इस ब्लॉग्स को सृजन करने में आप सभी से सादर सुझाव आमंत्रित हैं , कृपया अपने सुझाव और प्रविष्टियाँ प्रेषित करे , इसका संपूर्ण कार्य क्षेत्र विश्व ज्ञान समुदाय हैं , जो सभी प्रतियोगियों के कॅरिअर निर्माण महत्त्वपूर्ण योगदान देगा ,आप अपने सुझाव इस मेल पत्ते पर भेज सकते हैं - chandrashekhar.malav@yahoo.com
Networking: concept, need and advantages. types of networks, network topologies, wireless networking.
P- 04. Information Communication Technology for Libraries *
By :Usha Munshi,Paper Coordinator
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Definition of a computer network:
A computer network is an interconnected collection of autonomous computers where interconnected means that the computers can exchange information and autonomous means that no computer can start, stop or control another computer connected to the network.
A computer network consists of two or more computing devices that are connected with an aim of sharing the components, resources and stored information of your network, as shown in Figure 1. At a conceptual level, data network consists of nodes (any computer or digital device using the network) andlinks (the physical connections either wired or wireless) that carry messages between nodes [1].
Figure 1: Computer Network
Basic Components of a Computer Network
Most of the components of a computer network can be classified into one of the categories below [4].
- Node (or a workstation): A Computer with Network Interface Card which can act as a Sender and/or Receiver in a network.
2. Transmission Media: It carries electronic signals from one computer to another. It could be a wired (using coaxial cable, twisted pair cable, fibre optical cable etc) or it could be wireless through radio signals.
3. Network Operating Systems and Device Drivers: It is the program that manages the resources and services of a network. It also provides network security including permissions.
4. Protocols: Network Protocols are the languages that allow computers to communicate with each other. The protocols and data are transmitted through packets. Some of the important standard protocols are AppleTalk, Ethernet, NetBEUI, and TCP/IP
Need and advantages of a computer network
The following are some of the important benefits of a computer network [2,6,7].
File sharing: A computer network helps its users to share data files.
Hardware sharing: Users of the network can share devices such as printers, scanners, CD-ROM drives, hard drives etc. This will significantly reduce the cost of purchasing hardware.
Application sharing: Applications can be shared over the network. It inspires the implementation of client/server applications
User communication: Networks helps the users to communicate using e-mail, newsgroups, and video conferencing etc.
Network gaming: A lot of network games are available these days, which allow multi-users to play from different locations.
Remote access: Users are allowed to access the files, data, and messages even when they're not in the office. This access can even be given to mobile handheld devices. It saves the hassle of carrying a storage device every time data needs to be tranpsorted.
Data protection: Computer back up is one of the important and regular tasks these days. A network makes it easier to back up all of your company's data on an offsite server.
Workgroup communicating: Many users can work on a document or project concurrently.
Centralized software management: It allows the users to share software within the network easily. Networkable versions of software are available at considerable cost as compared to individually licensed version of the same software. Therefore large companies can reduce the cost of buying software by networking their computers.
Speed: Sharing and transferring files within networks is very rapid. This saves time while maintaining the integrity of files.
Increased Storage capacity: As there is more than one computer on a network which can share resources like hard disk so the issue of storage capacity gets resolved to a large extent. A standalone computer might fall short of storage capacity but when they on a network they can share each other’s storage capacity.
Performance Enhancement and Balancing: Under some circumstances, a network can be used to enhance the overall performance of some applications by distributing the computation tasks to various computers on the network.
Types of networks
LANs (Local Area Networks)
A network is any collection of independent computers that communicate with one another over a shared network medium. LANs are networks usually confined to a geographic area, such as a single building or a college campus. Data transfer speeds over a local area network can reach up to 10 Mbps (such as for an Ethernetnetwork) and 1 Gbps (as with FDDI or GigabitEthernet) [3].
A local area network can reach as many as 100, or even 1000, users. An example LAN is shown in figure 2.
A local area network can reach as many as 100, or even 1000, users. An example LAN is shown in figure 2.
Figure 2: Local Area Network (LAN)
On the basis of services, LAN works in two different operating modes:
- In a peer-to-peer (P2P) network, in which communication is carried out from one computer to another, without a central computer (as shown in figure 3), and where each computer has the same role and no computer occupies a privileged position. Each computer stores its own files and runs its own applications. Such networks are good choices for needs of small organizations where the users are allocated in the same general area, security is not an issue and the organization and the network will have limited growth within the foreseeable future [4,5].
- In a client/server environment, in which a central computer provides network services to users (as shown in figure 3). The term Client/server refers to the concept of sharing the work involved in processing data between the client computer and the most powerful server computer. It is the most efficient way to provide Databases and management of applications such as Spreadsheets, Accounting, Communications and Document management, Network management, Centralized file storage [4,5].
Figure 3: Client/Server and Peer to Peer networks
WANs (Wide Area Networks)
Wide Area Networks, are used across the globe, many networks connect with one another across continents to create one giant Wide Area Network (as shown in figure 4). It combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines (both synchronous and asynchronous), satellite links, and data packet carrier services. The speed available on a WAN varies depending on the cost of the connections (which increases with distance) and may be low. WANs operate using routers (a device that forwards data packets between computer networks on the basis of the address information in the packet to determine its ultimate destination), which can choose the most appropriate path for data to take to reach a network node. It spans large geographical area generally across cities or countries. [8] The largest example of a Wide Area Network is the internet itself, which connects all users to the information and data that is available on the internet.
Figure .4:Wide Area Network (WAN)
In order to transmit over a large distance, one of the important options is through geo-satellite. It leads to the transmission without wire over a large distance. You may use underwater fibre optic cables for large distance communication.
Metropolitan Area Networks MAN
Metropolitan Area Networks are not commonly used these days; they are used to create communication between systems in an entire city (as shown in figure 5). Hence a Metropolitan Area Network area falls between the sizes Local Area Networks, and Wide Area Networks. Metropolitan Area Networks are used by city specific businesses such as the New York Times in the state of New York.
Figure 5:
Types of networks continue
Internet
The Internet is a system of linked networks that are worldwide in scope and facilitate data communication services such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups. With the meteoric rise in demand for connectivity, the Internet has become a communications highway for millions of users. The Internet was initially restricted to military and academic institutions, but now it is a full-fledged conduit for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet.
Intranet
With the advancements made in browser-based software for the Internet, many private organizations are implementing intranets. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees.
VPN (Virtual Private Network)
VPN uses a technique known as tunneling to transfer data securely on the Internet to a remote access server on your workplace network. Using a VPN helps you save money by using the public Internet instead of making long–distance phone calls to connect securely with your private network. There are two ways to create a VPN connection, by dialing an Internet service provider (ISP), or connecting directly to Internet.
Network Topology
It is the physical layout of computers, cables and other components on a network. There are number of network topologies and a network could be build using multiple topologies [4].
Some of the most popular network topologies are;
Bus topology:
It uses a backbone to which all of the nodes (file server, workstations, and peripheral) on the network connect (as shown in figure 6). Systems connect to this backbone using T connectors or taps. Bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
Figure 6 Bus topology
Advantages of a Linear Bus Topology
- It is easy to connect a computer or peripheral to a linear bus.
- It requires less cable length as compared to some other topologies.
- If a computer fails, network still remains functional.
Disadvantages of a Linear Bus Topology
- In case the main cable breaks, the entire network shuts down.
- Terminators are required at both ends of the backbone cable to absorb the signal and prevent its bounce.
- It is relatively difficult to identify the problem if the entire network shuts down.
- It is not very scalable which is an important issue in networks these days.
Star topology
A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator (as shown in figure 7). Each device requires a single cable for point-to-point connection between the device and hub. It is one of the most widely implemented topology. Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. It also acts as a repeater for the data flow. A range limit of this topology is about 100 meters from the hub.
Figure 7: Star Topology
Advantages of a Star Topology
- No disruptions to the network is felt when a device is being connected or removed.
- It is easy to detect faults.
- It is easy to modify and add new computers to a star network without disturbing the rest of the network.
- If one node or workstation (beside the middle node) goes down, the rest of the network will still be functional.
- You can use several cable types in the same network if the hub you have can handle multiple cable types.
- Cable failure affects only a single user
- It is easy to troubleshoot and isolate problems.
- It is relatively scalable topology.
- Centralized management (hub) and monitoring of the traffic helps in easy administration of the network.
Disadvantages of a Star Topology
- It requires more cable length than a linear topology.
- If the hub, switch, or concentrator fails, the whole network fails.
- It is more expensive than linear bus topologies because of the cost of the hubs and connecting cables etc.
- It is comparatively difficult to implement.
Ring Topology
In a ring network, every device has exactly two neighbours to communicate with. It means each node is connected to the next and the last node is connected to the first (as shown in figure 8). All messages travel through a ring in the same direction (either clockwise or anti clockwise). Each computer regenerates the signal so that it my travel the distance required. A data token is used to grant permission for each computer to communicate. In reality, ring topology networks are not linked together in loops. They are actually linked to a distributor (called a MAU, Multi-station Access Unit) which manages communication between the computers linked to it, by giving each of them time to communicate.
Figure 8: Ring Topology
Advantages of ring topology:
- Ring topology is relatively easy to install and wire.
- Because every computer is given equal access to the token, no one computer can monopolize the network.
- It is easy to troubleshoot as cable faults are easily located.
- As there are no free ends, no terminators are required as in bus topology.
- Signal degeneration is low as each station on the way regenerates the signal to forward it.
Disadvantages of ring topology:
- It requires more cable than a bus topology.
- If one computer fails the whole network goes down. It means a single break in the cable can disrupt the entire network.
- It is difficult to identify the problem if the entire network shuts down.
- Expansion to the network can cause network disruption
Network Topology (Continue)
Mesh Topology
Each computer connects to every other (as shown in figure 9). So there is high level of redundancy in this topology. It involves the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. Even in a ring, although two cable paths exist, messages can only travel in one direction. Some WANs, most notably the Internet, employ mesh routing [9].
Figure 9:Mesh Topology
Advantages of mesh topology:
- There is an increased reliability (fault tolerance) since there are multiple paths for each node to take.
- The speed of this network might be increased since shortcuts have been created by add more cables/links.
- It is scalable easily.
- The network can be expanded without disruption. This is because multiple paths exists between nodes.
Disadvantages of mesh topology:
- The cost of cabling all the hosts together is expensive and time consuming.
- Wiring and implementation is very complicated.
- Troubleshooting a failed cable is difficult due to complicated cabling.
- It is difficult to administer and manage due to numerous connections.
Hybrid Topology
Due to altering advantages and disadvantages, it is typical for networks to implement mixture of topologies called hybrid (as shown in figure 10). One of the popular hybrid topology is star-bus topology in which numbers of star topologies are connected by central bus. Bus will connect hubs spread over distance.[10]
Figure 10 : Hybrid Topology
Advantages of hybrid 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.
- It is easy to increase the size of network by adding new components, without disturbing existing architecture.
- 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.
- Hybrid topology is the combination of two or more topologies, so we can design it in such a way that strengths of constituent topologies are maximized while there weaknesses are neutralized. For example we saw Ring Topology has good data reliability (achieved by use of tokens) and Star topology has high tolerance capability (as each node is not directly connected to other but through central device), so these two can be used effectively in hybrid star-ring topology.
Disadvantages of hybrid topology
- One of the biggest drawback of hybrid topology is its design. Its not easy to design this type of architecture and its a tough job for designers. Configuration and installation process needs to be very efficient.
- The hubs used to connect two distinct networks, are very expensive. These hubs are different from usual hubs as they need to be intelligent enough to work with different architectures and should be function even if a part of network is down.
- As hybrid architectures are usually larger in scale, they require a lot of cables, cooling systems, sophisticate network devices, etc.
Wireless Topology
It is a topology that does not require physical cabling (as shown in figure 11). It is particularly useful for remote access for laptop users. The network consists of transmitters that broadcast the packet using radio frequencies [11,12].
Figure 11: Wireless Topology
Advantages of wireless topology:
- Network can be expanded without disruption to current users.
- It allows wireless remote access.
- It eliminates cable faults and cable breaks.
- Troubleshooting failed devices is easy.
Disadvantages of wireless topology:
- Due to signal interference and security issue these are not useful in case of sensitive and important data.
- It has limited speed in comparison to other network topologies
- Potential security issues are associated with wireless transmissions.
- Links are unreliable due to bad weather, range, misalignment or line-of-sight issue.
Network Topology (Continue)
Terminology
Access point (AP): A station that provides access to the DS.
Basic service set (BSS): A set of stations controlled by a single AP.
Distribution system (DS): A system used to interconnect a set of BSSs to create an ESS.
DS is implementation-independent. It can be a wired 802.3 Ethernet LAN, 802.4 token bus, 802.5 token ring or another 802.11 medium.
Extended service set (ESS): Two or more BSS interconnected by DS
Wireless Fidelity
Wi-Fi is an abbreviation for Wireless Fidelity and a catch all phrase for the several different standards and recommendations that comprise wireless networking. Wi-Fi enables the user to deploy a computer network without needing to run cable throughout the facility.
Standard
IEEE 802.11.b –2.4GHz – 11Mbps
International standard for wireless networking that operates in the 2.4 GHz frequency range (2.4 GHz to 2.4835 GHz) and provides a throughput of up to 11 Mbps with a range of just over 300 feet indoors. This is a very commonly used frequency. Microwave ovens, cordless phones, medical and scientific equipment, as well as Bluetooth devices, all work within the 2.4 GHz frequency band.
Wireless LAN can work in two modes:
Infrastructure Mode
Infrastructure wireless LAN is shown in figure 12. We can see that two BSS are connected through AP’s which are making their DS.
Access points are interconnected via distribution system (ethernet). The interconnected network forms an extended service set
Figure 12: Infrastructure Mode
Ad hoc mode
In this case there is no base station. Nodes can only transmit to other nodes within link coverage (as shown in figure 13). Nodes organize themselves into a network and route among themselves.
Figure 13:Ad hoc networks
How it works
- A wireless network transmits and receives user information on a specific radio frequency. It keeps the radio signal frequency as narrow as possible. Radio receiver filters out all radio signals except the ones on its designated frequency. Cell consists of work stations and an access point.
A family of wireless LAN (WLAN) specifications developed by a working group at the Institute of Electrical and Electronic Engineers (IEEE) defines standard for WLANs using the following four technologies
- Frequency Hopping Spread Spectrum (FHSS)
- Direct Sequence Spread Spectrum (DSSS)
- Infrared (IR)
- Orthogonal Frequency Division Multiplexing (OFDM)
Most common versions are 802.11a, 802.11b, 802.11g, 802.11e, 802.11f, 802.11i. It should be noted that most wireless LAN products operate in unlicensed radio bands 2.4 GHz. No license is needed to operate in this band. Most wireless LANs use spread-spectrum radio for transmission because these are resistant to interference and hence are secure. Two most popular methods are: Frequency Hopping (FH) and Direct Sequence (DS).
FH systems use a radio carrier that “hops” from frequency to frequency in a pattern known to both transmitter and receiver. It is easy to implement and is resistant to noise. It has limited throughput (2-3 Mbps @ 2.4 GHz).
On the other hand, DS systems use a carrier that remains fixed to a specific frequency band. The data signal is spread onto a much larger range of frequencies (at a much lower power level) using a specific encoding scheme. Throughput is much higher as compared to FH (11 Mbps).It has better range and is less resistant to noise.
Satellite communication:
In telecommunications, the use of artificial satellites to provide communication links between various points on Earth. Satellite communications play a vital role in the global telecommunications system. Approximately 2,000 artificial satellites orbiting Earth relay analog and digital signals carrying voice, video, and data to and from one or many locations worldwide.
Satellite communication has two main components: the ground segment, which consists of fixed or mobile transmission, reception, and ancillary equipment, and the space segment, which primarily is the satellite itself. A typical satellite link involves the transmission or uplinking of a signal from an earth station to a satellite. The satellite then receives and amplifies the signal and retransmits it back to Earth, where it is received and re-amplified by Earth stations and terminals. Satellite receivers on the ground VSATs (very Small Aperture Terminals) including direct-to-home (DTH) satellite equipment, mobile reception equipment in aircraft, satellite telephones, and handheld devices.
Satellite applications
Advances in satellite technology have given rise to a healthy satellite services sector that provides various services to broadcasters, Internet service providers (ISPs), governments, the military and other sectors. There are three types of communication services that satellites provide: telecommunications, broadcasting, and data communications. Telecommunication services include telephone calls and services provided to telephone companies, as well as wireless, mobile, and cellular network providers.
Conclusion
Computer network is most important and exiting technological field these days. Every successful organization is utilizing it these days. We have discussed components of a computer network and justified the popularity of computer networks by discussing its advantages. We also discussed various types of networks on the basis of their geographical distance. We discussed various network topologies along with their advantages and disadvantages. In the end we discussed the upcoming wireless technology and introduction use of satellite in communication.
References
- http://www.techsoup.org/support/articles-and-how-tos/networking-101-concepts-and-definitions
- http://www.omnisecu.com/basic-networking/why-we-need-computer-network.php
- Tanenbaum, Andrew S. Computer networks. Vol. 4. Englewood Cliffs (NY): Prentice-Hall, 1989.
- Forouzan, A. Behrouz. Data Communications & Networking (sie). Tata McGraw-Hill Education, 2007.
- http://fcit.usf.edu/network/chap1/chap1.htm
- www.buzzle.com/articles/advantages-and-disadvantags-of-computer-networks.html
- http://www.tcpipguide.com/free/t_TheAdvantagesBenefitsofNetworking.htm
- http://en.kioskea.net/contents/266-types-of-networks
- http://networkwire.org/different-types-of-networks-in-computer-system.html
11. Stallings, William. Wireless Communications & Networks, 2/E. Pearson Education India, 2009.
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