Digital Communication System (With The Whole World)

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Digital communication systems have transformed the way that people communicate and connect with each other, enabling people to communicate with anyone, anywhere in the world, at any time. These systems use a range of technologies and protocols to transmit and process digital data and information, making it possible for people to communicate via text, audio, and video.

One of the main features of digital communication systems is their ability to transmit data over long distances with little or no degradation of quality. This has made it possible for people to communicate with each other in real time, regardless of where they are located.

Digital communication systems have also made it easier for people to communicate with large groups of people simultaneously. For example, social media platforms and other online communities allow people to share information and ideas with a wide audience, enabling the formation of online communities and networks.

In addition to facilitating real-time communication, digital communication systems have also made it easier for people to store, access, and share information. For example, cloud-based storage systems allow people to store and access data and documents from any device with an internet connection, enabling people to collaborate and work together more effectively.

One of the main drivers of the growth and development of digital communication systems has been the rapid advancement of technology. In recent years, there have been significant advances in areas such as broadband internet, mobile networking, and cloud computing, which have made it possible for people to communicate more easily and effectively.

In the coming years, it is likely that digital communication systems will continue to evolve and become even more sophisticated. For example, the development of 5G networks is expected to enable faster and more reliable communication, and the proliferation of artificial intelligence (AI) is likely to lead to the development of more advanced and intelligent communication systems.

Overall, digital communication systems have had a profound impact on the way that people communicate and connect with each other, and this trend is likely to continue in the coming years. As technology continues to advance, it is likely that digital communication systems will become even more integral to our daily lives.

Communication System

The communication system is the communication system. That is, communication with one another is called communication. Communication is basically about exchanging information. This exchange of information can take many forms.

Just as information is exchanged in a face-to-face conversation, information is also exchanged in the form of gestures that are made by shaking hands and feet from a distance. None of this falls under communication. In the past, the only means of communication with someone far away was by letter (or mail).

That too would arrive again after a long time. And now with the help of various technologies like TV, radio, internet, telephone, etc. to communicate with someone far away, the distance of communication has reduced a lot.

Today, almost all of the technologies that have developed this communication system send or receive data from one place to another. And this is how the communication system of today’s world is going.

Concept of Communication System

The word “communication” comes from the Latin word communicate, which means to share “or to make comm” meaning to share or enjoy everything. Communication is the transfer of information from one place to another.

In other words, the flow of information from source to destination is called communication. A communication system has five basic parts.

1. Source is the part where a message or information (human voice or a picture and sound on television, etc.) is created. If the information is not electrical, it needs to be converted into an electric signal before it can be moved from one place to another.

Transducers (such as microphones, cameras, etc.) are used for this conversion.

2. Transmitter: A transmitter modifies a signal as needed to effectively transmit it from one place to another. TV stations, radio stations, wifi cards, Bluetooth cards, modems, etc. are some examples of transmitters.

3. Channel is required for a signal to be transmitted from one place to another, this is called the channel. Metal wire, optical fiber or radio link (wireless), etc.

are several types of media or channels through which the signal from the transmitter is transmitted from one place to another. Different types of noise (Noise unexpected signals) cause the signal in the channel to change slightly.

4. Receiver: The function of the receiver is to receive the signal from the channel. It then reverses or reverses as much as the original signal has changed due to noise and emits the original signal. For example, TV or radio has a receiver part in everything. The TV radio receiver has an antenna attached to receive the signal.

5. Destination: The signal received by the receiver communicates with the destination. For example, the signal that the TV antenna receives is then shown on the TV screen. Similarly, the signal received by the radio antenna is heard on the radio speaker. In this case, TV screen and radio speaker are the destinations. Similarly, computer monitors, telephone sets, etc. are the destination.

Concept of Data Communication

Digital Communication System

“Data” is a type of information, the type of which depends on certain rules and regulations between the sender and the customer. For example, data sent to a computer is not suitable for being sent to a television.

Again, there is no benefit in sending telephone data to radio. Because in all cases the device or instruments follow certain rules. Therefore, if you want to communicate on a telephone, you have to do it with another telephone, not with a radio.

When we communicate, we actually exchange information. This exchange can take place near, or far away. Communicating in a remote place is called telecommunication (the Greek word “tele” means distance). Telephony, Telegraphy, Television, etc. Everything is Part of telecommunications.

Data is what is sent from one place to another in telecommunications. This is why it is often called ‘data communication’.

Data communication is the process of exchanging data between two devices or devices through a channel (e.g., its). In order for data communication to be complete, both the sender and the receiver must be part of a communication system that includes both hardware and software.

  • Different parts of data communication

Since data communication is a type of communication system, the five core components of the communication system (Figure 2.1) are also contained in data communication. Data communication basically consists of the following five parts (Figure 2.2).

1. Message: The information that is exchanged through communication is called a message. Letters, numbers, pictures, words, and videos are just some of the most commonly used types of messages. 2. Sender: The device that sends data is called the sender. Computers, laptops, telephones, video cameras, etc. are examples of senders.
3. Receiver: A device that receives data sent by a sender is called a receiver. Examples of receivers are computers, televisions, radios, telephones, and so on.

4. Channel: A channel is a path that takes a message from the sender to the customer. There are various types of media for data communication, such as twisted-pair wire, coaxial wire, fiber optic, radio wave, etc.

5. Protocol: Some rules are needed to control and manage data communication.

The sum of these rules is called a protocol. Transfer data between two devices The main condition of payment is protocol. The two devices may be connected to it, but if there is no protocol between them, no data will be exchanged.

  • Presentation of data in data communication

In data communication, information can be of different types, such as letters, numbers, pictures, audio, and video. They need to be modified to use in data communication. In data communication, the unit for sending information or data is called a bit.

The binary system works with only two digits. The two numbers are 0 and 1. Each of these 0’s and 1’s is called a bit. All data or information in data communication is composed of one or more bits.

Only by converting letters, numbers, pictures, words, videos, etc. into bits is it useful for use in data communication. For the convenience of calculation, each group of 8 bits is called 1 byte. For example, 10110010 has a total of 8 bits. It can also be called 1-byte data as it has 6 bits.

Bit and byte units are used in data communication. The binary method is discussed in detail in the third chapter.

1. Characters and numbers: Different bit patterns (Sections 0 and 1) are used to express text in data communication. A bit pattern is a combination of multiple bits.

Different types of bit patterns are created to express different characters. These types are called codes, and the method of expressing different characters with code is called coding. Coding is also required to express numbers like letters.

Chapter 3 discusses coding in detail.

2. Image: An image row is made up of many pixels. A pixel is a small drop or dot. The size of the pixel depends on the resolution. Each pixel is again coded into a binary number i.e. converted to a bit. For example, an image can be divided into 1,000 pixels, or even 10,000 pixels. But the next part will require more bits to code the image due to more pixels. The higher the bit, the more space will be required in the memory of a device. As a result, more space will be needed in memory to save the image.

3. Sound: It is necessary to record or propagate words in songs or speeches or in various activities. Words are different in nature than letters, numbers or pictures. Therefore, word-based tones or melodies are converted to digital or analog signals using special technology in different ways, suitable for data communication. 4. Video dramas, movies or any important news need to be recorded and disseminated for various purposes.

Like sound, video is converted to digital or analog signal with special technology for use in data communication.


Digital Communication System

In computer networking and computer science, bandwidth is a measure of the bit rate or rate of bit exchange of different parts of data communication. In other words, to be from one place to another or from one device.

The amount of data or binary bits transferred per unit time to another device is called data transmission rate or bandwidth. It is often called data bandwidth, band speed, network bandwidth, or digital bandwidth.

The unit of bandwidth is bit / s (bit / s). However, it can also be expressed in more convenient units, such as kilobits / second (Kbit / s), megabits / second (Mbit / s), gigabits / second (Gbit / s), etc.

The bitrate is the number of bits flowing at a single time. Bandwidth is often called the data rate. The amount of data that flows from one end of a network to another at a single time is called a detract.

It is possible to find out the data transmission speed of any network or device from bandwidth and bitrate. There are two types of bandwidth in data communication

  1.  Maroband O.
  2. Broadband or Wideband.


In telecommunications, the narrow frequency (band of bandwidth) that transmits voice information is called a narrowband. More precisely, the range from 50 kilobits / second to 64 kilobits / second is called narrowband. Mobile or radio services are used in this band. This band is narrow so it has a low frequency for data exchange.

The Broadband or Wideband The broad frequency bandwidth with which data is exchanged in telecommunications
Is called. In this case, there is a larger range of frequencies than the narrowband for sending data. As a result, as much data can be exchanged on a narrowband at a given time, much more data can be exchanged on broadband at the same time.

It is possible to get a minimum bitrate of 256 kilobits / second on broadband.

If the narrow batch is compared to a lane, then broadband can be compared to a highway. If the flowing data is compared to a car, then just as the narrow lane is narrow enough for a few cars to pass through, so narrow data flows there because of the narrow range of frequencies in the narrowband.

The highway is said to be wide, just as many cars can go there, so broadband has a wide range of frequencies so more data flows there. There is another type of bandwidth called voice band. This band contains frequencies that are within the auditory range.

Voices are usually sent or received as information in this band. The band rate of this band can be up to 9600 beats/second. Voice bands are commonly used to exchange data on telephone networks. Voice bands are also used to transfer data to computers and peripheral devices.

Data Transmission Method

Data transmission refers to the exchange of data. In data communication, connecting two devices to each other can lead to two ways of data transmission –

A. Serial method o
2. Parallel clouds.

A. Serial Method: When two devices are connected in a serial method, 1 bit of data is transmitted from one device to another at the same time.

B. Parallel Method: When two devices are connected in a parallel method, more than one bit of data is transmitted from one device to another at the same time.
Data is transmitted in 1 way in parallel or parallel method, but data can be transmitted in 3 ways in the serial method. Synchronous transmission method and

Asynchronous transmission method. In this case, there is a kind of mutual agreement between the devices. This compromise depends on the bit pattern of the data transmitted. The bit pattern again depends on how many bits there are in a group. Usually data is sent in a group of 8 bits (6 bits = 1 byte). Sender or transmitting device

Trams one or more groups whenever the channel is connected. This transmission does not meet any specific time, the data is sent whenever the channel is found empty.

Since no specific time is observed in the asynchronous method, the receiver does not know when the sender will send the next data group. So to warn the receiver about the arrival of new data groups, an extra bit is added at the beginning of each byte. This bit is called the start bit “. Usually the value of the start bit. The start bit indicates that the receiver is starting a new byte.

One or more extra bits are added to the end of the byte to indicate the end of the incoming byte to the receiver. These extra bits are called” stop bits “. The value of the stop bit is 1. In this method, the size of each byte increases from 8 bits to a minimum of 10, of which 8 bits are the data bits and the other two are the extra bits added at the beginning and end. The interval between the two bytes is used to denote the transmission.

By When an interval is created between two data groups, the asynchronous channel is in the “mark state.”

Disadvantages of asynchronous transmission
1. Data Size Large start bits, stop bits and multiple additional bits such as mark bits are used to increase the size of the transmitted data. All of this large-scale data does not transport the necessary information, rather

It also transmits data for transmission control along with information. These data are not necessary as information

However, these data are needed for control. 2. Less efficient: Its efficiency is relatively low compared to synchronous data transmission. 3. Speed: The speed of data transmission is relatively low.

Therefore, this method is used for tasks where data is not transmitted within a certain time (e.g., data input with keyboard).

Use of asynchronous transmission 1. Networks that transmit a small amount of data (such as a private network or a company)

Internal small network) asynchronous transmission is used. 2. This method is used to transfer data from computer to printer or from mouse, keyboard, or scanner to the computer.


Synchronous means are synchronous. In an asynchronous transmission system, both the sender and the receiver operate at the same time. The receiver receives the data at the rate at which the sender sends the data. That is why in this method the sender and receiver have to maintain the same speed or time.

Synchronous transmission is the uninterrupted and consistent transfer of data blocks at the same time. This method is usually used when a large amount of data is quickly transmitted from one place to another. Acceleration of the synchronous method is achieved when a lot of data is transmitted to a large block instead of transmitting a single bit of data. Data blocks are sorted into multiple groups, and some sync bits are placed at the beginning.

The receiver gets instructions on how much speed the receiver needs to maintain with these silk bits, or how much time the sender will send data from time to time. After receiving this instruction, the receiver prepares itself to receive the data and the cedar starts sending data to the receiver. Note that in the synchronous method, each device has to work at the same speed. This is why all devices follow a common clock speed or common clock speed.

For example, in a synchronous way, a text document is broken down into smaller paragraphs before being sent to a large text document receiver. Paragraphs are a group. Then those paragraphs are sent to the receiver one after the other.

Alternatively, the text document is divided into characters without paragraphs, then each character is separated.

Is sent to the receiver separately. Other methods take a lot of time as each letter has to be sent separately.

Advantages of synchronous transmission

1. Data size is small: Data size is small because no additional bits like start bit, stop bit, and mark writ is used. 2. More efficient: Its efficiency is higher than asynchronous data transmission.

3. Speed: The smaller the data size, the more data net is available. So the speed of synchronous data transmission is relatively high.

4. Short time: It takes less time to send data because the data rate is higher. Disadvantages of synchronous transmission

1. Complex: Technically a bit more complex than the asynchronous transmission method. 2. Additional components: A separate storage device is required to initially store data in the transmission part.
3. Expensive: The hardware used in this transmission is quite expensive. Use of synchronous transmission 1. Synchronous transmission is used to transmit data over large networks.

2. This method is used for data transmission from computer to computer or for data communication in mobile phone networks, television networks,s, etc.

C. Isochronous Transmission Method No delay in real-time audio-video data transmission is acceptable. But synchronous transmission can be delayed. The isochronous method is used in this case.

The isochronous method ensures the lowest delay (i.e. o) in data transmission. For example, the video we see on TV is actually a series of still images. TV stations send 30 or more stills every second. The images are said to be moving near the human brain because 30 stills are shown one second per second. This is what we call video.

This group of 30 stills is called a frame. Now if for some reason one / two frames are delayed, it will no longer be video. The isochronous method ensures that this delay is kept to a minimum.

Differences between asynchronous and asynchronous transmission methods

1. Synchronous means synchronous. In an asynchronous transmission system, both the cedar and the receiver work at the same time. Asynchronous means asymmetry, meaning that in this method the devices do not adhere to any specific time or there is no coordination between them.

2. In the synchronous transmission method the data is initially stored in a separate storage device in the sender. But there is no need to save data in the asynchronous transmission method.

As a result, no additional equipment is required.

3. The synchronous transmission method does not use any additional bits like start bit, stop bit, and mark bit, but asynchronous transmission requires start bit, stop bit, and mark bit.

4. Synchronous transmission The speed of data transfer in the cloud is very fast. But the speed of data transfer in the asynchronous transmission is comparatively less fast.

5. The synchronous transmission method does not use extra bits, so it is more efficient. But in asynchronous transmission

Its efficiency is relatively low as extra bits are used. . Synchronous transmission method takes less time to send data. On an asynchronous transmission, on the other hand, it takes a relatively long time to send data.

6. The synchronous transmission method is required to send data from computer to computer. On the other hand, the asynchronous transmission method is required to send data from keyboard or house to computer.

7. Synchronous transmission clouds are quite expensive. Asynchronous transmission costs less.

Data Transmission Mode

Data transmission mode refers to the direction of data flow between two communication devices. In other words, the data transmission turns from one of the two devices to the other. There are three modes or ways to transmit data.

The mode of communication in which data only flows from the sender to the receiver, i.e. the data flow is one-way, is called simplex. E.g., television broadcasting. Information from the TV station (or station) always comes to the TV kept in the house, information from the TV kept in the house does not go to the TV center.

In this case, the data is always flowing in one direction (from cedar to receiver).


1. The communication between the keyboard and the monitor is simple. Data goes from the keyboard to the computer monitor, never the other way around, that is, data does not come from the monitor to the keyboard, just as television broadcasting is a simplex method.

The direction of data flow 2 Another example of simplex mode is the loudspeaker system. The speaker’s voice in the microphone travels through an amplifier to all speakers (commonly called soundboxes).

3. Many fire extinguishing alarm systems operate in simplex mode.

Half Duplex

In this mode data flow can be on both sides, but not on both sides at the same time. At one point an end either acts as a saver or receiver, but does not act as a simultaneous sender and receiver. When one device acts as a sender (i.e. sends data), the other device acts as a receiver (i.e. receives that data). Again when the other device acts as the sender then the first device acts as the receiver. Half-duplex mode is commonly used for low-speed data transmission. For example walkie-talkie.


1. Walkie-talkie works in half-duplex mode. In a walkie-talkie, when someone speaks from one end, the one on the other end only hears, and when he speaks, he only hears the first thing he says. In the district cities of Bangladesh, it is common for the police and traffic police to use more walkie-talkies. Many also use it as a hobby.

2. At the top of Figure 2.6 it is seen that “A” computer is sending data to “B” computer, i.e. “A” is the sender and “Th” is the receiver. At the bottom of Figure 2.6, it is seen that computer “B” is sending data to computer “A”, i.e. “B” is the cedar and “A” is the receiver. Can’t send data.

In this mode, there are two connecting paths between the devices at the same time on both sides of the data flow. One way the data flows from the first device to the second device, the other way the data flows from the second device to the first device. This means that both devices can send and receive data at the same time. Full duplex mode is commonly used for high-speed data transmission.


1. The telephone network operates in full-duplex mode. When two people are talking on the telephone, they can talk at the same time and listen to each other at the same time. When one speaks like Wakitki, the other does not have to remain silent.

The transmission mode can also be further divided into three parts depending on the number of senders and receivers.

  • Unicast
  • Multicast
  • Unicast


In Unicast transmission mode, data flows from one device to another. In this case, there is one cedar and one receiver. Unicast mode is widely used in both Internet and LAN (LANLocal Area Network).

Figure 29 shows a unicast mode, where “A” computer, “B” computer is sending data.

In broadcast mode, the same data flows from one device to all other devices. In this case, the cedar has one but the receiver has more than one, and the same data is sent from the cedar to all the receivers. Figure 2.10 shows a broadcast system. The “A” computer in this system is the cedar. The same data from Ka is being sent to five receivers “b”, “” “”, “d”, “o” and “f”.


In multicast mode, the same Veta is sent from one or more Deders to multiple receivers. In this case, there may be one or more savers who send data to a specific group of receivers without sending data to all receivers. Some receivers will get data and some

No receiver will receive data. In multicult systems, it is fixed in advance.

The day is shown as a multicult system, where ‘and’ computers do not transmit any data from the two cedars “a”. Because they are not in the multicast group. Kho, ‘and “Tea Multicante’ are in the group so they receive data sent by” A “.

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