[Asterisk-Users] PSTN Incoming call on real line disrupts VoIP call over DSL circuit

[Hadar Pedhazur]

Bob Chiodini wrote:
> I'm a Bellsouth DSL user in FL too.  Here, the filter has a DSL/modem
> jack and a POTS jack.  So if a phone and modem share the same wall plate
> the filter does the split.

Interesting, I'm pretty sure that when they installed it in his 
apartment, they put in the Y cable, so it's definitely a supported 
Bellsouth configuration.

> I don't think connecting the DSL modem directly the loop is wise.
> That's assuming that the filter actually filters something on the DSL
> port and that the modem does not have a built-in filter.  My modem is a
> Westell.
> 
> http://en.wikipedia.org/wiki/DSL_filter

Thanks.

> One other possibility, the ringing is causing packet loss (UDP) that the
> HT486 is not handling very well.  Normal TCP traffic would generally
> recover.  The streaming audio test should confirm the loss.  Does the
> HT486 have any kind of logging?

I don't know about the logging, but you might be correct with regard to 
the packet loss.

Rich Adamson conjectured that's it's a firewall issue, and it certainly 
feels like that. Last night, it occurred to me that perhaps an answered 
POTS line causes the modem to request a new DHCP lease, meaning, it 
changes it's IP address. If that were the case, it would explain the 
behavior I'm seeing, namely that we can continue to hear him, because 
the HT can still find the remote end, but the remote end can no longer 
find him...

I don't know how easily I can verify that (remotely, I'm not sure I can 
talk my Dad through that one ;-), but perhaps I can prove that theory 
one way or another...

> I'm still testing VOIP (read newbie) and have not run across this
> scenario.  I'll add it to my list of things to test.

Welcome!

> Bob...
> 
> On Mon, 2006-05-08 at 15:23 -0400, Hadar Pedhazur wrote:
>> Juergen K. Zick wrote:
>>> Well, I have no idea how DSL lines are connected in the US but what 
>>> happens to a normal Internet connection when the phone is being picked up ?
>>> Test scenario could be that your Dad is listening to an Internet radio 
>>> station or other audio stream and then being called....
>> Great idea! It's possible that there is a "hiccup" when the phone gets 
>> picked up, which a streaming audio connection might feel as well, in 
>> which case Bellsouth would have to acknowledge the problem ;-). Thanks, 
>> I'll have him test that.
>>
>>> BTW, how are the "real" phones and the answering machine being connected 
>>> ? Is the HT in front of them in the POTS line ?
>> They are separated. The answering machine is in another room, connected 
>> to a normal phone jack, using a DSL filter to assure it doesn't get the 
>> "noise" of the DSL line.
>>
>> The HT is connected to the DSL modem, and there are no POTS lines 
>> connected to the FXO back-up port on the HT. In other words, the HT has 
>> only the WAN (to DSL) and LAN (to PC) ports connected, and an analog 
>> phone (a GE 5.8ghz handset) connected to it's FXS port. The only other 
>> possible connection problem (which I think I tested and rejected as a 
>> problem two months ago) is that there is a Y splitter coming out of the 
>> jack with a filter for the real phone, and no filter for the DSL modem 
>> (which is in front of the HT).
>>
>> I am reasonably sure that I had him remove the Y cable, and plug the DSL 
>> modem directly into the jack, and it still failed. However, I'll retry 
>> that again too now :-).
>>
>> Thanks Juergen!
>>
>>> --Juergen
>>>
>>>
>>>
>>>> I haven't seen anything this strange, and it's 100% reproducible. I'm 
>>>> hoping that there are some clever ideas out there for what to look 
>>>> for, since I can test to my heart's desire on this one...
>>>>
>>>> My Dad lives in Florida, and has a Bellsouth DSL line. Of course, he 
>>>> has a regular POTS line connected on the same line. He has the 
>>>> appropriate filters on every jack that has a phone connected to it, 
>>>> and he even replaced one or two of them (when I thought that was the 
>>>> problem).
>>>>
>>>> I sent him a HandyTone GS-486 (HT), configured to connect back to my 
>>>> Asterisk server. He only has a single computer in his apartment, so 
>>>> it's connected into the HT, and the HT is connected into the DSL modem.
>>>>
>>>> He can make and receive calls on the HT, and the quality is excellent. 
>>>> If he's speaking via the HT (meaning a VoIP-only call) and the "real" 
>>>> phone rings, everything continues fine (temporarily). If the real 
>>>> phone is answered, either by a person, or by the answering machine 
>>>> (which is in another room, connected to a filter on another jack), 
>>>> then the audio on the Asterisk conversation becomes _one way_. My 
>>>> father can be heard _perfectly_ by the remote side of the 
>>>> conversation, but he can hear nothing. When the POTS line is hung up, 
>>>> then both sides of the VoIP call go dead (audio-wise). Of course, he 
>>>> can now redial a VoIP call, and both sides work perfectly...
>>>>
>>>> At first, I couldn't imagine that it was anything other than a bad 
>>>> filter, but other than replacing the filter (which didn't help), 
>>>> nothing else stops working. He can continue to use the Internet 
>>>> connection on his PC just fine, and I can continue to hear him speak 
>>>> over the VoIP connection with no problems either, so the Internet 
>>>> connection has not been lost.
>>>>
>>>> I have to admit to being completely clueless as to what to even look 
>>>> for, so _any_ advice as to things to test for would be appreciated. As 
>>>> I said at the top, I can reproduce this 100% of the time, so I can 
>>>> easily setup any debugging environment in advance, and trigger the 
>>>> problem at will, etc.
>>>>
>>>> Thanks in advance!