http://www.pczone.com.tw/vbb3/thread/16/100142/29/#post1049651
編碼標準 Bit rate(Kbps) MOS G.711 64 4.3 G.726 32 4.0 G.723 6.3 3.8 G.728 16 3.9 G.729 8 4.0 GSM HR 5.6 3.5 GSM EFR 12.2 4.0
*MOS(Mean Opinion Score) 5-Excellent 4-Good == 收費品質要求（根據ITU-T Recommendation P.800） 3-Fair 2-Poor 1-Bad
iptel/voxalot/sip2sip
http://www.osslab.org.tw/VoIP/IP_PBX/%E8%BB%9F%E9%AB%94%E5%BC%8F_IP_PBX/Asterisk/Tips/%E5%90%84%E5%AE%B6_Provider_%E7%9A%84_SIP_Trunk_%E8%A8%AD%E5%AE%9A
