DCN-Data Communication

DATA COMMUNICATIONS

Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable .For data communications to occur, the communicating devices must be part of a communication system made up of a combination of hardware (physical equipment) and software (programs).

The effectiveness of data communication system depends on four factors:

1.  Delivery:  The data should be delivered  to  the  correct destination and correct user.

2.  Accuracy: The communication system should deliver the data accurately, without introducing  any  errors.  The  data  may  get corrupted  during  transmission  affecting  the  accuracy  of  the delivered data.

3.  Timeliness: Audio  and  Video  data  has  to  be  delivered  in  a timely manner without any delay; such a data delivery is called real time transmission of data.

4.  Jitter: It is the variation in the packet arrival time. Uneven Jitter may affect the timeliness of data being transmitted.

A data communications system has five components.

1. Message.  The  message  is  the  information  (data)  to  be  communicated.  Popular  forms  of information include text, numbers, pictures, audio, and video.
2. Sender.  The  sender  is  the  device  that  sends  the  data  message.  It  can  be  a  computer,workstation, telephone handset, video camera, and so on.
3. Receiver.  The  receiver  is  the  device  that  receives  the  message.  It  can  be  a  computer,workstation, telephone handset, television, and so on.
4. Transmission  medium.  The  transmission  medium  is  the  physical  path  by  which  a  message travels from sender to receiver.
5. Protocol.  A  protocol  is  a  set  of  rules  that  govern  data  communications.  It  represents  an agreement  between  the  communicating  devices.  Without a protocol, two  devices  may  be connected but not communicating.

Data Flow

Communication between two devices can be-

1-      Simplex

·        In Simplex, communication is unidirectional

·        Only  one  of  the  devices  sends  the  data  and  the  other one only receives the data.

Example:  in  the  above  diagram:  a  cpu  send  data  while  a monitor only receives data.

2-      Half Duplex

·        In half duplex both the stations can transmit as well as receive but not at the same time.

·        When  one  device  is  sending  other  can  only  receive  and  viceversa (as shown in figure above.)

Example: A walkie-talkie.

3-Full Duplex

·        In Full duplex mode, both stations can transmit and receive at the same time.

Example: mobile phones