Fax over GSM?

On Tue, 04 Apr 2006 17:34:27 GMT, John Navas
<spamfilter0@navasgroup.com> wrote:

>[POSTED TO alt.cellular.gsm - REPLY ON USENET PLEASE]
>
>In <4432abe8.3323750@news20.forteinc.com> on Tue, 04 Apr 2006 17:28:09 GMT,
>go.spam@somewhere.else (BigBen) wrote:
>
>>Does a GSM interface for pots network need any special features in
>>order to be able to send/receive fax?
>>
>>I mean, if a plain simple pots landline can suport send/receive fax,

Don't think it can be done. The bind is the need for a fax modem at
the other end of the GSM network where it interfaces with the land
line. You need a way to present the fax 'data' at the GSM phone
digitally, and I haven't seen a fax machine with an external modem
yet. Fax modems are very different creatures from the various data
modems normally utilized.

Alternatively if there was both an RS232C connection on both ends it
could probably be made to work, but there really is no such animal.

The Fax modem, like all modems capable of operation above 600 bits per
second relies on phase shift keying. Unfortunately the Vocoder used in
digital mobile phones (D-AMPS/GSM/CDMA) does not preserve phase
relationships when compressing/uncompressing the analog data. As a
result, you cannot use a modem to transmit data over a digital mobile.
(IT will work over an AMPS connection however). GSM and CDMA do allow
the digitized voice payload to be replaced by a digital payload, and
that is how data is transmitted.
>>ounce you have an analogue phone working connected to a GSM interface,
>>amaking and receiveing voice calls, is there anything else you need in
>>the GSM interface so you can connect a fax machine and start faxing??
>
>See the fax section of the FAQ below.

"BigBen" <go.spam@somewhere.else> wrote in message
news:4432abe8.3323750@news20.forteinc.com...
> Does a GSM interface for pots network need any special features in
> order to be able to send/receive fax?

The GSM digial CODEC is designed for the human voice only; not FAX or data.
FAXes can be sent and received via GSM but only as a digital signal. The FAX
modem that connects to the POTS is at the GSM switch. The usual way this is
implemented is as a virtual FAX running in a PC connected to the phone via a
virtual modem. I suppose there are some special case solutions that provide
for an H.T.G. FAX machine with a digital interface to a GSM device, but I've
never laid hands on one myself. To do any of this your carrier has to
support the feature (not all do) and you'll probably have to pay an extra
fee.

--
Donald R. Newcomb
DRNewcomb (at) attglobal (dot) net

BigBen wrote:

> Does a GSM interface for pots network need any special
> features in order to be able to send/receive fax?
>
> I mean, if a plain simple pots landline can suport
> send/receive fax, ounce you have an analogue phone working
> connected to a GSM interface, amaking and receiveing voice
> calls, is there anything else you need in the GSM interface so
> you can connect a fax machine and start faxing??

As others have mentioned, a GSM voice call has over-the-air
(OTA) characteristics which make it unsuitable for handling
faxes.

But GSM does support fax calls, if your carrier implements the
GSM fax protocol. In this mode, your GSM device acts like a
fax modem. In turn, this assumes it's connected to a computer
running fax sending/receiving software. I'm not aware of any
provision to connect a fax machine to a GSM device.

A GSM carrier handling fax calls uses an IWF (Inter-Working
Function) to connect to the POTS networks.

There are some further issues with using fax over GSM.

In order to send faxes, your carrier might require you to
subscribe to that service, and may charge extra for that
subscription.

Receiving faxes adds an extra layer of complexity. Unlike a fax
to a landline fax machine or fax modem, the GSM case requires
that the type of call (voice, data, fax, etc) is made known to
the IWF _prior_ to the GSM circuit being established to the
receiving device (to establish the right sort of call). This is
done by allocating a device different numbers for voice, data
and fax calls.

So to receive a fax on a GSM device, you need to have a
dedicated fax number, and your carrier will no doubt charge for
this, irrespective of whether it's ever used.

Sending a fax does not require that special number (unless your
carrier insists on configuring things that way - mine doesn't).
This is because the type of circuit required for the outgoing
OTA leg is known to the system immediately the call is
instigated (by virtue of the command sequence from sending
computer to GSM device).

In my case, I quite happily send faxes from my PC via a GSM
handset. But I don't subscribe to a fax number for it, so it's
technically impossible for me to receive them.

John

[POSTED TO alt.cellular.gsm - REPLY ON USENET PLEASE]

In <49gmcuFnvcfrU1@individual.net> on Wed, 05 Apr 2006 11:55:40 +1000, John
Henderson <jhenRemoveThis@talk21.com> wrote:

>In my case, I quite happily send faxes from my PC via a GSM
>handset. But I don't subscribe to a fax number for it, so it's
>technically impossible for me to receive them.

In my case, I use Internet fax services, which are much less hassle, free for
receiving, and cheap for sending.

--
Best regards, SEE THE FAQ FOR CINGULAR WIRELESS AT
John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>

"John Navas" <spamfilter0@navasgroup.com> wrote in message
news6yYf.684283$qk4.7344@bgtnsc05-news.ops.worldnet.att.net...
> [POSTED TO alt.cellular.gsm - REPLY ON USENET PLEASE]
>
> In <4432abe8.3323750@news20.forteinc.com> on Tue, 04 Apr 2006 17:28:09
> GMT,
> go.spam@somewhere.else (BigBen) wrote:
>
>>Does a GSM interface for pots network need any special features in
>>order to be able to send/receive fax?
>>
>>I mean, if a plain simple pots landline can suport send/receive fax,
>>ounce you have an analogue phone working connected to a GSM interface,
>>amaking and receiveing voice calls, is there anything else you need in
>>the GSM interface so you can connect a fax machine and start faxing??
>
> See the fax section of the FAQ below.
>
> --
> Best regards, SEE THE FAQ FOR CINGULAR WIRELESS AT
> John Navas <http://en.wikibooks.org/wiki/Cingular_Wireless_FAQ>
Hi, a lot of useful info, but as almost always, some bias too. If one's
favourite operator does not support fax, is it an unbiased view that other
options are better? Could be, or not, everybody should understand the
options and see what is best for him/herself. One promoting HSPA should also
note that facsimile service does not exist in UMTS (standard, not a question
of lag of implementation).

By the way, the fax protocol is able to negotiate a lower modem speed "for
bad conditions". Does anybody know if it goes as low as the speed that would
work through the cellular voice channel?

One more question related to later comments: if I have a subscription to
send fax messages from my service provider, I always get at the same time a
permission to receive fax messages, and the corresponding fax number. Is it
true that some operators give a subscription for sending faxes but not for
receiving? I thought the standard does not support separate subscriptions
but of course the operator may not assign an incoming number which
effectively would be equal to subscription for incoming faxes.

Me wrote:

> One promoting HSPA should also note that facsimile service
> does not exist in UMTS (standard, not a question of lag of
> implementation).

UMTS real-time fax support is certainly incorporated into 3GPP
standard 27.007. Do you have any other information?

> One more question related to later comments: if I have a
> subscription to send fax messages from my service provider, I
> always get at the same time a permission to receive fax
> messages, and the corresponding fax number. Is it true that
> some operators give a subscription for sending faxes but not
> for receiving? I thought the standard does not support
> separate subscriptions but of course the operator may not
> assign an incoming number which effectively would be equal to
> subscription for incoming faxes.

I need no subscription or special arrangement with the carrier
to send faxes in Australia using a Telstra pre-paid SIM. It
works by default.

John

"John Henderson" <jhenRemoveThis@talk21.com> wrote in message
news:49h7c4FockshU1@individual.net...
> Me wrote:
>
>> One promoting HSPA should also note that facsimile service
>> does not exist in UMTS (standard, not a question of lag of
>> implementation).
>
> UMTS real-time fax support is certainly incorporated into 3GPP
> standard 27.007. Do you have any other information?
Sorry that I was not accurate, UMTS has no facsimile teleservice, see e.g.
22.003 (note, GERAN supports all specified service, UMTS does not support
two, UTRAN does have "a better range of supported QoS parameters though):
Note 1: The facsimile services apply to GERAN only.

Note 2: The Voice Group Services, TS 91 and TS 92 apply to GERAN only.

This 27.007 does not seem to be too accurate, but it isn't supposed to cover
the actual services after all.
>
>> One more question related to later comments: if I have a
>> subscription to send fax messages from my service provider, I
>> always get at the same time a permission to receive fax
>> messages, and the corresponding fax number. Is it true that
>> some operators give a subscription for sending faxes but not
>> for receiving? I thought the standard does not support
>> separate subscriptions but of course the operator may not
>> assign an incoming number which effectively would be equal to
>> subscription for incoming faxes.
>
> I need no subscription or special arrangement with the carrier
> to send faxes in Australia using a Telstra pre-paid SIM. It
> works by default.
Interesting, technically there has to be this fax subscription bit set but
obviously it has been set by default for all subscribers. The subscription
bit should apply for incoming faxes too but if they don't give the fax
number, I guess that automatically disables that incoming fax service.
>
> John

On Wed, 05 Apr 2006 03:03:01 GMT, John Navas
<spamfilter0@navasgroup.com> wrote:

>In my case, I use Internet fax services, which are much less hassle, free for
>receiving, and cheap for sending.

Sounds nice - but I haven't found a service, yet, that provides me a
fax incoming number in Portugal ... and for less than what I would pay
for a landline rental, of course.

I guess I don't need fax that much - .pdf files over the Net are just
fine.

Thanks,

jbr