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Message 1 of 4

BT Stats

I'm trying to understand the router stats (data rate. maximum data rate, noise margin, line attenuation and signal attenuation). Does maximum data rate mean the maximum speed your line can support but data rate is what you actually get because of the noise margin? so what does 8., 9., and 10. mean?




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Message 2 of 4

Re: BT Stats

6: data rate is what you get, in your case, it's a good line, so you get 20 up and 80 down ~ish This is capped (limited) appropriate to the product you buy, in this case I'm guessing "BT Infinity 2", that's the technology known as VDSL FTTC, with "80 down, 20 up,"  throughput measured in Mbps, that's  MegaBITS per second (the bits is significant to compare with some things, so I've emphasized it)

7: Max data rate is what your line would support, based on the figures it sees/has seen recently, on that line, IF your ISP had not capped you to the 80/20 (20up[/80down, in the order it appears here)

8. More complicated. There's "the signal". And there is "the noise" There is a difference, the levels, the "headroom" between the two. This is the Signal-to-Noise Ratio
   In simplified terms - the difference between signal and noise, is 9.4 deciBels in the upstream band, and 6.8 deciBels in the downstream band. That means your signal is 9.4dB and 6.8dB "above" the noise.
Actually, it's a bit more complex than that, but for these purposes, S:N is good enough see
   As long as it's above the noise,(a positive dB figure) that's good. The higher the signal is above the noise, the better.
Low SNR (Signal:Noise ratio) means the speed will have to be reduce to keep the errors down
High SNRs mean the speed can be increased will little effect on the error rate.
   It is possible (with modern digital coding methods) to have a negative signal-noise ratio - this is most dramatic when used for syncronous Morse code or narrowband transmission methods at very low (slow) data rates but occasionally seen when your modem "hangs on" at 0dB or even lower for a while. This of course could simply be miscalculated or mis-diplayed by the modem, but I've seen several models of modem hanging on at -2 or -3dB before, for a while. Often, a resync happens, where the speed is re-negotiated to make it "safer", slower, to end up with more signal, less noise. 

9: Line attenuation is how much the signal is reduced/lost over the run of wiring from the cabinet (for FTTC) or from the exchange, (ADSL) to your modem. Short lines have less loss, Long lines have more. Damaged lines or incorrectly wired lines (bridged-taps, rather common) have more, as well as other problems too.

   Attenuation is the engineering term for loss, in this case, from the Openreach equipment (MSAN/DSLAM/"cabinet"/exchnage" to yours (CPE/"Homehub"/modem/"modem-router")

10: Signal attenuation - err, probably similar to the above 🙂 This will maybe vary if some extra attenuation is switched in by the equipment, or if the signal is increased(?), for some reason, automatically, maybe, possibly, I guess.

Message 3 of 4

Re: BT Stats

Ok thank you. So my Line attenuation and Signal attenuation are not being reduced at all? and another question that has been bugging me, data rate is 20000 / 79995 should'nt i be able to the full 76Mbs download and 20Mbs upload? I mean I get 75Mbs down and 19 up its only 1Mbs off but whats stopping it from getting the to max? 

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Message 4 of 4

Re: BT Stats

There are loads of reasons why you speedtest is slightly off your line speed max, mainly this will be due to the wider internet conditions. My service is via FTTP and surprisingly I will get a little above my advertised speed, but sometimes below.
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