asterisk users - Feb 2012 - OT - "T.38 unreliable on a LAN" : truth or obscurantism ?

Hi,

When someone says "T.38 is not reliable on a (normally loaded and
managed) LAN", would you rather agree or disagree ?
In this case, fax calls are coming in through an analog gateway,
passing trough Asterisk and then going out to ISDN through a digital
gateway.

Comments ?

Regards

----- Original Message -----
> Hi,
> 
> When someone says "T.38 is not reliable on a (normally loaded and
> managed) LAN", would you rather agree or disagree ?
> In this case, fax calls are coming in through an analog gateway,
> passing trough Asterisk and then going out to ISDN through a digital
> gateway.
> 
Is T.38 actually in use in this scenario? Or are you simply passing the fax call
through Asterisk as 'normal' audio (G.711u/a, etc)?

If so, you may want to see here: http://www.soft-switch.org/foip.html

--Tim

T.38 is tolerant of most network conditions, ... the challenges in getting
reliable performance are usually limited to getting the interop right once, but
the absolute success rate will depend on the quality of your T.38/PSTN
gateway's fax implementation. In general terms, T.38 is actually the right
way to cope with lossy or high jitter network conditions, and so it's
reliable over most networks.

The question people usually ask is whether fax over G.711 is unreliable on a
LAN. To which the answer would be a definite 'it depends' ;-)

-d


On Feb 15, 2012, at 3:03 PM, Olivier wrote:
> Hi,
> 
> When someone says "T.38 is not reliable on a (normally loaded and
> managed) LAN", would you rather agree or disagree ?
> In this case, fax calls are coming in through an analog gateway,
> passing trough Asterisk and then going out to ISDN through a digital
> gateway.
> 
> Comments ?
> 
> Regards
> 
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On 02/15/2012 03:03 PM, Olivier wrote:
> Hi,
>
> When someone says "T.38 is not reliable on a (normally loaded and
> managed) LAN", would you rather agree or disagree ?
> In this case, fax calls are coming in through an analog gateway,
> passing trough Asterisk and then going out to ISDN through a digital
> gateway.
>
> Comments ?
While I can't speak for Asterisk's T.38 performance (it was barely past 
the point of "okay, it compiles" at the time of this datapoint), T.38
in
general can handle nasty network conditions without a problem as long 
you enable some sort of error correction (either FEC or packet 
redundancy).  Case in point, I ran several hundred SIP-based T.38 calls 
a month over VSAT links.  The links ran anywhere from 550 to 750ms 
latency and would average around 1-2% packet loss (averaged over a 5 
minute period).  Those were with a Quintum ASG400 at the far end and a 
Quintum CMS960 going into PRIs at the VSAT hub.

So if T.38 can handle that, it can handle just about anything.