[Asterisk-Users] Asterisk - fax - spandsp

[Rich Adamson]

> > What is in the bug tracker helps make things clearer to people who know 
> > what they are doing. What we need is something that makes things clear 
> > to laymen. Saying internally and externally clocked doesn't cut it. It 
> > needs to be made clear to laymen that clocking internally is rarely 
> > right; that slaving to a PBX, when there is also a PSTN connection is 
> > almost never right; that the PSTN is the grand master of the telecoms 
> > universe, and all Asterisk boxes should be its slave.
> >
> 
> Maybe the confusion is because some pieces of the explanation are being 
> left out.  If you look at the leads on a synchronous RS232 interface it 
> is very clear:  Rx clock and Tx clock, and people understand that.  It's 
> not as clear-cut with T1/E1.
> 
> I'm not the person to explain this, but someone (Rich Adamson perhaps, 
> or a Digium engineer) needs to explain phase-locked loops and the 
> recovery of the timing signal from the data stream.  Perhaps 
> understanding that the timing comes from the data stream itself might 
> lead to better understanding.

How about this...

Replace the old text in /usr/src/zaptel/zaptel.conf.sample:
# span=<span num>,<timing>,<line build out (LBO)>,<framing>,<coding>[,yellow]
#                                                                           
# The timing parameter determines the selection of primary, secondary, and
# so on sync sources.  If this span should be considered a primary sync
# source, then give it a value of "1".  For a secondary, use "2", and so on.   
# To not use this as a sync source, just use "0"  

with this text:
# span=<span num>,<timing>,<line build out (LBO)>,<framing>,<coding>[,yellow]
# 
# All T1/E1 spans generate a clocking signal on the transmit side. The          
# timing parameter determines whether the clocking signal from the opposite
# end of the T1/E1 is used to sync our clock. For T1/E1's connected to a
# pstn provider (telco), chose 1 for using this T1 as the primary clock,
# 2 for a secondary (if multiple T1/E1's are in use and the second T1 is
# to be used for clock sync should the primary fail), or 3 for the next
# T1, etc.  If the T1/E1 is connected to a channel bank or if the T1/E1
# is not to be used for clock sync, then specify the timing as 0. (A quad
# T1/E1 card should only have a single T1/E1 specified as timing = 1, or
# primary clock sync.  Incorrect timing sync may cause clicks/noise in
# the audio, poor quality faxes, or fax failures, etc.)

If this is helpful, I'll submit a bug for the text. Thoughts anyone?

Rich