Computer networks

  * Computer networks:

 An arrangement of two or more inter-connected computers. Two computers are said to be inter-connected if they interchange information. Connection between two separate computers can be done via  copper wire, fiber-optics, microwaves or communication satellites.

                                                    *Distributed System:

  If one computer can forcibly start, stop or control other computers, then it is not autonomous. A system with one control unit and many slaves, or large computer with remote printers and terminals is not called computer network, it is called distributed system.

                                           *Computer networks:
 

        *Advantages:

1. Information Sharing

2. Resource Sharing

3. Cost Reduction

4. Communication through electronic mail

5. Flexible Access : complete work while working on any computer throughout network

6. Workgroup Computing : concurrent work on project

                                  *  Computer networks:

         *Disadvantages

1. Expensive to install

2. Crash

3. Data Insecurity

4. Privacy : Boss with all network privileges may read your private email.

                                                     *types of computer network:

        1.based on transmission technology
           
        2.beoadcast network

        3.based on geographical span

         4. based on network


          5.based on network topology

 

                                          *Communication  in  computer network:

1. Postal Method of Communication

2. Telephonic Method of Communication

                                  *Factors to be considered in Communication:

1. Cost of conveying message

2. Interference

3. Time to reach message

4. Safe and Secure

                                             * Computer-based Communication:

                        * Advantages:

 1.Telephonic calls cost uniformity

2. Pictures, sounds and written data can be sent

3. Message can be encoded so that it cannot be understood by anybody else

4. Message can be sent in any language from any part to any another part of world

5. No highly specified training is required for users

                                                        *Data Communication:
 

                Data + Communication

        *Fundamental characteristics of Effective data Communication:

1. Delivery : (correct destination)
 2.Accuracy : (accurate data)
 3.Timeliness : (in timely manner)

                              * Components of Data Communication:

1. Message

2. Sender

3. Receiver

4. Medium

                               * protocol used in data communication
    

     * Protocol functions:

    1.Data Sequencing

   2.Data Routing

    3.Data Formatting

     4.Flow Control

    5.Error Control

 6. Precedence and order of Transmission

 7. Connection Establishment and Termination

  8.Data Security

  9.Log Information

                                         *  Data Flow:

data flow in data communication three types:

 1.Simplex: data send only in one direction at a time.
            e.g:  CPU and
                peripherals

 2.Half-Duplex:data send in both direction ata time.
                e.g:Walky Talky

3. Full-Duplex:send and receive both but only one at a time.
                e.g:Telephone