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Options for Domestic Wired Networking / Broadband

Trev said:
Strange why the line rate went down and the noise went up after the glitch
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It's adapted to the new conditions. The noise is gradually coming down, but the line rate is still at 5500 - no doubt it will recover eventually.

I'll tidy up my wiring to final configuration (so nobody would know I had been at it), gather a few more of these examples, and then tackle BT about it.
 
Trev said:
Strange why the line rate went down and the noise went up after the glitch
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It's not strange at all. It's perfectly normal and is how things work. If the noise margin goes up, your speed is going to go down.
I used to get these noise spikes quite a lot - drove me mad. I rarely, if ever, get them now. Probably coincided with a pair change when BT fixed the last fault.
Most of my loss of about 2Mb over the last 5 years is down to interference from the bl@@dy neighbours.
When there's a power cut, their stuff goes off, mine doesn't and the noise margin has a large step up. I was at home once and happened to catch it. As all their kit restarted when the power came back, the noise margin gradually stepped back down.
 
prpr said:
It's not strange at all. It's perfectly normal and is how things work. If the noise margin goes up, your speed is going to go down.
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I realised that bit, but why is there a step increase in the noise? That's what I find strange.
 
prpr said:
If the noise margin goes up, your speed is going to go down.
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You're confusing cause and effect. The speed is gradually increased until the noise margin drops to a particular level. With BT VDSL it aims for a 3dB noise margin - currently the hub is reporting 2.9dB.
 
No overnight glitches, but the noise margin drifted up to 9dB again. Line rate still 5500.

(This all sounds the wrong way around to me. Shouldn't a higher noise margin be better?)
 
Oh yes, I see the point now, but that raises another question: why isn't my line rate training up and bringing the noise margin down to 3dB instead of sticking around at >6dB?
 
everthewatcher said:
You're confusing cause and effect.
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No, I'm not.
The speed is gradually increased until the noise margin drops to a particular level.
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Yes. But what happens if you get a burst of noise that overwhelms your existing margin? The answer is that the margin increases to the next band to try and protect against the extra noise. This results in a speed drop, because you have traded speed for resilience.
Black Hole said:
Shouldn't a higher noise margin be better?
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Better for what? Speed or resilience?
 
Black Hole said:
Oh yes, I see the point now, but that raises another question: why isn't my line rate training up and bringing the noise margin down to 3dB instead of sticking around at >6dB?
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I've no experience of ADSL as it was never an option here on 6.5km of copper. So I started a bit of research and soon found this:
networkengineering.stackexchange.com

What is SNR Margin and Line Attenuation?

I'm currently using an adsl connection and last week an engineer from my ISP came and told me that my SNR margin and line attenuation is not good, and they need to replace the main telephone cable to
networkengineering.stackexchange.com networkengineering.stackexchange.com
 
So far as I know, VDSL is little different in general concept than ADSL - it's just the next generation in a chain of development ADSL, ADSL2, ADSL2+, VDSL, VDSL2, VDSL2+... All tweaks to get ever increasing data bandwidth out of a long pair of wires.

Frankly, I find it astonishing that a small box at my end (and presumably a more sophisticated box at the other end) is able to selectively process 200-odd sub-carriers and combine the data transport capabilities of each into a multi-tens-of-megabits-per-second data stream. Our HDR-FOXes only process two data streams, each from one carrier.
 
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That brings another thought to mind: I am using a second-hand Netgear modem/router acquired from Trev. As line negotiations are limited at the highest common standard, the modem at my end could be the limiting factor.

I ditched the BT HomeHub4 because of its user configurability limitations, but it may well have a better modem than the Netgear. Unfortunately the HH4 is so locked down it can't be used as a modem only and connected to the Netgear's WAN input (according to the relevant forums).

Really, I'm more than happy with the speed improvement thus far for minimal expense (the drop-outs are the bug bear), but I am curious what more could be done. Maybe I should resurrect the HomeHub4 temporarily, just to see if it brings the rate up and give me an idea whether a new router would be worth the cost.
 
Black Hole said:
Unfortunately the HH4 is so locked down it can't be used as a modem only and connected to the Netgear's WAN input (according to the relevant forums).
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But you can achieve near enough the same result by putting [the] HH4 or other ISP-supplied router on it's own subnet and point your router's WAN port at it. It's what I've done here and means all my network settings are in my router (currently a it's a Netgear DGND3700v2) and not the BT Smart hub.
 
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