I’m using Asterisk with CAPI for my external ISDN connection and internal I have some SIP phones (Grandstream BT 100). I also have internal ISDN phones, connected via ZAPTEL (NT-Mode). Everything works quite well, except that I have problems with a lot of echos when using a sip phone. The effect is biggest when I call internal SIP-phone to internal SIP-phone. Calling from internal ISDN to external ISDN, there’s no echo at all. Calling from internal SIP to external ISDN, the echo is there, but not strong. Calling from internal SIP to internal SIP, the echo is extreme and very annoying.
What can I do to avoid this?
Thanks in advance!