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Odd numbers

aitch
Hooked
Posts: 6
Thanks: 1
Registered: ‎05-03-2008

Odd numbers

I'm on a 80/20 connection. I'm using a BT business smarthub router which gives me this info about my connection:

Data rate: 16.58 Mbps / 80.00 Mbps
Maximum data rate: 16584 / 82528
Noise margin: 6.2 dB / 3.3 dB
Line attenuation: 20.6 dB / 31 dB
Signal attenuation: 20.6 dB / 31 dB

If the straightforward reading of these numbers are correct (eg that the UP data rate is 16.58Mbps with a Noise margin of 6.2 and attenuations of 20.6) they don't seem to make sense. The BT line checker says that I should get an UP profile of 20Mbps, so why am I stuck at 16Mbps+?

9 REPLIES 9
mort7890
Pro
Posts: 534
Thanks: 86
Fixes: 4
Registered: ‎28-06-2007

Re: Odd numbers

Hi @aitch Profile is 20Mbps however you may not get the full amount as there are many variations on what is on the line and I think 16.58Mbps up is very good

aitch
Hooked
Posts: 6
Thanks: 1
Registered: ‎05-03-2008

Re: Odd numbers

HI mort7890, OK, yeah. I'm not really complaining - I don't do a lot of uploading, so it's not a problem. I am puzzled though by the fact that the modem/router and dslam are happy to negotiate a (very reliable) 80Mbps down synch with a SN margin  0f 3.3 but balk at 20Mbps up with SN of 6.3. And why is the down attenuation so much worse than the up in the same cable?

Hovever, the loss of 3.42Mbps is insignificant given Covid, Brexit and climate change.

198kHz
Seasoned Hero
Posts: 5,405
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Registered: ‎30-07-2008

Re: Odd numbers


@aitch wrote:

And why is the down attenuation so much worse than the up in the same cable?


It's not really worse, just different.

On any ADSL/VDSL line, the downstream uses higher frequencies than the upstream, amd will therefore have a higher attenuation.

To err is human; to purr, feline
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mort7890
Pro
Posts: 534
Thanks: 86
Fixes: 4
Registered: ‎28-06-2007

Re: Odd numbers

Hi @aitch Do a https://speedtest.btwholesale.com/  then the additional diagnostics on you telephone number this will then give you the acceptable range.

aitch
Hooked
Posts: 6
Thanks: 1
Registered: ‎05-03-2008

Re: Odd numbers

Hi Hero. OK that makes sense. Thanks.

aitch
Hooked
Posts: 6
Thanks: 1
Registered: ‎05-03-2008

Re: Odd numbers

Hi mort7890, Thanks, have done that and it says Down IP Profile is 73,65Mbps, Up IP Profile is 20Mbps. 

RealAleMadrid
Seasoned Champion
Posts: 1,791
Thanks: 774
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Registered: ‎07-07-2009

Re: Odd numbers

@aitch On an 80/20 FTTC connection the Upload IP profile is always 20Mbps but the speed you actually get is set by the sync speed of the modem which depends on the line characteristics. Also download speed can be increased by DLM reducing the noise margin to around 3dB as yours is but Upload default value is fixed at 6dB. Your upload speed does seem rather low but there isn't much you can do about it.

The only odd numbers I can see are your attenuation figures which are unusually high, on my line I can get just under 80Mbps downstream at 3 dB margin with an attenuation figure of around 15dB. I suspect that your modem is not reporting correct values.

Edit: Have you another modem/router you could try, it might give better you a better upload speed.

aitch
Hooked
Posts: 6
Thanks: 1
Registered: ‎05-03-2008

Re: Odd numbers

Hi RealAleMadrid, Thanks, useful info. I don't have an alternative router/modem that works at the moment. Anyway, as I say, it's not really a problem for me, so I'm not going to bust a gut over it.

Many thanks to you and mort7890 and Hero - I've learnt a lot from you all.

198kHz
Seasoned Hero
Posts: 5,405
Thanks: 2,284
Fixes: 34
Registered: ‎30-07-2008

Re: Odd numbers


@aitch wrote:

Hi Hero. OK that makes sense. Thanks.


You're very welcome.  🙂

Just for info - 'Hero' is the forum status - 198kHz is the username.

To err is human; to purr, feline
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BT technician (Retired)