL link, but IP then? So now 10% overhead due to the 48 bytes of IP payload in each 53 byte ATM cell.

On IPStream 10-13% of 4530Kbps is around 453Kbps - you need a sync of 4544 to get the 4Meg profile.

So I still don't really know if Sky are managing to get around the ATM overheads. Given its a fairly standard Netgear router I don't believe they are.

4530kbit on ipstream = 4000kbit - atm overheads - tcp overheads.
4530kbit on sky llu = 4530kbit - atm overheads - tcp overheads.

the atm overheads are still there but the IP profile overheads are not.

Indeed BRAS profiles are not a cure for ATM overheads, simply a way of vastly reducing the bandwith they might otherwise need if taken over the 5 million or so subscribers on MAX (if I was being cynical)

Both IPStream Max and Sky's LLU implementation suffer slightly from ATM overheads, the difference is BT also add a rather unnecessary 'penalty' with their BRAS profile implementation.

The bottom line is I download a lot quicker with the same ATM sync speed on Sky than I did with BT, and it's not down to congestion at the exchange or ISP, it's simply down to the profiles implemented by BT.

I'm not sure what Andrew is finding difficult to understand here?

On IPStream .....you need a sync of 4544 to get the 4Meg profile

True, but when have you ever known the actual usable data (that which is available as pure downloaded data for programs, browsing, download managers, etc.) on a 4Mbps IP profile (on IPstream) to actually be 4Mbps?
3.7Mbps might be a closer value.

I think what these people are saying, is not that with LLU (Sky, BE, etc.) you get more bang for your bucks, it's just your "bucks" don't need to increase by 0.5Mbps to get more "bang" (oh wait, then you do get more bang for your bucks ).
I'm pretty sure the Sky LLU throughput (that which is coming out of a download manager, for example, rather than that which is going back & forth between the router & DSLAM) for a 4544kbps sync will be pretty close to the 3.7Mbps you'd get from IPstream.
Sky (and the other LLU companies) are faster for most, because not too many people sync at smack on the IP profile threshold, so they get a higher speed than they'd be getting from IPstream.
That's, of course, not even taking into account the 5 day stupidity (if your sync goes up, on Sky/BE/etc., you don't have to hope if holds up for five days before getting an increase in throughput).

So, except in a few cases (where people sync exactly at a particular IP profile threshold level), LLU is faster than a BTw IPstream product, and LLU will also be faster (up to 1Mbps faster) than a BT WBC ADSL2+ product).

Edited by adebov (Fri 01-Aug-08 22:08:34)