asterisk users - Oct 2006 - How to create echo for learning purpose

Hi,

For teaching, I need to set up a lab with which engineers would learn VoIP
troubleshooting.

I was trying to avoid TDM but as this mailing list is full of echo problems
testimonies, I'm wondering if I should include something related to echo.

1. Would you include echo troubleshooting ?
2. If positive, how would you generate such echo ?

If possible, I would like to avoid any real connection to the outside would.
I would rather connect an asterisk server to another asterisk server or to
anything capable to generate echo so that people can learn echo cancelling
techniques.
The set up would then be :

SIP hardphones or softphones ------ Asterisk with echocan enabled board
---------- Box generating echo

Regards
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What would you say if the box generating echo was simply made of :
- an asterisk server with any TDM board (compliant to the other asterisk
server's board)
- a softphone
- a network impairment soft (like netem) which would simply introduce a
looooong delay between the softphone and asterisk

Regards
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