[Gllug] ADSL SNR

[Adrian McMenamin]

On Wed, 2006-06-07 at 18:26 +0100, Daniel P. Berrange wrote:
> On Wed, Jun 07, 2006 at 05:57:13PM +0100, - Tethys wrote:
> > >I didn't really notice the difference.  Most downloads still max out
> > >at around the 2 Mbps mark.
> > 
> > I noticed the difference. When I first switched from 2Mb/s to 8Mb/s,
> > my downlaod speeds dropped by 75%, and the reliability of the line got
> > noticably worse. Coincidentally (or perhaps not), this change happened
> > at the same time that my ISP was bought out by Pipex. Fortunately,
> > things have settled down somewhat now, and I get decent (~4Mb/s)
> > downloads and good reliability.
> 
> This actually correlates back to the question at the start of the
> thread - the max speed you can get over ADSL is directly related to
> the S/N ratio & line attenuation. Say, for sake of discussion[1], the
> thresholds are
> 
>    1mb  8db
>    2mb  10db
>    8mb  12db
> 
> Then if your line S/N is curently 10db & they re-grade you to an 8mb
> line, you'll clearly suffer from unreliability. I had this problem at
> my last place in London - we had dodgy internal wiring & so although
> BT tested the line & declared it good for 2mb service, the internal
> wiring was so crappy it would only cope with 512kbs service. Needless
> to say, when our ISP "upgraded" us (without telling us they were planning
> to do so) reliability went through the floor.
> 

Had much the same experience with Homechoice - paid to upgrade to 2
Mb/s, then they upgrade me to 4 for free and the service became close to
unusable. Funnily enough, it's become noticibly more stable in the last
three weeks and I can get 450 Mb/s downloads.

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