Computer Network

Computer networking is the engineering discipline concerned with the communication between computer systems or devices. A computer network is any set of computers or devices connected to each other with the ability to exchange data.[1] Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information technology and/or computer engineering since it relies heavily upon the theoretical and practical application of these scientific and engineering disciplines. The three types of networks are: the Internet, the intranet, and the extranet. Examples of different network methods are:

• Local area network (LAN), which is usually a small network constrained to a small geographic area. An example of a LAN would be a computer network within a building.
• Metropolitan area network (MAN), which is used for medium size area. examples for a city or a state.
• Wide area network (WAN) that is usually a larger network that covers a large geographic area.

• Wireless LANs and WANs (WLAN & WWAN) are the wireless equivalent of the LAN and WAN.

All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, power lines and various wireless technologies.^[2] The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet^[3]). Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs.^[4]

Network cards such as this one can receive data at high

rates over transmit and various types of network cables.
This card is a 'Combo' card which supports three cabling standards.

History of computer networks

Before the advent of computer networks that were based upon some type of telecommunicationssystem, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Many of the social behaviors seen in today's Internet were demonstrably present in the nineteenth century and arguably in even earlier networks using visual signals.

In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANet.

In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing SystemMIT, a research group supported by General Electric and Bell Labs used a computer DEC's to route and manage telephone connections. for distributed users of large computer systems. The same year, at

Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used datagrams or packets that could be used in a network between computer systems.

1965 Thomas Merrill and Lawrence G. Roberts created the first wide area network (WAN).

The first widely used PSTN switch that used true computer control was the Western Electric introduced in 1965.

In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANET network using 50 kbit/s circuits. Commercial services using X.25 were deployed in 1972, and later used as an underlying infrastructure for expanding TCP/IP networks.

Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user.

Today, computer networks are the core of modern communication. All modern aspects of the Public Switched Telephone Network (PSTN) are computer-controlled, and telephony increasingly runs over the Internet Protocol, although not necessarily the public Internet. The scope of communication has increased significantly in the past decade, and this boom in communications would not have been possible without the progressively advancing computer network.

Differences Between Internet , Intranet and Extranet

Picture," it also offers a global perspective. By providing connectivity to anyone with a computer and a telephone line, the Internet is the networking breakthrough of our lifetime. It includes everything from universal e-mail to transactions between individuals and between companies. Of course, this now includes commerce as well as information exchanges and new directories (such as search engines) that provide phone book-style accessibility for digital communications.

Some of the most important results of this networking revolution are new forms of marketing and outreach, new connections between customers and collaborators, new sources for news and research, and opportunities for new kinds of distribution of products (as well as of information). But because the Internet is the broadest information super-highway, it lacks some of the security and privacy that's needed for the internal workings of business organizations. Advanced features like multimedia are also more likely to be limited because most individuals are still using dial-up connections and, as a result, have very limited data bandwidth.

INTRANETS

Intranets are new kinds of internal networks. Think of "Intra" as it is used in Intramural sports. Intranets tend to resemble the architecture of a closed-circuit video network as opposed to the Internet which is more like broadcasting in terms of its reach. Intranets are used for more private communications, connectivity among work groups and larger organizations. For example, some companies use Intranets to offer corporate services such as benefits programs and other kinds of corporate communications. Also, Intranets enable information sharing that empowers employees who might otherwise be left "out of the loop." (See "Groupware" below.)

Because of their limited geographic range, Intranets offer more bandwidth, frequently Ethernet's 10Kbps or better. As a result of this bandwidth and the "closed loop" structure, more advanced networking features such as video and multimedia, as well as more technological control, are possible. For example, a company can specify that a specific web browser and even a specific version of that browser (licensed by the company) be used on its network. This enables a consistent and more dependable user experience than is possible on the Internet. Even Internet related services such as Pointcast can be customized for a particular company and its Intranet.

EXTRANETS

Extranets are a more complex implementation of the wired world. Just because an employee is telecommuting doesn't mean she shouldn't have access to the company Intranet. Sales people on the road are just as critical to a corporation's success as those who sit behind desks. And in today's world of virtual work groups, suppliers and other vendors are frequently critical members of the team and they may need an insider's degree of access. Extranet's provide these important networking "bridges" by combining the Internet with the Intranet.

By extending the corporate network to include the Internet, team members get the best of both worlds -- mobility with exclusivity. Because of the necessary security involved, Extranets frequently require the development of custom applications. For example, in order to give a remote sales person access to corporate sales statistics, the user needs remote access to a database that cannot be made visible to the competition. Most often, for something this sensitive, encryption is involved because password protection is not sufficient.

In most cases, Extranets do not involve high bandwidth applications like video and multimedia because of the limited bandwidth of remote users who most frequently use dial up connections.

Ethernet is the most widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless LANs. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD ) protocol.

Fast Ethernet or 100BASE-T provides transmission speeds up to 100 megabits per second and is typically used for LAN backbone systems, supporting workstations with 10BASE-T cards. Gigabit Ethernet provides an even higher level of backbone support at 1000 megabits per second (1 gigabit or 1 billion bits per second). 10-Gigabit Ethernet provides up to 10 billion bits per second.

Ethernet was named by Robert Metcalfe, one of its developers, for the passive substance called "luminiferous (light-transmitting) ether" that was once thought to pervade the universe, carrying light throughout. Ethernet was so- named to describe the way that cabling, also a passive medium, could similarly carry data everywhere throughout the network.

Perbazaan Antara 3 Topologi ( Star , Bus , Ring )

Topolgi bus

Tpologi jaringan bus meruapakan beberapa simpul/node dihubungkan dg jalur data (bus).topolgi ini menyediakan 1 saluran untuk komunikasisemua perangkat shgg setiap perangkat harus bergantian seluran tersebut.hanya ada 2perangkat yg saling berkomunikasi dalam 1 saat.tiap node dapat melakukan tugas-tugas dan operasi yg berbeda.Untuk mengifisiensi penggunaan jaringan digunukan metode CSMA/CD(Carrier Sense Multiplay Access/Collision Detected)yg mernguragi masa tenggang(saluran kosong)dg mendeteksi tabrakan informasi.

Keuntungan Topolgi Bus

1.Mengurangi kabel&jarak LAN tidak terbatas.
2.Biaya instalasi sgt murah.
3.Mudah untuk menambah atau mengurangkan kompuer &nod

Kekurangan Topologi Bus

1.Memerlukan terminator untuk kedua ujng kabel tulang belakang
2.Perlu pengulang (repeater0jika LAN jauh.
3.Jika kabel tulabg belakang (backbone)/mana-mana nodnya bermasalah rangkaian tidak dapat berfungsi.

Topologi Ring

Mempunyai satu titik kesalahan,terletak pd hub.jika pusat hub mengalami kegagalan,maka seluruh jaringan akan gagal beroperasi.Memerlukan alat pd central poin untuk membroadcast ulang atau pergantian traffic jaringan (switch network rraffic).Penempatan kabel yg diguib\nakan ring menggunakan desain yg sederhanh,pada topologi ring,setiap computer yg pertama.

Keuntungan Topologi Ring

1.Setiap computer hak akses yg sama terhadap token,sehingga tidak akan ada computer yg memonopoli jaringan.
2.Data yg mengalir dalam satu arah sehingga terjadinya collision dapat dihindarkan.

Kekurangan Topolgi ring

1.Apabila ada satu computer dlm ring yg gagal berfungsi,maka akan mempengaruhi keseluruhan jaringan.
2.Sulit mengatsi kerusakan di jaringan yg menggunakan topolgo ring.
3Menambah atau menguirangikomputer akan mengacaukaun jaringan.

Topologi Star

Dalam topologi star,semua kabel di hubungkan dr computer-computer ke lokasi pusat(central location),dimana semuanya rehubung ke suatu alat yg dinamakan hub

Keuntungan Topologi star

Cukup mudah untuk mengubah dan menambah computer kedalam jaringan yg menggunakan topologi star tanpa mengganggu aktivitas jaringan yg sedang berkangsung.Pusat dari jaringan star merupakan tempat yg baik untuk menentukan diagnosa kesalahan yg terjadi dalam jaringan.Kita dapat memakai beberapa tipe kabel didalam jaringan yg sama dg hub yg dapat mengakomodasi tipe kabel yg berbeda

Kekurangan Topologi star

Memepunyai satu titik kesalahan,terletak pd hub.Jika hub pusat mengalami kegagalan,maka seluruh jaringan akan gagal beroperasi.memerlukan alat pd central poin untuk membroadcast ulang ppergantian traffic jaringan (switch network traffic).

Topologi Mesh

Topologi Mesh adalah suatu bentuk hubungan antar perangkat,dimana perangkat terhubung secara langsung ke perangkat lainya yg ada didalam jaringan.Akibatnya,dalam topologi ini setiap perangkat dapat berlomunikasi langsung dgn parangkat yg dituju(dedicated links)

Keuntungan Topologi Mesh

Memiliki sifat Robust,yaitu apabila terjadi gangguan pada koneksi computer A dgn computer B karena ruasaknya kabel koneksi(links).Memudahkan proses identifikasi permasakahan pd saat terjadi kerusakan koneksi pd computer.

Kekurangan Topologi Mesh

Membutuhkan banyak kabel dan Port I/o.Semakin banyk computer didalam topologi mesh mk di[erlukan semakin banyak kabel links dan port I/O.Hal tersebut sekaligus jg mengindisikasikan bahwa topologi jenis ini membutuhkan biaya yg relative mahal.Karena setiap computer harus terkoneksi secara langsung dgn computer kainya mk instalasi dan konfigurasi menjadi sulit.

virus

Virus

Virus Selsema

Virus HIV

Virus H1N1

Network Topology

Network Topology

Network topology is defined as the interconnection of the various elements (links, nodes, etc.) of a computer network.^[1][2] Network Topologies can be physical or logical. Physical Topology means the physical design of a network including the devices, location and cable installation. Logical topology refers to the fact that how data actually transfers in a network as opposed to its physical design.

Topology can be considered as a virtual shape or structure of a network. This shape actually does not correspond to the actual physical design of the devices on the computer network. The computers on the home network can be arranged in a circle shape but it does not necessarily mean that it presents a ring topology.

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

A Local Area Network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of these links and nodes in a graph results in a geometrical shape that may be used to describe the physical topology of the network. Likewise, the mapping of the data flow between the nodes in the network determines the logical topology of the network. The physical and logical topologies may or may not be identical in any particular network.

Diagram of different network topologies

Basic topology types

The study of network topology recognizes five basic topologies:

• Bus topology
• Star topology
• Ring topology
• Tree topology
• Mesh topology

Bus

In local area networks where bus topology is used, each machine is connected to a single cable. Each computer or server is connected to the single bus cable through some kind of connector. A terminator is required at each end of the bus cable to pr ev ent the signal from bouncing back and forth on the bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the MAC add ress or IP address on the network that is the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data doe s match the machine address, the data is accepted. Sinc e the bus topology consists of only one wire, it is rather inexpensive to implement when compared t o other topologies. However, the low cost of implementing the technol ogy is offse t by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the netw ork cable breaks, the e ntire network will be down.

Bus network topology

Star

In local area networks with a star topology, each network host is connected to a central hub. In contrast to the bus topology, the star topology connect s ea ch node to the hub with a point-to-point connection. All traffic that transverses the ne twork passes through the central hub. The hub acts as a signal booster or repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star top ology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single

Star network topology

Ring

In local area networks where the ring topology is used, each computer is connected to the network in a closed loop or ring. Each machine or computer has a unique address that is used for identification purposes. The signal passes throug h e ach machine or computer connected to the ring in one direction. Ring topologies typically utili ze a token passing scheme, used to control access to the network. By utilizing this scheme, only one machine can transmit on the network at a time. The machines or computers connected to the ring act as signal boosters or repeaters which strengthen the signals that transverse the network. The primary disadvantage of ring topology is the failure of one machine will cause the entire network to fail.^{[citation needed]}

Ring network topology

Tree

Also known as a hierarchical network.

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the

second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are o

ne level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node tha

t has no other node above it in the hierarchy (The hierarchy of the tree is symmetrical.) Each node in the network having a specific fixed number, of nodes connected to it at the next lower l

evel in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree.

Tree network topology

Mesh

The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any

two endpoints, up to and including all the endpoints, is approximated by Reed's Law.

Partially connected mesh topology

Fully connected mesh topology

Network Architecture

Network architecture is the design of a communications network. It is a framework for the specification of a network's physical components and their functional organization and configuration, its operational principles and procedures, as well as data formats used in its operation.
In computing, the network architecture is a characteristics of a computer network. The most prominent architecture today is evident in the framework of the Internet, which is based on the Internet Protocol Suite.
In telecommunication, the specification of a network architecture may also include a detailed description of products and services delivered via a communications network, as well as detailed rate and billing structures under which services are compensated.
In distinct usage in distributed computing, network architecture is also sometimes used as a synonym for the structure and classification of distributed application architecture, as the participating nodes in a distributed application are often referred to as a network. For example, the applications architecture of the public switched telephone network (PSTN) has been termed the Advanced Intelligent Network. There are any number of specific classifications but all lie on a continuum between the dumb network (e.g., Internet) and the intelligent computer network (e.g., the telephone network). Other networks contain various elements of these two classical types to make them suitable for various types of applications. Recently the context aware network, which is a synthesis of the two, has gained much interest with its ability to combine the best elements of both.