Hello Scott,
Thanks for your reply and clarity given by adding needful information to
call flow.
If I understand correctly, there are three dependencies to implement
complete real time FoIP using T.38 (over both PSTN and VoIP). 1)
Asterisk 2) T.38 capable fax modem software 3) VoIP gateway (VoIP
provider) with T.38 support.
Please correct me, If I am wrong.
Now, Can I use "opalvoip" as T.38 capable fax modem software in our
flow? Can I add "opalvoip" as a plugin to "Asterisk" (like SpandDSP)?
I look forward to hearing from you.
Thank you.
Regards,
Chandra.
On 1/9/2014 8:39 PM, Scott Griepentrog wrote:
To add some details to your call flow for clarity, I would write it as:
Sending FAX machine (T.30) ==POTS==> Local CO ==PRI/G711/T.30==>
(PSTN) ==> VoIP Gateway with T.38 support ==IP/SIP/RTP/T.38==>
(INTERNET) ==> Asterisk (with T.38 capable fax modem software) =>
.TIFF file
I'm using ==protocol/stack==> to indicate the signalling/media
methods, and (network) to indicate a large complicated routing network
that isn't changing the datastream.
In this diagram, note that:
1) POTS Analog to Digital (G711) conversion is done by the CO's SLIC
2) The VoIP gateway when using T.38 does the G711/T.30 "Modem"
conversion to T.38. A way to understand this is that it's like the
serial port on the back of the old style modems, only the data is
carried in RTP packets and called T.38. Portions of the T.30 decoding
still have to be done by a software program inside or alongside Asterisk.
The same sequence where T.38 is not used - just a conventional T.30
fax over G711:
Sending FAX machine (T.30) ==POTS==> Local CO ==PRI/G711/T.30==>
(PSTN) ==> VoIP Gateway ==IP/SIP/RTP/G711/T.30 ==> (INTERNET) ==>
Asterisk (with fax modem software) => .TIFF file
Note that the "asterisk fax modem software" has to include the entire
T.30 stack including all the V.xx protocols, plus T.38 if needed.
On Thu, Jan 9, 2014 at 5:38 AM, Chandramouli P <[email protected]
<mailto:[email protected]>> wrote:
Hi,
I have some basis queries about the internal flow (conversion) and
architecture of FoIP. Please note that I have done enough research
on Internet to clarify my queries. But, I didn't get proper
information. I thought of sending you guys an email to clarify my
queries:
I want to implement a real time fax service with Asterisk (FoIP
with Asterisk) using T38 protocol. For this, first I would like to
clear with the basic internal flow of sending fax over IP.
*Send Fax -> Fax Modem -> Asterisk -> Receive Fax *
1) Please correct me, If I am wrong with the above flow.
2) Can we consider "opalvoip" as Fax modem?
3) Can we consider "SpanDSP" as Fax modem?
4) Can we consider "HylaFax" as Fax modem?
5) Can we consider "Fax Modem" as "T38 Gateway" in the above flow?
If not, where I need to put T38 Gateway in the above flow? Can you
please rewrite the flow?
6) Can I use "opalvoip" as Fax modem in the above flow?
7) T38 Gateway contains T38 Receiver and T38 Sender. Is it correct?
Hence request you to find some time to reply and also reply in inline.
I look forward to hearing from you.
Thanks in advance.
Regards,
Chandra.
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