I tested skype on a Windows machine and a Linux machine in the same office. Everything works for the Windows (using echo123). But when I try to communicate between the Windows and Linux (2 accounts), the connection seems good (with timer etc.), but there is no sound.

I can transfer files between the two machines, and hear rings from the Windows, but no other sounds can be heard on either machine.

I can play music, record sound on the Linux. I can hear music and my voice (using mic) at the same time (full-duplex?).

My Linux is Redhad9, kernel 2.4.20, OSS, Soundcard module i810_audio. I did use esddsp ./skype

Is this a problem of my soundcard or firewall config on the Linux machine?
Can someone please help? Thanks.

I guess it's a problem with the sound configuration on the Linux machine.

I suggest to first try running Skype with direct access to /dev/dsp (no esddsp or artsdsp) and making sure no other app is using sound.
Then test with IM, just to check if Skype can play notification sounds (you may need to check your options)
Finally try a call, an see if you can hear something.

PS: hearing yourself does not mean full-duplex as it's probably only hardware-mixing of input channel with output. You need to be able to record yourself while playing for having full-duplex working. (an then hear you in the file you did record)

Thanks for your suggestions.

I ran skype without esddsp, and it can play notification sounds, including rings, but only for the first time after I start skype. If I stop and start a call again, there was no notification sounds.

There is still nothing when I try a call.

I can record my voice when playing musics, so the card is full-duplex.

Any other thoughts? Thanks a lot.