Rusty Dekema wrote:
On 4/14/06, Rich Adamson <[EMAIL PROTECTED]> wrote:
I believe the TDM2400 has the capability of doing on-card fxo->fxs data
flows (without hitting the pci bus), but that function has not yet been
implemented. Its basically "required" to support faxes in an analog
environment. When it is implemented, that card should work. The TDM400
card will not work in 99% of the deployments.
I apologize if I'm being dense, but I don't understand why the fact
that a call traverses the PCI bus would kill a fax transmission. I
made the following setup, and it consistently gets 31200 and 33600
connects, no disconnects, good throughput:
Modem --- SIP ATA(G.711u) --- (LAN) --- Asterisk --- (TDM400FXS) --- Modem
I get the same thing (although alwyas 31200 connects, never 33600) with:
Modem --- (TDM400FXS) --- Asterisk --- (TDM400FXS_same_card) --- Modem
If this works, I don't see why a fax transmission wouldn't work. Is it
because the fax protocol doesn't have error correction? Is that even
true?
I realize that clearing up my confusion about this isn't probably
going to result in the problem being fixed, but I sure would like to
know...
The fax issue revolves around the fact that fax signals are analog audio
(eg, modem) that have to be accurately reproduced end-to-end (whatever
that happens to mean in your environment).
If a fax machine is attached to a sip ata device, the network
infrastructure has to be 100% rock solid (no dropped packets, no
congestion, relatively low utilization, no contention for resources
anywhere between asterisk and the adapter). If those items are unknown
or poor, the analog fax signal will not be accurately reproduced at any
sip ata device.
Likewise, the transfer of data across the pci bus has to be 100%
accurate with no dropped/slipped packets, no jitter, etc. "That" has
been an issue with an estimated 95% of the TDM implementations to date.
If you go visit some of the sites where developers work with real time
audio, you'll find lots of comments relative to the inadequacies of the
pci bus as implemented on many many mobo's. Most of what I've read
relates to the North/South pci bridge chipsets, and design errors in
those chipsets including some of the Intel products. Those same issues
seem to be impacting the TDM card in one form or another, and no one has
openly put a finger on exactly why.
The majority of implementations that need fax capability is related to
an internal fax machine (however its connected) to an "fxo" (pstn) port.
If you have "that" working via a TDM400 card, everyone on this list
would love to know "exactly" which mobo you are using.
A modem's error detection / error correction capability (which does not
exist in a lot of fax machines and point of sale devices) can handle
small amounts of those issues noted above. However, it cannot handle
anything more then a glitch here and there without significantly
impacting data throughput.
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