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Home > Archive > Voice Over IP in UK > February 2006 > Modem over VOIP
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| John Dann 2006-02-04, 5:45 pm |
| 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
| |
| Thomas Kenyon 2006-02-04, 5:45 pm |
| 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.
| |
| Brian Gregory [UK] 2006-02-04, 8:45 pm |
| "John Dann" <news@prodata.co.uk> wrote in message
news:5es9u15ske5q8b034t944m6c08aqhllsv0@
4ax.com...
> 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)
ng@bgdsv.co.uk
To email me remove the letter vee.
| |
| Martin Lukasik 2006-02-06, 5:45 pm |
| > 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.
| |
| John Dann 2006-02-06, 5:45 pm |
| On Mon, 6 Feb 2006 15:52:07 -0000, "Martin Lukasik"
<marcin@milea.pl.i.hate.this.spam> wrote:
>
>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
| |
| Heimo Hetl 2006-02-06, 5:45 pm |
| John Dann <news@prodata.co.uk> 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.
| |
| John Dann 2006-02-06, 5:45 pm |
| On Mon, 6 Feb 2006 18:13:41 +0100, trashcan@hetl.net (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
| |
| Bob Evans 2006-02-06, 5:45 pm |
| In article <2tseu1lnk35m6tlmauv1ssip2nga6raqgs@4ax.com>, John Dann
<news@prodata.co.uk> 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
| |
| Tim Bray 2006-02-06, 5:45 pm |
| 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
| |
| Heimo Hetl 2006-02-06, 5:45 pm |
| Bob Evans <news@eedl.demon.co.uk> 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.
| |
|
| "Bob Evans" <news@eedl.demon.co.uk> wrote in message
news:xmJ+RGr6F55DFA63@cygnus.eedl.demon.co.uk...
>
> 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 !
| |
| Bob Evans 2006-02-06, 5:45 pm |
| In article <1had1os.1myn1kk1fhxyyiN%trashcan@hetl.net>, Heimo Hetl
<trashcan@hetl.net> wrote
>Bob Evans <news@eedl.demon.co.uk> wrote:
[vbcol=seagreen]
>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
| |
| Mark Adamson 2006-02-06, 8:45 pm |
|
"Bob Evans" <news@eedl.demon.co.uk> wrote in message
news:h2A6FU4fh95DFA5v@cygnus.eedl.demon.co.uk...
> In article <1had1os.1myn1kk1fhxyyiN%trashcan@hetl.net>, Heimo Hetl
> <trashcan@hetl.net> 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.
>
> 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 2006-02-06, 8:45 pm |
|
"John Dann" <news@prodata.co.uk> wrote in message
news:5es9u15ske5q8b034t944m6c08aqhllsv0@
4ax.com...
> 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
| |
| John Dann 2006-02-07, 2:45 am |
| 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
| |
| Heimo Hetl 2006-02-07, 2:45 am |
| Mark Adamson <fliblebibble@adamsonfdfgdf.com> 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 2006-02-07, 2:45 am |
| Bob Evans <news@eedl.demon.co.uk> 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.
| |
| Thomas Kenyon 2006-02-07, 7:45 am |
| 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.
| |
| Martin 2006-02-07, 7:45 am |
| 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.
| |
| Ivor Jones 2006-02-07, 7:45 am |
|
"Heimo Hetl" <trashcan@hetl.net> wrote in message
news:1hadtoh.1deq2tz1d48sntN%trashcan@hetl.net
> Bob Evans <news@eedl.demon.co.uk> wrote:
>
>
> 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.
That's feasible when all you want is one or two individual phones. If
however you have an office full of analogue phones complete with a PABX,
it's a huge outlay to replace it all with unproven equipment. I haven't
seen a single dedicated IP phone that I like as yet.
Ivor
>
> cheers
> Heimo
| |
| Martin Lukasik 2006-02-07, 7:45 am |
| > Thomas Kenyon wrote:
>
> 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
Extactly, and that's what I meant.
Dialup using VoIP is not the best way to do it.
Creating "internet connection" using VoIP running on internet connection
is like buying a truck to put your small car on it in order to travel...
m.
| |
| Bob Evans 2006-02-07, 5:45 pm |
| In article <2rkgu1lgvc5gpapp2b34a6c1pb9m2s36ob@4ax.com>, John Dann
<news@prodata.co.uk> 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.
Ouch! Actually one of the things I do to earn my living is design (and
implement) industrial control and telemetry systems
>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.
As I and doubtless others here [and in demon.tech.pc where you also
enquired on this topic last week] learned when we all attended the
"Difficult Datacomms in the Real World" class, the simplest _workable_
solution is always best
> 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.
Unfortunately your preferred solution is not going to work. As
currently implemented, Internet-borne VoIP can be severely affected by
nondeterministic phase jitter, that may not matter too much for speech
traffic but is a killer for the modulation schemes used by "fast" POTS
modems. You might succeed in connecting (and keeping connected) a pair
of modems using a relatively robust pure-FSK mode, such as V.21 or
perhaps V.23, but the achievable data rates will be nowhere near the
9.6kbps minimum that you say is needed.
As others have noted, V150.1 is intended to address these issues.
However it has been more than 3 years in the drafting and is still not
published. That suggests to me that either there are serious technical
difficulties [of the kind that would only be fixed by a "redesign" of
the Internet] or that, among those who would actually put it into
practice, the telecoms equipment manufacturers, nobody is really that
interested.
> 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.
It may be simple but it's not going to do what you say you want 
OTOH there are plenty of products available to bridge "RS232" serial
data to IP over Ethernet [these are often called "Device Servers"]. Many
of those include a modem emulation mode and are specifically designed to
be driven by software that expects to be talking to a POTS modem.
Such a device could be supplied pre-configured for the non-technical end
user. [Typically, the only change then required in existing equipment
is to replace the list of phone numbers to be dialled with IP
addresses.]
HTH,
--
Bob Evans
| |
| Brian Gregory [UK] 2006-02-07, 5:45 pm |
| "Martin" <example@example.com> wrote in message
news:11uh01smu48dk0b@news.supernews.com...
> 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.
I would have thought it ought to be possible with V22bis or lower with error
correction switched on. You might also need to set the time before
disconnecting when no carrier received quite high.
--
Brian Gregory. (In the UK)
ng@bgdsv.co.uk
To email me remove the letter vee.
| |
| hairydog@despammed.com 2006-02-07, 5:45 pm |
| On Mon, 6 Feb 2006 22:56:05 -0000, "Vic" <jimmyjib@btinternet.com>
wrote:
>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)
Just think: if both of these managers could be trained to operate a
telephone, they could go straight from the first step to the last.
| |
| Chris Hopley 2006-02-09, 7:45 am |
| 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
Have you considered using a GSM/GPRS link? There are GSM and GPRS
modules designed specifically for this purpose. Take a look at
http://www.tdc.co.uk/gprs/gprs_siemens.htm for example.
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