Thursday, 19 April 2012

OSI Model

OSI Layers Protocols

The OSI model acts as the standard architecture for communication systems in modern society. The OSI model standardises the whole inter-communication process by dividing it into the seven layers each layer in the OSI model has their own individual tasks to complete.

The main aim of network layers is to solve a complex problem into smaller pieces and hiding information as it may be easy to hack data which is stashed in a single place. The OSI model is also very important because the OSI model provides a universal set of rules that make it possible for various manufacturers and developers to create software and hardware that is compatible with each other.

Layer 1: Is the physical layer which manages the electrical impulses and conveys light or radio waves through the network at mechanical and electrical levels. So it basically manages the physical hardware such as defining components such as cables and cards. The first layer of the OSI model is primarily concerned with media, the actual physical wiring that connects a network; and with the standards for a particular media the physical later is concerned with transmitting raw bits over the media. This layer is important because it is the only layer which actually operates physically. Although as a result this layer doesn’t have any idea on the actual contents of the messages.  This layer is closely linked to the 2nd because physical components such as an Ethernet cable but the actual maximum length are closely linked to the message format which is managed by the data link layer. At this layer data is transmitted using types of signaling such as electric voltages and pulses of infrared. This layer uses network devices such as repeaters which basically repeat a signal to a port from another port. The repeater which is located in this layer is then able to expand a network way past the distance limitations. That’s one factor which makes this layer so important. This is also an important layer because this is where the formatted data exits the network cable.

Layer 2: Manages the data link where data packets are encoded into bits. This layer also cleans up transmission protocols and also handles errors in the physical layer. It also manages the data flow. This layer although is divided into two layers which are the media access control and the logical link control. The media access manages how a computer on the network gains access to the data stored there and the gives permission for it to be transmitted. The error checking layer 2 uses is Frame checking sequence. The data is then taken up to layer if it passes the (FCS). This is an important layer because it ensures the data is error free by the time it reaches the network layer.

Layer 3: This layer manages the network part of the OSI model. So it primarily manages switching and routing technologies, but also handles error handling, congestion control and packet sequencing. So this layer is very important when it comes to transferring data to external sources. Layer 3 protocols include IP which stands for internet protocol. This layer is also responsible for compressing larger packets into smaller packets where it is then moved onto layer 4. This layer is important because it allocates unique addresses to nodes. An example of a piece of a hardware which uses the IP protocol is a router which allows Local area connection to connect to WAN.  This layer uses the IP information to then determine the best possible transmission path between the source and target. This layer is important because it obtains an IP header

Layer 4: This layer is the transport layer which provides transparent transfer to end systems and hosts. This layer is crucial because it ensures complete data transfer. This is the middle layer but does have much in common with the higher layers such as 5, 6 and 7 it relies on the lower layers to manage the process of transferring data. This layer has to be modernizes because as computers now mostly multitask so has to handle a number of different software applications which are both sending and receiving data. The transport layer must keep track of what data comes from each application. So that is can be sent in one flow to the lower levels. Another protocol this layer has to undergo is the reassembly of broken packets which may have been corrupt as a result of the editing and movement in layers in which it had to go through.  This layer is important because it ensures all the data is in the right sequence and error free. It uses flow control to enable that the information is sent with the correct properties. This layer obtains information linking with the TCP header which stands for transmission control protocol.

Layer 5: This layer which is called the session layer has important protocols such as managing and terminating connections. So this layer basically sets up conversations between applications at each end. This layer manages the transaction sequencing. This layer also keeps a log and notification if a message fails. A completed conversation will then enable the data to be moved up to layer 6. The layer is used to ensure the connection between two nodes and to make sure it remains maintained until it is disconnected. This layer is important because it manages the security of the session. Checksums will be used during data synchronization to ensure all the data reaches its destination without error. This layer is important because it sets up conversations between applications and then enables it to be sent to layer 6.

Layer 6: The presentation layer is unique from the others because it translates data into a network format but also has the capability of doing the opposite. It transforms data into a form the above layer which is the application can accept. It formats layers so that it can be sent over a network so you don’t have to worry about compatibility errors. Here is an example of some formats which would be converted. GIF,HTML and JPEG. This is important because the data needs to be in a form of information which is presentable for the application layer. The presentation layer is also in charge of the security of the data and the way it does this it encrypts data. Encryption is when data is locked in a sequence which can only be known by the user as it could have millions of possible combinations. All data stored here is either in graphical, video or sound format.

Layer 7: The top layer known as the application layer manages end user processes. It identifies several factors such as which you are communicating to and the quality of service. It keeps in mind privacy and any constraints on the data. Everything here is application specific so also provides services such as file transfer and e-mail. This is an important layer because it enables application to access the network, which is needed because it’s not executed by any of the other layers. The application layer also has to manage syntax rules. The application although isn’t the actually application but it’s the layer which provides the services. This player is also responsible in finding what resources are required. This layer will also enable your computer to communicate with other computers at a high level. When this layer has executed its tasks correctly it will then be able to present the data in a browser.

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