[asterisk-users] spandsp (foip)

Christopher Corn christopher_corn at yahoo.com
Sun Sep 24 23:43:16 MST 2006

  Thanks for the feedback.
  in most diagrams explaining t38, it shows, the sending fax machine connecting to a pots before connecting to a gateway,then the internet.  but if i've read and understood correctly, the sending end can use an ATA with t38 support instead of a pots. in that case, where does the packetization of the t30 data happen? at the ATA? level i presume?
  also, can you recommened a good asterisk compatible ATA adapter with t38 support? i believe cisco has one.
  Thanks in advance.

Lee Howard <faxguy at howardsilvan.com> wrote:
  Christopher Corn wrote:

> May I ask, from your own personal experience. is it not necessaritly 
> worth (the headaches) of investing mytime into setting up SPANDSP into 
> my asterisk system, but rather invest it into going to a company, like 
> packet8 that offers t38 conversion?

I am not really in a position to tell you what something will be worth 
to you - especially when I've not even used that something myself. I 
know and use spandsp as a library, with IAXmodem and HylaFAX, but I do 
not have any experience with spandsp in txfax/rxfax applications or in 
its new T.38 gatewaying. I suspect that I'll eventually get into 
spandsp's T.38 aspects, but without that I've only had a limited amount 
of hands-on exposure to T.38 applications in the form of t38modem and 
Cisco gateways (which experience was somewhat disenchanting - mostly 
because of the gateway T.30 processing).

If you have a T.38 fax machine or if you have a T.38-capable ATA 
connected to a fax machine and you do not have your own PSTN lines then 
I would suspect that it would be worthwhile to use T.38 pass-through on 
Asterisk 1.4 or OpenPBX in conjunction with a T.38-supporting FoIP 
provider. (Because otherwise you don't have any straight-forward, 
reliable means for faxing from your internal fax machines.)

> what does the future of faxing lean towards? before entering an era 
> when all fax machines run the t38 protocol. will we see more t38 
> termination services or faxing through g711?

T.38 is the end-all solution for faxing over IP networks. So I suspect 
that you will see the pervasiveness of T.38 implementations increase 
along with the pervasiveness of VoIP in general. That said, VoIP has 
its own fair share of problems that keeps it from being capable of 
replacing PSTN circuits entirely, and so as long as those problems are 
not generally resolvable for your average business or service provider 
then you'll continue to also see more of the same, traditional, 
modem-ing fax machines. So I strongly suspect that you'll see more of 
T.38, but I don't think that the PSTN (and traditional fax machines with 
it) is going away any time soon.

> from what i've read, using a service that does t38 termination, seems 
> to be where i should go.

I would say that it entirely depends upon whether or not you have PSTN 
lines yourself. If you do, then I would take whatever efforts you can 
to avoid the additional points of T.30 processing/relaying (therefore 
avoiding T.38 gatewaying). But if you do not have PSTN lines, then take 
whatever efforts you can to properly implement T.38 to your FoIP 
provider who will gateway for you.


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