DSL interference
July 18, 2004 6:08 PM   Subscribe

Strange DSL home network problem: using the phone freezes the internet. More inside...

I'm having a pretty weird problem with a home network at a new apartment. Despite many battles with wireless networking, this one has me stumped. I noticed that whenever someone talks on the phone here, the Internet slows to a crawl (or total freeze). At first I thought this was a simple cordless phone/wireless router interference problem. I also thought it could be our router which has been a little whacky in the past.

So I upgraded to a Wireless G router which we were going to do anyway. It turns out all the cordless phones are 900MHz so it should be a problem. I looked into this more, and the same thing happens even if I use a plugged phone, while also plugging in my computer to the router. So this is not an intereference problem. Any ideas?
posted by swank6 to Computers & Internet (9 answers total)
Do you have DSL filters on all the phone lines?
posted by jalexei at 6:16 PM on July 18, 2004

I realize they help the phones work, but you never know...
posted by jalexei at 6:18 PM on July 18, 2004

Filters definitely make a difference to DSL performance.

Owing to the rat's nest of wiring in my place, I accidentally got a phone wired in on the unfiltered side. Whenever there was a call, the DSL modem would drop and renegotiate the connection.

on preview: yeah, skallas has a point to. From my experience, if there's a dodgy connection between you and the exchange, the voltage change on the line caused by a call can radically change performance.
posted by i_am_joe's_spleen at 6:51 PM on July 18, 2004

No idea if this has happened since day one - I just moved back for the summer. My mom says she hasn't noticed, but I don't think she's ever tried using her Internet while on the phone.

I'm hoping this is something I can solve myself; I'm sure we all know how frustrating talking to DSL tech support can be. Where do you get these DSL filters?
posted by swank6 at 7:11 PM on July 18, 2004

Funny, I have the opposite problem. My DSL line slows down and then completely goes out unless I use my telepone at least a few times a week. It's been like this for two years. I just have to take my phone off the hook, or dial any local number, and the DSL light will come back on within 10 seconds and stay on for at least a day. I'm right at the edge of the max DSL line distance and I figured that if I don't use my phone the phone company idles the line somehow.
posted by Voivod at 7:19 PM on July 18, 2004

If you don't have DSL filters, then that's your problem right there. I'm suprised your DSL provider hadn't asked about this since this is FAQ #1 for ADSL. With ADSL you are sharing the phone line with your voice devices, and the filters are what allow them to work together. No filters == No ADSL if you're on the phone. Every phone in your house must be connected to a dongle instead of the wall. Only your DSL modem plugs into the wall. They are little dongles that plug into the phone jack on the wall, and then you plug your telephone into the dongle. You should have gotten some when the DSL line was installed. Call your DSL provider and ask for some.
posted by Voivod at 7:24 PM on July 18, 2004

Ok - apparently we do already have the filters. I thought you were talking about something extra that we could get.
posted by swank6 at 7:25 PM on July 18, 2004

Nah, voivod, it's the voltage from the phone line changing the resistance of your line. There will be some sort of cable fault between you and the exchange.

swank, can you monitor what your router is doing when the slowdown happens? Is is just dropping a lot of IP packets, or is it renegotiating your PPP connection, or what? Does it have a self test capability?
posted by i_am_joe's_spleen at 7:46 PM on July 18, 2004

You *definitely* don't have filters in all the right places.

Every phone on the line has to have a filter between it and the DSL modem, while the modem needs to have none between it and the line.

You can do this by putting a filter on every phone, or by splitting at the block and filtering once for all-the-phones and not filtering whichever line goes to the modem.

Note that unfiltered phones will cause trouble even if you don't talk on them: the ringing will try to ring them and cause a DSL signal drop.

They're at Rat Shack, among other places, though you can likely get then cheaper (and if you got a self-install kit from your telco, you probably got between 3 and 5 of them for free).

Filter everything: modems, answering machines, faxes; set-top boxes; *everything*.
posted by baylink at 8:28 AM on July 19, 2004

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