How to fix SIP echo?

[color=darkred]Is there anybody out there? (Pink Floyd)[/color]
Please give me a hint to search the SIP echo.
Should I upgrade to v1.2.16?

SIP echo doen’t always happen.

When I do > sip show peers
My 7 sip channels are from 157 to 360 ms away
Is that normal?

What is to blame?

My codecs are gsm|ulaw|alaw|speex|h263 and order:alaw,gsm,ulaw

For ISDN connection I use AVM C4 CAPI