Helmut,
you did a very thorough overview of ADSL. Good job.
me thinks it took more than 3 minutes to write.
The original poster did note that the problems are present when it is
ethernet only. Which means that the wifi explanation fades.
Not completely - wifi is always a problem and is never fast enough.
Given the information in your email, it says that at non peak times the
throughput should be better (as it is likely that no oneelse who is in
the 25/50 twisted pair bundle
is active on ADSL).
Since you have carefully explained the mindset of the ISP, it is up to
the original poster to find evidence of what failed. This will terminate
a mutual blame game
where everyone blames someone else.
My view is that you need to run a 24 hour test of connectivity and plot
the result. Email them the graph, and say this is not good enough. If it
is load and crosstalk,
there will be a correlation between day and night. (peak times/not peak)
Cheers,
Derek.
On 17/06/14 19:58, Helmut Walle wrote:
Ok, just to clarify a couple of points, a 3-minute ADSL crash course
in some relevant points only:
* The subscriber lines used for ADSL are simply the already existing
phone lines. This usually is one twisted pair per subscriber (with a
1:1 mapping of a line to a phone number). This means that the
subscriber, or their house, has exclusive access to this line, which
goes from the house to the local exchange. As ADSL uses the same wire
pair, the number of users on this "line" is simply the number of users
connecting via the ADSL router, and it sounds like that is "an apple
ipad and an oldish PC" in this case... not much by the sounds of it.
* However, these twisted pair lines are bundled into bundle cables of
something like 25 or 50 twisted pairs to physically keep them together
on their way to the local exchange, with just the right number of
twisted pairs branching out at the right spot to get to the properties
where the connections are required (obviously you can get several
lines for one house if you want). Now these bundle cables are designed
to minimise cross-coupling and interference between the twisted pairs.
BUT, these cables were designed with telephony in mind, where the
signal bandwidth is limited by filters to 4 kHz. Now ADSL uses a band
that starts with its lower end at several kHz above the telephone band
to provide a sufficient "safety margin", so that voice and DSL signals
can easily be separated by inserting a cheap splitter filter (these
filters often come with ADSL routers). But the ADSL band goes up to
frequencies just over 1 MHz! And this is way more than what these
cables were designed for... So you do get a bit of cross-coupling and
interference between twisted pairs that are next to each other within
these bundle cables. How much of a problem that is depends on various
parameters, including cable length, wire gauge, and on which other
pairs in the same bundle other people are using ADSL as well. (It is
worthwhile noting that, even without interference, a long line will
perform noticeably worse for ADSL than a short one. Also, thicker wire
gauge helps to minimise problems with long lines. But the lines are as
they are, and Telecom are not going to replace several kms of bundle
cable just to get a few more kbps of ADSL throughput...)
* I would expect that the usual line testing when a customer first
complains about ADSL problems would be a pretty quick check taking
only a few seconds to run, and this would establish that:
- all relevant components of the local exchange (including the Digital
Subscriber Line Access Multiplexer = DSLAM) are working, and
- there actually is a line from the local exchange to the customer's
premises, and
- that that line is physically intact all along the way and does not
have any significant measurable defects over its entire length, and
- possibly that an ADSL router is connected to the customer end of the
line.
That is all the ISP are responsible for, and once that is ascertained
any possible faults would then be the customer's to resolve. But in
this case here, it sounds like probably all of the above may be given
(maybe check and confirm?), however there is a quality of service
issue. And in order to get some traction on this, I can only second
Craig's suggestion to request some more thorough testing, with a
specific view towards highlighting the potential of cross-coupling or
interference from other users in the neighbourhood.
There is one further point to check: how are the computers accessing
the router? Ethernet cable? Or WiFi? If they are using WiFi, the there
obviously is a very real and fairly likely possibility that something
"is wrong" with the WiFi. And this also includes interference from the
neighbours. WiFi has been know to suffer from bandwidth degradation
due to interference for quite a while, and this is mainly an issue in
densely populated areas, but I can certainly tell when the neighbours
are active here in South Brighton...
To get back on topic slightly, on the WiFi side I am finding wavemon
useful - it runs on a text terminal using pretty minimal resources and
provides helpful real-time information on WiFi performance that helps
a lot to sort out antenna location problems etc.
Hope this helps somehow... let us know when you find out what was
causing the trouble!
Kind regards,
Helmut.
On 17/06/14 07:42, dave lilley wrote:
anyone here able to suggest anyway of testing number of
users connected to a line?
Mate who lives in Downs Rd South eyreton commented to me
about his link going down and he thinks too many people are
on it up stream.
mate says he spoke to the provider (not sure who it is) but
think they claimed the link was ok, I was hoping to nip out
using a linux lappie and test the line for some more solid
answers, They use an apple ipad and an oldish PC.
thanks for tips of many.
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