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A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications.

In the world of computers, networking is the practice of linking two or more computing devices together for the purpose of sharing data. Networking is the process by which two or more computers are linked together for a flawless communication. By creating a network, devices like printers and scanners, software, and files and data that are stored in the system can be shared. It helps the communication among multiple computers easy. Networks are built with a mix of computer hardware and computer software. It is a collection of computers and other hardware components interconnected by communication channels that allow sharing of resources and information. Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device, then the two devices are said to be in a network. In a simplify form, more than one computer interconnected through a communication medium for information interchange is called a computer network.

Networks may be classified according to a wide variety of characteristics, such as the medium used to transport the data, communications protocol used, scale, topology, benefit, and organizational scope. Computer networking is sometimes considered a sub-discipline of electrical engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of these disciplines.

 

Properties Of Computer Network

  1. Facilitate communications: Computer networks allows people to communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
  2. Permit sharing of files, data, and other types of information: In a network environment, authorized users may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.
  3. Share network and computing resources: In a networked environment, each computer on a network may access and use resources provided by devices on the network, such as printing a document on a shared network printer. Distributed computing uses computing resources across a network to accomplish tasks.
  4. May be insecure: A computer network may be used by computer hackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from normally accessing the network (denial of service).
  5. May be difficult to set up: A complex computer network may be difficult to set up. It may also be very costly to set up an effective computer network in a large organization or company.

 

Historical background of Computer Network

In the early 1980s, personal computer was developed with the concept of independent operation. With personal computer on your desktop, you could enter the information yourself, manipulate it, and produce the report you really wanted. While personal computer had become more powerful and applications for the computers included simple spreadsheet, databases, and word processors, the market for the computers exploded. For all its speed and power, the desktop computing environment had a difficulty in communicating among the users as computing information had became large and complicated. However, business information is useful only when it is communicated between human beings.

The obvious solution was to link the desktop computers together. So, the idea of a Local Area Network (LAN) was developed. The development of network technology is continuous up to present.

 

TYPES OF NETWORKS

The various types of network according to the architecture are

1) Ethernet: Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet was invented by engineer Robert Metcalfe. When first widely deployed in the 1980s.

The term Ethernet refers to the family of local area network (LAN) products covered by the IEEE 802.3 standard that defines what is commonly known as the CSMA/CD protocol. This is a system where each computer listens to the cable before sending anything through the network. If the network is clear, the computer will transmit. If some other node is already transmitting on the cable, the computer will wait and try again when the line is clear. Sometimes, two computers attempt to transmit at the same instant. When this happens a collision occurs. Each computer then backs off and waits a random amount of time before attempting to retransmit. With this access method, it is normal to have collisions. However, the delay caused by collisions and retransmitting is very small and does not normally affect the speed of transmission on the network. It is one of the most widely implemented LAN standards.

Three data rates are currently defined for operation over optical fiber and twisted-pair cables:

  • 10 Mbps-10Base-T Ethernet.
  • 100 Mbps-Fast Ethernet.
  • 1000 Mbps-Gigabit Ethernet.

 

Ethernet supported a maximum theoretical data rate of 10 megabits per second (Mbps). Later, so-called “Fast Ethernet” standards increased this maximum data rate to 100 Mbps. Today, Gigabit Ethernet technology further extends peak performance up to 1000 Mbps. Higher level network protocols like Internet Protocol (IP) use Ethernet as their transmission medium. Data travels over Ethernet inside protocol units called frames. The run length of individual Ethernet cables is limited to roughly 100 meters, but Ethernet networks can be easily extended to link entire schools or office buildings using network bridge devices.

 

2) Token Ring: Token ring local area network (LAN) technology is a protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring. Token-possession grants the possessor permission to transmit on the medium. Token ring frames travel completely around the loop.

The data transmission process goes as follows:

  • Empty information frames are continuously circulated on the ring.
  • When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.
  • The frame is then examined by each successive workstation. The workstation that identifies itself to be the destination for the message copies it from the frame and changes the token back to 0.
  • When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.
  • The frame continues to circulate as an “empty” frame, ready to be taken by a workstation when it has a message to send.

 

3) ArcNet: ArcNet is an acronyms for Attached Resource Computer Network. It was developed by Datapoint Corporation in 1977. It is a simple, inexpensive and flexible network architecture designed for workgroup-sized networks. It uses a token-ring architecture, supports data rates of 2.5 Mbps, and connects up to 255 computers. A special advantage of ARCnet 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. ArcNet does loosely comply to this token passing specification.

The token moves from one computer to another based on node addresses instead of the physical location of computers. This means that ArcNet passes the token to the next address regardless of whether the address is on a workstation in the same room or in a separate building. Each computer in an ArcNet network is connected by a cable to a hub, which can be an active, a passive or a smart hub. The standard cabling used for ArcNet is 93 ohm RG-62 A/U coaxial cable. ArcNet also supports twisted pair and fiber optic cables. The use of star topology and cable filtering make ArcNet networks reliable. In a distributed star design, ArcNet uses passive and active hubs to control and route data tokens from one workstation to the next. Since token passing is done at a fixed rate and collisions do not occur, ArcNet is very stable.

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