Hello, users! It is simple. I want to make a call among asterisk and netmeeting(192.168.1.107). chan_h323 & chan_vpb are loaded. The call from netmeeting to asterisk(chan_vpb) is established a connection and can communicate each other. The call from asterisk(chan_vpb) to netmeeting is also connected, but there is no sound even any noise. Perhaps is my dialplan wrong? My dialplan & configuration files are extensions.conf : [general] static=yes writeprotect=yes [globals] OUTERVPBCHAN1=vpb/1-7 OUTERVPBCHAN2=vpb/1-8 INNERVPBCHAN1=vpb/1-9 INNERVPBCHAN2=vpb/1-10 INNERVPBCHAN3=vpb/1-11 INNERVPBCHAN4=vpb/1-12 IPPHONE=h323/10.10.10.107 [vpb_default] exten => _0,1,dial(${IPPHONE}) exten => _0,2,hangup [h323_default] exten => s,1,dial(${INNERVPBCHAN2}) exten => s,2,hangup h323.conf : [general] port = 1720 bindaddr = 0.0.0.0 allow=adpcm allow=ilbc allow=alaw allow=gsm allow=lpc10 allow=ulaw allow=g726 gatekeeper = DISABLE vpb.conf : [general] type = v6pci cards = 1 [interfaces] board = 1 echocancel = on ; For OpenSwitch6; Note that V6PCI channel numbers start at 7! context = vpb_default mode = fxo channel = 7 channel = 8 mode = dialtone channel = 9 channel = 10 channel = 11 channel = 12