[cisco-voip] CME 4.0, SCCP ATA & fax pass-through

[Andre Beck]

Hi,

in a quite simple CME installation (3.4) I have to support several ATAs
which have fax machines connected. I set this up in "fax mode" as Cisco
calls it, meaning the ATA is hardwired to G.711 only. Sadly enough, there
are fax issues anyway. I assume they are due to echo cancellation and
maybe other signal processing side effects still present even with G.711
calls. Fax pass-through is supposed to fix this by detecting a fax call
and switching over to a special variant of G.711, disabling echo cancel,
reducing the packet size to 10ms and allowing redundancy (sending every
packet twice). Formerly this was not supported with CME and SCCP ATAs,
but with the H.323 ATA load going EOL next year, Cisco announces they
have implemented fax pass-through with SCCP ATAs on CME in CME 4.0.

So I installed 12.4(4)XC, bumped CME up to 4.0 and tried to get fax
pass-through. But I seem to fail, the codec in use is still G.711 µ-Law
instead of the a-Law I request with a modem passthrough nse statement
in voice service voip.

Anyone knows how this is supposed to be configured? Scanning the docs
for examples found no congruent results so far.

TIA,
Andre.
-- 
                  The _S_anta _C_laus _O_peration
  or "how to turn a complete illusion into a neverending money source"

-> Andre Beck    +++ ABP-RIPE +++    IBH Prof. Dr. Horn GmbH, Dresden <-