asterisk users - Nov 2003 - Echo Cancellation, TDMoE fails, X100P works

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!

>> System Diagram:
>>                             +- PRI --> modem bank
>>                             |
>> LEC <-- PRI -->  * with  <--+
>>                  T400P   <--+
>>                             |  (pri)
>>                             +- TDMoE -->  *
>>                                           with  <-- SIP -->  sip
phones
>> LEC <------ analog line --------------->  X100P
>
>
>> PS  The modem connections have been working just fine after some
initial
>>     problems and a CVS update.  Thanks Mark!  
>
>
>Would you be willing to share your T400P/NAS configuration?  I intend on 
>doing something very similar but was told that the T400P couldn't pass 
>traffic between the LEC PRI and the NAS and achieve v.90/v.92 connections.
Oh, but it DEFINATELY can!

# file: /etc/zaptel.conf  (on * with T400P)

loadzone=us
#                             pri from LEC
span=1,1,0,esf,b8zs
#                             pri T1 to portmaster (this one is online)
span=2,0,0,esf,b8zs
#                             pri T1 to portmaster (backup, testing)
span=3,0,0,esf,b8zs
#                             pri T1 (unused, next I will try using this to
#                             connect to the other * box if I can't stop the
#                             echos on TDMoE)
span=4,0,0,esf,b8zs

bchan=1-23
dchan=24
bchan=25-47
dchan=48

# For Testing: This maps channels straight across with as little involvement
#              as possible by * (the zaptel driver just shuffles bits).
# dacs=1-24:25

bchan=49-71
dchan=72
bchan=73-95
dchan=96

# TDMoE channels to PBX (* with X100P's)
dynamic=eth,eth1/00:01:02:9B:39:72,24,1
bchan=97-119
dchan=120



# file: /etc/asterisk/zapata.conf
[channels]
language=en

context=lec-pri
signalling=pri_cpe
switchtype=5ess
usecallerid=yes
group=1
echocancel = no
echocancelwhenbridged = no
channel => 1-23

context=outbound-pm
signalling=pri_net
switchtype=5ess
usecallerid=yes
group=2
echocancel = no
echocancelwhenbridged = no
channel => 25-47

context=outbound-pm
signalling=pri_net
usecallerid=yes
group=3
channel => 49-71

context=local
switchtype=5ess
signalling=pri_net
usecallerid=yes
group=4
channel => 73-95

;; TDMoE to PBX
context=local
usecallerid=yes
signalling=pri_net
group=5
channel => 97-119



# file: /etc/asterisk/extensions.conf

(excerpt)

[lec-pri]

; these numbers to our portmasters

exten => 5413452121,1,Dial(Zap/g2/5413452121)
exten => 5413452122,1,Dial(Zap/g2/5413452122)

; these DID's to PBX via TDMoE

exten => 5413452123,1,Dial(Zap/g5/5413452123)



Note the commented out line in zaptel.conf (# dacs=1-24:25). This was
new in CVS as of a couple of weeks ago and this was the first thing
that worked successfully with the 56k modem traffic.  Also note that
echo canceling is off in zapata.conf, it could only confuse the
modems.  Also, either * is _very_ fast when it shuffles bits between
channels and/or modems have some decent echo canceling software
builtin, because the modems operate at full speed.

Also note that neither the 'c' option nor the 'd' option is used
in the
Dial command in extensions.conf.  In all of our tests before talking to 
Mark we had used those options (seemed the obvious thing to do judging
from their descriptions).  Mark suggested taking them out, we did, it 
worked.  (I don't know if that is the whole difference between what worked
and what did not.  This was one of those situations where you go in thinking
the solution is straight forward, but after 6 or a dozen failed attempts 
you realize that you are in for a big trial and error session and you have
not kept exacting records on the initial failed attempts.)

Let me know if that helps.

Now, it seems to me that the only reason you would want to do what I did
is so that you can route some of the incoming calls somewhere else for 
another purpose, like a voice call.  And somewhere along the line you
will run into my problem: echo cancellation.  Maybe you can help me out
there.
>
>Also, your diagram looks like you're connecting two * boxes by plugging
one
>end of a cable into an ethernet jack, and the other into a T400P jack -- is 
>this correct?  I thought TDMoE was strictly ethernet<-->ethernet?
I left out some details for the sake of brevity.  Both * boxes have 2 ethernet
interfaces, one for normal IP and the other dedicated to the TDMoE traffic.
>
>
>Regards,
>Andrew
Gary