[VoIP] OT: Unusual Call Interruption

[Rusty Dekema]

I apologize for the off-topic post, but something happened during a
phone call that I've never heard before and it seems possible that
some of you might have an idea as to what could have caused it, or
might at least find it somewhat interesting:

I placed a long distance (in-state [Michigan], but inter-LATA) call
earlier this afternoon from a PBX-based landline at my office to a
Verizon Wireless subscriber who was in his home market, on the Verizon
network, and stationary at a location with a very strong Verizon
signal. I had been talking for about 10 minutes with no problems when
the audio from the other party suddenly cut out mid-sentence and I
heard a quiet hum for about five seconds. After that, I heard (one)
ringback tone and then a recorded message that said, "We're sorry, all
circuits are busy. Announcement 2, switch 8." (It was either that or
"Announcement 8, switch 2.") After the announcement, the call was
disconnected. When I called the same party back about a minute later,
everything proceeded normally and there were no further interruptions.

Like everyone else, I've been on calls involving mobile phones that
were suddenly disconnected, and I've received "all circuits are busy"
messages on occasion when trying to place a call. But I have never
been on a call that was interrupted and then received an "all circuits
are busy" message (or any other message), and I have no idea what
could have caused this to happen or where in the network it might have
occurred.

The voice on the recording was that of a female with a noticeably flat
tone and very neutral (American) accent. I did not recognize the voice
or format of the recording, but I wouldn't necessarily recognize a
Verizon Wireless recording if I heard one since I don't subscribe to
any of their services.

Our company's PBX (a Nortel SL-100) has its own set of recordings, and
neither the voice nor format of this recording sounded anything like
any other recordings I've heard from it. Our PBX has local trunks to
SBC (now the "new" AT&T), but uses Qwest for all in-state long
distance calls. (It sends inter-state long distance calls through VoIP
trunks to VoEX, now known as Intelepeer.) I do not know whether our
PBX sends calls to Qwest through its SBC trunks or whether it has
dedicated trunks to Qwest. I also don't know what Qwest's
announcements sound like, and I don't know a number I could dial to
hear one.

In order to compare announcement voices, I placed a call to a local
SBC number that I know is disconnected and the voice on that
announcement sounded nothing like the one I heard during the call in
question. I'm not sure how useful that information is though, since
there's no guarantee that SBC uses the same announcer for its
disconnected-number messages as its busy-circuits messages.

I would be very interested to know whether any of you have seen
something like this (especially if it was in the "modern" era of
telephony) or better yet if you have any theories on what might have
caused it to happen or where in the network it was likely to have
occurred.

Regards,
Rusty Dekema