Re: [hylafax-users] T.30 T2 timeout, expected signal not received

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

On 2004.08.11 10:02 Stephen Carville wrote:
> This looks like the Last Known Problem -- suggestions on fixing it are
>
> wqelcome :-)  In the last seven days this has accounted for 29 errors
> in 1289
> pages.

> Aug 11 07:24:15.49: [25776]: RECV received RCP frame
> Aug 11 07:24:17.08: [25776]: --> [10:NO CARRIER]
> Aug 11 07:24:17.08: [25776]: MODEM set XON/XOFF/DRAIN: input ignored,
> output
>  disabled Aug 11 07:24:17.08: [25776]: MODEM input buffering disabled
> Aug 11 07:24:17.08: [25776]: <-- [9:AT+FRH=3\r]
> Aug 11 07:24:20.95: [25776]: --> [7:CONNECT]
> Aug 11 07:24:21.21: [25776]: --> HDLC<6:FF C8 FD F4 40 00>
> Aug 11 07:24:21.21: [25776]: --> [5:ERROR]
> Aug 11 07:24:21.21: [25776]: MODEM Command error
> Aug 11 07:24:21.21: [25776]: FCS error

That "FF C8 FD F4 40 00" is the PPS-EOP signal, but it's missing one 
byte at the end, so it is a corrupt HDLC frame and produces an FCS 
error (thus, the ERROR message).  We expect the sender to retransmit 
the signal.  So we try again...

> Aug 11 07:24:21.21: [25776]: <-- [9:AT+FRH=3\r]
> Aug 11 07:24:21.26: [25776]: --> [7:CONNECT]
> Aug 11 07:24:22.24: [25776]: --> [20:0F 00 00 00 00 00 00 00 00 00 00
> 00 00 00 00 00 00 00 00 00]

And behold what is this???

> Aug 11 07:24:22.24: [25776]: --> [20:00 00 00 00 00 00
>  00 00 00 00 00 00 00 00 00 00 00 00 00 00]

Well, either the sender is actually sending a bunch of zeros, or 
something is wrong with the receiving modem.  I guess that a PBX 
in-between DCEs could also cause this problem, or perhaps a really 
nasty telco problem.

My guess is that whatever happened to the signal happened to it during 
the PPS-EOP HDLC frame and caused it to lose one byte.  That error 
persisted through the rest of the session, causing the zeros, etc.

At this point, check your lines, check your connection, check your 
modem.  If all else fails try a different modem (make and model) and 
see if the error continues.

Lee.

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