<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Times New Roman; font-size: 12pt; color: #000000'>Michael,<br><br>Here are the differences between the systems that I determined from the two SIP traces:<br><br>* Working system: no NAT, phone codec: G.729, Asterisk codec: G.729<br>* Non-working system: NAT, phone codec: G.729, Asterisk codec: A-law<br><br>Does the conversation have two-way audio prior to the hold? If it doesn't, your problem may be caused by NAT and/or codec transcoding. NAT is notorious for causing one-way audio and transcoding G.729 requires a commercial license from Digium.<br><br>After those two possible causes are ruled out, the only other thing that I can think of is a missing format translation path for the music-on-hold files. Does the AsteriskNOW system have modules loaded for both formats? I don't use either format, but I believe the required modules are "format_g729.so" and "format_pcm.so".<br><br>Regards,<br><br>Matthew Roth<br>InterMedia Marketing Solutions<br>Software Engineer and Systems Developer<br></div></body></html>