Yes, that's what I thought.

Are there actual performance questions?

I have just signed up , so should I wait until actually connected?

Ta.

Which ISP

Usual downstream

Usual upstream

IP Profiles (optional...you don't need to fill them in if you don't know)

Thats all it asks.

I'm curious about the download speeds reported in the survey and, for that matter, in posted/linked-to speedtest.net results.

Taking into account the ATM, PPPOE and TCP overheads then over 35Mbps should essentially be impossible ie

40000x(48/53)x(1492/1500)x(1452/1492) = 35067kbps

Presumably there's some more lost in the AAL5 encapsulation and in the FEC but my brain always hurt when thinking about AAL5 and I don't actually know what the FEC overhead is.

So how come people are reporting 37Mbps+? Do the speed testers attempt to "correct" for overheads in their calculations.

FWIW I'm syncing at 39879, IP profile 38717. BT speedtester 30Mbps, speedtest.net 34-35Mbps and TBB speedtest all over the place but 32Mbps this morning.

I forget the detail right now, but TC/IP overheads on BT Wholesale systems are accounted for within the IP Profile. There is also something different from normal about the Openreach-reported sync speeds - the phrase "data rate" springs to mind in relation to the 40Mbps maximum.

If you look at your upstream IP Profile as well, it equals the reported sync speed. At least it does for the 10Mbps upstream service.

Speedtest.net is known to give high readings, even when not affected by the user's IS, as it selects samples from its testing rather than the whole lot.

Too hot and too much to do to search for all aboiut the Openreach VDSL at the moment.

VDSL 2 doesn't have to use ATM it can, and usually does, use Ethernet which wipes out some of the overheads.

That was it I think .

Interesting, that would reduce the overheads quite a lot - doesn't do anything to make me feel better about only getting 30Mbps out of the BT speedtester though!

I forget the detail right now

I think the detail's in SIN 498. It's clear that this is ethernet over dsl - in fact the SIN even gives a figure of 39,282kb/s ethernet throughput based on a 40,000kbps sync and on the wire frame size of 1532bytes.

In reply to a post by Anonymous:

I forget the detail right now

I think the detail's in SIN 498. It's clear that this is ethernet over dsl - in fact the SIN even gives a figure of 39,282kb/s ethernet throughput based on a 40,000kbps sync and on the wire frame size of 1532bytes.

Yes, I'd found that but was "tired/in a rush/too much vino" and misread it because of the handover to CP description just before the relevant stuff you have quoted from.

Thanks .