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DSL modem interrupted because of analog modem on same line.

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Last Modified: 2013-12-27
We have a problem with a DSL modem reconnecting several times a day. We have traced the problem to incoming analog faxes on that same line. Every time a fax dials in and the analog modem starts squealing, the DSL drops out and renegotiates. The DSL company, CSDSL.net is at a loss to explain this. At the wall jack there is a splitter. One side of the splitter goes into a DSL filter and continues to the analog modem in a fax server. THe other side goes directly to the DSL modem. Apparently, the analog noise is going back through the DSL filter and hitting the DSL modem and confusing it. Any suggestions or explanations here?
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Commented:
The DSL filter should go directly to wall jack, why you have splitter there? Anyway, this phoneline issue and that can only fixed by telephone company. If the problem found outside your house, you dont have to pay for service charge, but if the problem inside your house you will have to pay.

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Commented:
no comment. Anyone else?

Commented:
FYI the filters are to keep the DSL noise off the analog lines.  It sounds like a bad splitter/filter.  I agree this is the phone companies to get going on and get fixed or get you a second line for DSL until they fix their problem.  You should not have to endure this.

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Commented:
Ok - I don't think you're understanding the problem. From my understanding, yes - the DSL filter filters out the DSL noise from continuing to the analog device it's connected to. But the problem here is that the analog modem is creating its own noise - analog modem sounds to communicate with the fax machine at the other end - and that noise is going back down the line, through the dsl filter, into the splitter, out to the phone company's line but also over to the dsl modem and interrupting it. Do you see what I mean?
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Well, it's not the phone company, per se. Verizon is our local carrier here, but this service is through CSDSL.net. Of course, they must use all the same lines, but maybe not the same equipment in the C.O. They also do not use the same modem as Verizon. Verizon uses a Westell usually. CSDSL.net uses a black modem of unknown make. Yes, that was my assumption, that the equipment should be able to handle that, because, by default, in almost every business install of DSL I've seen, they piggyback it on the fax line, because that's the one POTS copper line that businesses have that isn't tied into their digital phone systems.

And, I also understand what FeMAster is saying, that maybe we can affect the problem by relocating equipment... Although we shouldn't have to.

The owner has called CSDSL numerous times. They couldn't figure out the problem at all, apparently had never heard of such a thing!  I just noticed by chance while I was sitting there and an employee yelled out "Internet's down again!" and my subconscious registered the fact that I just heard a modem squeal from the server room seconds before. We tested and confirmed it.

That has been my feeling, that the onus is on them - the ISP. We'll continue in that vein.

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Commented:
x86fix - why do you say bad splitter or filter? The splitter is a simple 'Y' splitter, so anything being transmitted from the fax server should be expected to reach the dsl modem. Also, I would not think the dsl filter would be designed to filter analog signals in the reverse direction, otherwise faxes and data modems wouldn't work. There is no restriction on having modems on a DSL / voice line.

Commented:
If it is a simple Y then it is the problem.  The phone provders around here have always used a device that has filters built into it.  It makes more sense now.  That is the problem.  you need a filter between the FAX and the splitter.

Commented:
The filters block high frequencies that are used by dsl.  The high pitches made by the fax are still lower than these.  I have always heard the dsl humm on the line without the filter.  If you plug a phone into the fax line youl hear it.  The filter blocks the frequencies used by DSL and should also keep the fax sounds from poluting that frequency range.

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Commented:
x86fix - I'm not getting it. If the line looks like this:

                                     /--------|-------|DSL FILTER|---------|faxmodem in server|
--------POTS line-------/splitter  |
                                    \---------|-------|DSL modem|---> to network

I don't see how the DSL filter could be 'filtering' analog faxmodem sounds from going back out, since that would essentially kill the faxmodem connection with the fax on the other end. Am I wrong? The DSL Filter as far as I understood it, only filters the DSL noise off the line before it goes into an analog device (phone, faxmodem, answering machine, etc)

Commented:
Nice graphic.

That is how I see it should be.

Your fax is analog once it comes out on the phone line.  
That does not mean it needs to extend into the DSL frequency bands.  The DSL service is designed to stay out of the faxes ranges.  I don't actually know the numbers but I believe much of the DSL noise is above 15khz so most (especially older) people dont hear it.
The fax could be putting out some extra noise in those ranges.  Not having the filter allows it to interfere with the DSL.
I have never seen it any other way but I could be wrong.
The frequency removes the highest frequencies from the line.  The frequencies are barely audible and not needed by the fax.

Commented:
I think we are on the same page but here is a description that is consistent with my thoughts on this.
http://en.wikipedia.org/wiki/DSL_filter
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MASQUERAID - I don't think that's right. Everything I've ever been told from Verizon and DSL instructions is that you do not put filters on the wires leading to the dsl modem. If you did, you'd be filtering out the signal the dsl modem is supposed to receive!

This excerpt is from the link x86fix mentioned at Wikipedia:
---------------------------------------------
"A DSL filter is an analog low-pass filter installed on telephones and other analog devices to prevent interference between such devices and Digital Subscriber Line (DSL) service operating on the same line. Without the installation of DSL filters, high-frequency signals or echoes from analog devices can result in reduced performance and connection problems with DSL service, and the high-frequency signals from the DSL service can result in line noise and other issues for analog devices.

Typical installation for an existing home involves installing DSL filters on every telephone, fax machine, voiceband modem, and other voiceband device in the home, leaving the DSL modem as the only unfiltered device."
----------------------------------------------
The interesting part there, to me, is, "Without the installation of DSL filters, high-frequency signals or echoes from analog devices can result in reduced performance and connection problems with DSL service,"  That seems to indicate that the DSL filter plays a role in filtering noise from analog modems before it reaches the dsl modem.  

I think I may try some different filters. I wonder if there is a "high-pass" filter I could install on the DSL modem leg that would block all low-freq stuff?
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Commented:
Maybe we are talking about different filters.

Mine are effectively Y splitters. They connect to all the 'phone sockets in the house and have two sockets downstream one for phone (low freq) and one for DSL (high freq) - If I connect all the phones to filters but connect the DSL modem direct it still gets enough "phone" signal to drop when there's a call or fax.
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Commented:
no, they don't have a splitter device like that, but it is a good idea to put a different fax machine on that line and see what happens. Also, I can swap the modem in that server.

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Commented:
Well, here what my customer wrote about what the dsl company (cornerstone) CSDSL.net said:
"Cornerstone sent a tech today.  He did all kinds of stuff, triple filtered stuff, bypassed stuff and he says, it is not the PC, it is not Cornerstone, it is most likely a Verizon issue originating from their office from a module that cost 5grand that we are either the only who is having a problem or others are too and have not figured it out yet. A ticket has been called in and hopefully Verizon will be out tomorrow.  He says it is one for the books.  No one at Cornerstone (tech and service guys) ever heard of this before and I said that neither had you."

So, I'll let this go a few more days and see if they have resolved it with Verizon then I'll close out the question.

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Commented:
Well, the customer's problem is resolved. It turned out that it was Verizon's fault. The way Cornerstone (dsl ISP) described it, there's a card in a rack somewhere at Verizon's facility that has the problem. It's quite expensive so they end up switching our 'bad' card with someone else's 'good' card. That fixes  the problem for us, but causes a potential problem for others if they use a fax like we did.  Sooooo... how do I break up points to everyone?
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More Than One Expert Helped Solve My Problem - What Do I Do?
https://www.experts-exchange.com/help.jsp#hi69

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It is up to you.  I feel like I played a pretty sigificant role and got to the issue right off.

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x86fix got closest to the actual issue and did the most work on answering so the majority of points goes to x86fix. A sprinkling of points to the others for info that lead to the solution, directly or indirectly.
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