DCN | Lecture 4 | Transmission Modes in Data Communication System

Communication between two devices can be simplex, half-duplex, or full-duplex.

Types of Transmission Modes

1. Simplex :- In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive. Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input; the monitor can only accept output. The simplex mode can use the entire capacity of the channel to send data in one direction.

2. Half-Duplex :- In half-duplex mode, each station can both transmit and receive, but not at the same time.When one device is sending, the other can only receive, and vice versa. Walkie-talkies and CB (citizens band) radios are both half-duplex systems.

3. Full-Duplex :- In full-duplex mode( called duplex), both stations can transmit and receive simultaneously. In full-duplex mode, signals going in one direction share the capacity of the link: with signals going in the other direction. This sharing can occur in two ways: Either the link must contain two physically separate tranmission paths, one for sending and the other for receiving; or the capacity of the channel is divided between signals traveling in both directions. One common example of full-duplex communication is the telephone network.

See Previous Lectures -

DCN | Lecture 1 | Data Communication and its System Components

DCN | Lecture 2 | Basic Block Diagram of Data Communication System

DCN | Lecture 3 | Effectiveness of Data Communication System

DCN | Lecture 3 | Effectiveness of Data Communication System

The effectiveness of a data communications system depends on four fundamental characteristics :-

Effectiveness of Data Communication System

1. Delivery :-The system must deliver data to the correct destination. Data must be received 

by the intended device or user and only by that device or user.

2. Accuracy :- The system must deliver the data accurately. Data that have been altered 

in transmission and left uncorrected are unusable.

3. Timeliness :- The system must deliver data in a timely manner. Data delivered late are 

useless. In the case of video and audio, timely delivery means delivering data as they 

are produced, in the same order that they are produced, and without significant delay. This 

kind of delivery is called real-time transmission.

4. Jitter :- Jitter refers to the variation in the packet arrival time. It is the uneven delay 

in the delivery of audio or video packets.

See Previous Lectures -

DCN | Lecture 1 | Data Communication and its System Components

DCN | Lecture 2 | Basic Block Diagram of Data Communication System

DCN | Lecture 2 | Basic Block Diagram of Data Communication System

Block Diagram of Data Communication System

Figure  shows  the  basic  block  diagram  of  a  typical  Data Communication  System.  This  can  further  be broken  down  to three;  the  source  system,  transmission  system  and destination system. 

1.  Source :- The  source  generates  the  information  or  data  that  will  be transmitted  to  the  destination.  Popular  forms  of  information include text, numbers, pictures, audio, video or a combination of  any  of  these.  Information  are  put  together  in  analog  or digital form and broken  into  group  or  segment of data called packets. Each packet consists of the following: 
i. the actual data being sent 
ii. header 
iii. information about the type of data 
iv. where the data came from 
v. where it is going, and  
vi. How it should be reassembled so the  message  is  clear and in order when it arrives at the destination.  

2.  Transmitter :- The transmitter a  device  used  to convert  the  data  as per the destination requirement.  For example a modem, converts  the analog  (telephonic)  signal  to  digital  (computer)  signals  and alternatively digital to analog.   

3.  Transmission Medium :- The transmission  medium  is  the  physical path  by  which  data travels  from  transmitter  to  receiver.  Example  of  such channels  is  copper  wires,  optical  fibers  and  wireless communication channels etc.  

4.  Receiver :- This  receives  the  signals  from  the  transmission  medium  and converts  it  into  a  form  that  is  suitable  to  the  destination device. For  example,  a  modem  accepts  analog  signal from  a transmission channel and  transforms it into digital bit stream which is acceptable by computer system.  

5.  Destination :- It is simply a device for which source device sends the data. 


See Previous Lecture -

DCN | Lecture 1 | Data Communication and its System Components

DCN | Lecture 1 | Data Communication and its System Components

DATA COMMUNICATIONS -

Data communications are the exchange of data between two devices via some form 

of transmission medium such as a wire cable.

* When we communicate, we are sharing information.

* This sharing can be local or remote.

* Between individuals, local communication usually occurs face to face, while 

   remote communication takes place over distance.

* The term telecommunication, which includes telephony, telegraphy, and 

television, means communication at a distance (tele is Greek for "far").

* The word data refers to information presented in whatever form is agreed upon by 

the parties creating and using the data.

* 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).

Data Communication System Components

Message:- The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.

Sender:- The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.

Receiver:- The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.

Transmission medium:- The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.

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, just as a person speaking French cannot be understood by a person who speaks only Japanese.