Hi, All
Please forgive me if this posting should be in another newsgroup.

I am reading about the ITU V.32 and V.34 recommendations. While I
have been able to find descriptions of the signal constellations and
coding schemes, I have had a tough time finding out information on the
communications protocol. Specifically, I want to know how the calling
and answering modem keep the dial-up connection alive when neither
party has any data to communicate. Do they just broadcast 1.8kHz
tones? Are there ping-pong packets sent/received?

If anyone has any info on this (or knows which forum would be a better
fit than .modems), please let me know.

Thanks.

ecco

ecco wrote:


First, this is the right NG, but it is slowly dying for lack of
interest in analog modems.

Second, if you are asking "how does the phone co keep the connection
up" during a dial modem session, that's no different from a voice
call. The modems being "off-hook" will keep the connection up.

V32/V34 modems by nature do output a constant carrier signal, but
that's for their own use to pass data, if any, from the terminal
devices. The carrier signal does not, in itself, keep the connection up.

That said, some modems can be configured to cause a drop in the
connection (by going on-hook) if they sense Loss of Carrier, but
that's different.

--reed

On Tue, 30 Oct 2007, in the Usenet newsgroup comp.dcom.modems, in article
<13ifksqpp6sgq23@corp.supernews.com>, Reed wrote:

They are sending tones - a logical "1" which is the same as the
"stop bit" and opposite the value assigned to the "start bit". You
could say that the modem can hear the other modem, but it's not
_saying_ anything - just whistling because it has nothing to say.

Not at the _wire_ (modem) level. If you are using the connection to
dial in to an ISP, the _link_ level connection (PPP - RFC1661)
_may_ be sending LCP Echo packets (RFC1661 section 5.8), but that is
normally used only when the computers aren't using hardware handhshake
signals (CD) to determine that the link is still in use.

Carrier Detect follows presence of a signal - that's pretty much a
default. The communications application (like windoze DUN) may be
configured (probably is) to see the loss of Carrier Detect as a
broken connection, and tell the modem to hang up the phone.

Many modems can also be configured to have an Idle Disconnect - but
the command/register to set this is not standardized. For _SOME_
Rockwell or Conexant modems, register S24 sets the timeout in seconds
(0 to 255). For _SOME_ US Robotics, it's register S19 with the time
in minutes (again, 0 to 255). Other modems may use other registers,
or may not have this function. Aren't standards wonderful?

Old guy

~ >>Do they just broadcast 1.8kHz tones?

V.32 and V.34 signals are scrambled, so the audio in the channel will
always sound like white noise evenly distributed across the channel
(2400Hz wide for V.32, from 2400-3429Hz for V.34.)

~ >> Are there ping-pong packets sent/received?

~ Not at the _wire_ (modem) level. If you are using the connection to
~ dial in to an ISP, the _link_ level connection (PPP - RFC1661)
~ _may_ be sending LCP Echo packets (RFC1661 section 5.8), but that is
~ normally used only when the computers aren't using hardware handhshake
~ signals (CD) to determine that the link is still in use.

Between the modem (modulation) layer and the PPP (link) layer, there is
likely also an Error Control (LAPM) layer, which is sending bidirectional
idle flags when there's no user data to move.

If the modems aren't using an EC layer, then (assuming that the application
is full-duplex async), you get all 1's in both directions while idle.

Another Old Guy

On Nov 1, 1:17 pm, fl...@apaflo.com (Floyd L. Davidson) wrote in
http://groups.google.com/group/comp....1b0db05ef8396d :



What about if I were to use the currently present phone lines? Why
wouldn't this work?

Will someone please answer my question?