Re: [hylafax-users] faxgetty flailing and failing.

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

On 2005.01.11 09:31 Jean-Pierre Radley wrote:

> Jan 11 12:20:35.46: [11449]: RECV training at v.17 14400 bit/s
> Jan 11 12:20:35.49: [11449]: <-- [11:AT+FRM=145\r]
> Jan 11 12:20:37.04: [11449]: --> [7:CONNECT]
> Jan 11 12:20:38.10: [11449]: RECV: TCF 1804 bytes, 5% non-zero, 1699
> zero-run
> Jan 11 12:20:38.10: [11449]: RECV: reject TCF (zero run too short, min
> 1800)

At 14400 baud you need 1800 bytes to produce 1 sec, which if the 
"minimum" duration that HylaFAX is expecting a good TCF signal to 
last.  That's not happening, so it looks like the modem is slow to 
detect the data carrier and that the line is noisy.

> Jan 11 12:20:44.19: [11449]: RECV training at v.29 9600 bit/s
> Jan 11 12:20:44.22: [11449]: <-- [10:AT+FRM=96\r]
> Jan 11 12:20:44.64: [11449]: --> [7:CONNECT]
> Jan 11 12:20:46.27: [11449]: RECV: TCF 1890 bytes, 4% non-zero, 1801
> zero-run

1801 bytes at 9600 baud is 1.5 seconds, which indicates that you got a 
perfectly clear connection with V.29.  This may suggest that there is 
some problem with V.17 over this connection.

> Jan 11 12:20:46.27: [11449]: --> [10:NO CARRIER]
> Jan 11 12:20:46.27: [11449]: DELAY 75 ms
> Jan 11 12:20:46.35: [11449]: TRAINING succeeded
> Jan 11 12:20:46.35: [11449]: ACCEPT TSI "SSC Consolidation"
> Jan 11 12:20:46.35: [11449]: <-- [9:AT+FTH=3\r]
> Jan 11 12:20:46.40: [11449]: --> [7:CONNECT]
> Jan 11 12:20:47.70: [11449]: --> [2:OK]

The CFR signal is transmitted.  Now we are going to wait for the 
high-speed data carrier to receive the fax image...

> Jan 11 12:20:47.73: [11449]: <-- [10:AT+FRM=96\r]
> Jan 11 12:20:50.67: [11449]: --> [8:+FCERROR]
> Jan 11 12:20:50.67: [11449]: <-- [10:AT+FRM=96\r]
> Jan 11 12:20:51.06: [11449]: --> [8:+FCERROR]
> Jan 11 12:20:51.06: [11449]: <-- [10:AT+FRM=96\r]
> Jan 11 12:20:51.45: [11449]: --> [8:+FCERROR]
> Jan 11 12:20:51.45: [11449]: <-- [10:AT+FRM=96\r]
> Jan 11 12:20:58.60: [11449]: --> [2:OK]

What this indicates is that when the modem went to look for the V.29 
9600 baud carrier it found some other carrier there, probably V.21 (the 
carrier used to send the slow-speed messages).  There are a few 
different things that we could do at this point: 1) if the modem 
supported it and if HylaFAX supported it we could use the +FAR command 
to automatically adjust to receive whatever data the sender is 
transmitting at that point, unfortunately, most modems don't support 
+FAR, and currently HylaFAX doesn't, either; 2) we can just repeat 
AT+FRM=n until we get bored or until we get something other than 
+FCERROR; 3) we can assume that V.21 is being used and try listening 
for V.21 to see what it is that the sender is trying to tell us.

In my tests I found that #2 was usually a better approach than #3 
because usually the reason for +FCERROR is due to "mishaps" between the 
sender's and the receiver's modulators - such as "clicks" or "noise" in 
the raising and lowering of carriers.  However, in cases where the 
sender doesn't receive the CFR signal properly, it will likely transmit 
CRP, and this would also cause the same problem, and #3 would be a 
better choice.  However, in my tests I found that the likelihood of 
this proving to be beneficial was much less than when using #2.

If your modem supported +FAR (#1) then it may be a really nice thing to 
get it supported in HylaFAX.  I have some modems that do support +FAR, 
but this kind of scenario (where +FAR would be useful) plays out so 
infrequently for me that I haven't been able to justify the development 
cost to myself.

All of that said... the period after TCF is especially problematic for 
various reasons.  For this purpose we have the Class1MsgRecvHackCmd, 
paralleling Class1TCFRecvHack in some ways, which allows you to 
interject a command or a pause before raising the high-speed data 
reception carrier.  If this kind of error happens with all incoming 
faxes, then you may want to play with settings like: 
"Class1MsgRecvHackCmd: AT+FRS=1".

Lee.

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