Re: Dial-up Modem Question

Discussion in 'A+ Certification' started by MF, Sep 16, 2005.

  1. MF

    MF Guest

    You don't describe your connection, but this should be easy to test. Plug a
    phone into the same hole into which you plugged the modems. Does the phone

    Take a couple of the modems and test them on an analogue phone jack.
    Do any of them work?

    If the answer is yes to both, the modems will not work over VOIP. :-|


    "Barry Watzman" <> wrote in message
    > I've been trying to test some modems this afternoon (PC Card laptop
    > modems) and NONE of them are working, which I cannot believe. They dial
    > and you hear the "negotiation" tones, but they never connect. There are
    > 11 different modems, some "winmodems", some not, all the way from 28.8k to
    > about half being 56k.
    > Now here is my question: We don't have "real" phone service, we have
    > internet phone service (Vonage, specifically).
    > SHOULD a modem work over an intenet phone line, in general? My desktop
    > modem seems to work over the same phone line, also I have ONE 3Com PC card
    > modem (33.6k) that works.
    > What's the story on using dial-up modems over a VoIP phone line? What
    > should one reasonably expect?
    > [also, does anyone have any free "modem test numbers", numbers that you
    > can call just to test a modem?]
    MF, Sep 16, 2005
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  2. w_tom

    w_tom Guest

    If fax works, then what speed does the fax work at? Fax
    running in class 1 mode can use baud rates anywhere from 300
    (+FTM=3 and +FRM=3)) and 2400 (+FxM=24) up to 14.4K
    (+FxM=146). I am not sure how to monitor modem status when it
    is making a fax connection. However the modem status would
    automatically determine the maximum data rate on VoIP for both
    outgoing and incoming; and report these significant numbers.

    In theory, it should be possible to use Hyperterminal to all
    and connect to a fax machine. For example, in Hyperterminal,
    AT&F would first reset the modem. AT+FCLASS=1 would put the
    modem into class 1 fax mode. AT+FAE1 would enable the modem
    as an auto answer fax machine. ATA may also enable auto
    answer. One an incoming call, status information could be
    received on screen. AT+FAE? would obtain fax modem status.
    ATH0 (last character is zero) would hang up.

    To initiate a call, try ATDTxxxx where xxx is the phone

    Again, the intent is to let two fax machines determine what
    your max baud rate would be on VoIP, since fax machines can
    operate as low as 300 baud.

    Barry Watzman wrote:
    > There is no need to purchase a 2nd line, you can do faxing over the
    > first line. The only reason for having a 2nd line is to have different
    > phone numbers for voice and fax. There is no difference between the two
    > lines supported by a Vonage VoIP box.
    > Faxing definitely does work. However, the modulation techniques for the
    > higher speed data baud rates become quite exotic. Nothing over 33.6k
    > will even work on a conventional analog phone line unless the initial
    > A-to-D conversion is done at your local central office.
    > Some additional testing has produced inconsistent results; I'm inclined
    > to think that you cannot reliably use a modern high speed modem over a
    > VoIP telephone line, but I still accept that only as a likely answer,
    > and not as a "proven" answer.
    > Unfortunately, I don't have an analog phone line (a "real" phone line)
    > to test with.
    w_tom, Sep 22, 2005
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  3. w_tom

    w_tom Guest

    Unfortunately, until you can provide actual numbers, then we
    have no idea what speed a fax operates on VoIP. For example,
    in one location, I finally got someone in the CO whereby I
    demonstrated noise on the phone line unique and only in one
    direction. They finally admitted the connection from SLIC to
    central office was defective. Even all 9600 baud faxes would
    drop back to 2400 baud or less due to noise. But users never
    knew. And that is the point. Without specific numbers, then
    faxes on VoIP might appear to work just fine and yet actually
    work only at 2400 baud or less. How would you know? Actual
    numbers are essential before we know anything. I am very
    curious as to what those numbers really are.

    Barry Watzman wrote:
    > The top speed for fax is 14,400 baud, but many, many fax machines use
    > 9600 baud. I didn't note what speed was actually used when I sent a fax
    > (which I only do a couple of times a year). But Fax over VoIP
    > definitely does work, and I'm pretty sure that at least 9600 baud is
    > reliable (not based on my experience, but on the fact that Vonage
    > advertises fax as a way to suck people into buying a 2nd line).
    > However, 14,400 is unacceptably slow for data, so the ability to make
    > fax connections is irrelevant although one might conclude that a modem
    > that was connecting in fax mode would work in data modes at higher
    > speeds given a real analog phone line.
    w_tom, Sep 23, 2005
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