[Gllug] [OT] BT phone connections and ADSL

Chris Bell chrisbell at overview.demon.co.uk
Sat Jun 28 23:05:49 UTC 2008

On Sat 28 Jun, damion.yates at gmail.com wrote:
> Not Linux related, but I know this list will have people with ideas to
> help me.
> I've just bought a three level flat which doesn't appear to have a
> master BT socket.  The only visible phone connection is a small
> extension socket in the kitchen (the middle level).  My adsl router
> was able to get between 6000 and 8000 kbps which matches what an
> online test showed before I ordered adsl, latency on a basic ping was
> about 12ms, so I wasn't too bothered initially.

   There must be a BT line termination somewhere, perhaps in one of the
known sockets or in another socket hidden elsewhere, perhaps in a cupboard
under the stairs. There will be a few components at the termination
including a spark gap for some lightning protection, a relatively large
non-electrolytic capacitor, and a line test resistor. You should find a
single incoming pair connected, and at least a single pair plus a single
wire on to any extensions. Older properties may have an intermediate
connection between the incoming pair and the actual termination, possibly
the relics of an older system with series connected low impedance ringers.

> Now the problem.  I also need a phone socket for my TiVo and possibly
> Sky+HD box upstairs in the lounge (30m of cable away).  When I plug in
> a connection other than the small one via the filter to the router (ie
> a normal phone connection), my linespeed drops to just under 2Mb/sec.
> Two of the filters I have don't seem to work well, one causes a
> landline to ring constantly if plugged in, the other doesn't but both
> fail to get the line speed over 4Mb/sec, even on their own.

   Should ADSL work together with a Sky box???
> It gets worse.  So that the connection upstairs is more tidy, my dad
> and I started to lay cable around the skirting board and through
> several door frames towards the lounge.  The initial portion of this
> lies along where this extension socket comes in.  Since this was laid
> out, my latency is now a steady 50ms, this is pretty bad as my main
> use is interactive sessions via ssh, voip and gaming.

   Best by far: place your ADSL modem at the main BT termination, separate
everything from the ADSL using a single full BT specification filter at the
line termination, and connect all phones, phone extension cables, and other
kit to the filtered side. Use ethernet cables for a reliable local link.
   If that places the modem in an inconvenient location and you do not wish
to run ethernet data cables it is possible to use your mains wiring plus
linking hardware, not cheap but it does work well, even to another building,
as long as they are connected to the same mains distribution because it
stops at the meter.

> So, what is going on?  How can I find the master socket and will this
> improve matters?  Can a cable simply laying next to a phone line cause
> interference that would up latency but not limit line speed?  Is there
> such a thing as a wireless extension which would permit the modem in a
> TiVo to work?  Should I simply hack the TiVo (always planned to one
> day) to use the house lan for its connection from now on?

   Any phone extension cables can place a load on the line and reduce the
amount of carrier arriving at the modem.

> I'm tempted to pay BT to come and fit a new master connection, they
> can work out where it all comes from and sort it properly, but I worry
> that I'll not get anyone competant, that it won't fix it at all and
> will be very expensive.
> Manually plugging the tivo in for its updates, or rather, unplugging
> it for times I want a faster connection, solves the speed issue.  The
> nicer latency might return if I remove the cabling around the skirting
> board, otherwise I don't know where to start for investigating that
> issue.
> I'm willing to provide loads of free booze to anyone willing to come
> and help on this one if I can avoid paying BT.

   You do not even give the approximate location.

> Thanks for any advice,
> Damion

Chris Bell NEW alternative address: chrisbell at chrisbell.org.uk
Microsoft sells you Windows ... Linux gives you the whole house.

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