3.1 Simplex

3.2 Half-Duplex

3.3 Full-Duplex

3.4 Bit-serial Transmission

3.5 Data Transmission Speed
When a person is giving a lecture or speech, information is primarily conveyed in one direction. Duration a conversation between two person, how ever, spoken messages (information) are usually exchanged in both directions. These messages are normally exchanged alternately but, can of course, be exchanged simultaneously! Similarly, when data is transmitted between two pieces of equipment, three analogous modes of operation can be used:
Three types of Data Transmission:
  • Simplex
  • Half-Duplex
  • Full-Duplex


Data in a Simplex transmission is always one way. Simplex transmission are not often used because it is not possible to send back error or control signals to the transmit end.

It's like a one-way street. An example of simplex is sTelevision, or Radio.


Half Duplex
A half-duplex transmission can send and receive in one direction, but not at the same time. It's like a one-lane bridge where two-way traffic must give way in order to cross. Only one end transmits at a time, the other end receives. In addition, it is possible to perform error detection and request the sender to retransmit information that arrived corrupted. In some aspects, you can think of Internet surfing as being half-duplex, as a user issues a request for a web document, then that document is downloaded and displayed before the user issues another request.

Another example of half-duplex is talkback radio, and CB Radio (Citizens Band). You might have seen movies where a truck driver (drivers of very big trucks) communicates to each other, and when they want the other person to speak they say "over". This is because only one person can talk at a time


Full Duplex

Data can travel in both directions simultaneously. There is no need to switch from transmit to receive mode like in half duplex. It like a two lane bridge on a two-lane highway. Have you ever watched these television talk shows where the host has a number of people on the show, and they all try to talk at once. Well, that's full duplex!

Of course, in the world of data communications, full duplex allows both way communications simultaneously. An example can be a consumer, which uses a cable connection not only, receives TV channels, but also the same cable to support their phone and Internet surfing. All these activities can occur simultaneously.


Bit-Serial Transmission

In figure 1 and 2, A high signal relative to the reference indicates the transmission of Binary 1 while a low signal level, equal to the reference, represents a binary 0. With serial transmission the high-and low-level signals are normally positive and negative voltages relative to the reference.


Data Transmission Speed