In Point-point connections, data sent can either go one way (Simplex) or both ways (Duplex).
Simplex
There is only one-way that data can go
Half Duplex
Data can go either way, but there is only 1 stream so transmitting and receiving must take turns.
Half duplex follows CD as its communication protocol.
Full Duplex
There are designated transmitter and receiver endpoints. Data can be transmit and received at the same time.