Max line speed when you reach 6dB SNR

cavedog

cavedog

Honorary Master
Joined
Oct 19, 2007
Messages
27,370
Reaction score
13,466
Location
PTA
So this is what I have been noticing for everyone posting their line stats and the max speeds they are getting.

Looks like Telkom determines that your max speed is when you SNR reaches 6dB.

I did some googling and since Australia is basically the only other country doing ADSL like SA people have been manipulating the SNR value to 3dB or 4dB to have a higher sync rate.

Has anyone tried this? Its not easy and you would need a very specific router to do that. Even if you had the router to try it would would assume that under the best conditions lowest possible dB on SNR would be 3 so between 6dB and 3dB what would the sync rate increase too?

I currently syncing @ 13.2Mbps with a downstream SNR of you guessed it 6dB. Wish I had a router that I could try it out but it not something that is easy to find and not even sure if it would be worth it if you only get like 1Mbps increased sync speed.
 
/subbed

In my searching as per my thread some months ago, i read the same. Still lurking to see what is the BEST device to use on ADSL2+ and what one can get at 6db :).

Glad you made this thread cavedog :o

Edit: agentrfr mentioned getting a D-Link 2500u which allows to set a target SNR but i haven't got one and can be the guinea pig if you want :p [switching to upto 20Mbps next month]. Max i saw when line was testest was around 12Mbps +- but Telkom said No to giving it to me at that time :whistle:
 
Last edited:
I'd imagine 1st world countries have slightly more stable infrastructure and can thus cut things closer to the edge?

Personally I'd rather have the peace of mind of stability than the extra 10% speed, but to each his/her own.
 
I suspect there may be a correlation vs causation confusion going on here.

IOW, when your sync rate is faster, your SNR drops. This does not mean that the lower your SNR, the higher sync rate you're going to be able to achieve.
 
Crystal Web said:
I suspect there may be a correlation vs causation confusion going on here.

IOW, when your sync rate is faster, your SNR drops. This does not mean that the lower your SNR, the higher sync rate you're going to be able to achieve.
Click to expand...

Agreed, I have no clue what OP is on about.
 
Telkom's infrastructure (or sometimes the router) will not allow you to sync at a speed which will drop your SNR to below 6dB.

With some routers you are able to force it to sync at a higher speed and allow the SNR to drop below 6dB.
A lot of people in the Whirpool forum talk about it and which routers (chipsets) work best for lines which are longer etc.

I am quite sure most Broadcom chipsets allow you to do that via telnet. That is the preferred chipset on the Whirlpool forum considering it is very stable with longer lines and most people have longer lines and therefore try and get a router with a Broadcom chipset :D


I guess what OP is trying to ask is, what sort of speed increase is an extra 3dB of SNR going to provide if your max attainable sync rate were to be limited by your SNR.
 
Rickster said:
Agreed, I have no clue what OP is on about.
Click to expand...

So I assume you have done this before then with no speed increase? If not how can you make a statement like that then? I can post many findings that SNR is linked to sync rate. You can actually just google it to check it out.

I have no proof that Telkom is limiting max speed to 6dB SNR but I have my suspicion. I sync @ 13135k right now with SNR of 5.9dB. Should I restart my router I can bet that I might sync at 13058k with a SNR of 6dB. Lots of people have the proof in their line stats too.

So I can't confirm only Telkom can.
 
Crystal Web said:
I suspect there may be a correlation vs causation confusion going on here.

IOW, when your sync rate is faster, your SNR drops. This does not mean that the lower your SNR, the higher sync rate you're going to be able to achieve.
Click to expand...
As I understand it the question is can you force speeds higher (and thus drop SNR to 3db) despite Telkom's attempt to enforce 6db.
 
Yuu said:
/subbed

In my searching as per my thread some months ago, i read the same. Still lurking to see what is the BEST device to use on ADSL2+ and what one can get at 6db :).

Glad you made this thread cavedog :o

Edit: agentrfr mentioned getting a D-Link 2500u which allows to set a target SNR but i haven't got one and can be the guinea pig if you want :p [switching to upto 20Mbps next month]. Max i saw when line was testest was around 12Mbps +- but Telkom said No to giving it to me at that time :whistle:
Click to expand...

The SNR (and other line diagnostics) values that ISPs and Telkom read don't come from your router, so changing that value on your router won't make an iota of difference in terms of what you're able to achieve. When Telkom checks your line stats, they're not asking your router/modem for the information - they're asking their infrastructure to tell them what the line stats are, and this is the data the ISP uses too. So I'm at a loss as to how changing your router to manipulate the SNR value is likely to change anything at all. At most it may change attainable rates your router indicates, but if anything, reducing the SNR will lower the attainable rate your router reports. Shouldn't change anything at all on the actual service delivery side.
 
Crystal Web said:
The SNR (and other line diagnostics) values that ISPs and Telkom read don't come from your router, so changing that value on your router won't make an iota of difference in terms of what you're able to achieve. When Telkom checks your line stats, they're not asking your router/modem for the information - they're asking their infrastructure to tell them what the line stats are, and this is the data the ISP uses too.
Click to expand...
^true^
 
hmm...makes sense. I'm sure there was some story about being able to manipulate it router side though? Maybe that was upload? Dunno...but I vaguely recall a credible mybb poster doing something like that.
 
PsyCLown said:
I guess what OP is trying to ask is, what sort of speed increase is an extra 3dB of SNR going to provide if your max attainable sync rate were to be limited by your SNR.
Click to expand...

Exactly what I'm trying to say. To say sync speed is directly linked to or only determined by your SNR is a bit naive, but so is saying that SNR plays no role in the max sync rate you get.

I have noticed a few members here like Yuu and myself and another member in the VDSL forum that the SNR is in fact the limiting factor for higher sync speed. I'm also wondering why choose 6dB as the limit. Why not 5 or 8 or 10 :confused:
 
Crystal Web said:
The SNR (and other line diagnostics) values that ISPs and Telkom read don't come from your router, so changing that value on your router won't make an iota of difference in terms of what you're able to achieve. When Telkom checks your line stats, they're not asking your router/modem for the information - they're asking their infrastructure to tell them what the line stats are, and this is the data the ISP uses too. So I'm at a loss as to how changing your router to manipulate the SNR value is likely to change anything at all. At most it may change attainable rates your router indicates, but if anything, reducing the SNR will lower the attainable rate your router reports. Shouldn't change anything at all on the actual service delivery side.
Click to expand...

Hmm... So when Telkom came out to my house I was running their brand new Dlink 2750U which they gave me to test - as opposed to a Billion 7300W.

My SNR dropped from 24dB downstream to around 13dB downstream. The Telkom tech took out his laptop and did a line test and it showed the SNR which was the same as my router displayed. We then switched routers to my Billion and my downstream SNR went up to 24dB and when he did the test again it reflected the higher SNR?

cavedog said:
I have noticed a few members here like Yuu and myself and another member in the VDSL forum that the SNR is in fact the limiting factor for higher sync speed. I'm also wondering why choose 6dB as the limit. Why not 5 or 8 or 10 :confused:
Click to expand...

Possibly they just find it to be the best compromise between stability and speed. Your SNR can and does fluctuate - if it drops too low then your line will drop. The lower it is, the greater the chance of your line dropping.
If peoples lines dropped quite often then it would lead to more call outs and problems for Telkom etc.

At the same time us as clients want the fastest speed possible, especially if we are paying for an "upto 10Mbit" service, we would rather have 8Mbit over 6Mbit etc.
 
Last edited:
PsyCLown said:
Hmm... So when Telkom came out to my house I was running their brand new Dlink 2750U which they gave me to test - as opposed to a Billion 7300W.

My SNR dropped from 24dB downstream to around 13dB downstream. The Telkom tech took out his laptop and did a line test and it showed the SNR which was the same as my router displayed. We then switched routers to my Billion and my downstream SNR went up to 24dB and when he did the test again it reflected the higher SNR?
Click to expand...

I can't speak for the router manufacturers, but when a diagnostic test is performed it checks your line, not your router. If your router is sending noise to the line for some arbitrary reason, it can impact the test, but there is no mechanism built into every router from every manufacturer to send data to Telkom's servers when requested, and only Telkom's servers. The test is performed on the line, according to the stats the exchange is able to determine, not the router.
 
Crystal Web said:
I can't speak for the router manufacturers, but when a diagnostic test is performed it checks your line, not your router. If your router is sending noise to the line for some arbitrary reason, it can impact the test, but there is no mechanism built into every router from every manufacturer to send data to Telkom's servers when requested, and only Telkom's servers. The test is performed on the line, according to the stats the exchange is able to determine, not the router.
Click to expand...

How would the exchange "get" your SNR if its not getting it from the router? how would it determine that then? If the exchange is determining you max speed how does it get the data to determine it? It would need some stats from the router to determine distance amongst other thing otherwise how would the exchange know where the router is and what the line is capable of if it does not get anything from the router side?
 
Last edited:
I'm going to have to disagree there Paul/DJ.

The broadcom chips in various routers allow you to change the target snr through telnet. The snr reported on telkom's side matches what the router puts out. I'm no network technician but I can positively tell you that the target SNR can be manipulated client side to achieve faster than "normal" sync rates.

I do this often on a cheapie Dlink DSL-2500u (aka the jesus modem)

Without manipulating the target snr, max sync is 2 meg. I can successfully manipulate my target SNR to achieve rates of 3.8 meg stably (such as right now).

To do this I telnet into my router and give the following command:

Code: 
adsl configure --snr 30

The value set for the target snr is a logarithmic scale (some formula I remember reading somewhere on it), where 100 is "standard", lower values are a lower target SNR (i.e. higher sync) vice versa. I've found that a value of 30 gives me a stable and fast line without any impact on normal ADSL packet loss (~0.4%).
 
cavedog said:
How would the exchange "get" your SNR if its not getting it from the router? how would it determine that then? If the exchange is determining you max speed how does it get the data to determine it? It would need some stats from the router to determine distance amongst other thing otherwise how would the exchange know where the router is and what the line is capable of if it does not get anything from the router side?
Click to expand...

It knows the end-point connection, but to the best of my knowledge doesn't rely on the router dictating stats to it. Routers however can play a part, as previously mentioned though.
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X