New ADSL2+ Service Performance

Hi

I have done a bit of research and have found out how ADSL2+ works but I cannot relate the numbers to a 'level of expectation'. Can you help?

I have migrated from ADSL1 to ADSL2+. I was getting about 6 Mbps on ADSL1. On ADSL2+ I have a noise margin of 15dB dropping occassionally to 12dB, a sync speed of 11500 bps and a downstream attenuation of 26dB. The service has been running for about 10 days and I am getting a speed of about 7 Mbps which is less than I had hoped for.

I have used RouterStat to examine the tones and I am seeing a 37dB SNR for the lower frequency tones which are carrying 9 bits and a 22dB SNR for the high frequency tones which are carrying 2 bits. Bucket utilisation and SNR move down smoothly between lowest and highest frequencies and there is no reported bitswap.

Am I getting what I should expect, or is there more to come? If the latter, how can I force it to arrive more quickly?

Thanks

Paul

For ADSL2+, the equipment affects the connection greatly. What router are you using?
Who's the ISP?

Sorry - should have said!

I have a Netgear DG834 v4 and a Billion 7300G. I tried swapping from the Netgear to the Billion and the results were unchanged. I could not test the tones on the Billion but the overall speed was the same.

The ISP is Eurotel.

Thanks.

Edited by pieronip (Fri 03-Jul-09 21:40:43)

Ok, the router is fine - it should work well with ADSL2+, but the problem is the SNR is way too high. Hopefully there is a reason for that which your ISP should be able to help you with.
Unfortunately, the underlying service is provided by Tiscali

In reply to a post by BatBoy:

the SNR is way too high.

Excuse my confusion but I thought that a high SNR is what is wanted. THe figures I mentioned are for the individual tones. The router does not give an overall SNR.

I am about 1.2K from the exchange. What figures would you expect from the information I have given?

Many thanks.

You should see 17Mbps, but your SNR margin is soaking up a lot of that. If your SNR Margin was the standard: 6dB, you would get an extra 5Mbps or so. Your line length is about 1.6Km.

I'm sure your router does give an overall SNR margin somewhere...

so your sync speed is 11500, a speed test should get about 9600 from that. 7M is 73% of that which maybe isn't too bad for a contended service, is it better at 6am ?

You should also check out your computer's RWIN value as this can constrain TCP/IP throughput. Is it a wired connection ?

Phil

MaxDSL - goes as fast as it can and doesn't read the line checker first.

MaxDSL diagnostics
Are your kids pirates ? Limewire, Bearshare, Kazaa, BitTorrent, eMule are all tools of the trade.

The speed is pretty steady over time and it is a wired connection

I'll check the computer's TCP parameters.

The tones info from RouterStats suggests that the buckets are not filled to their capacity and I wonder if this will improve with time.

According to my understanding, I reckon - my highest frequency tones have a 21dB SNR. This should give me 7 bits at 3 dB per bit - but I only get 2 bits. Other tones seem proportionately reduced.

I expect I'll end up with a poorer service than I should have but with no grounds for complaint!

Hi

The tones info from RouterStats suggests that the buckets are not filled to their capacity and I wonder if this will improve with time.

Your SNR margin is high. The way a higher margin is achieved is by not loading the buckets to their fullest capacity. Note that not all buckets will be the same size so you can't fill them all to the same maximum unless you live in the telephone exchange.

Excuse my confusion but I thought that a high SNR is what is wanted. THe figures I mentioned are for the individual tones. The router does not give an overall SNR.

This is something dating back to fixed speed lines. If you had a fixed service of 1 Meg and an SNR margin of 20db, this is better than having a fixed 1 Meg service at 6 db, as the higher value indicates you have a better line and it would be much more stable. If you improved your wiring and the margin goes up, that is an improvement and so higher was better.

Now we don't have maximum caps like 1 Meg or 2 Meg, this means you can now "trade" all that extra SNR margin for faster speeds. It is generally accepted that having a margin of just 6db is all you need, so the rest above that is given up in order to achieve the faster speed. Those that only had 6db on a fixed rate service, have nothing to trade for higher speed and so see much smaller improvements on faster services.

So yes higher SNR margin is good, but to give you any benefit you need to give it up to get the speed.

Hope that makes sense.

Regards

Phil

Thanks Phil

Right, that makes sense. If my SNR margin were 6dB instead of 15dB the extra 'capacity' could go towards more bits per bucket.

Now, the critical question - can I do anything to lower the margin, can my ISP do anything or will it adjust with time.

A secondary question - why would the router/DSLAM negotiate such a high margin anyway?

Thanks again.

Paul