30-03-2011, 03:31 PM
SUBMITTED BY:
SUMIT KUMAR VISHWKARMA
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Introduction to Networks
A computer network, often simply referred to as a network, is a collection of computers and devices interconnected by communications channels that facilitate communications among users and allows users to share resources. Networks may be classified according to a wide variety of characteristics. A computer network allows sharing of resources and information among interconnected devices.
A computer network is a collection of PCs and other devices connected together with cables, so that they can communicate with each other for the purpose of sharing information and resources. Networks vary in size: some are within a single office, others span the globe.
There are various network technologies, the most common being Ethernet and Fast Ethernet. A network can be made up of one or more of these technologies. Ethernet and Fast Ethernet networks operate in a similar way, the main difference is the speed at which they transfer information; Ethernet operating at 10 Megabits per second (Mbps) and Fast Ethernet operating at 100 Megabits per second (Mbps).
How does a network net work?
Devices on a network communicate by transmitting information to each other in groups of small electrical pulses (known as packets). Each packet contains address information about the transmitting device (the source address) and the intended recipient (the destination address). This address information is used by some of the network equipment to help the packet reach its destination.
Ethernet and Fast Ethernet networks use a protocol called CSMA/CD (Carrier-sense Multiple Access with Collision Detection). This protocol operates by allowing only one device to communicate at any given time. When two devices try to communicate simultaneously, a collision occurs between the transmitted packets, and this is detected by the transmitting devices. The devices stop transmitting and wait before resending their packets. All this is part of normal network operation for Ethernet and Fast Ethernet networks, and is comparable to a conversation between people in a group; if two people speak at the same time, they both stop and then one will start to speak again.
History
Early networks of communicating computers included the military radar system Semi-Automatic Ground Environment (SAGE) and its relative the commercial airline reservation system Semi-Automatic Business Research Environment (SABRE), starting in the late 1950s.
In the 1960s, the Advanced Research Projects Agency (ARPA) started funding the design of the Advanced Research Projects Agency Network (ARPANET) for the United States Department of Defense. Development of the network began in 1969, based on designs developed during the 1960. The ARPANET evolved into the modern Internet.
Computer networks can be used for a variety of purposes:
• Facilitating communications. Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.
• Sharing hardware. In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer.
• Sharing files, data, and information. In a network environment, authorized user 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.
• Sharing software. Users connected to a network may run application programs on remote computers.
• Information preservation.
1.1. Basic of Networking
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 (see Advice Sheet 17 on the ICT Planning for pack). Fig 1 gives an example of a network in a comprising of a local area network or LAN connecting computers with each other, the internet, and various servers.
Broadly speaking, there are two types of network configuration, peer-to-peer networks and client/server networks.
Peer-to-peer networks are more commonly implemented where less then ten computers are involved and where strict security is not necessary. All computers have the same status, hence the term 'peer', and they communicate with each other on an equal footing. Files, such as word processing or spreadsheet documents, can be shared across the network and all the computers on the network can share devices, such as printers or scanners, which are connected to any one computer.
Client/server networks are more suitable for larger networks. A central computer, or 'server', acts as the storage location for files and applications shared on the network. Usually the server is a higher than average performance computer. The server also controls the network access of the other computers which are referred to as the 'client' computers. Typically, teachers and students in a will use the client computers for their work and only the network administrator (usually a designated staff member) will have access rights to the server.
Components of a Network
A computer network comprises the following components:
• A minimum of at least 2 computers
• Cables that connect the computers to each other, although wireless communication is becoming more common (see Advice Sheet 20 for more information)
• A network interface device on each computer (this is called a network interface card or NIC)
• A ‘Switch’ used to switch the data from one point to another. Hubs are outdated and are little used for new installations.
• Network operating system software
Structured Cabling
The two most popular types of structured network cabling are twisted-pair (also known as 10BaseT) and thin coax (also known as 10Base2). 10BaseT cabling looks like ordinary telephone wire, except that it has 8 wires inside instead of 4. Thin coax looks like the copper coaxial cabling that's often used to connect a Video Recorder to a TV.
10BaseT Cabling
When 10BaseT cabling is used, a strand of cabling is inserted between each computer and a hub. If you have 5 computers, you'll need 5 cables. Each cable cannot exceed 325 feet in length. Because the cables from all of the PCs converge at a common point, a 10BaseT network forms a star configuration.
10BaseT cabling is available in different grades or categories. Some grades, or "cats", are required for Fast Ethernet networks, while others are perfectly acceptable for standard 10Mbps networks--and less expensive, too. All new networks use a minimum of standard unshielded twisted-pair (UTP) Category 5e 10BaseT cabling because it offers a performance advantage over lower grades.
Network Interface Card (NIC)
A NIC (pronounced 'nick') is also known as a network card. It connects the computer to the cabling, which in turn links all of the computers on the network together. Each computer on a network must have a network card. Most modern network cards are 10/100 NICs and can operate at either 10Mbps or 100Mbps.
Only NICs supporting a minimum of 100Mbps should be used in new installations .
Computers with a wireless connection to a network also use a network card (see Advice Sheet 20 for more information on wireless networking).
Hub and Switch
A hub is a device used to connect a PC to the network. The function of a hub is to direct information around the network, facilitating communication between all connected devices. However in new installations switches should be used instead of hubs as they are more effective and provide better performance. A switch, which is often termed a 'smart hub'.
Switches and hubs are technologies or ‘boxes’ to which computers, printers, and other networking devices are connected. Switches are the more recent technology and the accepted way of building today's networks. With switching, each connection gets "dedicated bandwidth" and can operate at full speed. In contrast, a hub shares bandwidth across multiple connections such that activity from one PC or server can slow down the effective speed of other connections on the hub.
Now more affordable than ever, Dual-speed 10/100 autosensing switches are recommended for all networks. may want to consider upgrading any hub based networks with switches to improve network performance – ie speed of data on the network
