Modem over VOIP

Discussion in 'UK VOIP' started by John Dann, Feb 4, 2006.

  1. John Dann

    John Dann Guest

    Anyone tell me what the present status of trying to pass data via an
    analogue modem over a VOIP 'line' might be please?

    Just to clarify: In the traditional POTS world, one can use a standard
    analogue modem at a remote location connected to a data source to pass
    data across the phone network to a central PC (also fitted with a
    suitable modem of course). Can this yet be done reliably over a VOIP
    connection with a suitable adapter?

    JGD
     
    John Dann, Feb 4, 2006
    #1
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  2. John Dann wrote:
    > Anyone tell me what the present status of trying to pass data via an
    > analogue modem over a VOIP 'line' might be please?
    >
    > Just to clarify: In the traditional POTS world, one can use a standard
    > analogue modem at a remote location connected to a data source to pass
    > data across the phone network to a central PC (also fitted with a
    > suitable modem of course). Can this yet be done reliably over a VOIP
    > connection with a suitable adapter?
    >
    > JGD


    The is an ITU specification called ITU V.150.1 specifically for this
    purpose.

    This hasn't been implemented in Asterisk yet (I don't know if it's been
    implemented in any software) or any ATA that I'm aware of.

    So it's more a case of, It will happen at some point but don't hold your
    breath.
     
    Thomas Kenyon, Feb 4, 2006
    #2
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  3. "John Dann" <> wrote in message
    news:...
    > Anyone tell me what the present status of trying to pass data via an
    > analogue modem over a VOIP 'line' might be please?
    >
    > Just to clarify: In the traditional POTS world, one can use a standard
    > analogue modem at a remote location connected to a data source to pass
    > data across the phone network to a central PC (also fitted with a
    > suitable modem of course). Can this yet be done reliably over a VOIP
    > connection with a suitable adapter?


    Since you have a broadband connection wouldn't it make more sense to set up
    a VPN over the internet instead?

    --

    Brian Gregory. (In the UK)

    To email me remove the letter vee.
     
    Brian Gregory [UK], Feb 5, 2006
    #3
  4. > Anyone tell me what the present status of trying to pass data via an
    > analogue modem over a VOIP 'line' might be please?


    Can you tell me what do you need it for?
    VoIP is, itself, running on the "internet", means you have to be connected
    in order to make it working. And if it's working -- why do you want to
    dialup?

    m.
     
    Martin Lukasik, Feb 6, 2006
    #4
  5. John Dann

    John Dann Guest

    On Mon, 6 Feb 2006 15:52:07 -0000, "Martin Lukasik"
    <> wrote:

    >> Anyone tell me what the present status of trying to pass data via an
    >> analogue modem over a VOIP 'line' might be please?

    >
    >Can you tell me what do you need it for?
    >VoIP is, itself, running on the "internet", means you have to be connected
    >in order to make it working. And if it's working -- why do you want to
    >dialup?
    >

    Well, I thought that I'd briefly outlined the need for such a modem
    link, but let me try again:

    Let's say that you have an instrument at a remote location that you
    wish to 'talk to' (ie pass data to and from) from a PC at a central
    location. That instrument has an RS232 serial interface - OK this is a
    little old-fashioned but many scientific instruments still do work
    this way.

    With a conventional POTS landline you simply connect your remote
    instrument via its serial interface to eg a V90 modem connected to the
    landline at the remote end and equip your central PC with a similar
    modem. From the central PC you dial the remote modem and set up a call
    to your remote instrument and the two ends can talk to their hearts'
    content. But in practice there's a limit to how often you can do this
    for cost and maybe other reasons - it's fine for a once daily download
    of data, but the landline isn't (traditionally at least and unless
    it's a leased line) an always-on link suitable for continuous transfer
    of data.

    But eg ADSL is always-on and VOIP could be free-per-call. Since VOIP
    effectively passes a spectrum of audio signals across its link and a
    modem does just the same, I was wondering whether a traditional modem
    could be hooked into a VOIP setup to do the same thing, but the answer
    seems to be no in practice, for the moment at least.

    Of course there are other ways of achieving this functionality like
    setting up a WAN across an ADSL link and have a Device Server at the
    remote end, but this is potentially more complicated and expensive
    than using a simple V90 modem.

    JGD
     
    John Dann, Feb 6, 2006
    #5
  6. John Dann

    Heimo Hetl Guest

    John Dann <> wrote:

    > But eg ADSL is always-on and VOIP could be free-per-call. Since VOIP
    > effectively passes a spectrum of audio signals across its link and a
    > modem does just the same, I was wondering whether a traditional modem
    > could be hooked into a VOIP setup to do the same thing, but the answer
    > seems to be no in practice, for the moment at least.


    Well, it can definitely be hooked up, at least physically. Whether it
    actually works, and if so, at which throughput rates, depends on the
    analog signal quality the whole chain from your local media gateway (or
    ata box) to its remote counterpart can provide.

    If most of it is under your control, you may be lucky. If you can live
    with _really_ low speed connections (think 300 Baud), it will most
    certainly work. Maybe this will do for simple remote data collection?

    After all, fax over IP does work as well (if done properly). Your
    biggest enemies are jitter and latency. Of course, don't even dream of
    using a codec other than G.711.

    If you hook up a modem to a tradfitional POTS line, its audio will be
    converted to G.711 and back as well. The only difference is the network
    between the converters which is usually of undefined quality on the
    Internet, as opposed to the traditional TDM grid. So just give it a try
    - and let us know of the results.

    cheers
    Heimo


    --
    You never ask questions when God's on your side.
     
    Heimo Hetl, Feb 6, 2006
    #6
  7. John Dann

    John Dann Guest

    On Mon, 6 Feb 2006 18:13:41 +0100, (Heimo Hetl)
    wrote:

    >If you can live
    >with _really_ low speed connections (think 300 Baud), it will most
    >certainly work. Maybe this will do for simple remote data collection?
    >


    No sadly it needs 9k6 really as a minimum, preferably 19k2. So doesn't
    sound very likely to work.

    JGD
     
    John Dann, Feb 6, 2006
    #7
  8. John Dann wrote:
    > On Mon, 6 Feb 2006 18:13:41 +0100, (Heimo Hetl)
    > wrote:
    >
    >
    >>If you can live
    >>with _really_ low speed connections (think 300 Baud), it will most
    >>certainly work. Maybe this will do for simple remote data collection?
    >>

    > No sadly it needs 9k6 really as a minimum, preferably 19k2. So doesn't
    > sound very likely to work.
    >
    > JGD


    As I said in an earlier post, you will probably need to wait until
    ITU V.150.1 is implemented and in common use.

    Unless you want to think about using a VPN and something similar to a
    modem server. (lets you map a virtual COM port (or tty) to a remote
    machines COM port).
     
    Thomas Kenyon, Feb 6, 2006
    #8
  9. John Dann

    Bob Evans Guest

    In article <>, John Dann
    <> wrote
    >But eg ADSL is always-on and VOIP could be free-per-call. Since VOIP
    >effectively passes a spectrum of audio signals across its link and a
    >modem does just the same, I was wondering whether a traditional modem
    >could be hooked into a VOIP setup to do the same thing, but the answer
    >seems to be no in practice, for the moment at least.
    >
    >Of course there are other ways of achieving this functionality like
    >setting up a WAN across an ADSL link and have a Device Server at the
    >remote end, but this is potentially more complicated and expensive
    >than using a simple V90 modem.


    Am I the only one to think that the notion of taking some intrinsically
    digital data, converting it to an "analog" form and then immediately
    re-digitising it to pass through a "digital" channel is slightly
    perverse?

    --
    Bob Evans
     
    Bob Evans, Feb 6, 2006
    #9
  10. John Dann

    Tim Bray Guest

    Thomas Kenyon wrote:
    > Unless you want to think about using a VPN and something similar to a
    > modem server. (lets you map a virtual COM port (or tty) to a remote
    > machines COM port).


    This is the best way to do it. It is really easy to do on Linux
    machines. There is some commercial software that does it on windows.

    I have yet to see a `modem bank service provider` yet though.

    Tim
     
    Tim Bray, Feb 6, 2006
    #10
  11. John Dann

    Heimo Hetl Guest

    Bob Evans <> wrote:

    > Am I the only one to think that the notion of taking some intrinsically
    > digital data, converting it to an "analog" form and then immediately
    > re-digitising it to pass through a "digital" channel is slightly
    > perverse?


    It might be perceived that way, indeed. However, this is what's being
    done whenever someone hooks up a modem to a contemporary phone line:
    They all are digital inside, with media converters at the network
    boundaries. Only ISDN did away with that, but it turned out to be not
    that much more efficient than happily converting back-and-forth, so it
    failed to take over the world.

    cheers
    Heimo


    --
    You never ask questions when God's on your side.
     
    Heimo Hetl, Feb 6, 2006
    #11
  12. John Dann

    Vic Guest

    "Bob Evans" <> wrote in message
    news:...
    >
    > Am I the only one to think that the notion of taking some
    > intrinsically digital data, converting it to an "analog" form and
    > then immediately re-digitising it to pass through a "digital"
    > channel is slightly perverse?


    Not as bad as:

    Manager dictates a letter to secretary who writes it on her pad
    (speech to text - analogue)
    She then takes it to her office and types it into a word processor
    (analogue > digital)
    Then she prints it out on paper (digital > analogue)
    She then puts the page into a fax machine, which scans it (analogue >
    digital)
    The machine converts it into audio tones to send over its modem link
    (D>A)
    In the exchange it's converted to digital to send over a fibre link to
    the other end of the country (A>D)
    At the far end, it goes back to audio tones (D>A)
    The receiving fax machine converts it to digital to send to the
    printer (A>D)
    The printer prints it out on paper (D>A)
    The secretary then reads it out to her boss (text to speech)

    Happens in our office every day !
     
    Vic, Feb 6, 2006
    #12
  13. John Dann

    Bob Evans Guest

    In article <1had1os.1myn1kk1fhxyyiN%>, Heimo Hetl
    <> wrote
    >Bob Evans <> wrote:
    >>the notion of taking some intrinsically digital data, converting it
    >>to an "analog" form and then immediately re-digitising it to pass
    >>through a "digital" channel is slightly perverse


    >It might be perceived that way, indeed. However, this is what's being
    >done whenever someone hooks up a modem to a contemporary phone line:


    That was certainly how we *used* to do it. But in the "bad old days" we
    didn't have any choice - we were frequently forced by economics to push
    data through a network designed only to carry speech and whose endpoints
    were predominantly analog.

    But, given the scenario proposed by the OP [sending RS232 data over an
    ADSL circuit to a remote monitoring station], the idea of transforming
    the data into audio by modem, re-digitising that audio in a VoIP adaptor
    and then sending the resulting IP data to the far end of the link where
    the whole process would then be reversed, is just bizarre.

    It's the sort of thing one might try as a lash-up in an emergency but
    not the way to design a permanent link.

    >They all are digital inside, with media converters at the network
    >boundaries. Only ISDN did away with that, but it turned out to be not
    >that much more efficient than happily converting back-and-forth, so it
    >failed to take over the world.


    In the UK [and unlike some European countries], ISDN failed to take off
    for the majority of domestic users simply because of cost - a marketing
    choice made by the dominant telco - but the superiority of digital
    working over the local loop was never in doubt. However that is really
    a topic for uk.telecom :)

    --
    Bob Evans
     
    Bob Evans, Feb 6, 2006
    #13
  14. John Dann

    Mark Adamson Guest

    "Bob Evans" <> wrote in message
    news:...
    > In article <1had1os.1myn1kk1fhxyyiN%>, Heimo Hetl
    > <> wrote
    >>Bob Evans <> wrote:
    >>>the notion of taking some intrinsically digital data, converting it to
    >>>an "analog" form and then immediately re-digitising it to pass through a
    >>>"digital" channel is slightly perverse

    >
    >>It might be perceived that way, indeed. However, this is what's being
    >>done whenever someone hooks up a modem to a contemporary phone line:

    >
    > That was certainly how we *used* to do it. But in the "bad old days" we
    > didn't have any choice - we were frequently forced by economics to push
    > data through a network designed only to carry speech and whose endpoints
    > were predominantly analog.
    >
    > But, given the scenario proposed by the OP [sending RS232 data over an
    > ADSL circuit to a remote monitoring station], the idea of transforming the
    > data into audio by modem, re-digitising that audio in a VoIP adaptor and
    > then sending the resulting IP data to the far end of the link where the
    > whole process would then be reversed, is just bizarre.
    >
    > It's the sort of thing one might try as a lash-up in an emergency but not
    > the way to design a permanent link.
    >

    I would agree 100%.
     
    Mark Adamson, Feb 7, 2006
    #14
  15. John Dann

    Mark Adamson Guest

    "John Dann" <> wrote in message
    news:...
    > Anyone tell me what the present status of trying to pass data via an
    > analogue modem over a VOIP 'line' might be please?
    >
    > Just to clarify: In the traditional POTS world, one can use a standard
    > analogue modem at a remote location connected to a data source to pass
    > data across the phone network to a central PC (also fitted with a
    > suitable modem of course). Can this yet be done reliably over a VOIP
    > connection with a suitable adapter?
    >
    > JGD


    The cheapest way I can think of doing this is to get a WRT54GS or old
    WRT54G, and do the dual port serial port mod on it. You could then use
    ser2net on the WRT to proxy between network data and serial data. This would
    allow everything to remain in the digital domain, which seems far more
    sensible.

    An alternative to ser2net is serproxy, which is simpler, but less
    established

    MArk
     
    Mark Adamson, Feb 7, 2006
    #15
  16. John Dann

    John Dann Guest

    Thanks for some interesting comments, but I'd venture to suggest that
    some posters might need a re-introduction to the real world. I'm sure
    that any business with a decent IT department or an individual with a
    good grounding in comms technology wouldn't entertain using a modem
    for the sort of application I've described.

    But there are many less technically-aware small businesses and
    individuals who have the requirement I've described and for whom using
    a modem here is the simplest, most familiar and best-documented
    solution to this problem. It's explicitly supported by the data
    acquisition software running on the central PC and delivers a
    perfectly acceptable working solution. Anything more sophisticated
    would very possibly be unacceptable because no-one would
    know how to set it up and would cost more. You know it's not
    difficult, I know that it's not difficult but the fact is that in the
    real world it's too unfamiliar to many potential users. OTOH, for say
    a small business that has had a VOIP adapter with an analogue socket
    installed for them, what could be simpler than expecting to be able to
    plug in a modem in place of a standard handset.

    JGD
     
    John Dann, Feb 7, 2006
    #16
  17. John Dann

    Heimo Hetl Guest

    Mark Adamson <> wrote:

    > The cheapest way I can think of doing this is to get a WRT54GS or old
    > WRT54G, and do the dual port serial port mod on it.


    I do agree that establishing an all digital data path appears to be the
    most straightforward solution. However, this can only be done if there
    is some kind of internet connection available at the remote end, DSL or
    other. If there is only an analog POTS socket and a dumb device with a
    serial port, this might not be an option.

    cheers
    Heimo

    --
    You never ask questions when God's on your side.
     
    Heimo Hetl, Feb 7, 2006
    #17
  18. John Dann

    Heimo Hetl Guest

    Bob Evans <> wrote:

    > That was certainly how we *used* to do it. But in the "bad old days" we
    > didn't have any choice - we were frequently forced by economics to push
    > data through a network designed only to carry speech and whose endpoints
    > were predominantly analog.


    You are right, of course. But change is happening (and we are part of
    it.) However, as we are in a phase of transition, interoperability with
    the status quo is key and neither telcos nor most consumers are willing
    to trash all of their established infrastructure just for the sake of
    progress.

    Just consider how many people buy the various forms of ATAs just to be
    able to stick with traditional analog phone equipment instead of getting
    IP phones.

    cheers
    Heimo

    --
    You never ask questions when God's on your side.
     
    Heimo Hetl, Feb 7, 2006
    #18
  19. John Dann wrote:
    > Thanks for some interesting comments, but I'd venture to suggest that
    > some posters might need a re-introduction to the real world. I'm sure
    > that any business with a decent IT department or an individual with a
    > good grounding in comms technology wouldn't entertain using a modem
    > for the sort of application I've described.
    >

    Fwiw, I can't wait till MOIP is available so that I can use a PDQ and
    some bank software with VOIP lines.
     
    Thomas Kenyon, Feb 7, 2006
    #19
  20. John Dann

    Martin Guest

    Heimo Hetl wrote:

    > So just give it a try - and let us know of the results.


    Out of curiousity I tried this using a Dell laptop's internal modem to
    dial a Nildram 0845 number through a Sipura ATA 3000 running the G.711u
    codec (SP=Gradwell). The modems had a good old go at warbling lots of
    different ways but failed to actually establish a link.
     
    Martin, Feb 7, 2006
    #20
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