thnx for the response buddy.. it is quite explanatory..
but i think even in case of DSL/ADSL or cable modems the transmission from the modem to the Service provider's switch is actually a high frequency carrier modulated by a bit stream of 0s ans 1s... e.g. the link connecting the DSL modem to DSLAM switch carries the signals which are inherently analog in nature and not the pure bits.
If this is true, then any MODEM we talk of, would always involve Digital to Analog conversion, and vice versa for the purpose of transmission.
Now some CODECS (like G.711 and G.729 etc.) are not only used for encoding-decoding the video to be played and stored, but also used in sth like a digital phone where analog voice is to be converted to digital bitstream again for the purpose of transmission.
This is what blurs the line of distinction between the two.. and is wat i want to have more clarity on..