Digital Communication: Ø   Digital Communication  is the one which uses digital signals for transmitting information between source and destination. Digital  signal consists of discrete values rather than continuous values. Ø   Power requirement in case of digital communication is less a compared to Analog communication. Since the bandwidth requirement in digital systems is more thus, they consume less power.  Ø   Digital communication equipment’s are costly and digital signal require more bandwidth for transmission. Ø   Digital signal is represented by square wave. Ø   Digital signals are used in computers.

Analog Communication: Ø   The term analog refers to any physical device or signal that can continuously vary in strength or quantity. for example, voltage in a circuit. Ø   The term analog communication refers to any method of communication based on analogue principles. Ø   Typically, this term is associated with voice transmission because voice transmission facilities such as telephone were initially. Ø   Analog communication is used in phones (Both landline and cellular), modems, fax machines, cable television. Ø   In analog communication, the data is transferred from transmitter to receiver with the help of analog signal . Analog signal possesses continuous varying amplitude with time. Any type of data such as voice, sound etc. can be transferred through an analog signal. Ø   Firstly, the data needs to be converted into electrical form . As voice, sound is non-electric in nature, it can be converted into el

Parallel communication: Ø   In  telecommunication  and  data transmission ,  parallel communication  is the process of sending  multiple   bit s simultaneously over a  communication channel  or  computer bus . Ø   In Parallel Transmission multiple bits are sent together . Ø   Parallel Transmission is faster than serial transmission to transmit the bits. Ø   Parallel transmission is used for short distance i.e. computer to printer . Ø   In Parallel Transmission, eight bits are transferred at one clock pulse . It is a fast way to transmit as it uses many input/output lines for transferring the data. Ø   Parallel Transmission is half-duplex since the data is either sent or received . Ø   The installation and troubleshooting is easier in parallel transmission system due to its placement in a single physical cable. 

Communication Service Methods: Ø   There are several methods in which data can be transmitted between sender and receivers ·          Serial communication ·          Parallel communication A) Serial communication: Ø   In  telecommunication  and  data transmission ,  serial communication  is the process of sending  data  one  bit  at a time , sequentially, over a  communication channel  or  computer bus . Ø   In serial communication, data is in the form of binary pulses. In other words, we can say Binary One represents logic HIGH or 5 Volts , and zero represents a logic LOW or 0 Volts. Ø   Serial communication can take many forms depending on the type of transmission mode and data transfer. Ø   Generally, Serial Transmission is used for long distance I.e. computer to computer Ø   Serial Transmission is full-duplex as the sender can send as well as receive the data. Ø   Serial Transmission is simple and reliable .   Ø   Error and noise are least in serial

  Peer-to-peer Model Ø   The peer to peer systems contains nodes that are equal participants in data sharing . Ø     All the tasks are equally divided between all the nodes . Ø   The nodes interact with each other as required as share resources . This is done with the help of a network. Ø   Since nodes in peer to peer networks act as both clients and servers , it is difficult to provide adequate security for the nodes. This can lead to denial of service attacks. Ø   Most modern operating systems such as Windows and Mac OS contain software to implement peer to peer networks. Ø   Advantages of Peer to Peer Computing ·          Each computer in the peer to peer network manages itself . So, the network is quite easy to set up and maintain. ·          In the client server network, the server handles all the requests of the clients. This provision is not required in peer to peer computing and the cost of the serv

  Client/Server Model Ø   In client server systems, the client requests a resource and the server provides that resource. Ø   A server may serve multiple clients at the same time while a client is in contact with only one server. Both the client and server usually communicate via a computer network and so they are a part of distributed systems. Ø   The client server computing works with a system of request and response. The client sends a request to the server and the server responds with the desired information. Ø   The client and server should follow a common communication protocol so they can easily interact with each other. All the communication protocols are available at the application layer. Ø   A server can only accommodate a limited number of client requests at a time . So it uses a system based to priority to respond to the requests. Ø   An example of a client server computing system is a web server . It

  Distributed Systems Ø   In this type of processing different CPU are connected to the network and are controlled by single CPU. Ø   For example, in air reservation system there exists different terminals and processing is done from many locations and all the computers are controlled by the single main processor. Ø   This type of network is called  distributed network . Ø   A distributed system contains multiple nodes that are physically separate but linked together using the network . All the nodes in this system communicate with each other. Ø     Each of these nodes contains a small part of the distributed operating system software. Ø   A diagram to better explain the distributed system is: Ø   Types of Distributed Systems 1)      Client/Server System 2)      Peer-to-Peer System Ø   Advantages of Distributed Systems 1)    All the nodes in the distributed system are connected to each other. So,