[svlug] suddenly low bandwidth on lan cable

[Ivan Sergio Borgonovo]

On Sat, 18 Dec 2010 01:17:45 -0500
Andrew Wilcox <andrew.r.wilcox at gmail.com> wrote:

> On 17 Dec 2010, at 13:38, Ivan Sergio Borgonovo wrote:
> 
> > I've a cable crossing home 15-20m that connect the dsl modem to
> > the router.
> > [...]
> > I had over 10MB/s on that cable, now I get something between
> > 150KB/s and 50KB/s.
> 
> It may not be the cable.  Try another port on the router, as it
> could be the router.  It could even be the modem itself.  I have
> actually had a switch flake out on me (a 10 year old Cisco) that
> made three of the eight ports have this issue.  Replacing the
> switch on the fact that that's the only thing all three computers
> had in common worked.

> So, just because you have low bandwidth on it doesn't mean it's
> the cable, especially since you've checked it out so thoroughly.

Actually I didn't check the cable so thoroughly. It was placed there
10 years ago and it worked enough to support the bandwidth from
modem to router and more and I actually never really checked it.
During the years my expectations from that connection changed (DSL
lines got faster, for a certain period I had a PC with a 100Mb eth
etc..) but it keept on just working as expected. I never felt the
need to actually measure bandwidth till now.

Both devices at the ends (modem and router) were changed with new
ones as soon as I noticed the bandwidth on that cable dropped.
I coupled the devices differently (new modem/new router, new modem
old router etc...) but the result didn't change.

Since the only mechanical stress I could think of was at the ends I
re-crimped the rj45 at both ends.

So I'd say: connectors are OK, devices are OK... what's left is
something related to the cable.

Still it sounds strange the cable got broken after 10 years, living
quietly in a temperate apartment, with no rodents, inside a cable
duct and with very few mechanical stress.

I'd like to know if I'm wrong and actually a cable working for 10
years can stop to work or if I should be more careful to something
else?
I'm not excluding the cable had some defects or I didn't posed it
well etc... I'm just wondering how it could work for 10 years and
then stop without being touched.
The only thing I can think of is it was already broken 10 years
ago... and it was just waiting something to die. And since it was
placed in a quiet place that something happened after 10 years.

I'm really out of idea about what "something else" could be.
The cable pass nearby the home power lines (220V/50Hz) rarely and for
no more than 30cm on total. I disconnected the TV cable. So I really
can't think of anything else.
And anyway it worked perfectly near these source of interference for
10 years.

If up to your experience a broken cable in this situation is not
that improbable I won't get crazy thinking if my neighbourhood
decided to buy a magnetic gun or aliens are preparing their landing
on my roof from another dimension etc... ;)


-- 
Ivan Sergio Borgonovo
http://www.webthatworks.it