ADSL modulation types and line speed

[peterb]

I run a Draytek 2800 connecyed to a standard ADSL+ line provided by BT with Zen as my ISP. My line speed down is usually about 7520000, upload about 448000 with an S/N magin of 6dB and a loop attenuation of around 17dB - all pretty typical for the distance from my exchange (about 600 metres).

a few days ago after the cold weather my phone line developed an intermittent crackle, and would not ring in, although broadband seemed unaffected. A quick call to BT and it was soon sorted, but when I check the line stats, the down load speed had dropped to about 4480000 and an upload of about 2352000. The noise magin had improved, the loop attenuation was the same.

I left it overnight to see if it would improve, which it didn't, but I did notice that the modulation type had changed to T.1413 - a quick Google showed that to be the 'standard' modulation type for ADSL/ (wonderful things, standards - so many to choose from) and this was from the time when the line had been repaired (when the signal must have dropped)


Anyway, I reset the modulation type to G.dmt, rebooted, and my speeds and stas are back where they were.

I haven't done any more research on this, but anyone getting lower than expected speeds on an ADSL+ line might like to check their modulation type - and if anyone tell me what the differences are, I'd be interested to know!

Edit:

Just found this link, which gives some details...

http://forum.zensupport.co.uk/thread/13982.aspx

[peterb]

Quick update - line has been fine and the router is showing an uptime of 300hrs+. The ADSL uptime is 50+ so that was reset for somereason a couple of days ago, but reconnected using G.dmt.

Stats from the router:

Mode State Up Speed Down Speed SNR Margin Loop Att.
G.DMT SHOWTIME 448000 8128000 5.5 17.0

(Formatting seems to be lost, but I'm sure you can read down!)

[badass]

Quick update - line has been fine and the router is showing an uptime of 300hrs+. The ADSL uptime is 50+ so that was reset for somereason a couple of days ago, but reconnected using G.dmt.

Stats from the router:

Mode State Up Speed Down Speed SNR Margin Loop Att.
G.DMT SHOWTIME 448000 8128000 5.5 17.0

(Formatting seems to be lost, but I'm sure you can read down!)

With stats like that you'd see a big increase in speed by using ADSL2+

[peterb]

Yes - if it was available (I just tried connecting using the ADSL2+ protocol. Nothing! (although my re-established G.DMT connection is now a tad slower than it was, but I daresay it will settle down again. AFAIK my exchange isn't due to migrate to 21CN until next year.