# The Connections In Physical Structure Information Technology Essay

Two or more computers connected together and they able to share the data and other resources, then we can say that the computers in the network.

Networks are two types

Wireless Network.

Wired Network.

Wireless Network: wireless communication is one the fastest-growing technology. Connection using some telecommunication network whose inter connections between nodes is implemented without the use of physical cable. Radio waves are used to transmit the data between computes.

Wired connection: wired connection means connection through a physical cable (back bone).

There are two types of connections in physical structure.

Point to point

Multipoint.

Point to point: The point to point provides a dedicated connection between two devices .the entire capacity of the link is reserved for transmission the data between those two devices only. Multipoint: a multipoint connection is one in

Network Topologies: The term topology refers to the way in which a network is laid out. Two are more computers connected through a cable to a link; two are more links from topology. Topology of a network is representation of the connection of all links and nodes together. There are basically 4 types of topologies are possible

Bus Topology: In bus topology using a single cable to connect all devices. One long cable acts as a backbone to link all the devices in a network. Devices are connected to the bus cable by drop lines and taps. A drop line is a connection running between the systems/nodes and main cable. A tap is a connector that either splices into main cable or punctures the sheathing of a cable to create a contact with the metallic core. As a signal travel along the cable, some of its energy is transformed in to heat. Therefore, it become weaker as it travels tap to tap. Because of that we have a limited number of taps. And have to maintain proper distance between those taps.

The advantage of bus topology includes ease of installation. The cable which is used as a backbone is laid along the most sufficient path, and then connected to the nodes by drop lines of various lengths. Because of that, a bus uses the less hardware compared to other topologies like ring star mesh. The main advantage of this network is redundancy will be eliminated.

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The disadvantage of this network is it will be helpful if we have a limited number of devices. If more than few dozen computers will be added to the cable, performance will become low. If cable fails, the entire network becomes unusable.

Ring Topology: In a ring network, every system will connect exactly with the two neighbors for communication purpose. All messages travel through a ring in the same direction (clock wise or anticlockwise). If any cable or device breaks the loop and can take down the entire network.

A ring is relatively easy to install. To add or delete a device we require only two connections.

Generally in the ring network, information will go every time repeatedly. If one device does not working properly it gives an alarm. The alarm alerts the network operator to problem and where it happen

Anyhow, unidirectional traffic can be a disadvantage. In a simple ring network a brake in the ring will disable the entire network. This problem will be achieved by switch cable of closing off the break.

Star Topology: in a star topology each device will connect to a central hub. The devices are not directly connected with each other. The hub acts like a central server, if one device wants to send the data to another, its sends the data to the hub which then relay the information to another connected device

Each device needs only one link and one I/O port to connect it to any number of hubs. ThatÃ¢Ã¢â€šÂ¬Ã¢â€žÂ¢s why it is very is to install and reconfigure. Less cable is needed to configure the star topology .and additions moves and deletions are very easy. Between the hub and device. If

Tree Topology: tree network topology is a central node is connected to one or more other nodes that are one level lower in the hierarchy. It is combination of the bus and the Star Topologies. The tree like structure will allows you to have many servers on the network and you can branch out the network in many ways. Levant systems in their own network and yet connect to the big network in some way.

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Mesh Topology: In mesh topology every device has a direct link to all devices in the network.

If a device wants some data information will pass between those only directly, the main

advantage of this topology is redundancy will be redjuced .

## Calcutation of how many nodes will connected to a mesh topology:

In mesh each node must connected with another nodes (ie node 1 will connect to the n-1 nodes). We need n(n-1) physical links.however, If each physical link allows communication in both dirrections (duplex mode). We can devide the number of links by 2. In other words we can say that in a mesh topology , we need n(n-1)/2

Suppose if we are connecting 15 nodes in a mesh topology, then the number of cables required;

N = n (n-1)/2 N = Number of cables

= 15 (15 Ã¢Ã¢â€šÂ¬” 1)/2 n = Node

= 15*14/2

= 15*7

= 105

So the total number of cables required for connecting 15 nodes = 105.

## OSI MODEL:

OSI model is established in 1947, (Open System Interconnection Reference Model)

That covers all the aspect of network communications is the open system interconnection model. It was first introduced in 1970Ã¢Ã¢â€šÂ¬Ã¢â€žÂ¢s. An open system is a set of protocols that allows any two different systems to communicate regardless of their underlying architecture. The purpose of OSI model is to show how a facility communication between the systems without changing their logic of understanding and designing a network architecture that is flexible, and transferable. It is developed as part of open system interconnection. In its most basic form it consists of seven separate but related layers.

The OSI model is a layered framework for design of network systems that allows communication between all types of computer systems. It consists of seven layers, each of which defines a part of the process of moving information across the network.

http://homepages.ius.edu/RWISMAN/B438/HTML/ch1_8.jpg

Physical layer: physical layer coordinates the functions required to carry a bit stream over a physical link. It deals with mechanical and electrical specifications of interface and transmission medium. This layer deals with the physical devices of the media being used to transmit the information. The physical layer notifies the data link layer that a frame has been received and passes it up. The physical layer is responsible for movements of individual bits from one node to next node.

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## DATA LINK LAYER:

The data link layer transforms the physical layer, a raw transmission facility to a reliable link.

The data link layer deals with providing one or more data link connections between two or more network entities. Data link layer performs the error check discards the frame if an error is detected. The responsibilities of the data link layer are Framing, Error control, Flow control, Access control.

## NETWORK LAYER:

Network layer is responsible for the source-to-destination delivery of a data, possible across multiple networks. The layer provides switching and routing facilities. Creating the logical circuits for transmitting the data from node to node.

If two systems are connected to a same link, there is no need of network layer. If two systems are connected to different networks there is often required the network layer to complete the transmission between sources to destination.

The other responsibilities of the network layer are logical addressing, routing etc.

## TRANSPORT LAYER:

Transport layer Manages source-to-destination message delivery in network.

Provides reliable and sequential packet transfer through error recovery and flow control mechanisms

Provides connectionless oriented data (packet) transfer.

The main responsibilities of transport layer are service point addressing, segmentation and reassembly, connection control, flow control.

## SESSION LAYER:

In some processes the physical, data link and network layers are not provide sufficient

Service. The session layer is network dialog controller.

The session layer responsibilities are synchronization and dialog control.

## PRESENTATION LAYER:

The presentation layer deals with the syntax and semantics of the information exchanged between two systems. It masks the differences of data formats between dissimilar systems. The presentation layer is responsible for translation, compression and encryption. Presentation layer will encodes and decodes data; encrypts and decrypts the data; compresses and decompresses data.

## APPLICATION LAYER:

APPLICATION LAYER enables the user, access the network. Interface to user processes for communication and data transfer in network Provides standardized services such as virtual terminal, file and job transfer and operations application layer is responsible for providing service to the user.

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