8800NL: Increasing the target SNR rather than decreasing it

[gatekeeper]

I currently use a Billion 7800 and am about to purchase the 8800NL. For a few months the latter will be used in ADSL mode and so I'll want to take advantage of setting the target SNR of my line. Later, I hope to switch to FTTC (VDSL operation).

I see that Billion and others have published the numbers to input into the 8800NL required in order to decrease the target SNR by specific values and clearly this is very useful to those who want to get as much speed out of their line as possible. It appears that these numbers were changed from about model 7800DXL on. However, I want the opposite - I need the numbers to input into the 8800NL in order to get an INCREASE in target SNR, not a decrease. Can someone within these forums tell me what these are?

Here are some numbers that are already known for a decrease:

7800DXL and 8800NL -

2 = drop of 4dB
3 = drop of 3dB
6 = no change
4093 = drop of 9dB

But, with the 8800NL, what if I want to go:

From 6dB to 9dB
From 6dB to 12dB
From 6dB to 15dB
From 9dB to 12dB
From 9dB to 15dB
From 12dB to 15dB?

I'm currently on a long and quite noisy line to the exchange and normally have to operate at a line SNR of between 12 and 15dB. This renders me a highly stable connection but at the expense of some speed. I'm presuming that initially the 8800NL will negotiate a standard 6dB SNR but that'll be of no use to me, as at that SNR my line will be continually dropping out. So instead I'll want to force the negotiation to 12 - 15 dB right from the start.

[billion_fan]

I currently use a Billion 7800 and am about to purchase the 8800NL. For a few months the latter will be used in ADSL mode and so I'll want to take advantage of setting the target SNR of my line. Later, I hope to switch to FTTC (VDSL operation).

I see that Billion and others have published the numbers to input into the 8800NL required in order to decrease the target SNR by specific values and clearly this is very useful to those who want to get as much speed out of their line as possible. It appears that these numbers were changed from about model 7800DXL on. However, I want the opposite - I need the numbers to input into the 8800NL in order to get an INCREASE in target SNR, not a decrease. Can someone within these forums tell me what these are?

Here are some numbers that are already known for a decrease:

7800DXL and 8800NL -

2 = drop of 4dB
3 = drop of 3dB
6 = no change
4093 = drop of 9dB

But, with the 8800NL, what if I want to go:

From 6dB to 9dB
From 6dB to 12dB
From 6dB to 15dB
From 9dB to 12dB
From 9dB to 15dB
From 12dB to 15dB?

I'm currently on a long and quite noisy line to the exchange and normally have to operate at a line SNR of between 12 and 15dB. This renders me a highly stable connection but at the expense of some speed. I'm presuming that initially the 8800NL will negotiate a standard 6dB SNR but that'll be of no use to me, as at that SNR my line will be continually dropping out. So instead I'll want to force the negotiation to 12 - 15 dB right from the start.

Not really sure about the exact figures to increase your SNR, but if your base rate is 6db try 9, 12, 15, (these figures should higher your SNR)

[gatekeeper]

Thanks for your reply, billionfan, but you don't seem to be all that certain about it. Do you have any contacts within Billion itself who could answer this particular question? If so, I'd appreciate you getting in touch with them. You'd be doing thousands of users a big favour.

In a way, being able to INCREASE the Target SNR value is more important than being able to decrease it, as there are many of us still working under ADSL who are on long and quite often unstable lines which can be instantly remedied by an UPWARD move in the SNR. This is what's especially made Billion routers with Broadcom chips so good.

Frankly, the 8800NL will be completely useless to me as an ADSL router if I can't set my Target SNR to somewhere around 12 to 15dB.

Speaking generally and across the various models, superficially there doesn't seem to be any logic to the numbers required to change the target SNR in either a downward or upward direction. My guess is that it depends on a particular algorithm that Billion have chosen to use (and to change from time to time), and I think the required numbers are possibly hexadecimal as well. I and some others have noticed that the requisite numbers have changed since Billion upgraded from the 7800/N to the 7800DXL and thence to the 8800NL etc., but in the process Billion have forgotten to say what numbers are required in these newer models to push the SNR UPWARD as well as downward.

Something worth noting is that over recent years there has been some confusion among users as to whether the published SNR tweak tables show 'the CHANGE in dBs merely from an existing line target SNR' or instead refer to a 'change in dBs from a specific standard starting value of 6dB'. I'm not sure but I think the former is the case. Believe me, you can get the router ino one heck of a mess if the incorrect strategy is used for this and you input numbers that are non-valid or otherwise out-of-range. This is why it's ultra-important for Billion to publish the full range of acceptable numbers.

[billion_fan]

Thanks for your reply, billionfan, but you don't seem to be all that certain about it. Do you have any contacts within Billion itself who could answer this particular question? If so, I'd appreciate you getting in touch with them. You'd be doing thousands of users a big favour.

In a way, being able to INCREASE the Target SNR value is more important than being able to decrease it, as there are many of us still working under ADSL who are on long and quite often unstable lines which can be instantly remedied by an UPWARD move in the SNR. This is what's especially made Billion routers with Broadcom chips so good.

Frankly, the 8800NL will be completely useless to me as an ADSL router if I can't set my Target SNR to somewhere around 12 to 15dB.

Speaking generally and across the various models, superficially there doesn't seem to be any logic to the numbers required to change the target SNR in either a downward or upward direction. My guess is that it depends on a particular algorithm that Billion have chosen to use (and to change from time to time), and I think the required numbers are possibly hexadecimal as well. I and some others have noticed that the requisite numbers have changed since Billion upgraded from the 7800/N to the 7800DXL and thence to the 8800NL etc., but in the process Billion have forgotten to say what numbers are required in these newer models to push the SNR UPWARD as well as downward.

Something worth noting is that over recent years there has been some confusion among users as to whether the published SNR tweak tables show 'the CHANGE in dBs merely from an existing line target SNR' or instead refer to a 'change in dBs from a specific standard starting value of 6dB'. I'm not sure but I think the former is the case. Believe me, you can get the router ino one heck of a mess if the incorrect strategy is used for this and you input numbers that are non-valid or otherwise out-of-range. This is why it's ultra-important for Billion to publish the full range of acceptable numbers.

I had to write the SNR table my self (with the help of others on this forum, when the device was first released), Billion will only comment on values between 1-6. (and no one has really requested a table for highering the SNR, they normally want to lower the SNR to increase downstream value)

The values are set by Broadcom as it uses the Broadcom chipset, hence the reason I wrote a more advanced SNR table (unofficial tested with others)

The way it works is off the base rate of 6db, (default SNR set by BT when using values to 1-6) I can't test this now (highering the values), as my lines are always on DLM (you can imagine how many times we have to drop the DSL to change routers, test this, test that, test this config etc)

I expect if your default SNR is 6db, if you enter 9 you will get 9db, if you enter 15db, you will get 15db.

You can also request a higher SNR change with your ISP, most good providers will be able to accommodate you.

If you can post your finding, it might help someone else in future who might want to higher the SNR without the ISP intervention

[gatekeeper]

As far as I'm aware, the numbers that you can input are NOT absolute values, which is what you're suggesting. For example, there's no workable SNR that's 4093. Instead, 4093 will give a 9dB decrease in target SNR, RELATIVE TO THE STARTING POINT. This means that, for instance, if the starting point is not 6dB but happens to be 12dB, then inputting 4093 will render a new target SNR of 3dB. The starting point could just as easily be 15dB, though, or say 9dB, in which case the new SNRs would be 6dB and 0dB respectively.

Personally, I think you've misunderstood the way that it works. Instead, the inputted numbers all render RELATIVE changes in SNR. It doesn't matter one jot that everyone's starting SNR is different, therefore. That's the whole point of having a feature such as this in a router.

Once set (and assuming that the target value chosen is within sensible range of what the line will stably work at in the much longer term), the SNR of the line (as measured by the modem's stats) will thereafter not change very much at all. It'll just vary slightly up and down, as each day progresses and crosstalk and noise have their effects.

In my experience, ISPs are reluctant to change the target SNR, as they're not able to do this themselves. Instead, they have to do it by raising a request on Openreach. They then get charged by Openreach for that.

[billion_fan]

As far as I'm aware, the numbers that you can input are NOT absolute values, which is what you're suggesting. For example, there's no workable SNR that's 4093. Instead, 4093 will give a 9dB decrease in target SNR, RELATIVE TO THE STARTING POINT. This means that, for instance, if the starting point is not 6dB but happens to be 12dB, then inputting 4093 will render a new target SNR of 3dB. The starting point could just as easily be 15dB, though, or say 9dB, in which case the new SNRs would be 6dB and 0dB respectively.

Personally, I think you've misunderstood the way that it works. Instead, the inputted numbers all render RELATIVE changes in SNR. It doesn't matter one jot that everyone's starting SNR is different, therefore. That's the whole point of having a feature such as this in a router.

Once set (and assuming that the target value chosen is within sensible range of what the line will stably work at in the much longer term), the SNR of the line (as measured by the modem's stats) will thereafter not change very much at all. It'll just vary slightly up and down, as each day progresses and crosstalk and noise have their effects.

In my experience, ISPs are reluctant to change the target SNR, as they're not able to do this themselves. Instead, they have to do it by raising a request on Openreach. They then get charged by Openreach for that.

I fully understand how it works, like I stated before 6db base value will support values between 1-6, but other values I posted like 4093,4092,4096 etc will lower the SNR further (as we never know the default value we can only judge by other users results as found and tested here viewtopic.php?f=18&t=807

[gatekeeper]

I've managed to achieve a Target SNR of 15dB.

By looking in the xDSL stats in the router I found what my initial line SNR was, it being 12dB. (This was the line SNR as established by my prior 7800 together with the DSLAM). Initially, I tried inputting the number 15 into the SNR box in the 8800 but it rendered me an SNR of 21dB. Logically, the number 15 would produce a RELATIVE change of 9dB, but in my case it transpired that the starting point was 12dB, not 6dB. I then entered the number 9. I was, from this, expecting a relative change of 3dB, and indeed that's what I got. So I'm now sitting at 15dB line SNR, which is what I want.

I found that I didn't need to Restart in between. If you do, then I think the previous SNR gets taken as the new starting point.

(Clearly, this is why Billion state that they don't publish a definitive set of figures, that being because potentially everyone's SNR at the point of changing it can be different. The line value can be anywhere between about 0dB and 18dB, with perhaps the majority starting off at the default 6dB). Thereafter, every time you change the SNR you'll be starting from a different value, and this is why there are no definitive numbers you can use, only numbers that will produce RELATIVE changes).