Information and Communication Technology English Version chapter 2: Communication Systems and Networking

Chapter Two

Communication Systems and Networking

Figure: Ground Station of Bangladesh Satellite-1

It goes without saying that in the present world we humans are connected with one another almost like a family. In the past, the world might have overlooked a crime against humanity and the perpetrators would get away with it. But this is not possible anymore. War still exists in this world but we have mitigated most of it. We have technology to thank for it. No country in the world now can start an unnecessary war without answering the conscience of the whole world. Networking has made it possible for the whole world to live like a single family. To create this networking many different technologies work in tandem to create this vast family of conscience. This chapter will discuss some of the technologies that made this into reality.

After studying the chapter students will be able to

• Explain the concepts of communication systems
• Comprehend the concepts of data communication
• Explain the process behind data communication
• Classify the data transmission modes
• Compare between different modes of data transmission
• Understand the importance of optical fiber in data communication
• Identify the different mediums used for wireless communication
• Find the difference between data communication systems of different eras
• Know the importance of wireless communication technology in ICT
• Explain the concepts of a network
• Understand the importance of networks
• Explain the usage of different types of networks
• Understand network topology
• Understand the concept of cloud computing
• Know the advantages of cloud computing.

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2.1 Communication System

2.1.1 Concept of Communication System

Communication is a very natural process, humans and even animals and birds communicate with each other. Even before human civilization came to being human beings used different modes of communication among themselves. First they used sign language and then they invented languages for communication. Then with the ages human beings discovered the means to communicate with people in long distances - letters, telegrams, telephones were invented to progress the modes of communication. Radio and television are different types of communication media too where the presenter or anchor communicates with a mass number of audience. This sharing of information and expression is called a communication system. In the current day and age, the internet and cellular technology has progressed the communication system so far that now human beings not only communicate with themselves but they can now communicate with machines too.

So communication has become a medium of imparting or exchanging of information through a person or machine. This process connects the sender and receiver of information through one or more communication media and numeracy machine elements.

2.1.2 Concept of Data Communication

Communication is the process of establishing a link between two points for exchanging information. That is, a secure and efficient data exchange between sender and receiver. Figure 2.1 shows the structure of an electronic data communication system.

(figure: Figure 2.1: Different parts of Data Communication)

Labels: Source, Destination, Information Source, Input Transducer, Transmitter, Medium, Receiver, Output Transducer, Information Destination, Words, Symbol, Sound, Picture, Speech data etc., Information in Electrical form, Information in Original form, Information in Electrical form

Description: A block diagram of data communication. Two dashed boxes enclose the blocks at each end: on the left, Information Source feeds Input Transducer, and on the right, Output Transducer feeds Information Destination. Between them, Transmitter, Medium and Receiver are connected in a row from left to right. Labels below the diagram mark the input as Words, Symbol, Sound, Picture, Speech data etc., and mark the signals as Information in Electrical form between the transducers and the transmitter and receiver, and Information in Original form at the output. Source and Destination are shown as rounded shapes above the left and right ends.

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Here it is seen that using different parts of data communication, words, symbols, waves, pictures etc. from the source reach the destination as a medium. This process requires a transmitter and a receiver. Data from the source is converted to an electric signal (can also be a light signal) via an input transducer and sent to a medium (wire or wireless) through a transmitter. The receiver then converts the electric signal from the medium through the output transducer to the destination. The data source obtained here is like data.

It is noted that noise (intermittent unexpected electrical signals) may be added to the medium during the transmission of data from source to destination, this is known as telecommunication noise, which has a correction mechanism.

Examples of components used in data communication:

1. Source (data source + input transducer) - microphone, camera, keyboard, etc.

2. Transmitter - radio / television station, telephone, mobile phone, modem, router etc.

3. Medium - Telephone / Fiber Optic Cable, Radio / Microwave etc.

4. Receiver or customer device - telephone exchange, modem, router etc.

5. Destination (Output Transducer + Data Destination) - Loudspeaker, Telephone, Computer etc.

2.1.3 Bandwidth

As a resident of the present world most of us have a little bit of an idea about internet speeds. This speed of the internet depends on the signal's bandwidth. Bandwidth is a range of frequencies within a given band, in particular that used for transmitting a signal. Essentially it denotes the rate of data transfer. Bandwidth is usually calculated in bits per second(bps) units. But as the internet and communication medium improved now the bandwidth is calculated in kbps (1000 bits per second), Mbps(1,000,000 bits per second) or even Gbps(1,000,000,000 bits per second). A Byte consists of 8 bits. So 1MBps is equal to 8Mbps.

The bandwidth of a communication network depends on the communication medium and the equipment used in the network. For example an optical fiber cable can provide you with much more bandwidth than a telephone cable. But if you do not use the proper terminal equipment in conjunction with the optical fiber, you won’t get the desired bandwidth.

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As a communication network is used by many users, the network bandwidth is usually shared among the users. Sometimes a user or a service can forcibly use a larger share of the bandwidth by themselves limiting the bandwidth to the rest of the users. There are many systems available to measure the actual bandwidth an average user is getting. There are tools and systems to detect problems and faults in network design or problems with network equipment. Overall, bandwidth management is a very challenging task.

The 2.1 table shows the necessary minimum bandwidth required for certain services. If a user doesn't get the proper bandwidth for his services, he won't get the right results or experience from those services.

2.1.4 Data Transmission Methods

Data transmission refers to the process of transferring data between two or more digital devices. It depends on the distribution of bits.

Data transmission methods can be divided into two types - parallel and serial data transmission, depending on the bit distribution. Serial data transmission sends one bit at a time into one medium, whereas parallel transmission method uses multiple mediums to send multiple bits at a time.

Parallel Data Transmission

When data is sent using parallel data transmission, multiple data bits are transmitted over multiple channels at the same time.In this method one or two control lines are used alongside data lines to synchronise the transmitter and receiver. As the data is processed parallely inside the computer circuits, this is the more natural way to transmit data. This is obviously the faster way of transmitting data as it sends multiple bits over multiple channels at a time. But this is not the ideal way if you want long distance data transmission.

Printers along with parallel ports and cable use this transmission method too.

Serial Data Transmission:

When data is sent or received using serial data transmission, the data bits are organized in a specific order, since they can only be sent one after another. The order of the data bits is important as it dictates how the transmission is organized when it is

(figure: Figure 2.2: Parallel and Serial Data Communication)

Labels: Transmitter, Receiver, Parallel, Transmitter, Receiver, Serial

Description: Two block diagrams stacked vertically. The upper diagram shows a Transmitter box on the left and a Receiver box on the right, connected by multiple parallel arrows labelled Parallel. The lower diagram shows a Transmitter box and a Receiver box connected by a single arrow labelled Serial, with a small bracket-shaped marker at each end of the arrow.

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received. It is viewed as a reliable data transmission method because a data bit is only sent if the previous data bit has already been received. This transmission method is less noisy as there is only a single channel for data transmission. The popular Universal Serial Bus or USB port uses serial data transmission methods.

Bit Synchronization

The time a sender a data, the receiver should receive it simultaneously. In this case the clock should be similar for both of them. When using serial data transmission both the transmitter and receiver use a clock to synchronize bits. A bit is transmitted and received with each pulse of the clock. Here, clock pulse means an active state of the clock signal. Bit synchronization is a technique that determines the beginning and ending of a bit with the clock. With this a receiver can identify and recover data.

Depending on bit synchronization the serial data transmission can be classified into three types:

(figure: Figure 2.3: 3 Types of Data Communication)

Labels: Transmission Method, Parallel, Serial, Asynchronous, Synchronous, Isochronous

Description: A tree diagram. At the top is a box labelled Transmission Method, which branches into two boxes: Parallel on the left and Serial on the right. Serial branches further into three boxes: Asynchronous, Synchronous and Isochronous, from left to right.

1. Asynchronous Transmission
2. Synchronous Transmission &
3. Isochronous Transmission

Asynchronous Transmission

In asynchronous method data is transferred in character format. At a time only one character is transmitted. 1 character = 8bit. In asynchronous transmission the transmitter can send the data whenever it wants and the receiver is always prepared to receive data. The transmitter can even spend as much time it wants between two data transmissions. Prior to sending data the transmitter sends a starting bit from which the receiver knows that the transmission has started. At the end of transmission one or two stop bit is sent so the receiver can know the transmission is ended. In this case time interval between each character may not be the same. As in this technique a transmitter can send data anytime it does not need a primary storage device like RAM, Cache or CPU memory. This technique is useful when sending small amounts of data at a slower speed.

Figure

Labels: (Direction of Data Flow), (Stop Bits), (Start Bits), (delay time), SENDER, RECEIVER, 0110 0, 1 11111011 0, 1 110110

Description: A serial data stream of 8-bit characters flowing left to right from a yellow SENDER block to a RECEIVER block. Each character has a start bit (red-shaded, at the left) and a stop bit (at the right) marked with brackets. Red arrows mark the gap between characters as delay time.

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Computer keyboard uses asynchronous data transmission. As there can be an undetermined amount of time between two key presses, asynchronous transmission is used here.

Synchronous Transmission

Synchronous data transmission is a continuous process. With this technique a transmitter sends data to a receiver continuously until the transmission ends. In synchronous data transmissions, the receiver station divides the data characters into blocks or frames and stores them into a primary storage like RAM, Cache or CPU memory. Each block or frame is synchronized with the clock to transmit them with equal delays. At the beginning of each block 1 or 2 bytes are reserved for header information and at the end of the block 1 or 2 bytes are reserved for trailer information signals. Header and trailer bytes usually contain addresses or identification numbers to properly locate transmitter and receiver inside a network. Header signal is used by the receiver machine to synchronize its clock with the transmitter. Trailer signal denotes the end of a block and sometimes contains information for error correction in transmitted data.

Figure

Labels: Sender, (Direction of flow), Receiver, 10100011, 11111011, 11110110, 11110111, 00010000, 110

Description: A block labelled Sender on the left and a block labelled Receiver on the right, joined by a yellow bar of consecutive 8-bit blocks. A red arrow above the bar shows the direction of flow from left to right.

Although this is a more complex and costly process, synchronous data transmission is usually used to transmit data over long distances using a larger bandwidth. Larger networks like cellular networks and TV networks use this transmission technique.

Isochronous Transmission

Isochronous transmission is a cross between Synchronous and asynchronous transmission. This process uses the start and stop bits of asynchronous transmission but transmits data in blocks like synchronous transmissions. As this is not totally synchronous so primary storage devices are not needed. Real time applications such as multimedia communications, audio and video calls use this particular technique.