Open Systems Interconnection model:

Open Systems Interconnection model:

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OSI models

Introduction

OSI (open systems interconnection) is a framework describing how information in an application in a single computer passes through physical mediums to a software application in other machines. It was developed in the 1970s as computer networking was growing there were two models that were merged in 1983 to give birth of the current OSI model in 1984 (Bora, et al.,  2014). It consists of seven layers, each with its network function. Currently, it is an architectural model for computer intercommunication. It breaks down network communication into seven smaller, manageable tasks to be fulfilled by each layer. Better still, each layer is self-contained; thus, each is independent of all other layers.

Moreover, the Open System interconnection model is divided first into two layers. The upper layer majorly deals in application issues and is only software implemented. Additionally, it is closest to the end-user. The lower layer, on the other hand, deals with data transportation . here, both hardware and software are implemented. It is closest to the tangible physical parts in a networking environment (Kumar, et al., 2014). It is particularly required to keep and transfer information on the right physical medium ( the right wire or router).

The most important reason for understanding models of the OSI model is to guide software developers and hardware creators. When these companies have a proper understanding of which layer they are found in, they can create interoperability between different products of different companies to work together. Consequently, without these layers, it is possible that a router from one company suppose tplink may not work with a switch from cisco systems. At the very core, it is a representation of a model standardizing communication facilities of telecommunication systems regardless of neither technology nor internal structures.furthermore it is a product of international organization for standardization (ISO) (Kumar, et al.,  2014). In each layer, an entity implements functionality and interacts with the layer below it while providing proclivity to the layer above it.

We will discuss these layers in detail describing their functions, the type of data they deal with, and the hardware devices associated with these layers. We will conclude with a brief summary of what we have discussed, and I will give you a few mnemonics to help hardwire these layers into memory. We will discuss these layers from the farthest from the user and bring it closer while adding features until we can understand what we observe in our applications.

Layer1: physical layer

This layer is responsible for the reception and transmission of raw data between a device and a physical transmission medium. Data is converted into optical, radio, or electrical signals. Here data is transmitted in the form of bits, and its role is to move bits from a node to another. When it has received data, it converts it into bits 1s 0or 0s and sends it to the data link layer.

Roles

Through Bit synchronization, it keeps bits in sync by the use of a clock controlling both sender and receiver; moreover, it performs  Bit rate control by determining the number of bits transmitted per unit time; usually seconds (Suresh,  2016). Better still, it determines the Topology, which determines how devices are arranged on a network such as bus, star, or ring topology. It further determines theTransmission mode, which controls data flow simplex duplex or full-duplex.

Hardware associated with this layer includes repeaters, cables, hubs, and modems, and protocols used include Ethernet.

Layer2: datalink layer

It provides data transmission from a node to another when they are directly connected while looking for and solving errors in the physical layer. This layer transmits data using its MAC( media access control) address.

It is further divided into a medium access control layer (MAC) whose role is controlling how devices access media and permit to transmit data and logical link control (LLC) layer that identifies protocols while error checking and performing frame synchronization.

A packet from this layer is broken into frames, and the senders and receivers media access control are embedded in the header.

Roles

The data link layer performs several functions, including framing, which enables sending of meaningful to the receiver through some patterns in the bits. Moreover, it shows physical addressing by adding mac addresses in the frames. It goes further to error control in the detection and retransmission of lost or damaged structures (Suresh,  2016). It also controls the flow rate to prevent choking a network receiver, and finally, it regulates access in shared communication channels such as in bus topology.

Here data is in frames, and the physical components associated with this layer is the network interface card embedded into computers. Other hardware includes switches and bridges.

(PPP) point to point protocol is a data link protocol associated with this layer.

Layer3: network layer

On this layer, data is transmitted from one host to another in a different network. On this layer, data is in the form of packets. This layer is responsible for routing data from its source to its destination (Kumar, et al.,  2014). It also keeps track of devices located on the network while determining the best path for data to follow.

Roles

The major role of this layer is internetworking, which is providing logical connections between different devices. Moreover, it performs addressing to recognize devices on the internet by adding destination and source addresses to the frames. Its significant role, however, is routing, which is the determination of the optimum path for data to follow (Kumar, et al.,  2014). Finally, it performs packet sizing, which is converting data into packets through internet protocol (IP).

Data in this layer is in the form of packets, and it uses hardware such as routers the protocols associated with this layer includes (IPv4) internet protocol version four and the more recent (ipv6) internet protocol; version 6.

Layer 4:transport layer

This layer is in charge of end to end delivery of the complete information conveyed. To explain it better we will give an example. A wants to send an email to B. His data is cut to small pieces (segmentation) before transmission. The flow of data is monitored to ensure B can receive at the rate that A is sending with (flow control). To ensure data is not lost depending on the type of communication after A has transmitted a set number of segments B sends one back to show that the data has been received (error control) therefore in case data is not received or is damaged it can be re-sent or in case of a connection problem.

Roles

The first two roles are segmentation and reassembly, whereby data is broken down to segments transferred one at a time it more over-performs service point addressing whereby a header is added specifying the port address (Kumar, et al.,  2014). In our example above, we would use port 80.

Here data is implemented in the form of segments and is regarded to be the most important in the Open systems interconnect model.

Protocols in this layer include transmission control protocol (TCP) and user datagram protocol (UDP).

Layer 5: session layer

This layer is responsible for connection establishment, maintaining sessions, authentication, and providing security.

Roles

It creates connections with remote applications. It manages sessions by providing half-duplex, simplex, or full-duplex operations (Dialog control). Moreover, it performs checkpointing and recovery, restarting, or suspending a session. Furthermore, it is responsible for gracefully closing a meeting.

Layer 6: Presentation layer

On this layer, data is transmitted into a form the application layer can accept. It creates interdependence arising from different data representations providing freedom from incompatibility issues. The application format is converted to and from network format.

Roles

This layer performs different functions such as compression and decompression since it reduces data to be transmitted over the network. It also encrypts and decrypts data in an effort to maintain privacy, and finally, it performs translation to handle the different encoding methods (Bora, et al.,  2014). Senders data is converted toa common format that is transmitted over the network, and this format can now be converted to any format that the receiver wants to use.

Protocols in this layer include external data representation (XDR), Transmission layer security (TLS), and secure sockets layer (SSL).

Layer7: Application layer

This is the layer closest to te user, and these applications on this layer interact directly with these applications. The data to be trans-=mitted is created here while creating access to the network and displaying received information.

Roles

On this later file access, file transfer, and file management occurs by allowing the user to access files, organize and retrieve them from a remote source (Bora, et al.,  2014). Moreover, it provides mail services and directory services whereby one can locate resources as though they are at one point but are distributed all over the globe.

Cross-layer functions are functions that are not entirely tied to a single layer and end up affecting multiple layers; these include aspects of management and ensuring data security (Helgeson, et al.,  2014). Such services serve to improve the confidentiality and availability of transmitted data. This model, however, differs from the TCP/IP transmission control protocol or internet protocol in that it has seven layers as compared to TCP/IP 4 layers.

Conclusion

In conclusion, we have begun by giving the history of the Open systems interconnect model and then divided it into two layers.we have also learned why we need the OSI model. We have dug deep into the layers of OSI. We have described what happens in the sheets as well as the hardware and protocols associated with these layers. Finally, as we know that OSI is just a reference model, it is, however, challenging to learn networking without the OSI model as it gives protocols, and shows the contrast in various technologies. Finally, here are two mnemonics to remember the OSI model.

Please do not throw sausage pizza away

Peter doesn’t need to sell pickles anymore

Reference

Briscoe, N. (2000). Understanding the OSI 7-layer model. PC Network Advisor, 120(2).

Bora, G., Bora, S., Singh, S., & Arsalan, S. M. (2014). OSI reference model: An overview. International Journal of Computer Trends and Technology (IJCTT), 7(4), 214-218.

Kumar, S., Dalal, S., & Dixit, V. (2014). The OSI model: Overview of the seven layers of computer networks. International Journal of Computer Science and Information Technology Research, 2(3), 461-466.

Day, J. D., & Zimmermann, H. (1983). The OSI reference model. Proceedings of the IEEE, 71(12), 1334-1340.