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[Admacp]

Hi folks, hopefully someone can shed some light on a puzzling sync/snr problem I am experiencing.

I used to have an IP Profile of 1500 which changed suddenly one morning (around 6 weeks ago) down to 750. I have a Belkin uk7632(ver 8) router which can operate with DMT tools as it has a Broadcom chipset. I can force the SNR down to around 6 or 7dB to give me the 1500 IP Profile which seems to work perfectly until the 10th day and then the router resyncs with an snr of around 15.9dB with a downstream bitrate of 992kbits (also tried with my HomeHub 2 but gives even worse results of 17.3dB with an 864kbit connection). The amount of CRCs and Error Seconds are around a max. of 6-10 per 15 minute spell (usually 3 or 4 per 15mins.)

This has happened at least twice now and I am wondering if the BT DSLAM has something to do with it. The BT test socket doesn't give results any better so I assume the internal wiring is ok. The SNR is fairly constant and doesn't fluctuate more than 0.3-0.5dB at any time of the day. The IP Profile always changes quickly when I change the SNR and remains constant until the 10th day!

Any ideas?



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[jeffbb]

Hi
quote : which seems to work perfectly until the 10th day and then the router resyncs with an snr of around 15.9dB

I have not used the DMT tool yet ,but I seem to remember that if you want to your SNR tweak to survive a resynch it must be saved .

quote :The IP Profile always changes quickly when I change the SNR and remains constant until the 10th day!

Are you saying every 10 days it resynchs?

Regards Jeff

[roseway]

With Broadcom-based routers the noise margin tweaks can't be saved, so they don't survive a re-boot. I suspect that this is what is happening on the tenth day - something (high level of interference perhaps) is causing the router to re-boot, leading to loss of the tweak and a lower connection speed.

[jeffbb]

oops  got mixed up with DG team software .
Regards Jeff

[Admacp]

Yeah it's strange that it is on the 10th day. Can't tell if it is caused by interference or not but just seems more than a coincidence as it has happened at least twice now. What is really a problem is that it always reverts back to such a high snr even though the line is stable and the errors aren't too bad.

[jeffbb]

Hi
quote: What is really a problem is that it always reverts back to such a high snr even though the line is stable

It will revert back because as Roseway says the tweak cannot be saved to survive a resynch. So really you need to find out what is causing the resynch.
If your router is compatible try  Routerstats from http://vwlowen.co.uk/internet/files.htm then you can monitor your line for problems.

The application displays various stats(SNR etc)in a graphical form ,for as long as is  required .

The Target SNR may eventually come back down  .Unfortunately patience is required .If lucky and have VERY good stats (low errors) then about every 14 days The target snr will drop by 3db until it is back to default 6db. Sometimes however it takes much longer .For more info on SNR see link below
http://www.kitz.co.uk/adsl/linestats.htm#SNR
regards Jeff

[Admacp]

Thanks for the info. I've forced the snr back down to give me the 1500 IP Profile and the snr is currently sitting at 7.2. I might raise it a bit higher in the morning to (hopefully) allow less errors over the next 14 days and see if it lasts longer than the current 10 day resync I am experiencing. I'll keep you posted. I'm experiencing more errors now that the snr is slightly higher at 7.2 -7.8 than I have been over the last few days when it was hovering between 5.8 - 6.2 which is strange???

[roseway]

I don't want to assign the blame without evidence, but I must say that Belkin routers are quite a long way down my list of preferences. One option you might like to consider is to get a Netgear DG834Gv4 (must be v4) which also has a Broadcom chipset. With this router you can upgrade to the DGTeam firmware, (as mentioned by Jeff) which provides a means of tweaking the noise margin from its web interface, and does save the changes.

[Admacp]

I was thinking about that (is the v4 version better than the GT version?) as I had the Netgear 834GT in mind. The Belkin seems to be ok and appears to be 100% reliable (apart from this dropout/resync every 10 days). Do you think that it is the BT DSLAM that is maybe trying to automate things and it has set the SNRM too high? I'm thinking that it "sees" an artificial snr figure from my router which doesn't match with something else (maybe amount or type of errors either from my router or on it's database). I'm saying that because I regularly use the adsl exchange & line checker (on Kitz website) and it changes from week to week. When I joined BT about 3 months ago it said I could achieve 1Mb fixed and 1.5Mb Max ADSL. It changed after a few weeks and fell down to 0.5Mb for fixed & max then rose back up to 1Mb for both before finally falling back down to 0.5Mb again in the last couple of weeks. This is despite the fact that through snr "tweaking" my dsl connection has given me an IP Profile of 1500 to 1750 for the last 4 weeks or so with no problems, relatively low error counts and no dropouts or resyncs other than the 10 day resync and associated reduced sync speed/raised snr.

It seems strange that in contrast my next door neighbour has also changed from 1Mb down to 0.5Mb and is now currently enjoying 2Mb fixed & 2Mb max adsl stats. Is it also possible that people on the same street share the same physical phone line and more bandwidth is allocated to certain houses?

If I get the Netgear router and DGTeam software and configure it and save to give me an IP Profile of say 1500 does that mean that if the DSLAM decides to "retrain" with my router and wants to drop the sync speed/raise the snr to what it "wants" the router will force the snr down to the saved figure automatically so that the IP Profile won't drop to 750 which is what is happening to me at the moment?

I forced the snr down a bit this morning and subsequently raised the sync speed a little while still remaining in the IP Profile band of 1500. There was a burst of CRC errors on connection to the internet and then the errors have since reduced.


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[roseway]

I was thinking about that (is the v4 version better than the GT version?) as I had the Netgear 834GT in mind.

The DG834GT is a different router. It uses the same BCM6348 chipset as the DG834Gv4, and is more expensive, which is why I suggested the latter. Their performance should be very similar. But you may have trouble finding a DG834Gv4, as it has been superseded by a v5 version using a Conexant chipset which probably doesn't have such good performance.

Do you think that it is the BT DSLAM that is maybe trying to automate things and it has set the SNRM too high? I'm thinking that it "sees" an artificial snr figure from my router which doesn't match with something else (maybe amount or type of errors either from my router or on it's database).

The 'culprit' is Dynamic Line Management (DLM) and it responds to what it sees as instability by increasing the target noise margin to give more room for changes in noise level, and so make the connection more stable. This is what must have happened in your case - there must have been a period of instability which resulted in the target noise margin getting bumped up to the maximum 15 dB. Unfortunately the instability could have been in part the result of your own tweaking, with the consequent re-syncs.

If I get the Netgear router and DGTeam software and configure it and save to give me an IP Profile of say 1500 does that mean that if the DSLAM decides to "retrain" with my router and wants to drop the sync speed/raise the snr to what it "wants" the router will force the snr down to the saved figure automatically so that the IP Profile won't drop to 750 which is what is happening to me at the moment?

If your target noise margin as set by DLM is already at 15 dB it can't go any higher. You can tweak this down to about 9 dB using any of the tweaking methods, and with the DGTeam firmware this tweak will stick, so DLM can't push it back up again.

[Admacp]

I noticed something strange in the internal phone wiring throughout my house. Some of the cables are 4 strand and some are 6 strand. The 6 strand cable is currently connected to my main BT box and taken to an outlet in the kitchen then loops to another outlet in the utility room (where the router is located). Then from the Utility room it is 4 strand to 2 outlets located in the living room. I disconnected the 4 strand cable located on the router outlet and noticed that once the router had re-established it's connection the upstream speed increased from 386kbps to 416kbps although the downstream speed hadn't changed. I read somewhere that if your upstream speed is not as high as expected (I thought that I should be at 448kbps on ADSL up to 8Mb) then that is normally a sign of internal cable faults.

My question is - should the internal cabling be in 6 strand or should it be in the 4 strand cable which I have disconnected. The 2 types don't seem to match when used together even though the 4 strand cable was used after the router outlet point. The blue/white strand is connected to point 2 and the white/blue is connected to point 5. No other strands/wires are connected. Looks like a re-wire job is required but I'm unsure which type of cable to use. Some say cat 5 and some say standard good quality telephone cable - any thoughts?

[roseway]

It doesn't matter whether the cable is 4-strand or 6-strand, so long as a twisted pair (e.g. blue/white and white/blue) is used to connect pins 2 and 5 on the master to the same two pins on the extensions. What you shouldn't do is use two wires from different twisted pairs. You don't need to connect to any of the other pins, and it's better not to. In the unlikely event that you have a phone which needs a ring wire connection, plugging it into a microfilter will deal with that.

[waltergmw]

Hi Admacp,

It might be a good idea to experiment and connect the modem to the test socket within the master socket just to see if that produces a better result.
If so, and your house wiring allows, you could consider using homeplugs to distribute the ethernet signal anywhere within the house from the master socket. That would save on wiring upheaval and the costs / trouble saving might compensate for the home plugs purchase.

Kind regards,
Walter