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NETWORK BASICS

Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  


Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…

BASIC NETWORK

BASIC NETWORK
A network is any collection of independent computers that communicate with one another over a shared network medium. A computer network is a collection of two or more connected computers. When these computers are joined in a network, people can share files and peripherals such as modems, printers, tape backup drives, or CD-ROM drives. When networks at multiple locations are connected using services available from phone companies, people can send e-mail, share links to the global Internet, or conduct video conferences in real time with other remote users. Computer networking becomes increasingly more important. 

Every network includes

  • At least two computers Server or Client workstation. 
  • Networking Interface Card's (NIC) 
  • A connection medium, usually a wire or cable, although wireless communication between      Networked computers and peripherals is also possible. 
  • Network Operating system software, such as Microsoft Windows NT or 2003, 2008, 2012 Nov-ell Net-Ware, UNIX and Linux. 
Benefits of networking

There are lots of advantages from build up a network, but the three big facts are-  File Sharing  Through sharing files you can view, modify, and copy files stored on a different computer on the network just as easily as if they were stored on your computer.  Resource Sharing  Resources such as printers, fax machines, Storage Devices (HDD, FDD and CD Drives), Webcam, Scanners, Modem and many more devices can be shared. Program Sharing  Just as you can share files on a network, you can often also share program on a network. For example, if you have the right type of software license, you can have a shared copy of Microsoft Office, or some other program, and keep it on the network server, from where it is also run. 

Classification of network 

As we are very much familiar with the term “network”, it has classified into three parts which are discussed below. 
Intranet 

An intranet is basically a network that is local to a company. In other words, users from within this company can find all of their resources without having to go outside of the company. An intranet can include LANs, private WANs and MANs, 

Extra-net

An extra-net is an extended intranet, where certain internal services are made available to known external users or external business partners at remote locations. 

➣ Internet An internet is used when unknown external users need to access internal resources in your network. In other words, your company might have a web site that sells various products, and you want any external user to be able to access this service. 

Categories of network There are many ways in which different networks can be classified, such as their size, capabilities and the geographical distance they cover. A network is simply a group of two or more computer systems linked together in some way so that they can share data between them. Different types of networks provide different services, and require different things to work properly. In term of network categorization network are categorized into two types i)peer to peer network ii)server based network. 

i)peer to peer network: A peer-to-peer (P2P) network is group of computers, each of which acts as a node for sharing files within the group. Instead of having a central server to act as a shared drive, each computer acts as the server for the files stored upon it. When a P2P network is established over the Internet, a central server can be used to index files, or a distributed network can be established where the sharing of files is split between all the users in the network that are storing a given file. In the most basic sense, a peer-to-peer network is a simple network where each computer doubles as a node and a server for the files it exclusively holds. These are the same as a home network or office network. However, when P2P networks are established over the internet, the size of the network and the files available allow huge amounts of data to be shared.  

ii) Server based network: In a server-based network, the server is the central location where users share and access network resources this dedicated computer controls the level of access that users have to shared resources. Shared data is in one location, making it easy to back up critical business information. Each computer that connects to the network is called a client computer. In a server-based network, users have one user account and password to log on to the server and to access shared resources. Server operating systems are designed to handle the load when multiple client computers access server-based resources. 

Most network types are known as different types of ‘area’ networks – this is due to the history of networks, and dates back to the time when computer networks were defined by their literal scale. This is no longer always the case due to new technology. Some of the most common types of network you are likely to encounter are detailed here below: 

LAN (Local Area Network) 

A Local Area Network is a privately owned computer network covering a small Networks geographical area, like a home, office, or groups of buildings e.g. a school Network. A LAN is used to connect the computers and other network devices so that the devices can communicate with each other to share the resources. The resources to be shared can be a hardware device like printer, software like an application program or data. The size of LAN is usually small. The various devices in LAN are connected to central devices called Hub or Switch using a cable. Now-a-days LANs are being installed using wireless technologies. Such a system makes use of access point or APs to transmit and receive data. One of the computers in a network can become a server serving all the remaining computers called Clients. For example, a library will have a wired or wireless LAN Network for users to interconnect local networking devices e.g., printers and servers to connect to the internet. LAN offers high speed communication of data rates of 4 to 16 megabits per second (Mbps). IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s. LANs Network may have connections with other LANs Network via leased lines, leased services. WLANs (Wireless Local Area Networks or sometimes referred to as LAWN, for local area wireless network) provide wireless network communication over short distances using radio or infrared signals instead of traditional network cabling. WLANs (Wireless Local Area Networks) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection. 

Types of LAN 

There are basically two types of Local Area Networks namely: ARC-net and Ethernet.

o ARC-NET (Attached Resource Computer Network) is one of the oldest, simplest, and least expensive types of Local-Area Network protocol, similar in purpose to Ethernet or Token Ring. ARC-NET was the first widely available networking system for microcomputers and became popular in the 1980s for office automation tasks. ARC-net was introduced by Data point Corporation in 1977.  A special advantage of ARC-NET is that it permits various types of transmission media twisted-pair wire, coaxial cable, and fiber optic cable to be mixed on the same network. The specification is ANSI 878.1. It can have up to 255 nodes per network. A new specification, called ARCnet Plus, will support data rates of 20 Mbps 

o Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired local area network technologies. Ethernet uses a bus or star topology Network and supports data transfer rates of 10 Mbps. Ethernet Network uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards. A newer version of Ethernet Network, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second. Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet Network was invented by engineer Robert Metcalfe. 

MAN (Metropolitan Area Networks)

MAN stands for Metropolitan Area Networks is one of a number of types of networks. A MAN is a relatively new class of network. MAN is larger than a local area network and as its name implies, covers the area of a single city. MANs rarely extend beyond 100 KM and frequently comprise a combination of different hardware and transmission media. It can be single network such as a cable TV network, or it is a means of connecting a number of LANs into a larger network so that resources can be shared LAN to LAN as well as device to device. A MAN can be created as a single network such as Cable TV Network, covering the entire city or a group of several Local Area Networks (LANs). It this way resource can be shared from LAN to LAN and from computer to computer also. MANs are usually owned by large organizations to interconnect its various branches across a city. MAN is based on IEEE 802.6 standard known as DQDB (Distributed Queue Dual Bus). DQDB uses two unidirectional cables (buses) and all the computers are connected to these two buses. Each bus has a specialized device that initiates the transmission activity. This device is called head end. Data that is to be sent to the computer on the right hand side of the sender is transmitted on upper bus. Data that is to be sent to the left hand side of the sender is transmitted on lower bus. 

The two most important components of MANs are security and standardization. Security is important because information is being shared between dissimilar systems. Standardization is necessary to ensure reliable data communication. A MAN usually interconnects a number of local area networks using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks and the Internet. The Metropolitan Area Networks (MAN) protocols are mostly at the data link level (layer 2 in the OSI model), which are defined by IEEE, ITU-T, etc. 

WAN (Wide Area Networks)

A wide area network (WAN) is a telecommunication network. A wide area network is simply a LAN of LANs or Network of Networks. WANs connect LANs that may be on opposite sides of a building, across the country or around the world. WANS are characterized by the slowest data communication rates and the largest distances. WANs can be of two types: an enterprise WAN and Global WAN. Computers connected to a Wide Area Networks are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet. Some segments of the Internet, like VPN based extra-nets, are also WANs in themselves. Finally, many WANs are corporate or research networks that utilize leased lines. Numerous WANs have been constructed, including public packet networks, large corporate networks, military networks, banking networks, stock brokerage networks, and airline reservation networks. 

A WLAN typically extends an existing wired local area network. WLANs (Wireless Local Area Networks) are built by attaching a device called the access point (AP) to the edge of the wired network. Clients communicate with the AP using a wireless network adapter similar in function to a traditional Ethernet adapter. Network security remains an important issue for WLANs (Wireless Local Area Networks). Random wireless clients must usually be prohibited from joining the WLAN. Technologies like WEP raise the level of security on wireless networks to rival that of traditional wired networks.  

Storage Area Network (SAN)

A storage area network (SAN) is a type of local area network (LAN) is a high-speed special-purpose network. A SAN typically supports data storage, retrieval and replication on business networks using high-end servers, multiple disk arrays and Fiber Channel interconnection technology. Storage Area Networks (SANs) technology is similar but distinct from network attached storage (NAS) technology. While SANs traditionally employ low-level network protocols for transferring disk blocks, a NAS device typically works over TCP/IP and can be integrated fairly easily into home computer networks. The term SAN can sometimes refer to system area networks instead of a storage area network. System area networks are clusters of high performance computers used for distributed processing applications requiring fast local network performance. Storage area networks, on the other, are designed specifically for data management. 

Campus Area Network (CAN)

A campus area networks (CANs) is a computer network interconnecting a few local area networks (LANs) within a university campus or corporate campus Network. Campus area network may link a variety of campus buildings. A campus area network is larger than a local area network but smaller than a metropolitan area network (MAN) or wide area network (WAN). CAN also stand for corporate area network.  

Personal Area Network (PAN)

A personal area network is a computer network organized around an individual person. Personal area networks typically involve a mobile computer, Personal area networks can be constructed with cables or wirelessly. Personal area networks generally cover a Network range of less than 10 meters (about 30 feet). 

Understanding the Differences between Internet Connections

When determining which type of Internet connection is right for you or your family, it’s important to understand the distinction between each connection. In today’s age, there are numerous ways to connect laptops, desktops, mobile phones, gaming consoles, e-readers and tablets to the Internet. Some of the most widely used Internet connections are described below. 

Wireless

Radio frequency bands are used in place of telephone or cable networks. One of the greatest advantages of wireless Internet connections is the “always-on” connection that can be accessed from any location that falls within network coverage. Wireless connections are made possible through the use of a modem, which picks up Internet signals and sends them to other devices. 
  
Mobile

Many cell phone and smartphone providers offer voice plans with Internet access. Mobile Internet connections provide good speeds and allow you to access the Internet on the go. 

Hotspots

Hotspots are sites that offer Internet access over a wireless local area network (WLAN) by way of a router that then connects to an Internet service provider. Hotspots utilize Wi-Fi technology, which allows electronic devices to connect to the Internet or exchange data wirelessly through radio waves. Hotspots can be phone-based or free-standing, commercial or free to the public. 
  
Dial-Up

Dial-up connections require users to link their phone line to a computer in order to access the Internet. This particular type of connection—also referred to as analog—does not permit users to make or receive phone calls through their home phone service while using the Internet. 

Broadband

This high-speed Internet connection is provided through either cable or telephone companies. One of the fastest options available, broadband Internet uses multiple data channels to send large quantities of information. The term broadband is shorthand for broad bandwidth. Broadband Internet connections such as DSL and cable are considered high-bandwidth connections. Although many DSL connections can be considered broadband, not all broadband connections are DSL. 

DSL 

DSL, which stands for Digital Subscriber Line, uses existing 2-wire copper telephone line connected to one’s home so service is delivered at the same time as landline telephone service. Customers can still place calls while surfing the Internet. 

Cable

Cable Internet connection is a form of broadband access. Through use of a cable modem, users can access the Internet over cable TV lines. Cable modems can provide extremely fast access to the Internet. 

Satellite

In certain areas where broadband connection is not yet offered, a satellite Internet option may be available. Similar to wireless access, satellite connection utilizes a modem. 

ISDN 

ISDN (Integrated Services Digital Network) allows users to send data, voice and video content over digital telephone lines or standard telephone wires. The installation of an ISDN adapter is required at both ends of the transmission—on the part of the user as well as the Internet access provider. 

There are quite a few other Internet connection options available, including T-1 lines, T-3 lines, OC (Optical Carrier) and other DSL technologies. 

Network protocols & types

When two humans converse, they may have to use the same language but they generally understand each other without having to adhere to rigid rules of grammar or formal language frameworks. Computers, on the other hand, have to have everything explicitly defined and structured. If computers wish to communicate with one another, they have to know in advance exactly how information is to be exchanged and precisely what the format will be. Therefore, standard methods of transmitting and processing various kinds of information are used and these methods are called "protocols". Protocols are established by international agreement and ensure that computers everywhere can talk to one another. There are a variety of protocols for different kinds of information and functions. In this segment we will discuss some of the common protocols. 

TCP TCP (Transmission Control Protocol) and IP (Internet Protocol) are two different procedures that are often linked together. The linking of several protocols is common since the functions of different protocols can be complementary so that together they carry out some complete task. The combination of several protocols to carry out a particular task is often called a "stack" because it has layers of operations. In fact, the term "TCP/IP" is normally used to refer to a whole suite of protocols, each with different functions. This suite of protocols is what carries out the basic operations of the Web. TCP/IP is also used on many local area networks. 
IP Internet Protocol (IP) is the method used to route information to the proper address. Every computer on the Internet has to have its own unique address known as the IP address. Every packet sent will contain an IP address showing where it is supposed to go. A packet may go through a number of computer routers before arriving at its final destination and IP controls the process of getting everything to the designated computer. Note that IP does not make physical connections between computers but relies on TCP for this function. IP is also used in conjunction with other protocols that create connections. IP address is also known as an "IP number" or simply an "IP," this is a code made up of numbers separated by three dots that identifies a particular computer on the Internet. Every computer, whether it be a Web server or the computer you're using right now, requires an IP address to connect to the Internet. IP addresses consist of four sets of numbers from 0 to 255, separated by three dots. For example "66.72.98.236" or "216.239.115.148". Your Internet Service Provider (ISP), will assign you either a static IP address (which is always the same) or a dynamic IP address, (which changes every time you log on).IP address is classified in two types IPv4 (32 bit) & IPv6 (128 bit). 
Hypertext Transfer Protocol Web pages are constructed according to a standard method called Hypertext Markup Language (HTML). An HTML page is transmitted over the Web in a standard way and format known as Hypertext Transfer Protocol (HTTP). This protocol uses TCP/IP to manage the Web transmission. A related protocol is "Hypertext Transfer Protocol over Secure Socket Layer" (HTTPS), first introduced by Netscape. It provides for the transmission in encrypted form to provide security for sensitive data. A Web page using this protocol will have https: at the front of its URL. 

➣ File Transfer Protocol File Transfer Protocol (FTP) lives up to its name and provides a method for copying files over a network from one computer to another. More generally, it provides for some simple file management on the contents of a remote computer. It is an old protocol and is used less than it was before the World Wide Web came along. Today, Its primary use is uploading files to a Web site. It can also be used for downloading from the Web but, more often than not, downloading is done via HTTP.  
POP3 : Post Office Protocol version 3 (POP3) is a standard mail protocol used to receive emails from a remote server to a local email client. POP3 allows you to download email messages on your local computer and read them even when you are offline. Note, that when you use POP3 to connect to your email account, messages are downloaded locally and removed from the servers.  
IMAP  The Internet Message Access Protocol (IMAP) is a mail protocol used for accessing email on a remote web server from a local client. IMAP and POP3 are the two most commonly used Internet mail protocols for retrieving emails. Both protocols are supported by all modern email clients and web servers. 
➣ SMTP SMTP (Simple Mail Transfer Protocol) is a TCP/IP protocol used in sending and receiving email. However, since it is limited in its ability to queue messages at the receiving end, it is usually used with one of two other protocols, POP3 or IMAP that let the user save messages in a server mailbox and download them periodically from the server.  

Topology

Computers in a network have to be connected in some logical manner. The layout pattern of the interconnections between computers in a network is called network topology. You can think of topology as the virtual shape or structure of the network. Network topology is also referred to as 'network architecture. Devices on the network are referred to as 'nodes.' The most common nodes are computers and peripheral devices. Network topology is illustrated by showing these nodes and their connections using cables. There are a number of different types of network topologies, including point-to-point, bus, star, ring, mesh, tree and hybrid. Let's review these main types. 

Point-to-Point topology

Point-to-point topology is the simplest of all the network topologies. The network consists of a direct link between two computers. This is faster and more reliable than other types of connections since there is a direct connection. The disadvantage is that it can only be used for small areas where computers are in close proximity.  

Bus Topology

Bus topology uses one main cable to which all nodes are directly connected. The main cable acts as a backbone for the network. One of the computers in the network typically acts as the computer server.  

Advantages of bus topology  

  • It works well when you have a small network. 
  • Easiest network topology for connecting computers or peripherals in a linear fashion. 
  • Requires less cable length than a star topology. 

Disadvantages of bus topology

  • Difficult to identify the problems if the whole network goes down. 
  • Not great for large networks. 
  • Terminators are required for both ends of the main cable. 
  • Additional devices slow the network down. 
  • If a main cable is damaged, the network fails or splits into two. 

Star Topology

In star topology, each computer is connected to a central hub using a point-to-point connection. The central hub can be a computer server that manages the network, or it can be a much simpler device that only makes the connections between computers over the network possible. Star topology is very popular because the startup costs are low. It is also easy to add new nodes to the network. The network is robust in the sense that if one connection between a computer and the hub fails, the other connections remain intact. If the central hub fails, however, the entire network goes down. It also requires more cable than bus topology and is, therefore, more expensive.  

Advantages of star topology

  • Centralized management of the network, through the use of the central computer, hub, or switch. 
  • Easy to add another computer to the network. 
  • If one computer on the network fails, the rest of the network continues to function normally. 

Disadvantages of star topology

  • Can have a higher cost to implement, especially when using a switch or router as the central network device. 
  • The central network device determines the performance and number of nodes the network can handle. 
  • If the central computer, hub, or switch fails, the entire network goes down and all computers are disconnected from the network. 

Ring Topology

In ring topology, the computers in the network are connected in a circular fashion, and the data travels in one direction. Each computer is directly connected to the next computer, forming a single pathway for signals through the network. This type of network is easy to install and manage. If there's a problem in the network, it is easy to pinpoint which connection is defective. It is also good for handling high-volume traffic over long distances since every computer can act as a booster of the signal. On the downside, adding computers to this type of network is more cumbersome, and if one single computer fails, the entire network goes down. 

Advantages of ring topology

  • All data flows in one direction, reducing the chance of packet collisions. 
  • A network server is not needed to control network connectivity between each workstation. 
  • Data can transfer between workstations at high speeds. 
  • Additional workstations can be added without impacting performance of the network. 

Disadvantages of ring topology

  • All data being transferred over the network must pass through each workstation on the network, which can make it slower than a star topology. 
  • The entire network will be impacted if one workstation shuts down. 
  • The hardware needed to connect each workstation to the network is more expensive than Ethernet cards and hubs/switches. 

Mesh Topology

In mesh topology, every node has a direct point-to-point connection to every other node. Because all connections are direct, the network can handle very high-volume traffic. It is also robust because if one connection fails, the others remain intact. Security is also high since data travels along a dedicated connection.  Advantages of MESH topology 

  • A broken node won’t distract the transmission of data in a mesh network. Each node is connected to several other nodes which make it easier to relay data. A broken device will be ignored by the signals and will then find a new one that is connected with the node.  
  • Additional devices in a mesh topology will not affect its network connection. Hence it will improve the traffic in the network. Mesh topology makes a large data center that simulates useful information to its nodes. 
A mesh topology can handle high amount of network traffic since every additional device into the network is considered a node. Interconnected devices can simultaneously transfer data smoothly and will not complicate the network connection. 

Disadvantages of MESH topology

  • Maintaining mesh networks can be very hard to manage. It requires continuous supervision because of the redundancy present in the network. Skilled network administrators will find it easy to manage this kind of topology. 
  • Due to the fact that building this topology requires a lot of devices it will need a lot of capital to invest in. It may be expensive but the service it provides you will definitely give back the invested capital. 
Tree Topology

Alternatively referred to as a star bus topology, tree topology is one of the most common network setups that is similar to a bus topology and a star topology. A tree topology connects one star network to other star networks. Below is a visual example of a tree topology, with a simple computer set up on a network using the star topology, connected to another network using the star topology. 

Advantages of Tree Topology

  • It is an extension of Star and bus Topologies, so in networks where these topologies can't be implemented individually for reasons related to scalability, tree topology is the best alternative. 
  • Expansion of Network is possible and easy. 
  • Here, we divide the whole network into segments (star networks), which can be easily managed and maintained.  
  • Error detection and correction is easy. 
  • Each segment is provided with dedicated point-to-point wiring to the central hub. 
  • If one segment is damaged, other segments are not affected. 

Disadvantages of Tree Topology

  •  Because of its basic structure, tree topology, relies heavily on the main bus cable, if it breaks whole network is crippled. 
  • As more and more nodes and segments are added, the maintenance becomes difficult. 
  •  Scalability of the network depends on the type of cable used. 
Hybrid Topology

Hybrid network topology is a combination of two or more different basic network topologies. For example, it can be star-ring, star-bus topologies, etc. It must be certainly different topologies, because for example two star topologies form the star topology. The resulting hybrid topology has the features and limitations of its components. 

Advantages of Hybrid Network Topology

  • Unlike other networks, fault detection and troubleshooting is easy in this type of topology. The part in which fault is detected can be isolated from the rest of network and required corrective measures can be taken, WITHOUT affecting the functioning of rest of the network.  
  • Hybrid Network can be designed according to the requirements of the organization and by optimizing the available resources. Special care can be given to nodes where traffic is high as well as where chances of fault are high.  
Disadvantages of Hybrid Network Topology

  • One of the biggest drawback of hybrid topology is its design. It’s not easy to design this type of architecture and it’s a tough job for designers. Configuration and installation process needs to be very efficient. 
  • As hybrid architectures are usually larger in scale, they require a lot of cables, cooling systems, sophisticate network devices, etc. 
Network Devices

Now we will discuss about the some very important networking devices such as Network Interface Card (NIC) adapters, routers, hubs, switches, modems. So let’s have a look. 

HUB

Hub is one of the basic icons of networking devices which works at physical layer and hence connect networking devices physically together. Hubs are fundamentally used in networks that use twisted pair cabling to connect devices. They are designed to transmit the packets to the other appended devices without altering any of the transmitted packets received. They act as pathways to direct electrical signals to travel along. They transmit the information regardless of the fact if data packet is destined for the device connected or not. Hub falls in two categories: Active Hub & Passive Hub 
  •  Active Hub They are smarter than the passive hubs. They not only provide the path for the data signals in fact they regenerate, concentrate and strengthen the signals before sending them to their destinations. Active hubs are also termed as ‘repeaters’. 
  • Passive Hub: They are more like point contact for the wires to build in the physical network. They have nothing to do with modifying the signals. 
Switch 

The working of a networking Hub is not much different from a Switch. The advancement in Switches is that they have switching table in them which makes a network more secure and faster. The difference is between the technology and technique through which data is sent. A Switch has the ability to store the MAC address of computers so the data will only be sent to the required point instead of sending it to every point. Talking about network devices Router is one of the very basic networking components. A router has software called routing table and the source and destination addresses are stored in the routing table.  

Bridge

A bridge is a computer networking device that builds the connection with the other bridge networks which use the same protocol. It works at the Data Link layer of the OSI Model and connects the different networks together and develops communication between them. It connects two local-area networks; two physical LANs into larger logical LAN or two segments of the same LAN that use the same protocol.  

Router 

A Router is responsible for connecting two physical and logically different networks. Routers are connected in a series in a WAN or a LAN and they are called Hop in the series. The working of Router is very simple a Router in a LAN or a WAN finds the IP address of the next hop (next router) and the data is sent toward and so on. D-Link, TP-Link, Link-Sys, Cisco and Aztec are some well-known Router manufacturing companies. Routers are of two Basic types DSL routers and Wi-Fi routers. Nearly every ISP, banks, organizations, universities, End-users use Routers to connect to internet or interconnect in to their virtual private networks over the internet.  

NIC 

Network cards also known as Network Interface Cards (NICs) are hardware devices that connect a computer with the network. They are installed on the mother board. They are responsible for developing a physical connection between the network and the computer. Computer data is translated into electrical signals send to the network via Network Interface Cards.  

MODEM

Modem is a device which converts the computer-generated digital signals of a computer into analog signals to enable their travelling via phone lines. The ‘modulatordemodulator’ or modem can be used as a dial up for LAN or to connect to an ISP. Modems can be both external, as in the device which connects to the USB or the serial port of a computer, or proprietary devices for handheld gadgets and other devices, as well as internal; in the form of add-in expansion cards for computers and PCMCIA cards for laptops.  

Network Cable

Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. 

The following sections discuss the types of cables used in networks and other related topics. 

  • Twisted pair cable 
  • Coaxial Cable 
  • Fiber Optic Cable 

Twisted pair Cable

Twisted pair eventually emerged during the 1990s as the leading cabling standard for Ethernet, starting with 10 Mbps (10BASE-T, also known as Category 3 or Cat3), later followed by improved versions for 100 Mbps (100BASE-TX, Cat5 and Cat5e) and successively higher speeds up to 10 Gbps (10GBASE-T). Ethernet twisted pair cables contain up to 8 wires wound together in pairs to minimize electromagnetic interference. Two primary types of twisted pair cable industry standards are defined Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP). Modern Ethernet cables use UTP wiring due to its lower cost, while STP cabling can be found in some other types of networks such as FDDI. 

Coaxial Cable

First invented in the 1880s, "coax" was best known as the kind of cable that connected television sets to home antennas. Coaxial cable is also a standard for 10 Mbps Ethernet cables. When 10 Mbps Ethernet was most popular, during the 1980s and early 1990s, networks typically utilized one of two kinds of coax cable thinnet (10BASE2 standard) or thick net (10BASE5). These cables consist of an inner copper wire of 

varying thickness surrounded by insulation and other shielding. Their stiffness caused network administrators difficulty in installing and maintaining thinnet and thick net. 

Fiber Optic cable

Instead of insulated metal wires transmitting electrical signals, fiber optic network cables work using strands of glass and pulses of light. These network cables are bendable despite being made of glass. They have proven especially useful in wide area network (WANs) installations where long distance underground or outdoor cable runs are required and also in office buildings where a high volume of communication traffic is common. Two primary types of fiber optic cable industry standards are defined single-mode (100BaseBX standard) and multi-mode (100BaseSX standard). Long-distance telecommunications networks more commonly use single-mode for its relatively higher bandwidth capacity, while local networks typically use multi-mode instead due to its lower cost. 

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Create Different Scenarios 
Note: You can simply type in a different revenue and Cost into cell B2 and B3 respectively to see the corresponding result of a scenario in cell B4. However, what-if analysis enables you to easily compare the results of different scenarios.  
I. On the Data tab, click What-If Analysis and select Scenario Manager from the list. The Scenario Manager Dialog box appears  II. Add a scenario by clicking on Add.  III. Type a name (e.g. “First Case”), select cell B2 and B3 (represents “Revenue” and “…

PROFESSIONAL ENGLISH

Asking For and Giving Opinions on Likes and Dislikes

Words Meaning Sample Sentence Opinion A statement or judgment formed about some matter. Bhoomika gave her final opinion on the company’s matter. Dialogue A conversation between two or more people. Her dialogue stated her opinion about the company’s matter. Expression The action of making known one’s thought or feelings. Her expression was sad at the meeting. Frank An open, honest, and direct speech or writing Bhoomika is very frank with her friends. Recover Return to normal state of health, mind or strength. The company’s economic crisis will be recovered soon. Turmoil A state of great disturbance. The company is facing financial turmoil. Economics The branch of knowledge concerned with the production, consumption, and transfer of wealth. Bhoomika studied Economics at the State University. Betrayed Expose to danger by treacherously giving information to an enemy.

DAILY LIFE VOCABULARY

Apology Etiquette and Office Vocabulary 

Chapter Vocabulary

Word Meaning Sample Sentence Stressed A state of any mental or emotional tension. Ram seems much stressed after his poor exam. Launch An act of instance of starting something. The government launched a new scheme for the poor people. Error A mistake Ravi found a grammatical error in his new grammar book. Scold Blaming someone for any wrong doing Bhuvan scolded his employees for their poor performance. Accuse Claiming that someone has done something wrong. Bharati accuses her friend Chaya for stealing her necklace. Fair Good and honest Ravi got promoted for doing a fair job. Ashamed Embarrassed or guilty because of one’s action. <