Re: Impact of hardware with bad SNR & Attenuation
- From: Phil Thompson <phil.thompson@xxxxxxxxxxx>
- Date: Wed, 31 Aug 2005 12:42:13 +0100
On Wed, 31 Aug 2005 11:56:45 +0100, "Mark Rogers"
<mark-news@xxxxxxxxxxxxxx> wrote:
>I'm struggling to find comprehensive (or at least convincingly accurate)
>information on what I'm sure must be a FAQ:
sounds like you need a training course ;-)
>- What are the "good" values for SNR/attenuation for
6 dB of SNR margin is a typical minimum for reasonable service, 10 dB
or higher should be robust.
> different line speeds, and more importantly:
> - what are the symptoms of borderline low SNR?
disconnections, lots of errors.
> - what are the symptoms of borderline high
> attenuation?
none, unless it results in low SNR margin
> - what (in each case) if the upstream figures
> are good and downstream bad?
> - Vice versa?
BT's 512k products will slow down the data rate if the upstream margin
is too low, should show up as a low upstream speed (fairly rare). 1M
and above will fail to sync if inadequate upstream SNR margin.
>- Regarding CRC errors:
> - what causes them?
> - what is a "good reading? (Obviously 0 is good
> but at what figure should I worry about them?)
> - what impact do they have?
errored seconds (seconds with one or more errors) can be useful, 5 in
an hour isn't a problem, is. CRC errors arise when the signal is
corrupted by interference or by being too weak for the modem.
>- What impact does hardware play in making up for
> borderline figures? Eg:
> - having a crap filter?
> - having crap cable?
> - having a crap modem?
> - having too much or crap telephone equipment
> hung on the same telephone line?
all of these things can reduce the SNR, attenuation is more robust.
>- What does environmental conditions (eg weather)
> affect:
> - the SNR and attenuation readings?
> - the impact of bad values?
thunderstorms generate noise that reduces SNR. Rain can affect damaged
cables.
>To put the whole question another way: I want to have a reasonable idea if I
>visit a customer with ADSL issues, when I look at the information the router
>can tell me, what I should do. In which cases will changing the hardware
>help (and in those cases what should I be changing).
if you are going in as a diagnostic expert I would suggest you carry a
"golden modem" known to work well on a battery powered laptop. Take
along a known good filter and an RJ11-BT adaptor too. Diagnosis by
changing / removing things seems the most practical.
The most common problem area IMO is the domestic extension phone
wiring. Use the test socket (where available) to separate this out
http://www.adslguide.org.uk/newsarchive.asp?item=2182
Phil
--
Tiscali - dialup speeds at Broadband prices, see
http://bbs.adslguide.org.uk/postlist.php?Cat=&Board=tiscali
AOL - the unlimited ISP of choice for heavy downloaders.
.
- References:
- Impact of hardware with bad SNR & Attenuation
- From: Mark Rogers
- Impact of hardware with bad SNR & Attenuation
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