If your on a 40/10 package do you actually get 40/10.

Let's just say for arguements sake your connection is capable of 80/20, but your on a 40/10 package. Would you recieve the full 40/10 or would it be a bit below? The reason I ask is when I see people on 40/10 packages and they post speedtest results it always shows results like 38Mb/s dl and 8.2Mb/s upload. If that's the case it seems like false advertising especially if your connection is capable of the full advertised speed.

BT say Up to 38Mb download speed and Up to 9.5Mb upload speed

So it's just Sky and people in these forums who are confusing people by saying 40/10 when they should be saying 38/9.5? Not really a big deal, but thanks for clearing it up.

I always thought what ever way the connection comes in at on the phone line you always get a bit less than connection speed.

What my unlocked modem says.



Path 0 Path 1
Downstream Upstream Downstream Upstream
Line rate (kbit/s) 39998 10000 0 0


A normal speed test, gets to 8 point something sometimes on upload and 38 down on a good day

http://www.speedtest.net/result/2110204271.png

There are at least three speeds: they sync speed, the ip profile, and the speed you really get. The first two are a little different because of the way the count overheads.
A sync speed of 40 will give an ip profile of IP profile of 39.39 so so.

Then you lose a bit more in the real speed for various other reasons, hence a typical speedtest of 38. That loss is much more variable as it depends partly on other users.

Edited by StephenTodd (Thu 09-Aug-12 15:08:13)

In reply to a post by StephenTodd:

There are at least three speeds: they sync speed, the ip profile, and the speed you really get. The first two are a little different because of the way the count overheads.
A sync speed of 40 will give an ip profile of IP profile of 39.39 so so.

Surely that's not right. IIRC 38.72Mbps?

On Sky and TT however there will be no IP Profile, so far as I know. That's a BT Wholesale "feature".

In reply to a post by RobertoS:

Surely that's not right. IIRC 38.72Mbps?

Yes, 38.72 is the maximum, which will typically give a maximum download speed of a shade over 37.5Mbps. The majority of ISPs do not advertise speeds of 40Mbps down/10Mbps up any more as they are not allowed to, though some may label a package as "40/10" which is not the same thing.

I've just been used to using Virgin. Like when I had the 30Mb package I actually got like 31Mb/s. Again, not a big deal, I was just curious.

In reply to a post by lowe88:

I've just been used to using Virgin. Like when I had the 30Mb package I actually got like 31Mb/s. Again, not a big deal, I was just curious.

That's because Virgin Media's _cable_ service works very differently to all the ADSL and VDSL services. (FTTC Is really VDSL).

You are likely to get sync rates just shy of 40,000 and 10,000 kbit/s in cases where your line is capable of more, but the observed throughput rates will be lower for a number of reasons. Downstream there is a "profile" in place which acts as a rate limiter. There are overheads for every protocol in the stack that your data is wrapped in, even if there are no errors, and there are retransmissions (due to transmission errors caused by line noise) to account for. For ADSL it used to be that you should expect 85% of your sync rate as your maximum throughput. For FTTC downstream I think this is more like 92% (hence getting a touch more than 37Mbit out of a 40mbit sync rate) - this agrees with what I saw downstream on 40/10, though upstream I never saw more than ~8.5mbit as an observed rate.

Note that because of the complications of analogue comms, as used between you and the cab, you are not guaranteed to get a 40/10 sync rate on a 40/10 product if your line would give you more on 80/20. IIRC the 80/20 product uses frequency bands spread over an 18MHz range were the slower product just uses a subset of those (over a range of about 9Mhz) - if your line experiences a good bit of signal loss in that subset of frequencies then you are going to get less than 40/10 on the 40/10 products but might still get more than 40/10 on 80/20 products (but not the full 80/20) because the extra usable bandwidth in the other frequencies makes up for the deficiency in the other bands.

In reply to a post by dspillett:

IIRC the 80/20 product uses frequency bands spread over an 18MHz range were the slower product just uses a subset of those (over a range of about 9Mhz) - if your line experiences a good bit of signal loss in that subset of frequencies then you are going to get less than 40/10 on the 40/10 products but might still get more than 40/10 on 80/20 products (but not the full 80/20) because the extra usable bandwidth in the other frequencies makes up for the deficiency in the other bands.

I do not believe that is true. AFAIK both products use the same frequencies and have since the change to 17a, one has a 40/10 sync cap, the other has an 80/20 sync cap.

In reply to a post by kasg:

I do not believe that is true. AFAIK both products use the same frequencies and have since the change to 17a, one has a 40/10 sync cap, the other has an 80/20 sync cap.

I was working on the impression that only the faster lines were using 17a, though I could easily have grasped the wrong end of the stick. Having a sync cap would be easier to manage than having two sets of customers on different standard versions, so probably makes more sense.

Edited by deleted (Tue 14-Aug-12 14:18:19)

In reply to a post by dspillett:

I was working on the impression that only the faster lines were using 17a, though I could easily have grasped the wrong end of the stick.

No, everything has been on 17a for some time now - last year I think.

Yes, I've been on 17a for a long time, on a 40/10 then a 40/2. Currently 80/20.

I started on the 40/2 8c profile in June 2011.

I was auto-switched to the 17a profile in October 2011.

I experimented with the 80/20 trial service with my ISP Plusnet, but there was no speed increase whatsoever, so I reverted to the 40/2 service after a couple of weeks.

Strangely (or not) my connection initially achieved higher speeds using fewer available tones on the 8c profile than it does on 17a.

Crosstalk from increased numbers of users may have restricted my achievable sync speeds.
I believe I was one of the first users (if not the first user) to be connected to my cabinet.
For the first month or so of being connected, BT were still claiming FTTC was not envisaged in my area during the next 6 months.
My original Plusnet speed estimate was 14.6Mb & I achieved 33Mb actual throughput until lots of physical issues messed everything up.

I am too far from the cabinet (attenuation-wise) to utilise the highest frequency band & can only use part of the middle frequency band.
I can use all of the lower frequency band.

My current & stable connection sync speed is around 28Mb & was up to 35Mb on the 8c profile.

I have asked if it is possible to revert to the 8c profile (as an experiment for sub-40Mb connections).
However, it is not currently possible to do that.