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Networks | Computer


NETWORK TOPOLOGY

A network topology is the arrangement of nodes — usually switches, routers, or software switch/router features — and connections in a network often represented as a graph. The topology of the network and the relative locations of the source and destination of traffic flows on the network, determine the optimum path for each flow and the extent to which redundant options for routing exist in the event of a failure. There are two ways of defining network geometry: the physical topology and the logical (or signal) topology. The physical topology of a network is the layout of nodes and physical connections, including wires (Ethernet, DSL), fiber optics, and microwave. There are several common physical topologies, as described below, and as shown in the illustration.


Types of physical topologies

In the bus network topology, every node is connected in series along a linear path. This arrangement is found today primarily in cable broadband distribution networks.

In the star network topology, a central node has a direct connection to all other nodes. Switched local-area networks (LANs) based on Ethernet switches, including most wired home and office networks, have a physical star topology.

In the ring network topology, the nodes are connected in a closedloop configuration. Some rings will pass data only in one direction, while others are capable of transmission in both directions. These bidirectional ring networks are more resilient than bus networks because traffic can reach a node by moving in either direction. Metro networks based on Synchronous Optical Network Technology (SONET) are the primary example of ring networks today.

The mesh network topology links nodes with connections so that multiple paths between at least some points of the network are available. A network is said to have fully meshed if all nodes are directly connected to all other nodes and partially meshed if only some nodes have multiple connections to others. Meshing to create multiple paths increases resiliency under failure, but increases cost. The Internet is a mesh network.

The tree network topology, also called a star of stars, is a network where star topologies are themselves connected in a star configuration. Many larger Ethernet switch networks including data center networks are configured as trees


Bus Topology

In the bus topology, the server is at one end, and the client PCs (devices) are connected at different points or positions along with the network. All signals pass through each of the devices. Each device has a unique identity and can recognize those signals intended for it. It is easy and simple to design and implement.


Advantages:

• Easy to implement and extend

• Well suited for temporary or small networks not requiring high speeds

• Cheaper than other topologies.

• Cost-effective as only a single cable is used.

• Cable faults are easily identified.


Disadvantages:

• Limited cable length and the number of stations. • If there is a problem with the cable, the entire network goes down. • Maintenance costs may be higher in the long run. • It works best with a limited number of nodes. • It is slower than the other topologies.


Star Topology

This is a form of LAN architecture in which nodes on a network are connected to a common central hub or switch, and this is done by the use of dedicated links.

• In this kind of topology all the cables run from the computers to the central location where they are all connected by a device called hub or switch (or host node).

• Each computer on a star network communicates with a central device that resends the message either to each computer or only to the destination computer, e.g. if it is a hub then it will send to all and if it is a switch then it will send to the only destination computer.

• When network expansion is expected and when the greater reliability is needed, star topology is the best.


Advantages:

1) It is easy to modify and add new computers without disturbing the rest of the network.

2) The centre of the star network is a good place to diagnose the faults.

3) Single computer failure does not necessarily bring down the whole star network.


Disadvantages:

1) If the central device (or the host node) fails the whole network fails to operate.

2) Star networking is expensive because all network cables must be pulled to one central point, requires more cable than other network topologies.


Ring Topology

• This topology is a simple design and consists of a single cable that forms the main data path in the shape of a ring. Each device is connected to a closed-loop of cable. Signals travel in one direction from one node to all other nodes around the loop.

• In this type, each computer is connected to the next computer with the last one connected to the first.

• Each retransmits what it receives from the previous computer. The message flows around the ring in one direction.

• The ring network does not subject to signal loss problems as a bus network experience.

• There is no termination because there is no end to the ring.


Advantages:

1) Each node has equal access.

2) Capable of high-speed data transfer.


Disadvantages:

1) Failure of one computer on the ring can affect the whole network.

2) Difficult to troubleshoot the network


 

NETWORK APPLICATIONS

A network is a collection or set of computing devices connected to one another to establish communication and also share available resources. A network will comprise of software and hardware devices. You can have a network even if you are not connected to the internet. Computer networks make it possible for people to transfer files from one place to another and to communicate taking the shortest time possible.


Computer network applications are network software applications that utilize the Internet or other network hardware infrastructure to perform useful functions for example file transfers within a network. They help us to transfer data from one point to another within the network.


There are 2 types of network applications:

1. Pure network applications

2. Standalone network application


(A) Pure Network Applications

These are applications created to be used in networks; using pure network applications on a single computer doesn't make sense. They help us to transfer data and communicate within a network. Such applications have a separate and distinct user interface that users must learn for instance:


1. Email programs

They allow users to type messages at their local nodes and then send to someone on the network. It is a fast and easy way of transferring mail from one computer to another. Examples of electronic mail programs (Clients) are:

• Pegasus mail

• Outlook express

• Eudora Windows mail

• Fox mail

• Opera

• Mozilla Thunderbird

• Windows mail


2. File transfer protocol (FTP)

This application facilities transfer of files from one computer to another e.g. from a client to a server. There are 2 common processes involved in FTP

Downloading: This is the process of obtaining files from a server to a workstation or a client (for example when you download programs and music from a server).

Uploading: This is obtaining of files from a workstation to a server (for instance when you attach documents and upload them to a server, a good example being when you upload photos to Facebook).

Examples of FTP programs are: • FTP in Unix • FTP in Linux or • FTP in Windows


3. Terminal Emulation (TELNET)

It allows a workstation to access the server for an application program. This enables you to control the server and communicate with other servers on the network. The workstation appears as a down terminal that is directly attached to the server. The user feels like he/she is using the server directly. TELNET enables PCs and workstations to function as dumb terminals in sessions with hosts on inter-networks.


4. Groupware

These applications are used to automate the administration functions of a modern office for instance video conferencing and chatting. They facilitate the work of groups and improve on their productivity; they can be used to communicate, co-operate, coordinate, solve problems, compete, and negotiate among others.


  1. Video Conferencing

  2. Chatting

(B) Stand Alone Applications

These are applications that run on standalone computers (computers not connected to any other). In order to extend their activity, they are rebuilt to run on network environments e.g. word processors, spreadsheets, database management systems, presentations graphics, project management etc. They function even when the computer is offline.


 

TYPES OF NETWORK

A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications. A computer network can be categorized by their size. A computer network is mainly of three types:

1. LAN (Local Area Network)

2. MAN (Metropolitan Area Network)

3. WAN (Wide Area Network)


LAN (Local Area Network)

• Local Area Network is a group of computers connected to each other in a small area such as building, office.

• LAN is used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc.

• It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and ethernet cables.

• The data is transferred at an extremely faster rate in the Local Area Network.

• Local Area Network provides higher security.


MAN (Metropolitan Area Network)

• A metropolitan area network is a network that covers a larger geographic area by interconnecting a different LAN to form a larger network.

• Government agencies use MAN to connect to the citizens and private industries.

• In MAN, various LANs are connected to each other through a telephone exchange line.

• The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL, etc.

• It has a higher range than the Local Area Network (LAN).


Uses of Metropolitan Area Network:

• MAN is used in communication between the banks in a city.

• It can be used in an Airline Reservation.

• It can be used in a college within a city.

• It can also be used for communication in the military.


WAN (Wide Area Network)

• A Wide Area Network is a network that extends over a large geographical area such as states or countries.

• A Wide Area Network is quite a bigger network than the LAN.

• A Wide Area Network is not limited to a single location, but it spans over a large geographical area through a telephone line, fiber optic cable, or satellite links.

• The internet is one of the biggest WAN in the world.

• A Wide Area Network is widely used in the field of Business, government, and education.


Examples of Wide Area Network:

Mobile Broadband: A 4G network is widely used across a region or country.

Last-mile: A telecom company is used to provide internet services to the customers in hundreds of cities by connecting their home with fiber.

Private network: A bank provides a private network that connects the 44 offices. This network is made by using the telephone leased line provided by the telecom company.


Advantages of Wide Area Network:

Following are the advantages of the Wide Area Network:

  • Geographical area: A Wide Area Network provides a large geographical area. Suppose if the branch of our office is in a different city then we can connect with them through WAN. The internet provides a leased line through which we can connect with another branch.

  • Centralized data: In the case of the WAN network, data is centralized. Therefore, we do not need to buy the emails, files, or back up servers.

  • Get updated files: Software companies work on the live server. Therefore, the programmers get the updated files within seconds.

  • Exchange messages: In a WAN network, messages are transmitted fast. The web application like Facebook, WhatsApp, Skype allows you to communicate with friends.

  • Sharing of software and resources: In the WAN network, we can share the software and other resources like a hard drive, RAM.

  • Global business: We can do business over the internet globally.

  • High bandwidth: If we use the leased lines for our company then this gives the high bandwidth. The high bandwidth increases the data transfer rate which in turn increases the productivity of our company.


Disadvantages of Wide Area Network:

The following are the disadvantages of the Wide Area Network:

  • Security issue: A WAN network has more security issues as compared to LAN and MAN network as all the technologies are combined together that creates the security problem.

  • Needs Firewall & antivirus software: The data is transferred on the internet which can be changed or hacked by the hackers, so the firewall needs to be used. Some people can inject the virus in our system so antivirus is needed to protect from such a virus.

  • High Setup cost: An installation cost of the WAN network is high as it involves the purchasing of routers, switches.

  • Troubleshooting problems: It covers a large area so fixing the problem is difficult.


 

NETWORK CONFIGURATION HARDWARE

Network configuration is the process of setting a network’s controls, flow, and operation to support the network communication of an organization and/or network owner. This broad term incorporates multiple configuration and setup processes on network hardware, software, and other supporting devices and components.


Node

Any system or device connected to a network is also called a node. For example, if a network connects a file server, five computers, and two printers, there are eight nodes on the network. Each device on the network has a network address, such as a MAC address, which uniquely identifies each device. This helps keep track of where data is being transferred to and from on the network.

A node can also refer to a leaf, which is a folder or file on your hard disk. In physics, a node, or nodal point, is a point of minimum displacement or where multiple waves converge, creating a net amplitude of zero. In communication networks, a node is an active electronic device that is attached to a network and is capable of sending, receiving, or forwarding information over a communications channel.


Server

  • A computer or application, that provides a service to client software on other computers. Servers are used for web hosting and other web applications

  • A high-end computer with specific software that allows other computers to use its facilities for connection to data drives, email, printers, the Internet, or other services.

  • A computer or device on a network that manages network resources. For example, a file server is a computer and storage device dedicated to storing files. Any user on the network can store files on the server.


A server is a computer program or device that provides a service to another computer program and its user, also known as the client. In a data centre, the physical computer that a server program runs on is also frequently referred to as a server. That machine may be a dedicated server or it may be used for other purposes as well. In the client/server programming model, a server program awaits and fulfils requests from client programs, which may be running in the same or other computers. A given application in a computer may function as a client with requests for services from other programs and also as a server of requests from other programs.


Types of servers

Servers are often categorized in terms of their purpose. A few examples of the types of servers available are:

  • A Web server is a computer program that serves requested HTML pages or files. In this case, a Web browser acts as the client.

  • An application server is a program in a computer in a distributed network that provides the business logic for an application program.

  • A proxy server is software that acts as an intermediary between an endpoint device, such as a computer, and another server from which a user or client is requesting a service.

  • A mail server is an application that receives incoming e-mails from local users (people within the same domain) and remote senders and forwards outgoing e-mails for delivery.

  • A virtual server is a program running on a shared server that is configured in such a way that it seems to each user that they have complete control of a server.

  • A blade server is a server chassis housing multiple thin, modular electronic circuit boards, known as server blades. Each blade is a server in its own right, often dedicated to a single application.

  • A file server is a computer responsible for the central storage and management of data files so that other computers on the same network can access them.

  • A policy server is a security component of a policy-based network that provides authorization services and facilitates tracking and control of files.


 

CHANNEL

A Channel can take many forms, including ones suitable for storage which can communicate a message over time as well as space. A connection between initiating and terminating nodes of a circuit. A single path provided by a transmission medium via either physical separation, such as by multi-pair cable.


Types of Channel

Fiber optic “cable”

Coaxial Cable Types

Twisted Pair


Fiber optic cable

  • Speed: Fiber optic networks operate at high speeds – up into the gigabits

  • Bandwidth: large carrying capacity

  • Distance: Signals can be transmitted further without needing to be “refreshed” or strengthened.

  • Resistance: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables.

  • Maintenance: Fiber optic cables cost much less to maintain.


Coaxial Cable

Coaxial cable, or coax, is a cable consisting of an inner conductor, surrounded by a tubular insulating layer typically made from a flexible material, all of which is then surrounded by another conductive layer and then finally covered again with a thin insulating layer on the outside.

The Coaxial cable is used as a transmission line for radio frequency signals, in applications such as connecting radio transmitters and receivers with their antennas, carrying internet connections, and distributing cable television.


Twisted Pair

A type of cable made by intertwining two separate insulated wires together. There are two types of twisted pair: shielded and unshielded. Shielded Twisted Pair (STP) has a fine wire mesh surrounding the wires to protect the transmission;

Unshielded Twisted Pair (UTP) does not. Shielded cable is used in older telephone networks, networks, and data communications to reduce outside interference.


 

HUBS

A Hub is a networking device which receives a signal from the source, amplifies it and send it to multiple destinations or computers. If you ever some across subject 'Computer Networking' then you must hear this word. Sometimes, hubs are also called Ethernet Hub, Repeater Hub, Active Hub, and Network Hub. Basically, it is a networking device which is used multiple devices like Computers, Servers etc to each other and make them work as a single network segment. Hubs are used in 'Physical Layer' of OSI Model.


Types of Hub:

On the basis of its working methods, the Hubs can be divided into three types, given as:

  • Active Hub: As its name suggests, Active Hub is a hub which can amplify or regenerate the information signal. This type of bus has an advantage as it also amplifies the incoming signal as well as forward it to multiple devices. This Bus is also known as Multiport Repeater. It can upgrade the properties if incoming signal before sending them to a destination.

  • Passive Hub: Passive Hub works like a simple Bridge. It is used for just creating a connection between various devices. It does not have the ability to amplify or regenerate any incoming signal. It receives a signal and then forwards it to multiple devices.

  • Intelligent Hub: This is the third and last type of Bus. It can perform tasks of both Active and Passive buses. Also, it can perform some other tasks like Bridging and routing. It increases the speed and effectiveness of total network thus makes the performance of the whole network fast and efficient.


 

NETWORK INTERFACE CARD

A network interface card (NIC) is a hardware component without which a computer cannot be connected over a network. It is a circuit board installed in a computer that provides a dedicated network connection to the computer. It is also called a network interface controller, network adapter, or LAN adapter.


Purpose

• NIC allows both wired and wireless communications.

• NIC allows communications between computers connected via local area network (LAN) as well as communications over the large-scale network through Internet Protocol (IP).

• NIC is both a physical layer and a data link layer device, i.e. it provides the necessary hardware circuitry so that the physical layer processes and some data link layer processes can run on it.


Types of NIC Cards

NIC cards are of two types −

  • Internal Network Cards

  • External Network Cards


ARCNET

ARCNET is a widely-installed local area network (LAN) technology that uses a token-bus scheme for managing line sharing among the workstations and other devices connected to the LAN. The LAN server continuously circulates empty message frames on a bus (a line in which every message goes through every device on the line and a device uses only those with its address). When a device wants to send a message, it inserts a “token” (this can be as simple as setting a token bit to 1) in an empty frame in which it also inserts the message. When the destination device or LAN server reads the message, it resets the token to 0 so that the frame can be reused by any other device. The scheme is very efficient when traffic increases since all devices are afforded the same opportunity to use the shared network.

• ARCNET is a widely-installed local area network (LAN) technology that uses a token-bus scheme for managing line sharing among the workstations and other devices connected on the LAN

• ARCNET can use coaxial cable or fiber-optic lines.

• ARCNET is one of four major LAN technologies


Ethernet

Ethernet is the traditional technology for connecting wired local area networks (LANs), enabling devices to communicate with each other via a protocol — a set of rules or common network language. As a data-link layer protocol in the TCP/IP stack, Ethernet describes how network devices can format and transmit data packets so other devices on the same local or campus area network segment can recognize, receive and process them. An Ethernet cable is the physical, encased wiring over which the data travels. Any device accessing a geographically localized network using a cable — i.e., with a wired rather than wireless connection — likely uses Ethernet — whether in a home, school, or office setting. From businesses to gamers, diverse end users depend on the benefits of Ethernet connectivity, including reliability and security.

Compared to wireless LAN technology, Ethernet is typically less vulnerable to disruptions — whether from radio wave interference, physical barriers, or bandwidth hogs. It can also offer a greater degree of network security and control than wireless technology, as devices must connect using physical cabling — making it difficult for outsiders to access network data or hijack bandwidth for unsanctioned devices.


How Ethernet works

The Institute of Electrical and Electronics Engineers Inc. (IEEE) specifies in the family of standards called IEEE 802.3 that the Ethernet protocol touches both Layer 1 — the physical layer — and Layer 2 — the data link layer — on the OSI network protocol model. Ethernet defines two units of transmission: packet and frame. The frame includes not just the payload of data being transmitted, but also:

• the physical media access control (MAC) addresses of both the sender and receiver;

• VLAN tagging and quality of service information; and

• error correction information to detect transmission problems.


Each frame is wrapped in a packet that contains several bytes of information to establish the connection and mark where the frame starts. Engineers at Xerox first developed Ethernet in the 1970s. Ethernet initially ran over coaxial cables, while a typical Ethernet LAN today uses special grades of twisted pair cables or fiber optic cabling. Early Ethernet connected multiple devices into network segments through hubs — Layer 1 devices responsible for transporting network data — using either a daisy chain or star topology.


If two devices that share a hub try to transmit data at the same time, however, the packets can collide and create connectivity problems. To alleviate these digital traffic jams, the IEEE developed the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, which allows devices to check whether a given line is in use before initiating new transmissions.


Later, Ethernet hubs largely gave way to network switches, their more sophisticated and modern counterparts. Because a hub cannot discriminate between points on a network segment, it can’t send data directly from point A to point B. Instead, whenever a network device sends a transmission via an input port, the hub copies the data and distributes it to all the available output ports.


 

NETWORK SOFTWARE

Network software encompasses a broad range of software used for the design, implementation, and operation and monitoring of computer networks. Traditional networks were hardware-based with software embedded. With the advent of Software-Defined Networking (SDN), the software is separated from the hardware thus making it more adaptable to the ever-changing nature of the computer network.


Functions of Network Software

1. Helps to set up and install computer networks

2. Enables users to have access to network resources in a seamless manner

3. Allows administrations to add or remove users from the network

4. Helps to define locations of data storage and allows users to access that data

5. Helps administrators and security system to protect the network from data breaches, unauthorized access and attacks on a network

6. Enables network virtualizations


SDN Framework

The Software-Defined Networking framework has three layers as depicted in the following diagram:

  • Application Layer: SDN applications reside in the Application Layer. The applications convey their needs for resources and services to the control layer through APIs.

  • Control Layer: The Network Control Software, bundled into the Network Operating System, lies in this layer. It provides an abstract view of the underlying network infrastructure. It receives the requirements of the SDN applications and relays them to the network components.

  • Infrastructure Layer: Also called the Data Plane Layer, this layer contains the actual network components. The network devices reside in this layer that shows their network capabilities through the Control to data-Plane Interface


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