SRA not working?

[MartinP99]

My ISP is Merula, and they have recently switched my phone line from BT ADSL Max to TalkTalk LLU so I can get ADSL2+ Annex M. Still with Merula, just different provider at the exchange.

I have used the SNR feature to tweak my downstream speeds, which bumps my downstream speeds from ~9mbps to nearly 11 with a noise margin of about 2.8dB at sync time.

The problem I have is that when the line noise varies my noise margin can drop until it is negative. While the WAN Statistics show zero errors or drops, the actual download speeds fall off a cliff. For instance, this was at a Sync of 12055 / 1411 - upload speed is ~83% of sync as expected, but download is only 3% of sync:-


I'm a little confused why the error & drop counts stay at zero, but I'm not surprised to get performance problems at very low noise margins.



However, I do have SRA enabled, which I thought would take care of this according to the manual and knowledgebase:-

SRA, short for Seamless Rate Adaptation, is a technology used to adapt the rate seamlessly without any influence to the working system, to assure of the quality of the ADSL system.

Posted by Milton on 25 July 2008 04:02 PM
SRA (Seamless Rate Adaptation), a protocol which, by decoupling the modulation and framing layer, can change the transmission data rate parameters (applied by the modulation layer) without changing any of the frame layer parameters, so there is no need for restarting or resynchronizing the two end systems.

Has anyone had SRA actually adjust their sync speeds?

cheers, Martin

PS I've just turned off PhyR, will see if that has any effect.

[Tomken]

Enabling SRA is only effective if your ISP use it as their line management and have it activated at the exchange.

TalkTalk have their own which is Dynamic Line Management (DLM) and you can request for it to be switched off.

Billion tech support don't advocate the use of PhyR (don't know why) and I have found that it can keep the SNRM too low and can cause connectivity problems, which may or not be related to longer lines.

For proper line stats regarding error reporting it is better to use telnet as my errors can be quite high at times and they still don't show up in the router.

[MartinP99]

OK, that's disappointing, but thanks.

I've managed to telnet to the router, but what commands would I use to check for errors? Is there a way to drop / restart the ADSl connection via telnet?

Thanks again.

cheers, Martin

[Tomken]

The telnet cmd for line stats is adsl info --stats and you can restart the router from telnet by the cmd reboot

All cmds are executed by pressing Enter and notice the space before the two dashes.

However, the telnet page is not dynamic and cannot be refreshed and once the router has resync'd, pressing any key will log you out of telnet and you will have to log back in to see the stats.

For usage of telnet cmds enter adsl --help and for a list of the categories enter help at the cmd prompt.

Entering any of those categories at the cmd prompt will show its usage.

Hope this will be of help.

[MartinP99]

Thanks for the stats info - I'll start looking into that.

And, BTW, I found how to stop & restart the ADSL connection without restarting the router:-
http://192.168.1.254/snr.cgi?snr=100

It reconfigures the router for a particular SNR level (in this case the default 100), which the 7800N then takes as the signal to restart the ADSL connection targetting that SNR. Works whether or not you're setting the same value that's already configured.

This is also the only method I've found to restart ADSL from within the management pages (go to the /snr.html page, then click apply without changing anything).

Importantly, this seems to allow downloads to seamlessly continue once the connection is restored, which wouldn't happen if the router was fully rebooted.

cheers, Martin

[Tomken]

The value for default SNRM on mine is -1 but I'll try those others out. Thanks.

[MartinP99]

Apparently, the number is just a percentage, but I guess 100% and -1 could do something different.

cheers, Martin

[Tomken]

If having tweaked the SNRM and you want to revert to your original ISP profile, then -1 is the value you enter.

The table of the values you can enter to reduce the SNRM by a given amount can be found at http://www.spaldwick.com/broadband/billion-7800n (I printed the 2 pages out) and if you want to temporarily increase your SNRM from your ISP profile should you start to experience instability problems, entering the value of 150 will increase it by 3dB and 200 will increase it by 6dB.

3dB equates to a difference in speed of about 300kbps either way depending on whether you reduce or increase your SNRM.

When I first went into the tweaking page, the value was set at 0 but if you enter that after tweaking, it responds with an invalid value error.

I haven't got round to trying those others out yet as I'm not sure if BT's local area fibre installation is causing problems or if it's down to the refurbishment work that is going on (demolishing/rebuilding properties), but my Downstream Atten. has increased from 49.5-50 to 50.5 and has been giving lower resync problems and as I've finally gotten it back to somewhere where I like it, don't want to risk any more resets.

[MartinP99]

If having tweaked the SNRM and you want to revert to your original ISP profile, then -1 is the value you enter.

The table of the values you can enter to reduce the SNRM by a given amount can be found at http://www.spaldwick.com/broadband/billion-7800n (I printed the 2 pages out) and if you want to temporarily increase your SNRM from your ISP profile should you start to experience instability problems, entering the value of 150 will increase it by 3dB and 200 will increase it by 6dB.

3dB equates to a difference in speed of about 300kbps either way depending on whether you reduce or increase your SNRM.

When I first went into the tweaking page, the value was set at 0 but if you enter that after tweaking, it responds with an invalid value error.

I haven't got round to trying those others out yet as I'm not sure if BT's local area fibre installation is causing problems or if it's down to the refurbishment work that is going on (demolishing/rebuilding properties), but my Downstream Atten. has increased from 49.5-50 to 50.5 and has been giving lower resync problems and as I've finally gotten it back to somewhere where I like it, don't want to risk any more resets.

This suggested 100= "No change/reset to default value" (not an official site, of course - and the numbers don't seem to work unless the default noise margin is 6dB):-
http://www.increasebroadbandspeed.co.uk/billion-7800n



I configured RouterStats so that it issues a "reboot" if noise margin drops below 2dB for more than 20s (four samples at 5s-between-samples), but set the "reboot" URL to be the SNR= one.

It just issued the DSL restart in the middle of watching a youtube video, and the DSL restart was complete before it ran out of buffering (I was lucky it had buffered well ahead). The rest of the video buffered almost instantly when the connection came back - in fact even before the "internet" LED came on.

cheers, Martin

[Tomken]

I may watch the odd youtube video when I'm researching something and if it starts to buffer, I just pause it and run CCleaner to clear the cache which also clears the Flash Player cache and that usually does the job.

If the buffering is down to lag and it becomes unwatchable, then I'll probably close it down and look for another source or wire up, which normally increases the SNRM and lessens any lag.

The problem with having it auto reboot as well as interupting videos, is that if it happens too often, then the line management will kick in and increase your SNRM so rather than risk having too many of these auto reboots when your line is a bit buggy, just wire up as insurance when you stream any videos.