Types of Communication: Synchronous, Asynchronous and Isochronous

Synchronization:

Synchronization is the process of receiving data in the same manner and same time by receiver as it was send. If two communication parties are not synchronized then there may be error in received data. The receiver must know at what time there is transition in the level of signal. It is good to know the phase and frequency of source so that receiver can receive the data in same way. Sender can send clock mentioning the phase and frequency.

Asynchronous Communication:

Asynchronous is one type of serial communication in which communication is done by sending one bit at a time. Serial communication is cheaper than parallel communication. This is why it is very popular.

In asynchronous communication, data is converted into 8-bits of packet with additional start bit and end bit. The receiver after receiving the start bit of packet, it then starts to count 8-bit of data and encodes that 8-bit into signal. This helps to receive data as it was sent. The gaps between packets of data may be represented by some series of 0s and 1s. The gap is not fixed. This type of communication is found in telephone conversation in which sender can speak at any time and remain ideal for random period of time.

Synchronous Communication:

In synchronous communication, data is converted into number of frames consisting of different packets. There is no start and stop bits in the packet. The synchronization is done by either sending clock by source or destination itself can keep clock after receiving first bit. There may be arbitrary gaps between two frames. This type of communication is very fast, since there is no additional bits. Communication between two computers is an example of synchronous communication.

Isochronous Communication:

In isochronous communication, data is transferred at fixed rate and is received at same rate. There is no gaps between packets. This type of communication is important in multimedia communication. For example: video conference.

Communication and its Components

Communication:

Communication is a process of transferring data information from one place to another. For example: transferring emails over internet.

Modes of communication:

There are three modes of communication. They are explained below.

1.  Simplex: communication takes place in one direction only. For example: FM, radio.
2. Half Duplex: communication takes place in both the directions but not at the same time. For example: walkie-talkie.
3. Duplex: communication takes place in both directions at the same time. For example: telephone.

Communication Components:

A communication system has following components:

1.        Source: generates data.
2.        Transmitter: converts data into signal so that it can be transmitted.
3.        Transmission media: carries signal.
4.        Receiver: converts signal into data.
5.        Destination: accepts data.

Fig: Block diagram of communication system

Computer Network Architectures

Client Server Architecture:

In this type of architecture, there is one or more server and others are clients. Client computer is active with direct interaction of user. It request and receive services to or from the server. Server responses after receiving request of computer.

The network consisting of web-server is client-server architecture. The web server is created using network operating systems like Windows Server 2012 and web server application like Apache.

The advantage of this architecture is that data is located at the center to which security can be maintained easily through manageable routers or firewall. Another advantage is easiness to update data in server.

Disadvantage of this type of network is, there is only one failure point. That is, if the server is crashed, then the data is lost.

Moreover, there may be high load of request to server.

Peer-to-Peer Architecture:

In this type of network, there is no particular server. Every computer can act simultaneously as server and client. There may not be any restriction for any information access. In fact, computer simply connected in network is in peer-to-peer network. This type of network is easy to establish.

Computer Network Introduction

Computer Network is a set of devices connected through communication lines. Each device in network is called node. Nodes may be workstation, server, modem, router, switch etc. which are capable of generating or receiving data in network. Computer network has following components:-

•          Computer system
•          Network Integrated Card (NIC)
•          Communication lines
•          Peripherals

The boarder of any network is called network edge. Network edge generally consists of host or any other peripherals. Host is computer that may be client, server or peer.

The main purpose of network is sharing resources that may be either hardware or software. This creates the environment for sharing, transferring information in network.

A computer network must have the following properties:

ü  Reliable:

It means to resist with failure. If some link is down then there must be alternative link for communication.

ü Secure:

Network share valuable information that may be confidential. Thus network must be secure from outer attack. Security can be maintained through firewall, access list or other means.

ü Timeliness:

Network must be capable of transferring information in time.

A simple Computer Network:

                                                                         

Types of network:

1.       Local Area Network (LAN):

It is network owned by one organization, generally located in small geographical area. It generally has high data transfer rate and more secure. For example: Intranet.

2.       Wide Area Network (WAN):

It is network owned by different organization spread in large geographical area. It consists of heterogeneous networks that may be wired or wireless. Generally data transfer rate is lower than LAN and some security technique must be employed. For example: Internet.

3.       Metropolitan Area Network (MAN):

MAN spreads larger area than LAN and is owned by one company.