MTNL Mumbai ADSL2+ router always defaults to Annex M

Hi guys, when I select Annex A on this UTStar router, I am getting Downstream SNR Margin of 15 and Attenuation of 20.
On Annex M, I get SNR Margin drops to 6 and Attenuation is 26

But when I save the settings at Annex A and reboot modem, it always goes back to Annex M. I want to know if MTNL selects modes themselves or there is some problem in this router? I have been using this router since 2010.

It saves the rest of the settings like DNS settings, PPPoE etc fine. Other problem I noticed is the router home page does not open sometimes. I have to repeatedly refresh the page for it to open.

The main settings are set by MTNL on their server. If they set it to Annex M and nothing else, then your modem would have to sync only at Annex M. However, you are able to sync at Annex A as well. That would mean it is allowed as well. The issue is with your modem not remembering this change. Maybe MTNL uses TR-069 to remotely alter the settings? Check if it is so.

Regarding the modem page not opening, it could be another issue with the modem itself, maybe getting overloaded. You could reset it to default settings are reconfigure it from scratch and see if that helps.

thanks bro.. I spoke with them and seems like the modem is fault...but strangely it's doing it's job fine. Even at downstream SNR of 6 db, there is never a major disconnection problem.

Do you think I should just stick with this modem or go for a replacement? What is the major advantage of having a SNR margin of 15 compared to 6? Can the line profile be pushed to 16000 kbps? Right now the profile is at 10000 kbps and I get download speed of about 7.5. The broadband is more or less stable now...only an occasional disconnection.

If your line quility is good then there would be no reason for disconnection. 6dB for DSL is considered border line target for noise margin, any lower will start causing issues. If it remains stable at that value, then nothing to worry about.

DSL modems are available at dirt cheap prices these days due to it being old technology, just lookup a good one on Amazon and change it, if you wish.

SNR is Signal to Noise Ratio, the higher the SNR, the more room there is for noise to co-exist with your actual usable signal (bandwidth). If it gets too low (<6dB), the noise starts to interfere with the actual signal leading to connectivity issues.

As for whether your line can be pushed to any higher sync rate depends more on the attenuation than the SNR itself. Post a screenshot of the modem where is shows the SNR and the attenuation, can let you know if it can be done or not. However, it ultimately depends on MTNL, they have software on their end that checks what is the max feasible rate you line would support, it is according to that they go by.