Noise, attenuation and CRC figures?

Finally got broadband yesterday, and I've been having a look at my
router's logs. Three things I noticed, as follows:

Operation Data Upstream Downstream
Noise Margin 31 dB 31 dB
Attenuation 28 dB 25 dB

Defect Indication
Indicator Name Near End Indicator Far End Indicator
Fast Path CRC Error 7 0



Router is 3Com 3CRWDR100A-72, ISP is Pipex.

Are the noise and attenuation figures about right?
What is the Fast Path CRC Error? Anything to worry about?
Can anyone suggest a resource about this sort of data?



--
Nigel M

"Time may be a great healer,
but he's a lousy beautician"

"Nigel M" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Finally got broadband yesterday, and I've been having a look at my
> router's logs. Three things I noticed, as follows:
>
> Operation Data Upstream Downstream
> Noise Margin 31 dB 31 dB
> Attenuation 28 dB 25 dB
>
> Defect Indication
> Indicator Name Near End Indicator Far End Indicator
> Fast Path CRC Error 7 0
>
>
>
> Router is 3Com 3CRWDR100A-72, ISP is Pipex.
>
> Are the noise and attenuation figures about right?
> What is the Fast Path CRC Error? Anything to worry about?
> Can anyone suggest a resource about this sort of data?
>
>
>
> --
> Nigel M
>
> "Time may be a great healer,
> but he's a lousy beautician"

Hi Nigel,

I don't know about the CRC figures but the noise margin must be more than
about 10 or 12dB, in fact, the higher the better, so you're fine with those
figures. The attenuation has to be no more than about 60dB for the 1Mb
service and no more than 41dB for the 2Mb, so you'll be OK for the faster
services as they come along.

Mogweed.

"Nigel M" (E-Mail Removed) wrote in message
news:(E-Mail Removed)
>
> Operation Data Upstream Downstream
> Noise Margin 31 dB 31 dB
> Attenuation 28 dB 25 dB
>
> Defect Indication
> Indicator Name Near End Indicator Far End Indicator
> Fast Path CRC Error 7 0
>
> Are the noise and attenuation figures about right?

Look very good.

From my frequently dodgy long reach Pipex/3Com:

> Operation Data Downstream
> Noise Margin 9 dB
> Attenuation 64 dB
>
> Defect Indication
> Indicator Name Near End Indicator Far End Indicator
> Fast Path CRC Error 47845 331

"Grant" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> "Nigel M" (E-Mail Removed) wrote in message
> news:(E-Mail Removed)
>>
>> Operation Data Upstream Downstream
>> Noise Margin 31 dB 31 dB
>> Attenuation 28 dB 25 dB
>>
>> Defect Indication
>> Indicator Name Near End Indicator Far End Indicator
>> Fast Path CRC Error 7 0
>>
>> Are the noise and attenuation figures about right?
>
> Look very good.
>
> From my frequently dodgy long reach Pipex/3Com:
>
>> Operation Data Downstream
>> Noise Margin 9 dB
>> Attenuation 64 dB
>>
>> Defect Indication
>> Indicator Name Near End Indicator Far End Indicator
>> Fast Path CRC Error 47845 331

Yes, very good results.

I'm about 100 metres from my local exchange as the crow flies and the wires
can't be more than twice that distance. My results are:

Downstream Upstream
Line Attenuation 30.3 dB 31.0 dB
Noise Margin 6.0 dB 5.5 dB


Very good attentuation figures but the noise margin is nowhere near as good
as the OP's.


So far, the speed tests that I have done have varied between 1.2 and 1.9
Mbit/sec (for a 2Mbit/sec service), so it doesn't affect the transfer rate.
I'm sure the lower speed results are simply due to contention.

In uk.telecom.broadband, Martin Underwood wrote:

>>> Operation Data Upstream Downstream
>>> Noise Margin 31 dB 31 dB
>>> Attenuation 28 dB 25 dB

>Yes, very good results.

Thanks for all the replies.

Coming from a background of broadcast TV engineering, it is hard to
think of 28dB attenuation, or 31db noise margin, as being "good" ;-)

I'm about to have my second line removed, so I can now do so without
thinking "what would that one have been like?".


--
Nigel M

"Time may be a great healer,
but he's a lousy beautician"

Martin Underwood wrote:
>
> I'm about 100 metres from my local exchange as the crow flies and the wires
> can't be more than twice that distance. My results are:
>
> Downstream Upstream
> Line Attenuation 30.3 dB 31.0 dB
> Noise Margin 6.0 dB 5.5 dB
>
>

They seem truly awful for your situation, unless you've quoted in reverse !
I am at 300m and get 8dB att, 40dB margin

Bill

"Nigel M" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Finally got broadband yesterday, and I've been having a look at my
> router's logs. Three things I noticed, as follows:
>
> Operation Data Upstream Downstream
> Noise Margin 31 dB 31 dB
> Attenuation 28 dB 25 dB
>
> Defect Indication
> Indicator Name Near End Indicator Far End Indicator
> Fast Path CRC Error 7 0
>
>
>
> Router is 3Com 3CRWDR100A-72, ISP is Pipex.
>
> Are the noise and attenuation figures about right?
> What is the Fast Path CRC Error? Anything to worry about?
> Can anyone suggest a resource about this sort of data?
>
>
>
> --
> Nigel M
>
> "Time may be a great healer,
> but he's a lousy beautician"

What speed is your downstream connection Nigel?
This would be quite relevant to the figures.

John

In uk.telecom.broadband, John wrote:

>What speed is your downstream connection Nigel?

500 ATM, waiting for upgrade to 1000

--
Nigel M

"Time may be a great healer,
but he's a lousy beautician"

"Martin Underwood" <(E-Mail Removed)> wrote in message
news:426a5b1c$0$83089$(E-Mail Removed)...
> "Grant" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> > "Nigel M" (E-Mail Removed) wrote in message
> > news:(E-Mail Removed)
> >>
> >> Operation Data Upstream Downstream
> >> Noise Margin 31 dB 31 dB
> >> Attenuation 28 dB 25 dB
> >>
> >> Defect Indication
> >> Indicator Name Near End Indicator Far End Indicator
> >> Fast Path CRC Error 7 0
> >>
> >> Are the noise and attenuation figures about right?
> >
> > Look very good.
> >
> > From my frequently dodgy long reach Pipex/3Com:
> >
> >> Operation Data Downstream
> >> Noise Margin 9 dB
> >> Attenuation 64 dB
> >>
> >> Defect Indication
> >> Indicator Name Near End Indicator Far End Indicator
> >> Fast Path CRC Error 47845 331
>
> Yes, very good results.
>
> I'm about 100 metres from my local exchange as the crow flies and the
wires
> can't be more than twice that distance. My results are:
>
> Downstream Upstream
> Line Attenuation 30.3 dB 31.0 dB
> Noise Margin 6.0 dB 5.5 dB
>
>
> Very good attentuation figures but the noise margin is nowhere near as
good
> as the OP's.

Agreed. And since at this kind of attenuation you should have much better
noise margin, there may well be a problem on your system.

I had to fix a similar issue for a family member (with higher attenuation,
so margin was around 4 dB) - once we sorted out the house wiring the noise
figures improved by 10 dB......
>
>
> So far, the speed tests that I have done have varied between 1.2 and 1.9
> Mbit/sec (for a 2Mbit/sec service), so it doesn't affect the transfer
rate.
> I'm sure the lower speed results are simply due to contention.
--
Regards

Stephen Hope - return address needs fewer xxs

"stephen" <(E-Mail Removed)> wrote in message
news:R9Lae.3206$(E-Mail Removed)...
> "Martin Underwood" <(E-Mail Removed)> wrote in message
>>
>> I'm about 100 metres from my local exchange as the crow flies and the
> wires
>> can't be more than twice that distance. My results are:
>>
>> Downstream Upstream
>> Line Attenuation 30.3 dB 31.0 dB
>> Noise Margin 6.0 dB 5.5 dB
>>
>>
>> Very good attentuation figures but the noise margin is nowhere near as
> good
>> as the OP's.
>
> Agreed. And since at this kind of attenuation you should have much better
> noise margin, there may well be a problem on your system.
>
> I had to fix a similar issue for a family member (with higher attenuation,
> so margin was around 4 dB) - once we sorted out the house wiring the noise
> figures improved by 10 dB......

Well the underground wiring to the house will have been installed about four
years ago and probably takes a direct line back to the exchange since all
the land was derelict before my development was built so they didn't need to
go via the road. Even if they did go via the main road, the length is
probably not more than 200-300 metres.

The socket where the router is plugged in was installed by BT: from the
master socket, it goes through the outside wall, up the outside and in
through the bedroom wall to the socket. It's good thick 2-core BT wire -
looks like the sort that they use between the pole and your house. In
parallel with this, also leading off the master socket, is wiring installed
by the builder which leads to further sockets in the lounge and in another
bedroom. It would be interesting (but illegal!) to disconnect the house
wiring and BT-installed wiring to see if it made any difference.

When I first got the router, before my broadband was enabled, I tried it at
my parents' house and got very similar figures for much older wiring and
much further distance - probably about 1.5 km. And long lengths of
non-BT-installed wiring from the master socket, with several junctions and
splitters.

I've just tried plugging the router into my master socket to see if the
figures
changed at all, but it made an improvement (increase) of only about 0.5 dB
to the
upstream noise and an improvement (decrease) in downstream attenuation of 1
dB; interestingly the downstream noise figure stayed the same despite
slightly less attenuation.

But since I'm getting good transfer rates (apart from connection) then the
noise figure is a bit academic really!