Dear all: The scenario is that, when I use 3CX (PCMA) to call XLite, 3CX will hear loud noise but XLite is fine. And I found that it would only happen when XLite supports PCMA and PCMU simultaneously. If XLite only support PCMA, everything is fine. Maybe it is because of the old version of Freeswitch, I download the latest version yesterday and re-test. The result is that 3CX hear nothing instead of noise. I use Wireshark to survey packages, and the server does not transfer UDP packages to 3CX. I check the log file, it is as below. -----3CX hears nothing----- 2011-02-24 20:17:30.724125 [DEBUG] sofia.c:4683 Channel sofia/internal/1000@thisjoy.x.x:5060 entering state [completed][200] 2011-02-24 20:17:30.724125 [DEBUG] switch_core_session.c:709 Send signal sofia/internal/1000@thisjoy.x.x:5060 [BREAK] 2011-02-24 20:17:30.724125 [DEBUG] switch_channel.c:2790 (sofia/internal/1000@thisjoy.x.x:5060) Callstate Change EARLY -> ACTIVE 2011-02-24 20:17:30.724125 [NOTICE] switch_ivr_originate.c:3363 Channel [sofia/internal/1000@thisjoy.x.x:5060] has been answered 2011-02-24 20:17:30.724125 [DEBUG] switch_ivr_originate.c:3408 Originate Resulted in Success: [sofia/internal/sip:1001@114.24.x.x:56922] 2011-02-24 20:17:30.739750 [DEBUG] switch_ivr_originate.c:3408 Originate Resulted in Success: [sofia/internal/sip:1001@114.24.x.x:56922] 2011-02-24 20:17:30.739750 [DEBUG] switch_core_session.c:709 Send signal sofia/internal/sip:1001@114.24.x.x:56922 [BREAK] 2011-02-24 20:17:30.739750 [DEBUG] switch_core_session.c:709 Send signal sofia/internal/1000@thisjoy.x.x:5060 [BREAK] 2011-02-24 20:17:30.739750 [DEBUG] switch_ivr_bridge.c:1234 (sofia/internal/sip:1001@114.24.x.x:56922) State Change CS_CONSUME_MEDIA -> CS_EXCHANGE_MEDIA 2011-02-24 20:17:30.739750 [DEBUG] switch_core_session.c:1116 Send signal sofia/internal/sip:1001@114.24.x.x:56922 [BREAK] 2011-02-24 20:17:30.739750 [DEBUG] switch_core_state_machine.c:320 (sofia/internal/sip:1001@114.24.x.x:56922) Running State Change CS_EXCHANGE_MEDIA 2011-02-24 20:17:30.739750 [DEBUG] switch_core_state_machine.c:369 (sofia/internal/sip:1001@114.24.x.x:56922) State EXCHANGE_MEDIA 2011-02-24 20:17:30.739750 [DEBUG] mod_sofia.c:552 SOFIA EXCHANGE_MEDIA 2011-02-24 20:17:30.974125 [DEBUG] switch_rtp.c:2985 Correct ip/port confirmed. 2011-02-24 20:17:30.974125 [DEBUG] sofia.c:4683 Channel sofia/internal/1000@thisjoy.x.x:5060 entering state [ready][200] 2011-02-24 20:17:31.021000 [DEBUG] switch_core_session.c:771 Send signal sofia/internal/sip:1001@114.24.x.x:56922 [BREAK] 2011-02-24 20:17:31.021000 [DEBUG] switch_core_session.c:771 Send signal sofia/internal/1000@thisjoy.x.x:5060 [BREAK] -----log end----- When XLite only supports PCMA, it would be an additional log: 2011-02-24 20:16:06.661625 [INFO] switch_rtp.c:2968 Auto Changing port from 192.168.1.1:51508 to 114.24.x.x:51508 And I test it again by using a public VoIP server ( sip.lowratevoip.com), there is no noise or silence situation, everything is fine. Does XLite get bugs? Why the public server can deal with the situation? Could anyone help me? Sincerely yours, thisjoy.