Computer Networking

Introduction

What is a Computer Network?

Computer Network is a group of computers connected with each other through wires, optical fibres or optical links so that various devices can interact with each other through a network.

The aim of the computer network is the sharing of resources among various devices.

In the case of computer network technology, there are several types of networks that vary from simple to complex level.

Components of Computer Network:

Major components of a computer network are:

NIC(Network interface card)

NIC is a device that helps the computer to communicate with another device. The network interface card contains the hardware addresses, the data-link layer protocol use this address to identify the system on the network so that it transfers the data to the correct destination.

There are two types of NIC: wireless NIC and wired NIC.

Wireless NIC: All the modern laptops use the wireless NIC. In Wireless NIC, a connection is made using the antenna that employs the radio wave technology.

Wired NIC: Cables use the wired NIC to transfer the data over the medium.

Hub

Hub is a central device that splits the network connection into multiple devices. When computer requests for information from a computer, it sends the request to the Hub. Hub distributes this request to all the interconnected computers.

Switches

Switch is a networking device that groups all the devices over the network to transfer the data to another device. A switch is better than Hub as it does not broadcast the message over the network, i.e., it sends the message to the device for which it belongs to. Therefore, we can say that switch sends the message directly from source to the destination.

Cables and connectors

Cable is a transmission media that transmits the communication signals. There are three types of cables:

Twisted pair cable: It is a high-speed cable that transmits the data over 1Gbps or more.

Coaxial cable: Coaxial cable resembles like a TV installation cable. Coaxial cable is more expensive than twisted pair cable, but it provides the high data transmission speed.

Fibre optic cable: Fibre optic cable is a high-speed cable that transmits the data using light beams. It provides high data transmission speed as compared to other cables. It is more expensive as compared to other cables, so it is installed at the government level.

Router

Router is a device that connects the LAN to the internet. The router is mainly used to connect the distinct networks or connect the internet to multiple computers.

Modem

Modem connects the computer to the internet over the existing telephone line. A modem is not integrated with the computer motherboard. A modem is a separate part on the PC slot found on the motherboard.

Communication concept

How Does a Computer Network Work?

Basics building blocks of a Computer network are Nodes and Links. A Network Node can be illustrated as Equipment for Data Communication like a Modem, Router, etc., or Equipment of a Data Terminal like connecting two computers or more. Link in Computer Networks can be defined as wires or cables or free space of wireless networks.

The working of Computer Networks can be simply defined as rules or protocols which help in sending and receiving data via the links which allow Computer networks to communicate. Each device has an IP Address, that helps in identifying a device.

Basic Terminologies of Computer Networks

Network: A network is a collection of computers and devices that are connected together to enable communication and data exchange.

Nodes: Nodes are devices that are connected to a network. These can include computers, Servers, Printers, Routers, Switches, and other devices.

Protocol: A protocol is a set of rules and standards that govern how data is transmitted over a network. Examples of protocols include TCP/IP, HTTP, and FTP.

Topology: Network topology refers to the physical and logical arrangement of nodes on a network. The common network topologies include bus, star, ring, mesh, and tree.

Service Provider Networks: These types of Networks give permission to take Network Capacity and Functionality on lease from the Provider. Service Provider Networks include Wireless Communications, Data Carriers, etc.

IP Address: An IP address is a unique numerical identifier that is assigned to every device on a network. IP addresses are used to identify devices and enable communication between them.

DNS: The Domain Name System (DNS) is a protocol that is used to translate human-readable domain names (such as www.google.com) into IP addresses that computers can understand.

Firewall: A firewall is a security device that is used to monitor and control incoming and outgoing network traffic. Firewalls are used to protect networks from unauthorized access and other security threats.

Remote terminals

What Does Remote Terminal Mean?

A remote terminal is any electronic device, computer, hardware or other networking equipment located outside the premises of an organization. It uses remote capabilities to provide and facilitate services, processes or business functions.

A remote terminal connects to a host organization through a network link. Remote terminal devices include:

Telecommunication equipment geographically located at a distance from a public switched telephone network (PSTN)

A networked computer with connectivity capability that is installed at another office location

Networking equipment that is remotely deployed and used to connect a main office with field employees

What is an example of remote access?

What is an example of remote access? An example of remote access is when you use a computer, Smartphone or tablet to connect to another computer or network from a different location.

What are the different types of communication terminals?

There are several types of terminals: dumb terminals, smart terminals, and graphics terminals.

Communication networks

What is communication network?

 

A communication network refers to the way communication flows between workers or members within an organization. It is the method in which an organization facilitates information throughout a group or team. Communication in an organization can flow downward, upward, horizontal, or diagonal.

What are the different types of communication networks?

Communication networks have three different types or channels known as simplex, half-duplex, and full-duplex.

Networks in Communication

Following are the most common networks in various organizations:

Vertical Network

This is a kind of a formal network. So consequently it is suitable for communications between different levels of employees. For example a higher ranking manager and a lower-ranking official.

This network thus enables two-way communication wherein immediate feedback is a common practice. This is a direct link between the employees and their subordinates and thus the chance of miscommunication is very low.

Circuit Network

In this type of network, two people or nodes will communicate with each other continuously. One of the nodes will produce messages and the other a feedback to the messages. The communication is thus two people communicating with each other, sending messages and feedbacks and thus forming a loop or a circuit.

This circuit or loop is what we call the circuit network. Usually, the two people that are interacting via this form of networks are of the same hierarchical level. This is different from the Vertical Network where the feedback and the messages are two-way communication.

Chain Network

A company or the organization is like a platoon. It has its leader at the front and the troop following right behind. For communications that are for the more than two nodes or more than two levels of employees, we can employ this method of communication.

Here the network traces a chain of command. This may start with a senior or a high ranking employee or a manager, who hands it over to the next level and so on. For example, the communication starts from a C E O and trickles down to the employees of a lower level.

The C E O may pass the information on to the managers who will pass it to the lower levels without alteration. Notice that the message which generates at the higher level has to trickle down to the lowest level without any alteration.

Wheel and Spoke Network

This is like the vertical communication but with the difference that there are several people communicating with a central figure or person. Here a single controlling authority is involved in a vertical type communication and radiates instructions and orders to several of his employees who are working under him.

This is an improvement over the chain communication and provides a direct link between the top command and the employees. However, due to the nature of this communication, it constitutes a form of the micro-management and will thus be very taxing.

An advantage of the wheel and spoke network is that it relays instructions and orders directly from the highest level to any subordinate levels. There are no middle parties or disruptions to the communication channel.

Star Network

The star communication network has several participants. Each of these participants enables two-way communication between each of the nodes or people that are participating in the network.

Consider this as a wheel and spoke network that does not have a central focus point. The members of this network are free to communicate. They can exchange data and information with each other without any hurdles or restrictions.

LAN and WAN

Difference between LAN and WAN

 Local Area Network (LAN): LAN is a group of network devices that allow communication between connected devices. The private ownership has the control over the local area network rather than the public. LAN has a short propagation delay than MAN as well as WAN. It covers the smallest area such as College, School Hospital and so on. 

Wide Area Network (WAN): WAN covers a large area than LAN as well as MAN such as Country/Continent etc. WAN is expensive and should or might not be owned by one organization. PSTN or Satellite medium is used for wide area networks. 

Difference between LAN and WAN:

S.NO	LAN	WAN
1.	LAN stands for Local Area Network.	Whereas WAN stands for Wide Area Network.
2.	LAN’s ownership is private.	But WAN’s ownership can be private or public.
3.	The speed of LAN is high(more than WAN).	While the speed of WAN is slower than LAN.
4.	The propagation delay is short in LAN.	Whereas the propagation delay in WAN is long(longer than LAN).
5.	There is less congestion in LAN(local area network).	While there is more congestion in WAN(Wide Area Network).
6.	There is more fault tolerance in LAN.	While there is less fault tolerance in WAN.
7.	LAN’s design and maintenance is easy.	While it’s design and maintenance is difficult than WAN.
8.	LAN covers small area i.e. within the building.	While WAN covers large geographical area.
9.	LAN operates on the principle of broadcasting.	While WAN works on the principle of point to point.
10.	Transmission medium used in LAN is co-axial or UTP cable.	Whereas WAN uses PSTN or satellite link as a transmission or communication medium.
11.	LAN has a higher data transfer rate.	WAN has a lower data transfer rate as compared to LAN.
12.	LANs technologies used like ethernet and token.	WANs technologies used like Frame Relay and X.25 for connectivity for longer distances.
13.	LANs technologies is data transfer rate is 10mbps.	WANs technologies data transfer rate 150mbps
14.	LANs is cheaply compared to WAN	WAN is costly compared to LAN.
15.	In LAN Co-axial cables are generally used to connect the computer and other devices.	In WAN links are established using microwave or satellite.
16.	Due to short distance short circuit error or other noise error are minimum.	In this network, short circuit errors, noise errors are higher than any other network.
17.	For eg: A computer lab in a college.	For eg: pager

Protocols and OSI model.

What is OSI Model?

The OSI Model is a logical and conceptual model that defines network communication used by systems open to interconnection and communication with other systems. The Open System Interconnection (OSI Model) also defines a logical network and effectively describes computer packet transfer by using various layers of

Characteristics of OSI Model

A layer should only be created where the definite levels of abstraction are needed.

The function of each layer should be selected as per the internationally standardized protocols.

The number of layers should be large so that separate functions should not be put in the same layer. At the same time, it should be small enough so that architecture doesn’t become very complicated.

In the OSI model, each layer relies on the next lower layer to perform primitive functions. Every level should able to provide services to the next higher layer

Changes made in one layer should not need changes in other lavers.

Why OSI Model?

Helps you to understand communication over a network

Troubleshooting is easier by separating functions into different network layers.

Helps you to understand new technologies as they are developed.

Allows you to compare primary functional relationships on various network layers.

History of OSI Model

Here are essential landmarks from the history of OSI model:

In the late 1970s, the ISO conducted a program to develop general standards and methods of networking.

In 1973, an Experimental Packet Switched System in the UK identified the requirement for defining the higher-level protocols.

In the year 1983, OSI model was initially intended to be a detailed specification of actual interfaces.

In 1984, the OSI architecture was formally adopted by ISO as an international standard

7 Layers of the OSI Model

OSI model is a layered server architecture system in which each layer is defined according to a specific function to perform. All these seven layers work collaboratively to transmit the data from one layer to another.

The Upper Layers: It deals with application issues and mostly implemented only in software. The highest is closest to the end system user. In this layer, communication from one end-user to another begins by using the interaction between the application layer. It will process all the way to end-user.

The Lower Layers: These layers handle activities related to data transport. The physical layer and datalink layers also implemented in software and hardware.

Upper and Lower layers further divide network architecture into seven different layers as below

Application

Presentation

Session

Transport

Network, Data-link

Physical layers

Network Layers Diagram

Physical Layer

The physical layer helps you to define the electrical and physical specifications of the data connection. This level establishes the relationship between a device and a physical transmission medium. The physical layer is not concerned with protocols or other such higher-layer items. One example of a technology that operates at the physical layer in telecommunications is PRI (Primary Rate Interface). To learn more about PRI and how it works, you can visit this informative article.

Examples of hardware in the physical layer are network adapters, ethernet, repeaters, networking hubs, etc.

Data Link Layer:

Data link layer corrects errors which can occur at the physical layer. The layer allows you to define the protocol to establish and terminates a connection between two connected network devices.

It is IP address understandable layer, which helps you to define logical addressing so that any endpoint should be identified.

The layer also helps you implement routing of packets through a network. It helps you to define the best path, which allows you to take data from the source to the destination.

The data link layer is subdivided into two types of sub layers:

Media Access Control (MAC) layer- It is responsible for controlling how device in a network gain access to medium and permits to transmit data.

Logical link control layer- This layer is responsible for identity and encapsulating network-layer protocols and allows you to find the error.

Important Functions of Datalink Layer:

Framing which divides the data from Network layer into frames.

Allows you to add header to the frame to define the physical address of the source and the destination machine

Adds Logical addresses of the sender and receivers

It is also responsible for the sourcing process to the destination process delivery of the entire message.

It also offers a system for error control in which it detects retransmits damage or lost frames.

Datalink layer also provides a mechanism to transmit data over independent networks which are linked together.

Transport Layer:

The transport layer builds on the network layer to provide data transport from a process on a source machine to a process on a destination machine. It is hosted using single or multiple networks, and also maintains the quality of service functions.

It determines how much data should be sent where and at what rate. This layer builds on the message which are received from the application layer. It helps ensure that data units are delivered error-free and in sequence.

Transport layer helps you to control the reliability of a link through flow control, error control, and segmentation or desegmentation.

The transport layer also offers an acknowledgment of the successful data transmission and sends the next data in case no errors occurred. TCP is the best-known example of the transport layer.

Important functions of Transport Layers:

It divides the message received from the session layer into segments and numbers them to make a sequence.

Transport layer makes sure that the message is delivered to the correct process on the destination machine.

It also makes sure that the entire message arrives without any error else it should be retransmitted.

Network Layer:

The network layer provides the functional and procedural means of transferring variable length data sequences from one node to another connected in “different networks”.

Message delivery at the network layer does not give any guaranteed to be reliable network layer protocol.

Layer-management protocols that belong to the network layer are:

Routing protocols

Multicast group management

Network-layer address assignment.

Session Layer

Session Layer controls the dialogues between computers. It helps you to establish starting and terminating the connections between the local and remote application.

This layer request for a logical connection which should be established on end user’s requirement. This layer handles all the important log-on or password validation.

Session layer offers services like dialog discipline, which can be duplex or half-duplex. It is mostly implemented in application environments that use remote procedure calls.

Important function of Session Layer:

It establishes, maintains, and ends a session.

Session layer enables two systems to enter into a dialog

It also allows a process to add a checkpoint to steam of data.

Presentation Layer

Presentation layer allows you to define the form in which the data is to exchange between the two communicating entities. It also helps you to handles data compression and data encryption.

This layer transforms data into the form which is accepted by the application. It also formats and encrypts data which should be sent across all the networks. This layer is also known as a syntax layer.

The function of Presentation Layers:

Character code translation from ASCII to EBCDIC.

Data compression: Allows to reduce the number of bits that needs to be transmitted on the network.

Data encryption: Helps you to encrypt data for security purposes — for example, password encryption.

It provides a user interface and support for services like email and file transfer.

Application Layer

Application layer interacts with an application program, which is the highest level of OSI model. The application layer is the OSI layer, which is closest to the end-user. It means OSI application layer allows users to interact with other software application.

Application layer interacts with software applications to implement a communicating component. The interpretation of data by the application program is always outside the scope of the OSI model.

Example of the application layer is an application such as file transfer, email, remote login, etc.

The functions of the Application Layers are:

Application-layer helps you to identify communication partners, determining resource availability, and synchronizing communication.

It allows users to log on to a remote host

This layer provides various e-mail services

This application offers distributed database sources and access for global information about various objects and services.

Interaction Between OSI Model Layers

Information sent from a one computer application to another needs to pass through each of the OSI layers.

This is explained in the below-given example:

Every layer within an OSI model communicates with the other two layers which are below it and its peer layer in some another networked computing system.

In the below-given diagram, you can see that the data link layer of the first system communicates with two layers, the network layer and the physical layer of the system. It also helps you to communicate with the data link layer of, the second system.

Protocols supported at various levels

Layer	Name	Protocols
Layer 7	Application	SMTP, HTTP, FTP, POP3, SNMP
Layer 6	Presentation	MPEG, ASCH, SSL, TLS
Layer 5	Session	NetBIOS, SAP
Layer 4	Transport	TCP, UDP
Layer 3	Network	IPV5, IPV6, ICMP, IPSEC, ARP, MPLS.
Layer 2	Data Link	RAPA, PPP, Frame Relay, ATM, Fiber Cable, etc.
Layer 1	Physical	RS232, 100BaseTX, ISDN, 11.

Differences between OSI & TCP/IP

Here, are some important differences between the OSI & TCP/IP model:

OSI Model	TCP/IP model
OSI model provides a clear distinction between interfaces, services, and protocols.	TCP/IP doesn’t offer any clear distinguishing points between services, interfaces, and protocols.
OSI uses the network layer to define routing standards and protocols.	TCP/IP uses only the Internet layer.
OSI model use two separate layers physical and data link to define the functionality of the bottom layers	TCP/IP uses only one layer (link).
OSI model, the transport layer is only connection-oriented.	A layer of the TCP/IP model is both connection-oriented and connectionless.
In OSI model, data link layer and physical are separate layers.	In TCP data link layer and physical layer are combined as a single host-to-network layer.
The minimum size of the OSI header is 5 bytes.	Minimum header size is 20 bytes.

Advantages of the OSI Model

Here, are major benefits/pros of using the OSI model :

It helps you to standardize router, switch, motherboard, and other hardware

Reduces complexity and standardizes interfaces

Facilitates modular engineering

Helps you to ensure interoperable technology

Helps you to accelerate the evolution

Protocols can be replaced by new protocols when technology changes.

Provide support for connection-oriented services as well as connectionless service.

It is a standard model in computer networking.

Supports connectionless and connection-oriented services.

Offers flexibility to adapt to various types of protocols

Disadvantages of the OSI Model

Here are some cons/ drawbacks of using OSI Model:

Fitting of protocols is a tedious task.

You can only use it as a reference model.

Doesn’t define any specific protocol.

In the OSI network layer model, some services are duplicated in many layers such as the transport and data link layers

Layers can’t work in parallel as each layer need to wait to obtain data from the previous layer.