ASDL vs ADSL2+ modulation on 37dB attenuation

[davej99]

My local exchange was recently upgraded to 21CN. Previously I had 20CN ADSLMax interleaved sync of 8128, a profile of 7125, attenuation of 35dB and a noise margin of 6.3dB. Line was very stable, never lost sync and gave working download speeds of 6300 to 6500.

After a week on 21CN modulated to the default ADSLMax, I get a sync of 7360, a profile of 6490, attenuation of 37dB, a noise margin of 9.3dB and working download speeds of 6000 to 6300. Some times I get a sync of 7400 with a profile of 6610. I did notice syncs up to 8000 initially.

The move to 21CN coincided with a faulty Gb switch, which meant I had to swap out routers and change settings by way of diagnostics, leading to several reboots, so this might have influenced any training.

Kitz suggests my 21CN 37db attenuation should support an ADSL2+ sync of 10656 and a profile of 9000. Tech support say I can have ADSL2+ modulation, but it may not be better and it could be worse.

So my question is what do you think I should do and is there a charge to swap back and forth?

Thanks, Dave

[Rik]

I'd check the cause of the increased NM first.

[Ardua]

My experience of the switch to 21CN, a year ago, was that my downstream SNR rose to 15 and it stayed there for 4 months before falling by 3 thereafter every month or so. Initially, I was getting about 10Mbps downstream but I now have a very stable connection at c.17Mbps. I went through routers, ring wires, filters and faceplates in an attempt to get the downstream speeds indicated on various sites and testers (13Mbps) for my line attenuation. I know from personal experience how difficult it is not to fiddle, and how frustrating it is when the 'promised' speed isn't realised but my advice would be 'leave things well alone for at least a month and then check the stats again' - you might be surprised.

[davej99]

Thx, Rik. Can't think of anything my end that has changed. I have never been subject to resyncs or line problems. All the usual stuff on primary faceplate filters and bell wires was done years ago. Because I was not expecting 21CN ADSLMax modulation I was not monitoring the situation. I was in fact wrestling with low download speeds for no apparent reason. It looked like exchange congestion because syncs and profiles were good and speeds were in the hundreds, both before and after 21CN conversion.  It turned out I had a problem Gb switch, which meant I had to swap out routers, change settings and reboot several times by way of diagnostics. Not sure if 21CN trains, if it does, this may have trashed the sync and margin. But it does not pay to ignore good advice, so I think I will do some testing at the primary. Otherwise I do not know how I ended up with a 9dB margin after four years at 6dB. I can only speculate that for ADSL2+ a higher margin is required to handle higher bin frequencies employed.

Thx, Ardua. At present I am still on ADSLMax modulation, that is I have moved to 21CN but the service is still the old ADSL 8128 max sync, rather than the higher ADSL2+. Did you move over straight away or was your NM increase for ADSL modulation too?

Dave

[Rik]

Multiple resyncs will still tend to wake DLM from its slumbers and bump the target NM upwards.

[Ardua]

Thx, Ardua. At present I am still on ADSLMax modulation, that is I have moved to 21CN but the service is still the old ADSL 8128 max sync, rather than the higher ADSL2+. Did you move over straight away or was your NM increase for ADSL modulation too?

Dave

I went straight to 21CN and have stayed there. I purchased a new Netgear dual band router in anticipation of the change and from the off it just keep re-synching. Every time the phone rang or I tried to make a call 'Bingo'. I then borrowed a Netgear 1000 from IDNet and the connection was slightly more stable and, eventually, I purchased a FB7390 - primarily, too rule out DECT interference. The rate of re-synchs dropped but still happened whenever I got an incoming call. Once I had double filtered the phone line, there was a marked improvement but I was still getting lots of errors and a disconnect about every 1 to 3 weeks. As I said before, it took 3 to 4 months before anything began to change. I have no idea why. Best of luck trying to solve your issues.

[davej99]

Thx, Ardua. Your experience seems quite common after switching, so I was happy to go to ADSL modulation over 21CN to begin with. The problem is we cannot explain why sync is lower and noise margin is higher.

Rik, have now done quite line test and primary socket tests (faceplate removed) using older DG834v3 and newer DGN 2200 router. Line is quiet with barely audible white noise on a passive phone. Syncs and NMs are all very similar, with DG834 a little worse, but none much different than usual configuration with filtered faceplate fitted and router connected to its dedicated ADSL extention. Had a look at SNR per tone on DG834, (DGN2200 blocks telnet). SNR roll off looks typical for my line, losing margin above bins over 252.  Interleaved. Errors look normal. Any further thoughts?

Thx, Dave

[Rik]

Patience? I think you may have to allow things to settle, Dave.

[davej99]

After a week running 21CN/ADSL modulation very stabily with a sync of 7,360kbps, 37dB attenuation and an 9dB margin, and after a chat with Brian in tech support, who was extremely helpfull, we decided to give ADSL2+ modulation a try.

It came up on Tuesday with good results. An 8,904kbps sync, 40dB attenuation and an 8.9dB margin. After a couple of days and after the first re-sync, initiated by training I think, I now get 10,075/1,135kbps sync, 8,890/832kKbps profile, 39.5/20.1dB attenuation, 5.8/5.1dB margin, down/up. Download speeds are flat lining at the profile and Speedtest.net is reporting 8,690/960Kbps, down/up.

That is a whole lot better than the 6,000-6,500/330kbps I used to get with 20CN ADSL from stats of 8,128kbps sync, 7,125kbps profile, 35dB attenuation and 6dB margin. Pings to IDNET have fallen from about 42ms on 20CN ADSL, to 38ms on 21CN ADSL to 22ms on ADSL2+, so I guess interleaving is now off.

Overall for a line that just held a maximum 8,128lbps with 35dB attenuation and 6dB margin on 20CN I am very pleased to be getting much improved performance with ADSL2+.

So well done IDNET/BTW.

Ed: Perhaps this thread should go in the Broadband section.

[Rik]

And it has...