Data communication is the means to communicate the data from one source to a distination
The whoe data si being transmitted in various ways or the instance
they are the following;-
1. source
2. transmitter
3. communication system
4. reciever
5. destination
here...
1. source meant to the computer that allow contains the data and that is to be transmitted to the various other destination.
source contains the computer laptops any medium that contains the data...
2. transmitter is treat itself as a converter that converts the data language of the source to the needed language that an communication channel needs so that it could understand..
this channel could contains the electrical electronic or the optical signals...
3. communication system is the medium that contains the physical layer that could be of co-axial cable  or the parallel cable or the optical cable or the LAN or WAN or MAN
4. reciever is the reconvertor of the signal that is being came from the communication no it convert into the electrical electronic or the optical signals to be read or being understand by the destination..
5. destination is the ttarget to which the signal is to be send or we can say the data is to be send..
now there is the fact that 'd(t)' the data that comes in the process when data is shifting from source to transmitter
and similarlly the s(t) is the signal that is being formed in btwnt transmitter and communication channel