Using PJSIP 2.9 Using all IPv4 but the hostname is AAAA resolvale. Processing 200 OK and sending ACK fails because the stack does not try the IPv4 address after IPv6 address is detected as PJSIP_EUNSUPTRANSPOR REGISTER/INVITE/BYE: all will try IPv6(fail) then IPv4 address For INVITE processing 200 OK to send ACK it does not fall back to IPv4. I narrowed the cause to sip_util.c: 1119 if (sent == -PJ_EPENDING) { 1120 /* This is the initial process. 1121 * When the process started, this function will be called by 1122 * stateless_send_resolver_callback() with sent argument set to 1123 * -PJ_EPENDING. 1124 */ 1125 cont = PJ_TRUE; 1126 } else { 1127 /* There are two conditions here: 1128 * (1) Message is sent (i.e. sent > 0), 1129 * (2) Failure (i.e. sent <= 0) 1130 */ 1131 cont = (sent > 0) ? PJ_FALSE : 1132 (tdata->dest_info.cur_addr<tdata->dest_info.addr.count-1); 1133 if (stateless_data->app_cb) { 1134 (*stateless_data->app_cb)(stateless_data, sent, &cont); 1135 } else { 1136 /* Doesn't have application callback. 1137 * Terminate the process. 1138 */ 1139 cont = PJ_FALSE; 1140 } 1141 } Sending ACK, cont is set to PJ_FALSE. Cheers Anthony _______________________________________________ Visit our blog: http://blog.pjsip.org pjsip mailing list pjsip@xxxxxxxxxxxxxxx http://lists.pjsip.org/mailman/listinfo/pjsip_lists.pjsip.org