Estimate of maximum speed

I�ve had FTTC since January and then my initial line stats from the Sky Hub were;

Downstream Upstream
Connection Speed 39998 kbps 9999 kbps
Line Attenuation 15.6 dB 0.0 dB
Noise Margin 24.4 dB 28.28 db

I went for the Sky 40/10 package and have been very happy with it, but I am now toying with going with the Pro 80/20 package instead. My current line stats are

Downstream Upstream
Connection Speed 40000 kbps 9999 kbps
Line Attenuation 15.8 dB 0.0 dB
Noise Margin 15.3 dB 20.20 dB

With these figures and from what I�ve been able to read, I feel I probably won�t get the full 80/20 but more like 60/20. Would this seem correct?

The values given on the BT availability checker are

High Low High Low
FTTC Range A (Clean) 80 62.7 20 20
FTTC Range B (Impacted) 76.5 51.9 20 15.8

Stephen.

That attenuation is right on the edge of getting max speed or not. I think the estimate is correct - somewhere between 60-80. Plus you'll be helped by G.INP.

Thanks for confirming that. Is there anyway to tell if G.INP is enabled, given I have a Sky Hub?

It looks like it is. If your cabinet is a Huawei then chances are that G.INP is enabled.

At 16.6dB attenuation I get around 76Mbps. So at 15.6dB you "should" be looking at 79-80Mbps - it will ultimately depend on the noise levels which could push it don, so look towards 70-80 Mbps. And you could be looking at full Upstream

It looks to me like you'll sync at max speed or just below...

It also look like G.INP is enabled on your connection as your current sync is 40000 where a connection without G.INP maxes out at 39999..

In reply to a post by mlmclaren:

where a connection without G.INP maxes out at 39999 39998

Fixed that for you. Due to the INP codewords that you just don't get with G.INP

In reply to a post by mlmclaren:

where a connection without G.INP maxes out at 39999 39998

For Reference: http://s1119.photobucket.com/user/44_bh/media/OR_sta...

Edited by mlmclaren (Wed 11-Nov-15 23:28:42)

That picture was taken prior to G.INP being implemented unfortunately

Exactly my point... did you not read my post?

You misunderstand.

39999 before G.INP existed - 23 September 2011.

39998 in the OP after G.INP implemented but not active.

The OP said that in January their stats:

Connection Speed 39998 kbps 9999 kbps

now they are Connection Speed 40000 kbps 9999 kbps

My point is that without G.INP the maximum sync was 39999kbps and with G.INP it is 40000kbps....

I mentioned nothing about the 39998kbps or any INP or other error correction, and to be honest it was pretty unimportant to mention it.

In reply to a post by mlmclaren:

My point is that without G.INP the maximum sync was 39999kbps and with G.INP it is 40000kbps....

That was the case before G.INP was implemented but nowadays the choice is between 39998 and 40000.

Right ... but why are you mentioning this...

So you can tell your neighbour.

To bring thr thread back on track.

If you have access to an unlocked HG612 modem you will be able to see a max achievable figure that will be a very good indication.

edit to add:

Just looking at the noise figures from install and recent again - there has been an 8dB change in both in that time. Were you an early install in the cabinet? If so, newer ones have certainly given you more cross talk to contend with. Or have you move the modem or other electronic equipment at home?

Edited by MHC (Thu 12-Nov-15 10:23:23)

I've removed several posts here from a few users who were acting a bit unhelpfully.. would be great if everyone could adjust their approach slightly

As an overly-simplistic conclusion, the attenuation tells us your line is certainly capable of getting 80/20 speeds.

However, crosstalk (noise caused by other FTTC subscribers) can reduce the actual line speed, as can any other errors on the line induced by all forms of noise.

In your case, we can see that your noise margin has reduced by 9dB - very likely because of the extra noise caused by other subscribers. This is a common result.

The VDSL2 modems still work to a noise margin target of 6dB, so you still have 9dB of room for your speeds to increase.

My rules-of-thumb for what spare noise margin is worth on the downstream are:
- At speeds of 40-50Mbps, 3dB is worth around 8Mbps
- At a speed of 60Mbps, 3dB is worth around 10mbps
- At 70Mbps or above, 3dB is worth around 11Mbps.

That 9dB of spare noise margin seems likely to get you around 25Mbps more - to around 65Mbps.

However, you could continue to lose more of the noise margin to crosstalk, so the top speed might continue to reduce over time.

In reply to a post by MHC:

To bring thr thread back on track.

If you have access to an unlocked HG612 modem you will be able to see a max achievable figure that will be a very good indication.

edit to add:

Just looking at the noise figures from install and recent again - there has been an 8dB change in both in that time. Were you an early install in the cabinet? If so, newer ones have certainly given you more cross talk to contend with. Or have you move the modem or other electronic equipment at home?

Yes I think I would have been an early install as I got it less than a month after the cabinet went live.

Thanks for all the replies confirming what I thought.

Edited by deleted (Thu 12-Nov-15 19:47:42)

If you cannot borrow one, you could invest £10 in an HG612 - unlock it and see what you could get. Then put it back up for sale and recover most of your outlay.