At 22:01 28/02/2001, Daniel Omundsen wrote:

> >From what we can figure out so far, in many cases the problem is modems
>losing synchronisation with the network and having to retrain. The theory is
>that this is most likely caused by line noise.

Interesting however that this problem only started occurring "recently"
when i first had DSL at the place I am currently there wasn't a problem,
I'm not sure exactly when it started to happen but I haven't seen a huge
increase in people buying arc welding equipment and this seems to be a
reasonably common fault with a large number of DSL users I have come into
contact with.

>When your neighbor kindly fires up his electric arc welder and puts a
>sustained burst of noise on your line, the ADSL signal is disrupted. In some
>cases this causes the modem to renegotiate the entire connection which takes
>about 30 seconds or so. You can see this happen if you unplug and then
>reconnect your modem.

[ snip ]

>interested in any feedback as to whether users of devices other than Nokia
>see the same thing - Asus, D-Link, Zyxel, Alcatel, Cisco, etc. Do Lucent
>have an ADSL router, Josh? What does it do?)

We recently setup a nation wide VPN using ISDN and DSL where Centrix lines
were not available for a customer wanting to do basic ssh/telnet type
traffic back to a machine connected via a perm link here in auckland.

After two to three months of constant problems with the DSL sites we ended
up ripping the entire lot out and replacing them with Dialup ISDN circuits
due to the dropouts. Faults were logged with these circuits and telecom did
find some problems with the DSL lines in various locations, but after these
were fixed the "micro outages" still persisted seemingly at random and
after telecom playing the old jedi mind trick of "there is no problem..."
and wanting us to *prove* that there was a fault we simply gave up.

Now we refuse to call DSL a "business quality" connection and recommend
that customers use something more reliable if they wish to do anything past
simple web access and e-mail.

This was all put together with cisco 827's and 1600/2600 routers.

I guess it was all in our imagination.

>There is nothing wrong with the ATM network, it actually relates to the
>quality of your own telephone line. If the ATM network were to break alarms
>go off all over the place and all hell breaks loose inside Telecom.
>
>The problem does not seriously affect our other ADSL service, IP.Networking,
>because that provides businesses with a non-Internet, private IP network
>with full routing and therefore does not use NAT in the modem.

We were not useing NAT in the modem's either, we used the 827's to
establish a tunnel to a 2600 and simply tunneled private IP's thru this,
any NAT on this network was done by a firewall in the main site in auckland.

Mabee it didn't affect your service because it was all internal to telecom
? so possibly the problem is with the gateways between telecom and the
ISP's ? after all, this would also cause small "micro outages" as well ?
one thing I did find to be interesting was that my *routes* would vanish -
yet the modem itself wouldn't reset - however, most of this was experienced
from work or when i was at a remote location and couldn't check to see if
the modem was retraining - another interesting thing to note was that no
authentication requests would ever appear in our radius server logfiles -
mind you, i only ever checked this a few dozen times, and only for a couple
of specific customers (in this case a mixture of Nokia 1122 and Cisco gear)
so mabee sometimes the modem would re-authenticate the PPP layer.

Possibly there are a couple of problems, one with the modems actually
resetting (line noise caused by neighbors taking up ARC Welding ?) and
route dropouts (caused by something on the telecom internal network talking
through the CAR ?)

Mabee we should try and separate these out - people log times and dates and
ask their ISP's to see if authentication requests were sent through the
ISP's Authentication servers ? - I realise this is a pain for ISP's to have
to monitor and for home users to setup to log - but it could persuade
telecom that the problem is real - isn't related to "line noise" and asking
them to "Defrag your hard drive and scan for virii then call me back" wont
make it go away

>You'll know if the problem happens to you while you are using Jetstream,
>because you will see the DSL light on the modem suddenly turn red or start
>flashing. One thing to check is to see if it happens when you pick up your
>phone receiver or when someone rings you. If that is the case then the
>problem is likely to be your house wiring and you need to check your
>installation.

the problem we had with our customer running the VPN wasn't related to this
- they didnt have a phone even plugged into the DSL lines and the wiring
was checked out and at times found to be faulty and fixed - but the problem
happened to *all* the sites on reasonably regular occasions (3-4 times a
day in some cases)

I have also noticed here that when we have a "mico outage" i traceroute to
DSL IP's starting with 210.48.81.1 (our static range and my home IP) and
count upwards (210.48.81.2.. etc etc) and usually get up to around 10 or so
before the routes start sending the packets back thru the CAR to ipnet -
funny how my home wiring and line noise is affecting the first 10 or so
static ADSL customers at exactly the same time...hmm

>We are trying to figure out ways to stop this happening. One theoretical
>option is to adjust the noise sensitivity in the DSLAM, but that works by
>decreasing the amount of data that the network sends which reduces the speed
>of the line. As every line is different not everybody will need this, so we
>do not want to do this to all the lines by default. Hold tight and we'll let
>the list know when we come up with something.
>
>If this is a real issue for you right now, then other potential options are
>to use a different modem if anyone here can suggest one that isn't affected,
>or get into clever stuff like the solution that Tom Parker has found.
>
>It doesn't happen to everyone by the way, it is entirely dependant on the
>quality of the line and what noise is present in the neighborhood. For the
>majority of users that are affected it is not a big deal, browsing is
>interrupted for a few seconds and that is all. The only problem is if it
>happens in the middle of a big download and you have to restart. That seems
>rare though - it has only happened three times in the last month at my place
>according to the modem logs, and I have never noticed it while actually
>surfing.

Use a download manager ? you seem to forget that the Internet is NOT simply
transferring files and browsing the web..

>(BTW, 3 * 30sec = 90sec this month which equates to 99.996% availability for
>normal Internet usage at my place so I am not complaining :-)

except when these outages cause interactive sessions to vanish and in so
doing (be it bad database design or whatnot) cause an outage in say - a
database server, which then needs to be rebuilt after hours and locks up
records..

oh, that's right, this setup isn't common - therefore we will go back to
the jedi mind tricks and see if we can persuade people to use the internet
for what it was designed for.. browsing websites for pr0n ! how DARE they
try to use a DSL connection for anything semi-serious.

>Hope this helps.

only if it means someone at telecom will pull finger and start treating
this as a real problem. Upgrading your CAR's from 4500's may be a start as
well.

--
Steve.
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