The following couple of audio lecture discuss PSTNs, POTS, DSL, ADSL, modulation techniques (FM, AM, PSK, QAM) and multiplexing techniques (TDM, FDM, CDM). If you can not see this chirbit, listen to it here http://chirb.it/dnDk0e
Read morePSTN, ADSL, Modulation Techniques and Multiplexing
