Introduction of Computer Network

History of Computer Networks

• In 1960, the ARPANET (Advanced Research Projects Agency Network) was widely recognized as the world’s first operational packet-switching computer network and the foundational technology of the modern internet.
  • Developed By: The U.S. Department of Defense’s Advanced Research Projects Agency (ARPA, now DARPA).
  • First Operational: 1969.
  • Key Milestone: The first successful message transmission occurred on October 29, 1969, between nodes at UCLA and the Stanford Research Institute (SRI).
  • Precursor to the Internet: ARPANET directly evolved into the core network of what became the modern Internet.
• The Internet is the world’s largest network by far, both in terms of geographical reach and the sheer number of connected devices and users.

Introduction to Computer Networks

• The process of interconnection between two/more different networks is called internetworking. The main purpose of interconnecting is to allow any node or any network (e.g., Ethernet) to access/share data to any other node on any other network. (e.g., ATM). 
• The process of interconnection within a typical network is called intranetworking.
• All data communication in a computer network is finally in digital form.
• The Computers on a network may be linked through Cables, telephone lines, radio waves, microwaves, satellites, etc.
• A Computer network includes the network operating system in the client and server machines, the cables/air, which connect different computers, and all supporting hardware in between, such as bridges, routers, and switches. In wireless systems, antennas and towers are also part of the network. 
• There are so many common reasons for having different networks in the world(thus different protocols) –
  • Many personal computers use the TCP/IP protocol suite due to their requirements & platforms/OS environment.
  • Many larger business organizations still use IBM mainframes with the specific SNA Protocol.
  • A large number of telecommunications companies also provide/use the ATM network protocol suite.
  • Some PCs still run on Novell’s NCP/IPX or AppleTalk protocol suite.
  • Wireless Network will have a totally different protocol suite.
• Due to different network architecture, they have different parameters in their encoding techniques at the physical layer, frame formats at the data link layer, packet length in network layer, quality of services in transport layer, error handling mechanisms, flow control mechanism and congestion control mechanism in data link layer, security issues and addressing mechanisms in network layer. Hence, these parameters must be taken into consideration before making/interconnecting a typical network.

Difference between Data and Signal

Communication/Transmission Process

• • The exchange of information by speaking, writing, or using some other medium.- Oxford Dictionary.
  • Digital communications is the physical transfer of data or information in a computer network in the form of bits over a communication channel from a source to a destination.

Components of a Network/Data Communication System

• • In the present world, a computer does not work as a standalone system but as part of a communication system.
  • The data in a communication system may be transmitted either in analog or digital form over a single path serially or number of parallel paths.
  • The data in a communication system can be sent asynchronously (when both the source and receiver are not following the proper timing interval) or synchronously (when both sender and receiver agree on the sequence of arrival of data).
  • The data in a communication system follows any transmission mode from all three methods – Simplex, Half duplex, and Full duplex/duplex.
  • The most important factors affecting the transfer of a signal over a medium are noise and attenuation. Noise is the external disturbance, whereas attenuation is defined as the degradation of the signal.

• • There are the following major components of a typical communication system has –

• • • Sender/Source/Transmitter Devices :
      
      • A source who/which is trying to originates a message to the receiver.
      • Source produces a message or sequence of messages to be communicated to the receiver.
      • The source output may be in many different forms, such as a waveform, a sequence of binary digits, and a set of outputs from sensors in a space probe, or many other similar forms.
      • Normally transmitter transmits the source’s produced data, but in a few cases source and transmitter are different, and in a few cases source and transmitter are the same.
    • Message/Information(Data)/Signal :
      
      • The actual/main content in a communication system is transferred to the receiver.
      • Here, information/data are mainly in electromagnetic signals, such as an electrical voltage, radio wave, microwave, or infrared signal.
      • The data transmitted can be pure digital messages generated from a digital data source, like a computer or a keyboard. However, it may also be an analog signal, such as a human voice over a phone call, which could be digitized.
    • Networking Devices :
      
      • Several related/networking devices are also used to connect multiple devices, which are finally used to transmit/receive the data with certain specific modifications as per need.
      • For example – Modem, Encoder, Decoder, Switch, Hub, Repeater, Bridges, Routers, NIC, Gateways, Firewalls, Access Points, etc.
      • The specific devices used will depend on the network’s size, complexity, and intended use.
      • Many modern networking devices combine functionalities. For example, a home router often includes a modem, switch, and wireless access point in a single unit for convenience.
      • The explanation of networking devices is as follows –
        
        • Encoder:
          
          • In most cases, data/message is taken from the source and then encoded (by the encoder) for safety reasons, and then put over the medium for transmission.
          • It makes the original data unintelligible/unreadable.
          • The encoder does related processing of the source messages/signals before transmission. The processing might include, for example, any combination of modulation, data reduction, and insertion of redundancy to combat the channel noise.
        • Decoder:
          
          • Decoding (by the decoder) of the encoded message is done at the receiver end before final handover to the receiver.
          • It makes the unintelligent form of data into an original user-defined/readable form.
          • A decoder does the processing of channel-encoded data to produce an accepted replica of the input at the destination.
        • Routers: Direct data traffic between different networks. They use routing tables to determine the best path for data packets.
        • Switches: Connect devices within a single network and use MAC addresses to forward data to the correct destination.
        • Hubs: (Less common now) Simple devices that broadcast data to all connected devices, leading to potential collisions.
        • Modems: Convert digital data from a network into analog signals for transmission over phone lines or cable and vice versa.
        • Access Points: Create wireless networks by broadcasting a signal that devices can connect to.
        • Firewalls: Security devices that monitor and control incoming and outgoing network traffic based on predetermined security rules.
        • Network Interface Cards (NICs): Hardware components that allow computers to connect to a network.
        • Repeaters: Amplify signals to extend the reach of a network.
        • Bridges: Connect two different network segments and filter traffic between them.
        • Gateways: Act as a “gate” between different networks using different protocols, translating data as needed.
    • Communication Medium/Channel :
      
      • The medium (mostly wire/air/wave/water) through which data is transmitted in the form of a signal between the transmitter and receiver.
      • Typically, it may be a telephone line, a high-frequency radio link, a space communication link, or a storage medium.
      • The channel or medium could be air (for wireless/mobile communication), or cables through copper wires, or optical fibers.
    • Receiver/Destination Devices:
      
      • A destination that is trying to receive a message, finally.
      • It may be the person, devices, or other objects for whom the message is intended.

Definition of Computer Network

• A computer network can be simply defined as the interconnection of two or more independent computers for a specific purpose.
• A computer network is a collection and connection of more than one autonomous computer, servers, mainframes, network devices, peripherals, or other related devices connected to one another in a pre-defined plan to allow the sharing of data/resources.
• A computer network is a collection of hardware components and computers interconnected by communication channels that allow the sharing of resources and information.

Data Transmission Standard

• The data in a communication system follows these data transmission standards.

(A) Data Transmission Types

(a) Serial Data Transmission

• • A type of digital data communication in which sequential transmission of bits occurs over a single channel.
  • It uses less processing power and has fewer chances for error.
  • It has a lower data transfer rate comparatively.
  • The start and stop of a communication in this transmission is specified by LSB (Least Significant Bit) and MSB (Most Significant Bit).
  • In serial transmission, the byte(data) plus the parity bit(for error detection) is transmitted one bit after another in a continuous line.
  • Serial data transmission is of two types –

(i) Synchronous Data Transmission

• • • In synchronous transmission, both receiver and sender have an agreement (or are aware) about timing for the sending and receiving data, so that both sender and receiver can coordinate (synchronize) their data signals.
    • In case of this transmission, there is no use of any start and stop bits, but instead of that clock signal (clock is built into each end of transmission) is being used for synchronizing the data transmission at both the receiving and sending end. For this, a constant stream of bits is sent between the sender and receiver. As clock synchronization may be disturbed, the possibility of error arises in this transmission.
    • It has higher transmission speeds than asynchronous, because the system has a lower possibility of error. But, if an error takes place, there is a chance that the complete set of data is lost instead of a single character.
    • This transmission is mainly used for high-speed communication between computers.
    • It is unsuitable where the characters are transferred at irregular intervals.
    • It gives lower overheads because of no start and stop bits and thus, greater throughput.
    • The processing mechanism is more complex.
    • It is not very cost-effective as the hardware used is more expensive.

(ii) Asynchronous Data Transmission

• • • In asynchronous transmission, both receiver and sender have no agreement (or awareness) about timing for the sending data, i.e., no coordination between sender and receiver before transmission.
    • The asynchronous transmission uses start and stop bits to signify the beginning of transmission. For example, if a sender wants to send some data such as  10011101, it will be appended with the start bit(0) and stop bit(1), and finally look like “1 10011101 0”, where we have assumed that ‘0’ is the start bit and ‘1’ is the stop bit.
    • Asynchronous transmission is best suitable in the case where the characters are transferred at irregular intervals, as in data entry from the keyboard.
    • In this transmission, each character is surrounded by start and stop bits, i.e., each character is a complete unit, and hence if there is an error in a character, other sequences of characters are not affected. However, errors in start and stop bits (s) may cause serious problems in data transfer.
    • It doesn’t require synchronization of both communication sides.
    •  It is cost-effective.
    • The speed of this transmission is limited.
    • It has large processing overheads because of the presence of a large no. of start and stop bits with the data, which are uniquely used for control purposes.

(b) Parallel Data Transmission

• • A type of digital data communication in which simultaneous transmission of multiple bits over two or more separate channels.
  • It has a high data transfer rate.
  • It uses high processing power and has more chances for error.
  • Parallel data transmission is less reliable for long distances because error correction is not very simple and economical.
  • In parallel transmission, 8 bits (a byte) plus a parity bit are transmitted at the same time over nine separate paths. Thus, parallel transmission is generally faster than serial transmission.

(B) Data Transmission/Communication Modes

Normally an information is transmitted between a source and destination during the communication process using any one of three modes –

(a) Simplex Transmission Mode

• • Simplex mode of data/signal transmission is one-way transmission, i.e., data flow is unidirectional.
  • Here, one station is a transmitter and the other is a receiver.
  • Here, signals/data are transmitted or travel in only one direction, i.e., from a sender to a receiver only and not its vice-versa.
  • In this mode, the receiver cannot respond to the sender. 
  • This mode uses a simple process and hardware.
  • For example – A keyboard connected to the computer, Telecasting of a Radio & Television/TV programs data is transmitted from a Radio/TV station to our radio or TV sets.. 

(b) Half Duplex Transmission Mode

• • When data transmission can take place in both directions, but not at the same time, i.e., both stations may transmit, but only one at a time. It may be that either the sender or the receiver(one side) can transmit at a time.
  • In this transmission mode, the sender and receiver both transmit on the same frequency.
  • For example, walky-talky & citizen’s band.

(c) Full Duplex/Duplex Transmission Mode

• • The transmission of data/signal between sender and receiver can take place in both directions at the same time/simultaneously.
  • It is like a two-lane road with traffic moving in both directions at the same time.
  • In this mode of transmission, signals going in either direction share the capacity, i.e., half of the bandwidth is used for sending data in one direction, while the other half is used for receiving data from the other direction.
  • For example, a telephone or mobile conversation is an example of full-duplex communication, where both sender and receiver can hear and say something to each other at the same time.

(C) Types of Transmitted Data/Signal

Click for Analog and Digital data details

Examples of Computer Networks

• There are just a few examples below, and the world of computer networks is constantly evolving with new technologies and applications emerging regularly.
• The impact of these networks extends far beyond their technical specifications, shaping communication, commerce, research, and countless other aspects of our lives.
  • The Internet: It is an excellent example of a computer network is the Internet. It is the global network of interconnected networks, the largest and most impactful computer network in existence. It revolutionized communication, information access, and countless aspects of modern life.
  • ARPANET: The precursor to the Internet, developed by the U.S. Department of Defense in the 1960s. It pioneered packet switching technology and laid the foundation for the modern internet.
  • NSFNET: The National Science Foundation Network, which played a crucial role in expanding internet access in the United States during the 1980s and 1990s.
  • Amazon Web Services (AWS): A massive cloud computing network offering a wide range of services, including computing power, storage, and databases. It powers numerous websites, applications, and services worldwide.
  • Microsoft Azure: Another major cloud computing network, offering similar services to AWS and competing for a significant market share.
  • Google Cloud Platform: Google’s cloud computing network, known for its powerful search and data analytics capabilities.
  • Facebook’s Social Network: While not a traditional computer network in the technical sense, Facebook’s vast infrastructure connects billions of users globally, facilitating communication and information sharing on an unprecedented scale.
  • Bitcoin Network: A decentralized peer-to-peer network that underpins the Bitcoin cryptocurrency. It demonstrates the potential of distributed networks for secure and transparent transactions.
  • Content Delivery Networks (CDNs): Networks like Cloudflare and Akamai optimize the delivery of web content by caching it at strategically located servers around the world, reducing latency and improving user experience.
  • Research and Education Networks: Networks like GEANT in Europe and Internet2 in the United States connect universities, research institutions, and government agencies, facilitating collaboration and data sharing for scientific and educational purposes.

Goals/Objectives of Computer Network

The objectives of a typical computer network are as follows –

• Cost reduction by sharing hardware and software resources.
• Provide high reliability due to multiple sources of supply.
• Provide an efficient transportation structure for large volumes of data among various locations, hence high throughput.
• Provide inter-process communication among users and processors.
• Reduction in delay in driving data transport.
• Increase productivity by making it easier to share data among users.
• Repairs, upgrades, expansions, and changes to the network should be performed with minimal impact on the majority of network users.
• Standards and protocols should be supported to allow many types of equipment from different vendors to share the network (Interoperability).
• Provide centralised/distributed management and allocation of the network resources like host processors, transmission facilities, etc.

Advantages of Computer Networks

• Increases productivity, i.e., makes it easier to share data among other users.
• Store vast amounts of information and reduce waste.
• Keeps us connected to all the nodes of a network.
• Improves system abilities.
• Save time & cost.

Disadvantages of Computer Networks

• Viruses can spread to other computers throughout a computer network.
• Purchasing the network cabling, equipment, and file servers can be expensive.
• A comparatively complex structure than a standalone system. 
• It lacks independence.
• It poses security difficulties.
• It lacks robustness.
• It requires an efficient/skillful handler.
• It requires an expensive setup.

Applications/Uses of Computer Networks

• Applications of computer networks are found everywhere in every field of life. They are used in our homes, schools, colleges, railway stations, offices, businesses, and many other places.
• They help us to send an email, watch a live sports event on our computer, book rail/air tickets, chat with our friends, and several other.
• The following are common/popular applications of a computer network in human life: –

• • Resource sharing
    • It allows sharing of application programs such as MS Office, equipment, and data available to any component on the network, irrespective of the physical location of the resource and the user.
    • A network is needed because of the desire to share the sharable programs, data, and equipment available to anyone on the network without regard to the physical location of the resource and the user. We can also share processing load on various networked resources.
    • Using computer networks, we can share any resource, CPU processing power, peripherals (like printers, scanners, etc), information (like files and data and even software), etc, among the components of that network. This sharing is done by communicating with the machine through which we want to share.
    • In hardware sharing, users can share devices present in that network, such as printers, scanners, CD/DVD-ROM drives, hard drives, modems, fax machines, etc.
  • Reliability/Flexibility
    • It provides high reliability in its service, having alternative sources of data if one of them is unavailable/corrupt/fails due to hardware failure or any other reason, the other source is available and can be used.
    • A network may have alternative sources of supply (e.g., replicated files, multiple CPUs, etc.). In case of one resource failure, the others could be used, and the system continues to operate at reduced performance. This feature is very important/useful for military, banking, air traffic control, and many other sensitive applications.
  • Scalability
    • Scalability is the ability to increase system performance gradually by adding more processors (i.e., incremental upgrade).
  • Powerful Electronic Communication Medium
    • Using computer networks, users can share their communication/message through the computer networks as email, chatting, audio/video conferencing, etc., no matter their location.
    • It provides a powerful communication medium among widely separated users easily where it previously had been impossible.
    • In the long run, the use of networks to enhance human-to-human communication may prove more important than technical goals such as improved reliability.
  • Inexpensive
    • Data transmission through a computer network is believed to be comparatively inexpensive.
  • Information Broadcasting and Search
    • This is also a mostly used application these days to create new websites, blogs, social networking websites, search engines, etc.
    • Computer networks provide us tremendous opportunity for information broadcasting, display, searching, and information retrieval. 
  • Storage capacity
    • A computer network provides a huge capacity to store data reliably.
  • Cost Efficient
    • The output of a computer network is believed to be very cost-efficient with respect to a single/standalone system.
  • In Some Specific Applications
    • To make a Computer network environment for a Campus for computing and resource sharing work mainly.
    • In Collaborative research and development work.
    • In developing, an Integrated system for design + manufacturing, + inventory.
    • In making Electronic commerce, publishing, and digital libraries.
    • In Multimedia communication (tele-training, video conferencing, etc.)
    • In Healthcare delivery (remote diagnosis, telemedicine, etc.) systems.
    • To use the Video-on-demand facility.
    • In Online learning.