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Let's say I want to set up my own dialin server. I don't have a spare PSTN
phone connection. Getting a geographic incoming number is usually
straightforward (Sipgate et al are free). What are the issues with trying
to do this with VOIP? I suppose the problem is I don't actually want V near
any IP. Is there any protocol to having the PSTN-VOIP gateway act as a
modem, rather than a voice sampler? I know there are protocols for fax, but
for modem data?

Is there some way I could get, say, an encapsulated PPP stream over the net?
Are there services that provide this?

Thanks
Theo

Theo Markettos wrote:
> Let's say I want to set up my own dialin server. I don't have a spare PSTN
> phone connection. Getting a geographic incoming number is usually
> straightforward (Sipgate et al are free). What are the issues with trying
> to do this with VOIP? I suppose the problem is I don't actually want V near
> any IP. Is there any protocol to having the PSTN-VOIP gateway act as a
> modem, rather than a voice sampler? I know there are protocols for fax, but
> for modem data?
>
> Is there some way I could get, say, an encapsulated PPP stream over the net?
> Are there services that provide this?
>
> Thanks
> Theo

This is difficult to make work. What bitrate you can achieve will
depend on the quality of the IP link between you and your VoIP service
provider. I'd say to probably hope for around 14,400bps using g711a/u
codec. There is an ITU standard called V.150.1 which is the modem
equivalent of t.38 but I've never heard of any equipment or service
providers using it. Timing critical connections such as modem and faxes
are always going to be a pain over IP due to the lack of strict timing
between source and destination on a IP network.

If you are using a Linksys ATA then your best bet is to read this I
wrote a while ago about faxing over IP:

http://www.provu.co.uk/pdf/sipura/ip...ra_linksys.pdf

otherwise, try and apply the same settings to whatever ATA you have. It
basically involves turning off features such as variable jitter buffers
and echo cancellation which can all interfere with the modem comms.

Someone asked this very same question on here not so long ago I'm sure.
Try searching the list archives to see who it was and if they got
anywhere with it.

Another option would be to search for a dialup ISP who simply allow you
to connect as and when you want for no charge other than the phone call,
such companies exist... the name Geoisp springs to mind although I could
be imagining it.

cheers,
Paul.

Desk Rabbit <nospam@example.com> wrote:
> What you need is one of these
> http://networking.ringofsaturn.com/R...Portmaster.php

A bit more than I wanted :) And doesn't it require a POTS or ISDN line to
operate?

> Seriously though, what are you *actually* trying to achieve? If you want
> to connect to your PC then use any one of the many remote control
> programs. Are you wanting to give a dialup service for clients and
> customers? If so use one of the many free dialup numbers such as
> http://www.adial.co.uk/
> http://www.free-dialup.net/
> http://www.nocostdialup.co.uk/

'Free' dialup comes from the same school as 'unlimited' broadband - ie it
isn't. If you use it for anything more than trivial lengths of time you end
up with a very large phone bill.

I'm wanting a dialup with a geographic number. I'm also wanting one that
doesn't become engaged or congested at busy times (which rules out GeoISP
and similar). It's an advantage for it to terminate in my network because
then I have control over onward routing, rather than at some random ISP. Of
course I could tunnel, but then I'd waste precious dialup bandwidth on the
encapsulation.

Now it seems to me that an ATA is more complex than a modem, so I can't see
why the PSTN-Internet interface couldn't accommodate a modem too. And get
better rates than an analogue-analogue connection because a device
synchronised to digital PSTN can do 56K.

I suppose the problem is the business model - Sipgate only make a tiny
amount from incoming calls and most of their revenue is from outgoing calls.
Such a system wouldn't have anything outgoing. But I'm not averse to paying
an up-front fee.

Theo

Theo Markettos schreef:
> Let's say I want to set up my own dialin server. I don't have a spare PSTN
> phone connection. Getting a geographic incoming number is usually
> straightforward (Sipgate et al are free). What are the issues with trying
> to do this with VOIP? I suppose the problem is I don't actually want V near
> any IP. Is there any protocol to having the PSTN-VOIP gateway act as a
> modem, rather than a voice sampler? I know there are protocols for fax, but
> for modem data?
>
> Is there some way I could get, say, an encapsulated PPP stream over the net?
> Are there services that provide this?
>
> Thanks
> Theo

I guess not, this wheel has already been invented for you....it was hard
enough :)

--

The Fug.

( VoIP/SIP switched by: www.mysipswitch.com )

In article <jir*9z+-r@news.chiark.greenend.org.uk>,
Theo Markettos <theom+news@chiark.greenend.org.uk> wrote:
>Desk Rabbit <nospam@example.com> wrote:
>> What you need is one of these
>> http://networking.ringofsaturn.com/R...Portmaster.php
>
>A bit more than I wanted :) And doesn't it require a POTS or ISDN line to
>operate?
>
>> Seriously though, what are you *actually* trying to achieve? If you want
>> to connect to your PC then use any one of the many remote control
>> programs. Are you wanting to give a dialup service for clients and
>> customers? If so use one of the many free dialup numbers such as
>> http://www.adial.co.uk/
>> http://www.free-dialup.net/
>> http://www.nocostdialup.co.uk/
>
>'Free' dialup comes from the same school as 'unlimited' broadband - ie it
>isn't. If you use it for anything more than trivial lengths of time you end
>up with a very large phone bill.
>
>I'm wanting a dialup with a geographic number. I'm also wanting one that
>doesn't become engaged or congested at busy times (which rules out GeoISP
>and similar). It's an advantage for it to terminate in my network because
>then I have control over onward routing, rather than at some random ISP. Of
>course I could tunnel, but then I'd waste precious dialup bandwidth on the
>encapsulation.
>
>Now it seems to me that an ATA is more complex than a modem, so I can't see
>why the PSTN-Internet interface couldn't accommodate a modem too. And get
>better rates than an analogue-analogue connection because a device
>synchronised to digital PSTN can do 56K.

I think you'll struggle to get 56K.

So, PC (digital) -> Modem (analogue) -> PSTN (digital) -> ITSP (maybe
same digital?) -> Internet -> ATA -> Modem (analogue)

I think that because you've got a 2nd analog link in there that 33K6 is
the best you could expect.

In paractice because of the nature of the Internet, jitter, packet loss
then maintaining a modem signal might be tricky...

Saying that, I've experimented with sending FAXes over the Internet (fax
machine -> ATA -> Internet -> Asterisk -> email) and it's generally
worked OK, but I'd not like to rely on it.

>I suppose the problem is the business model - Sipgate only make a tiny
>amount from incoming calls and most of their revenue is from outgoing calls.
>Such a system wouldn't have anything outgoing. But I'm not averse to paying
>an up-front fee.

You've nothing to lose (well a few pence) by connecting a modem to a BT
line and dialling your Sipgate number with an ATA connected to a modem
(connected to eg. a Linux box running PPP) and seeing what happens...

Good luck!

Gordon

"Desk Rabbit" <spam-me-not@example.com> wrote in message
news:ZfOdnZUxW9Q9J5zVnZ2dnUVZ8saonZ2d@pipex.net...
> Gordon Henderson wrote:
> > In article <jir*9z+-r@news.chiark.greenend.org.uk>,
> > Theo Markettos <theom+news@chiark.greenend.org.uk> wrote:
> >
> >>Desk Rabbit <nospam@example.com> wrote:
> >>
> >>>What you need is one of these
> >>>http://networking.ringofsaturn.com/R...Portmaster.php
> >>
> >>A bit more than I wanted :) And doesn't it require a POTS or ISDN line
to
> >>operate?
> >>
> >>
> >>>Seriously though, what are you *actually* trying to achieve? If you
want
> >>>to connect to your PC then use any one of the many remote control
> >>>programs. Are you wanting to give a dialup service for clients and
> >>>customers? If so use one of the many free dialup numbers such as
> >>>http://www.adial.co.uk/
> >>>http://www.free-dialup.net/
> >>>http://www.nocostdialup.co.uk/
> >>
> >>'Free' dialup comes from the same school as 'unlimited' broadband - ie
it
> >>isn't. If you use it for anything more than trivial lengths of time you
end
> >>up with a very large phone bill.
> >>
> >>I'm wanting a dialup with a geographic number. I'm also wanting one
that
> >>doesn't become engaged or congested at busy times (which rules out
GeoISP
> >>and similar). It's an advantage for it to terminate in my network
because
> >>then I have control over onward routing, rather than at some random ISP.
Of
> >>course I could tunnel, but then I'd waste precious dialup bandwidth on
the
> >>encapsulation.
> >>
> >>Now it seems to me that an ATA is more complex than a modem, so I can't
see
> >>why the PSTN-Internet interface couldn't accommodate a modem too. And
get
> >>better rates than an analogue-analogue connection because a device
> >>synchronised to digital PSTN can do 56K.
> >
> >
> > I think you'll struggle to get 56K.
> Indeed. 56K back to back doesn't work. From Wikipedia:-

not quite - the test describes the ISP digital modems are doing the reverse
conversion.

what this is saying is 2 V.92? modems wont give you 56kbps back to back if
you go thru 2 analog to PCM conversions in between (ie modem ->analog
line -> PCM - analog -> modem).

obviously there is kit that can cope with 1 conversion, since all those old
modem dial in banks run by ISPs did exactly that - although they had to
hooked up in a particular way to make it work.
>
> "56k modems can only work at 56k if there is one pulse-code modulation
> to analog conversion in the path between the internet service provider's
> digital equipment and the user's modem. When this is not the case or
> when two 56k modems are used to communicate with each other they will
> generally fall back to 33.6 kbit/s using V.34 analog modulation. The 56
> kbit/s transmission exploits the fact that most telephone exchanges are
> interconnected with digital lines and so can use more efficient
> transmission techniques over twisted-pair lines."
>
> http://en.wikipedia.org/wiki/56k_modem
--
Regards

stephen_hope@xyzworld.com - replace xyz with ntl

In article <iHkMj.79571$5i5.38214@newsfe6-gui.ntli.net>,
stephen <stephen_hope@xyzworld.com> wrote:

>obviously there is kit that can cope with 1 conversion, since all those old
>modem dial in banks run by ISPs did exactly that - although they had to
>hooked up in a particular way to make it work.

They went by various names - eg. Livingston Portmonster, or "not
modems" .... They plumbed into the PSTN via E1 / ISDN30 lines and took
the data digitally with no intervening analogue conversion stage, other
than the modem at the customers end. (hence the term "not modem") They
did clever DSP type work internally to recreate the original digital
data out of the digitally encoded analogue data, ran the other end of
the (usually) PPP link, then presented it as an IP connection out on an
Ethernet line.

Gordon

In message <ftsokn$scd$1@energise.enta.net>, Gordon Henderson
<gordon+usenet@drogon.net> writes
>They went by various names - eg. Livingston Portmonster, or "not
>modems" .... They plumbed into the PSTN via E1 / ISDN30 lines and took
>the data digitally with no intervening analogue conversion stage, other
>than the modem at the customers end. (hence the term "not modem")
Sort of a Mod without the EM
>They
>did clever DSP type work internally to recreate the original digital
>data out of the digitally encoded analogue data, ran the other end of
>the (usually) PPP link, then presented it as an IP connection out on an
>Ethernet line.
>
>Gordon

--
Clint Sharp

Clint Sharp <clint@clintsmc.demon.co.uk> wrote:
> In message <ftsokn$scd$1@energise.enta.net>, Gordon Henderson
> <gordon+usenet@drogon.net> writes
> >They went by various names - eg. Livingston Portmonster, or "not
> >modems" .... They plumbed into the PSTN via E1 / ISDN30 lines and took
> >the data digitally with no intervening analogue conversion stage, other
> >than the modem at the customers end. (hence the term "not modem")
> Sort of a Mod without the EM

That was the sort of thing I was thinking of: after all, I imagine Sipgate
don't have a big bank of analogue lines plugged into thousands of ATAs.
They'll have an E3 or STM-1 feeding into a box with an Ethernet port on the
other side, and data is converted digitally. Assuming all this conversion
was in software (it probably won't be) it'd just be a case of reprogramming
to turn from a VOIP gateway to a 'modem' bank. It's probably harder work to
convert modem tones into PPP than voice samples into VOIP but the I/Os
are the same.

I could buy a box that did the same, the problem being that unlike IP it's
hard for the consumer to get access to the digital PSTN (without renting an
E1 or similar).

Looks like V.150.1 is exactly what I wanted, but I'll have to wait a few
years until it's deployed.

Theo

Theo Markettos <theom+news@chiark.greenend.org.uk> wrote:
> That was the sort of thing I was thinking of: after all, I imagine Sipgate
> don't have a big bank of analogue lines plugged into thousands of ATAs.
> They'll have an E3 or STM-1 feeding into a box with an Ethernet port on the

Well, probably more like an E1 per box... I was getting myself confused
between the quantity of numbers they issue (lots) and the quantity of
incoming lines (much smaller).

Theo