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JinxterX2
SNR
1. Signal-to-noise ratio is an engineering term for the power ratio between a signal (meaningful information) and the background noise.
2. When your modem attempts to negotiate ADSL it looks at the line and basically sees attenuation and noise put together. Attenuation gradually increases as frequency increases and noise is a random pattern of low level interference in the background.It's very similar to a conversation at a party and it's dealt with in the same way; we naturally account for both distance from the other person and the amount of background noise. When we do we don't just talk loud enough to be heard, we speak a bit louder waiting for the idiot with the stupid, loud laugh to start up again. We add a bit extra on to make sure we're louder than the average change in background noise. This is a SNR margin.
ST516v6
3. The SpeedTouch 5x6 products are ADSL2+ replacements for the SpeedTouch 510E, 536 and 510 switch models.
The 516v6 uses the Broadcom chipset, BCM6338 which is the cheaper, more integrated version of the BCM6348.
DMT Modem Tool
4. A nice bit of software (from Germany) that allows you to tweak and monitor certain models of Speedtouch routers (516 536 546 585 608 706 716 780).
Although this software is in German it can be switched to English via 'Extras>weitere Einstellungen' (Special>Misc. Options) and then initiating a program restart OR it will automatically switch to English if it detects a Annex A connection.
How do I use DMT Tool?
Use this picture as a reference
A. Fill in your login details and click Connect.
B. Click the modemoptions tab.
C. Untick default.
D. Tick modify.
E. Enter a value into option 00.
F. Click apply/resync, wait for the new sync and click save settings if you are happy with the result.
G. Click Refresh to confirm settings or check if telnet session is still active.
How does it work and what settings should I use?
Changing the value in modemoption00 increases or decreases the gain on the SNR margin across all the tones in the frequency range. Think of it as a volume control.
The settings you should use are highly dependant on your own line conditions and can only be determined through experimentation, however as a rough guide this is what I have discovered for my own situation:
Line length: 4.5Km
SNR Margin in DSLAM: 15db
Router Signal Attenutation: 46-49db
value* - margin
08 - 10db
10 - 10.5db
18 - 11db
20 - 11.5db
28 - 12db
30 - 12.5db
38 - 13db
40 - 13.5db
48 - 14db
50 - 14.5db
58 - 15db
60 - 15.5db
68 - 16db
70 - 16.5db
78 - 17db
80 - 17.5db
* - hexadecimal.
Why should I tweak?
Simple, to find the best performance vs stability level for your ADSL(MAX) line. Please note you must be realistic about the capabilities of your line. If you try and push the limits too far, your sync will fail when the line is exposed to large amounts of noise or interference, especially at nightime.
Example
I've made a small movie showing clearly the effects of tweaking the SNR margin and it's impact on high frequencies and tone bit loading.
Watch it here
You can download the DMT screenshots used in the movie from here.
Good luck and happy tweaking
Links to sources
1. Wikipedia
2. Whirpool
3. Speedtouch
4. DMT tool
I use firmware R6.1.0.5 on my router, you can get this here.
Jinx.
Edited by JinxterX2 (Mon 22-May-06 16:06:32)
