[Asterisk-Users] Echo Cancellation, TDMoE fails, X100P works

[Gary Mart]

We have been pretty much able to solve our echo problems, except for
the primary mode in which we desire to operate our system.

See system diagram at bottom.

Prior to making adjustments to cancel echos (all echocancel=no):

Call Type                                    Result (Before)
---------                                    ---------------
CP <- LEC PRI  * TDMoE * FXO -> AP           no echo
CP <- LEC PRI  * TDMoE * SIP -> sip phone    no echo
AP <- LEC PRI  * TDMoE * FXO -> AP           moderate echo on both ends
AP <- LEC PRI  * TDMoE * SIP -> sip phone    bad echo on sip phone
                                             no echo on other end
AP <- LEC analog   FXO * SIP -> sip phone    bad echo on sip phone
                                             no echo on other end
AP <- LEC analog   FXO * FXO -> LEC -> AP    slight echo on both ends

(AP stands for analog phone and CP stands for cell phone)


After changes to the * with the X100P cards; latest CVS (11/21/03),
echocancel=yes and echocancelwhenbridged=yes in zapata.conf,
KFLAGS+=-DECHO_CAN_MARK2 and KFLAGS+=-DAGGRESSIVE_SUPPRESSOR in
/zaptel/Makefile:

Call Type                                    Result (After)
---------                                    --------------
CP <- LEC PRI  * TDMoE * FXO -> AP           no echo
CP <- LEC PRI  * TDMoE * SIP -> sip phone    no echo
AP <- LEC PRI  * TDMoE * FXO -> AP           slight echo on both ends
AP <- LEC PRI  * TDMoE * SIP -> sip phone    BAD echo on sip phone (STILL)
                                             no echo on other end
AP <- LEC analog   FXO * SIP -> sip phone    short echo on sip phone, gets
                                             much better after a few seconds
                                             no echo on other end
AP <- LEC analog   FXO * FXO -> LEC -> AP    negligible echo

(AP stands for analog phone and CP stands for cell phone)


It appears that echo cancel does work if an FXO (X100P) channel is
involved in the call but does not work for TDMoE <--> * <--> SIP.
The TDMoE is configured as a pri_cpe in zapata.conf on the * box with
the X100P boards, and has the same echocancel configuration as the
X100P channels.

Any ideas as to why echo cancel works for the X100P channels but
does not work for the TDMoE channels?

Do the echo cancel algorithms even work at all on TDMoE channels?
I could detect NO difference with echo canceling on for a TDMoE call
through * to a sip phone while there was a big difference with echo
canceling on for an FXO call through * to a sip phone.

I have not done echo canceling on the * box connected by PRI to the LEC
because, as I understand, it may cause problems for the modem connections
that go through that machine.  

Also, it is clear that the echo heard on the sip phone originates with the
the analog phone at the far end of the connection.  As was pointed out in
an earlier posting (and my tests confirm), digital cell phones don't 
generate an echo.

System Diagram:
                            +- PRI --> modem bank
                            |
LEC <-- PRI -->  * with  <--+
                 T400P   <--+
                            |  (pri)
                            +- TDMoE -->  *
                                          with  <-- SIP -->  sip phones
LEC <------ analog line --------------->  X100P



Gary Mart


PS  The modem connections have been working just fine after some initial
    problems and a CVS update.  Thanks Mark!