Fax/Modem-like tone on incoming calls while connected over VPN

My sister has a weird problem. Her company's IT manager is looking into it
but I thought I'd ask on here as well.

She has conventional ADSL over a BT line, using a Netgear DG834G router. In
addition there is another box (description unknown) which may be a separate
firewall for use when accessing her company's VPN software (called
Timbuktoo).

Everything works fine, except that if she receives an incoming phone call on
this line while she's connected over VPN, both she and the caller hear a fax
or modem burble for about 30 seconds after she answers; after this time it
goes away and they can have a conversation. It only affects incoming calls,
not ones that she makes, and it only happens while she's got a VPN session
open, not at other times when she's accessing the web.

The interesting thing is that she says it's a varying burble not just a
continuous high-pitched tone, which suggests that two devices are sending
data. Difficult to imagine what's causing that: if you ever ring a fax
number or modem with an ordinary phone by accident, it doesn't usually
respond to the tones in your voice but just emits a continuous tone.

I think the dial-up modem is connected to the phone line (so she can send
faxes), so I wonder if the auto-answer of the modem is somehow being
activated when the VPN software is running.

I've not heard the symptom myself, so I'm just going on what she's told me.
I'm seeing her next Tuesday so I'll have a quick "look but don't touch" when
I'm there!

"Martin Underwood" <(E-Mail Removed)> wrote in news:437775d7$0$82676
$(E-Mail Removed):

> The interesting thing is that she says it's a varying burble

It is possible that she's hearing the re-negotiation. Remember when you
dialup the initial sounds go through a sequence until the link is
established? If she is picking up the handset and something is bleeding
through then it could be interfering with whatever it is that she hears
causing it to attempt to re-establish the connection until it gives up.

As to the cause, dodgy filter perhaps?

--
Colin
*Drop DEAD from the email address to reply*

On Sun, 13 Nov 2005 17:20:15 +0000, Martin Underwood wrote:

> My sister has a weird problem. Her company's IT manager is looking into it
> but I thought I'd ask on here as well.
>
> She has conventional ADSL over a BT line, using a Netgear DG834G router.
> In addition there is another box (description unknown) which may be a
> separate firewall for use when accessing her company's VPN software
> (called Timbuktoo).
>
> Everything works fine, except that if she receives an incoming phone call
> on this line while she's connected over VPN, both she and the caller hear
> a fax or modem burble for about 30 seconds after she answers; after this
> time it goes away and they can have a conversation. It only affects
> incoming calls, not ones that she makes, and it only happens while she's
> got a VPN session open, not at other times when she's accessing the web.
>
> The interesting thing is that she says it's a varying burble not just a
> continuous high-pitched tone, which suggests that two devices are sending
> data. Difficult to imagine what's causing that: if you ever ring a fax
> number or modem with an ordinary phone by accident, it doesn't usually
> respond to the tones in your voice but just emits a continuous tone.
>
> I think the dial-up modem is connected to the phone line (so she can send
> faxes), so I wonder if the auto-answer of the modem is somehow being
> activated when the VPN software is running.

Sounds like it is something to do with that given it is only for
incoming calls, the obvious test is to disconnect it and see if the
symptoms still happen.

> I've not heard the symptom myself, so I'm just going on what she's told
> me. I'm seeing her next Tuesday so I'll have a quick "look but don't
> touch" when I'm there!

We if its a don't touch rule then not much you can do.

steve wrote in
(E-Mail Removed):

>> I think the dial-up modem is connected to the phone line (so she can
>> send faxes), so I wonder if the auto-answer of the modem is somehow
>> being activated when the VPN software is running.
>
> Sounds like it is something to do with that given it is only for
> incoming calls, the obvious test is to disconnect it and see if the
> symptoms still happen.

The more I think about it the more I think this must be an explanation.

>> I've not heard the symptom myself, so I'm just going on what she's
>> told me. I'm seeing her next Tuesday so I'll have a quick "look but
>> don't touch" when I'm there!
>
> We if its a don't touch rule then not much you can do.

I might try something simple and totally reversable like this, to prove
whether or not it's the explanation.

On Sun, 13 Nov 2005 21:16:29 +0000, Martin Underwood wrote:

> steve wrote in
> (E-Mail Removed):
>
>>> I think the dial-up modem is connected to the phone line (so she can
>>> send faxes), so I wonder if the auto-answer of the modem is somehow
>>> being activated when the VPN software is running.
>>
>> Sounds like it is something to do with that given it is only for
>> incoming calls, the obvious test is to disconnect it and see if the
>> symptoms still happen.
>
> The more I think about it the more I think this must be an explanation.

True, if it were to do with filters then presumably outgoing calls would
be affected, unless the incoming ring signal does something nasty to a
filter. So try taking a spare along too.

>
>>> I've not heard the symptom myself, so I'm just going on what she's
>>> told me. I'm seeing her next Tuesday so I'll have a quick "look but
>>> don't touch" when I'm there!
>>
>> We if its a don't touch rule then not much you can do.
>
> I might try something simple and totally reversable like this, to prove
> whether or not it's the explanation.

Last time I had windows and a modem I vaguely recall an option on telling
a modem not to answer, although you imply this is disabled by is affected
by the VPN software. I suppose it is no unfeasible for the VPN to do
something with the modem as any co-existing dial-in/out connection would
enable access inside the VPN.

steve wrote in
(E-Mail Removed):

> Last time I had windows and a modem I vaguely recall an option on
> telling a modem not to answer, although you imply this is disabled by
> is affected by the VPN software. I suppose it is no unfeasible for
> the VPN to do something with the modem as any co-existing dial-in/out
> connection would enable access inside the VPN

Well my sister *said* it was set not to auto answer, but I bet the VPN
software is misbehaving. I'm glad it's not my problem to solve ;-)