HDLL HDLL over LSD PPP over HDLC T120 PPP T120 on H320 MLP PPP on H320 MLP PPP on H320 HSD PPP on H320 LSD X25 over MLP X25 over HSD X25 over LSD T120 over MLP HDLC over HSD PPP over LSD X25 MLP LAPD LAPB TDM Audio Transparent HDLC V14E MeetMe Audio Transparent X25 multichannel X25 on D channel X25 on B channel LAPB HDLC V14E