[Asterisk-Users] Echo Cancellation

[Stephen R. Besch]

I am trying to optimize echo cancellation. Originally (with only one 
phone attached), echo cancellation worked well.  Echo was only obvious 
in the first second or so of a call.  Now, with multiple phones on the 
system, the echo does not go away. It is quiet, but audible and somewhat 
annoying.  I have the following configuration:

PSTN (4 lines) <-> ADTRAN TSU600 <-> T1 <-> T100P <-> asterisk <-> 
Budgetone 100 (20 phones)

The budgetone phones and the * server are all on the same local branch 
of a full duplex switched LAN (100BaseT/10BaseT, Baystack 450 switches). 
  Typical delay times (from SIP SHOW PEERS) are 3-8 msec.  Am I better 
off to just set echocancel=yes, or should I experiment with setting the 
number of taps?    Does echo cancel=yes mean "hunt" for the optimal 
number of taps, based on transmission delay?

Also, can I help matters with the type of service setting (tos) in 
sip.conf?  What exactly is "tos"?

Stephen R. Besch