[Asterisk-Users] Cisco's description of echo

[Michael George]

We are having trouble with an installation that is getting a lot of echo on
some calls.  The installation is all SIP phones and they have a VoIP provider.

When we call through the voip provider and into another of their customers
(voip throughout) there is no echo problem.  If we call in their landline,
through the TDM400's FXO to one of the SIP phones, there is no echo problem.

Sometimes when we dial from SIP --> Voip provider --> PSTN --> destination it
is okay, but other times the echo is horrible.

In trying to figure this out, I found this article at Cisco's site:
http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b68.shtml#1041385

It claims that echo always comes from the far end of the connection.  So if I
hear echo, then the origin of the echo is in the equipment on the end of the
line near the person to whom I'm talking.

The description seems to make sense, but the zapata.conf setting for echo
cancellation seem to also help echo on the near end of the connection.

I have read about echo on the wiki and in the mailing list, but it almost
always discusses it with respect to the digium cards, not SIP alone.

Is the Cisco article accurate?  Thanks!

-- 
-M

There are 10 kinds of people in this world:
	Those who can count in binary and those who cannot.