Asterisk with modems instead of phonecards

Discussion in 'VOIP' started by acc admin, Jan 24, 2005.

  1. acc admin

    acc admin Guest

    Hello everyone,
    I'm a newby

    My company does not want to invest in FX0 cards for an office with two
    phones. We already have some modems though.

    Is it possible to setup Asterisk linux PBX with four modems (two for pstn
    two lines, and two for inside phone cables going to phones), and then
    through Asterisk make that work?

    Or this could be even better if Asterisk server would have two modems
    connecting to PSTN lines and act as a gateway for two IP phones via tcp/ip.

    Thanks a Lot!
    acc admin, Jan 24, 2005
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  2. acc admin

    BlueRinse Guest

    Is it possible to setup Asterisk linux PBX with four modems (two for pstn
    The short answer is, no.
    BlueRinse, Jan 24, 2005
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  3. acc admin

    Kyler Laird Guest

    Is it possible to setup Asterisk linux PBX with four modems (two for pstn
    The slightly longer and more correct answer is yes.

    Make sure that you realize what "modem" means in this case. For connection
    to the PSTN you'll need an "FXO" device and for connection to the telephones
    you'll need "FXS" devices. There are more or less standard modems which
    will do some of this. (I have used a Digium X100P modem with Asterisk.) I
    recommend sticking with things that are designed to work with Asterisk.

    The Digium product to do this all on one card is the TDM400P. (I have one.)
    You'd then add two FXS and two FXO modules for a cost of over $300.

    I hate the sloppiness that results from connecting to a POTS line and I've
    found my IP phones and Sipura devices to be much more satisfying so I don't
    use Digium hardware anymore.

    Kyler Laird, Jan 24, 2005
  4. acc admin

    acc admin Guest


    Ok, to simplify this, can i achieve the following:
    Build an Asterisk Server with one SIP IP phone connected inside and an
    outside phone line connected to a standard external modem, so that Asterisk
    would be a PSTN gateway for that One phone?
    acc admin, Jan 24, 2005
  5. acc admin

    Kyler Laird Guest

    Again iff you use the right modem, sure, it's no problem. The X100P is one
    such modem. At only $30 there's not much point in messing around with other

    Also consider a Sipura SPA-3000. I suspect it'll do all that you want for
    only $100.

    Kyler Laird, Jan 25, 2005
  6. acc admin

    Miguel Cruz Guest

    What do you mean by "standard external modem"? If you mean a 2400bps Hayes
    MNP, then the answer is no. There are very few (if any) data modems that
    provide satisfactory full-duplex voice operation. The chance that you will
    happen to have one lying around without having bought it for that purpose is
    quite low.

    Miguel Cruz, Jan 25, 2005
  7. acc admin

    syd Guest

    (Miguel Cruz) wrote in
    Silly Questions #2

    If i have a user with a analog modem can he dial out through *?

    If I wanted to present myself as a dial up solution for low price, could i
    purchase a "local" number in another area and have that user modem in to my
    * and route that call to a computer on my network? I know my h.323 ATA is
    really dsesigned to handle a fax machine, and that is a half duplex modem
    for all intents and purposes.
    syd, Jan 25, 2005
  8. acc admin

    BlueRinse Guest

    Again iff you use the right modem, sure, it's no problem. The X100P is
    I thought (hey I could have been wrong, but it appears I was not) by modem
    he was saying any modem. This question comes up ten times a day in the
    mailing list and on IRC and it almost always means "I have a modem [voice
    modem, several modems] can I use this with *

    The answer is, no.
    BlueRinse, Jan 25, 2005
  9. acc admin

    Miguel Cruz Guest

    You don't need asterisk for that; just script it in your favorite language.
    I think you'll have trouble routing modem calls over VoIP links. Anyway,
    it's a very inefficient way of doing things. Just make a deal with one of
    the zillions of companies bulk-selling dialin services. You definitely can't
    compete with them; their margins are tiny.

    Miguel Cruz, Jan 25, 2005
  10. Modems through VOIP links get at best around 9600-14400 baud
    connections before they start crapping out using typical CODECs out there.

    Obviously, you'd be restricted to 28800 speeds at best anyway, because
    you'd be going through more than the one D/A conversion restriction
    that makes 56k modems even work.

    Seems like alot to go through just to get something like that.
    Doug McIntyre, Jan 26, 2005
  11. acc admin

    Kyler Laird Guest

    Sure, analog modems can handle data fast enough for some voice calls.
    You can use any (PPP/SLIP/...) IP connection to your Asterisk box for voice
    calls as long as the connection provides sufficient bandwidth for the codec
    you use and has latency you find satisfactory.

    Kyler Laird, Jan 26, 2005
  12. There is a basic misunderstanding here. The cards that may act as FXO
    interfaces are so-called Winmodems (or Linmodems when used under Linux):
    devices where most of the encoding/decoding work when acting as modems is
    actually done by the CPU under the control of a device driver, and by a
    DSP also loaded with firmware by the device driver. Writing a suitable
    alternate device driver, one can give those cards a new lease of life as
    FXO interfaces towards POTS lines.

    Unfortunately, the characteristics of those cards vary from model to
    model, so there is no way of writing a universal driver for all the
    existing Winmodems. The Zaptel drivers for Asterisk include one (wcfxo.c)
    that works for two models: one, called by Digium X100P, based on a
    Motorola SM56 chipset (PCI ID: 0x1057, 0x5608); and another one, called by
    Digium X101P, based on an Intel chipset with TigerJet Network Tiger
    300/320 PCI interface (PCI ID: 0xE159, 0x0001). For any other Winmodem
    card, you are on your own...

    Enzo Michelangeli, Feb 4, 2005
  13. acc admin


    Aug 29, 2010
    Likes Received:
    I'm sorry to ask this and I feel stupid, but...

    I have seen many questions and discussions about using an old modem of some kind as an FXO with an Asterisk Setup. I am wanting to know if I can setup Asterisk with an SIP Provider and then use the modem as an FXS to plug my analog phone into. This way I can have the Asterisk Machine connected through Ethernet to my Network and then to the Internet connecting to my SIP Provider and then my Analog Cordless Telephone plugged into the modem. Is this idea crazy? If you can't do this then what kind of equipment do I need to look for to use to plug the analog phone into the the VOIP server? I have just started trying to do this since last night for fun. I am trying to see how far I can take my Google Voice and SIPGate Accounts and what all I can do for free with them. Any help would be greatly appreciated, because at this point I have about 5 hours of experience with this field!!! Thank you very much in advance.

    Althage, Aug 29, 2010
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