networking concept and types of topology

Definition: A computer Network is interconnection of two or more independent computer for the purpose of sharing Resources and information.

Network Goals:
The main goals of network are:
(a) Resource Sharing:
All the programs, data and peripheral devices should be available to all the users on the network irrespective of the physical location of the resources and the user.
(b) Reliability:
Having multiple copies of a single file in different system is more reliable since loss of data can be avoided since network connects multiple systems and keeps a copy of file in different systems.
(c) Cost Factor:
The normal Shared File-Server system (micro system) is costly and has less performance. Instead of Server system we can use less costly Personal Computer and we can connect them using Network.
(d) Communication Medium:
Using network we can easily communicate with person in different places regardless of distance and this speeds up the process efficiently.
For example using a network, it is possible to manage the financial report of the company while sitting at home. The changes at one end can be immediately noticed at another end.

Need of Networking:
i. File sharing provides sharing and grouping of data files over the network.
ii. Print sharing of computer resources such as hard disk and printers etc.
iii. Email tools for communication with the e-mail address.
iv. Remote access able to access data and information, around the globe.
v. Sharing database to multiple users at the same time by ensuring the integrity.

ARPANET
The Advanced Research Projects Agency NETwork(ARPANET) was one of the world’s first computer (operational packet switching)networks, the first network to implement TCP/IP (Transmission Control Protocol/Internet Protocol), and later it become the global Internet.

OSI (Open System Interconnection) Reference Model:
The OSI is a reference tool for understanding data communications between any two networked systems. It divides the communications processes into seven layers.

The Physical Layer:
Physical layer is concerned with transmitting raw bits over a communication medium. It also deals with mechanical, electrical and timing interfaces.

The Data Link Layer:
The main function of the data link layer is to send and receive messages. It also detects error and errorless message is sent to Network layer.

The Network Layer:
The network layer is to determine how packets are transmitted from source to destination by controlling operations on subnet addresses.
[Note: The original message is broken into small parts called as packet.]

The Transport Layer:
Transport Layer accept data from the above layer and split it up into smaller units if needed, and ensure that the pieces all arrive in correct order at the other end. It also determines type of service to provide to the session layer.

The Session Layer:
The session layer allows users on different machines to establish sessions between them. It includes dialog control, token m

1. NETWORKING CONCEPT A computer Network is interconnection of two or more independent computer for the purpose of sharing Resources and information .

2. Network Goals Resource Sharing: All the programs, data and devices should be available to all the users on the network irrespective of the physical location of the resources and the user. Reliability : Having multiple copies of a single file in different system is more reliable since loss of data can be avoided since network connects multiple systems and keeps a copy of file in different systems. Cost Factor : The normal Shared File-Server system (micro system) is costly and has less performance. Instead of Server system we can use less costly Personal Computer and we can connect them using Network. Communication Medium : Using network we can easily communicate with person in different places regardless of distance and this speeds up the process efficiently. For example using a network, it is possible to manage the financial report of the company while sitting at home. The changes at one end can be immediately noticed at another end.

3. Need of Networking File sharing provides sharing and grouping of data files over the network. Print sharing of computer resources such as hard disk and printers etc. Email tools for communication with the e-mail address. Remote access able to access data and information, around the globe. Sharing database to multiple users at the same time by ensuring the integrity.

4. ARPANET The A dvanced R esearch P rojects Agency NET work (ARPANET) was one of the world’s first computer networks.

5. The INTERNET Internet is an interconnection of large and small networks around the globe. The internet is made up of many networks each run by a different company and interconnected at peering points. The INTERSPACE Inter space is a client/server software program that allows multiple users to communicate online with real-time audio, video and text chat in dynamic environments.

6. Elementary Terminology of Networks Some of typical hardware components of network are: ( i ) Nodes (Workstations) The term nodes refer to the computer that are attached to a network and are seeking to share the resources of the network. (ii) Server: In network environment one computer can control all other workstations is called server. Servers are of two types: (1) Non-dedicated servers (2) Dedicated servers Non-dedicated Servers: On small networks, a workstation that can act as a server is known as non-dedicated server Dedicated Servers: On bigger network installations, there is a computer reserved for server's job and its only job is to help workstations access data, software and hardware resources. And it cannot be used as a workstations and such a server is known as dedicated server. The networks using such server are known as MASTER-SLAVE networks.

7. TYPES OF NETWORKS A computer Network is interconnection of two or more independent computer for the purpose of sharing Resources and information . The computers are classified on the basis of geographical arrangements there can be 3 types of networks: ( i ) Local Area Networks (LANs). (ii) Wide Area Networks (WANs) (iii) Metropolitan Area Networks (MANs)

8. Local Area Networks (LANs) Small computer networks that are restricted to a localized area (e.g., an office, a building or a factory) are known as Local Area Networks (LANs). The range of LAN is 10meter to15 meters. The key purpose of a LAN is the resource sharing. In a LAN one computer is designated as the file server . And it stores all the software and controls the network. Computers connected to the file server are called as workstation. The workstations can be less powerful than the file server.

9. Metropolitan Area Networks (MANs) This is a network which is larger than a LAN but smaller than a WAN. Metropolitan Area Networks (MANs) are the networks spread over a city. For example, cable TV networks that are spread over a city. The purpose of a MAN is also the sharing of the hardware and the software resources among its users. It uses the multiplexer to speed up the transmission. Multiplexer is a device that merges several low level transmissions into one high level transmission. It typically owned by a single person or company.

10. Wide Area Networks (WANs) The networks spread across the countries are known as WANs. A Wide Area Networks (WANs) is a group of computers that are separated by large distances and tied together. It can even be a group of LANs that are spread across several locations and connected together to look like one large LAN. The WANs link computers to facilitate fast and efficient exchange of information at lesser cost and higher speeds.

11. Network Topology: The actual geographical appearance of computer systems and its resources in a network is termed as Network Topology . Mainly there are Bus or Linear Topology Ring or Circular Topology Star Topology Tree Topology Mesh Topology

12. Bus or Linear Topology It connects the entire computer (Node) to a common straight cable. In this topology the host at one end of the bus. The transmitted data travels in the bus in both directions and can be received by any workstations. The Bus has a terminator at either end which absorbs the signals, removing it from the bus.

13. Advantages of the Linear Topology Short cable and simple wiring layout, since a single cable connects all the nodes. The installation cost is less and easy to maintain this layout. Easy Architecture. Easy to extend at any point of the network. The failure of one system does not effect to the other system. Disadvantages of the linear topology Control of the network is not centralized in any particular node. For long distances in Bus topologies have to arrange repeater to boost the signal. There should be a minimum distance between systems.

14. Ring or Circular Topology In this topology each computers (node) is connected in the form of ring (loop). In ring topologies that has no start and end point. Thus data travels in one direction only, from node to node around the ring. In this type of network, the data is passed through each node in the ring.

15. Advantages of the Ring topology Short cable length. The less connections will be needed. Less cost Each computer has equal access to resources. Disadvantage of the Ring topology The failure of one node will effect to the entire network.

16. STAR TOPOLOGY This topology consists of a central node to which all other nodes are connected. All communications between the nodes have to pass through the central computer. Star networks allow the network administrator to give selected nodes higher priority . It allow to centralized the data.

17. Advantages of Star Topology Easy to add another system to the network. Failure of a single system does not effect to whole network. Central system can make an administrator’s. Disadvantages of the Ring topology If the hub fails, the entire network comes down. It is too cost.

18. The Tree Topology It combines characteristics of linear bus and star topologies. It consists of group of star topology connected to a linear bus topology. Transmission in this topology takes place in the same way as in the bus topology. The transmitted data travels in the bus in both directions and can be received by any workstations. The Bus has a terminator at either end which absorbs the signals, removing it from the bus.

19. Advantages of Star Topology The network can be easily extended. Faulty nodes can easily be removed. Disadvantages of the Ring topology Use large amount of cable. It is expensive.

20. Mesh topology In this topology, each node is interconnected with other nodes. Communication is possible between any two nodes on the network either directly or by passing through other nodes . The mesh topology is commonly used in internet working environments .

21. Advantages of Star Topology The mesh topology is fault tolerance. (If there is break in cable it can be rerouted through a different pathway to send data from one system to another) Disadvantages of the Ring topology It require lot of wire It is very expensive