[asterisk-ss7] ss7-27-knk: Some findings, possible improvements

Pavel Troller patrol at sinus.cz
Tue Mar 26 08:05:16 CDT 2013

  So, I'm getting familiar with this improved SS7 support. It seems really
improved compared to the standard one, but it still requires some modifications
to be even better :-).
  1) Overlap receiving support.
  It seems to be partially implemented. The channel can receive SAMs, but only
if the PBX was not started yet. It's not my case here. My dialplan starts
always on the first digit (my main extension is _X!) and it directs the channel
to receive more digits by the Incomplete() application. However, we are sending
CC 28 back immediately, when we see AST_CONTROL_INCOMPLETE.
  I looked at sig_pri.c, where the overlap receiving works even in this case,
and adapted sig_ss7.c as well. It now ignores the INCOMPLETE event and waits
for possible SAMs. If they really arrive, it reads the digits and sends them
to the core using the DTMF frames, exactly as sig_pri does.
  The patch is available. What's the ss7 list policy regarding the patches? May
they be posted here, or is it necessary to create a JIRA issue for them ? If yes,
how ? I'm familiar with issues for main Asterisk branches, not for those special
  2) Remapping hexadecimal digits.
  Hexadecimal addresses are used heavily in our network. We are using them for
various prefixes like Network Routing Numbers, Operator Routing Numbers and
Number Portability prefixes. One of the widely used prefixes is EFxxx, which is
converted to *#xxx by current version of libss7.
  Of course it was easy to patch it (the dialplan is fully prepared to handle
pure hex), but it's not generally usable solution. I'm thinking about making
this feature configurable. But this functionality is performed by libss7, not
sig_ss7, which makes passing such config options more complicated. BTW it would
require more advanced configuration, because for example, our EWSD systems use
different mapping, if requested: * is hex B and # is hex C.
  What do you think about this ?
  3) A question at the end: Is overlap sending supported as of now ?
  I can't find any place, where a SAM is being sent...

  With regards,

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