OSI stands for open systems interconnection. This is a type of conceptual model that has been put together by the International Organization for Standardization for the purpose of enabling diverse communication systems to communicate with the use of standard protocols.
If that sounds like a bit of a mouthful, in more simple terms, OSI provides a standard for various computer systems so that they can communicate with one another effectively. The main rival to the OSI model is the TCP/IP model, which you may be familiar with.
This is viewed as a universal computer networking language. It is based on the concept of splitting up communication into seven OSI model layers, with each one stacked on top of the last.
In this post, we will explore the pros and cons of the OSI model in further detail so that you can get a better understanding.
Understanding the OSI Model layers
To understand the OSI model, we need to look at the different layers. These are as follows:
Layer 1 – The physical layer
This layer transmits raw bit stream via a physical medium. It is the bottom-most and first layer of the OSI model, mainly providing bit-stream transmission. It also characterizes the signal type, connector type, and media type utilized for communication.
Layer one will provide a transmission interface between the transmission media and devices, as well as define the kind of topology to be used for networking along with the kind of transmission mode that is needed for transmission.
Some layer one devices include the likes of Ethernet cable connectors, repeaters, and hubs. These are the basic devices that are used for transmitting data via a physical medium that is appropriate as per the network requirements.
Layer 2 – The datalink layer
This layer defines the format of the data on the network. The main aim of this layer is to carry out error detection, as well as combine the data bites into frames. Raw data is combined into bytes, and bytes are combined into frames, which transmit the data packet to the network layer of the desired destination host.
At the destination end, this data link layer will get a signal, which is then decoded into frames and delivered to the hardware.
Layer 3 – The network layer
The network layer determines the physical path the data is going to take. This layer is accountable for accomplishing the routing of data packets from the source to the destination host, between intra networks and inter networks that operate on different or same protocols.
In basic terms, this layer is all about finding the easiest, time-efficient, and shortest way out between the receiver and sender in terms of exchanging data with the use of routing protocols, error detection, switching, and addressing techniques.
Layer 4 – The transport layer
The transport layer will transmit data with the use of transmission protocols, including UDP and TCP. It is all about controlling the transfer of data between hosts and systems. It includes data rates, where the data ends up, and how much to send. If you see UCP or TCP, this layer is where these protocols really come into play.
You will often find that the transport layer is grouped as a middle layer with layer three, the network layer, as being responsible for routing.
Layer 5 – The session layer
The session layer maintains connections and is responsible for controlling sessions and ports. It is all about communication between the two devices. It opens the session and it ensures that it remains open while the data is being transmitted. There are also checkpoints, which means that a session is able to pick up where it left off if for some reason it closes prematurely.
Layer 6 – The presentation layer
This layer makes sure the data is in a usable format, and this is where the encryption of the data happens. It is all about preparing the data so that it is ready for the final layer; the application layer. The activity here specifically revolves around compressing, encrypting, and encoding the data, so that it is received by the application correctly.
Layer 7 – The application layer
The final layer is the human-computer interaction layer, which is where applications are able to access network services. It makes the most of end software, such as email clients or browsers. It gives you the ability to receive and send information that is relevant to the user, such as DNS, SMTP/POP, FTP, and HTTP.
What are the pros and cons of the OSI model?
Now that you have a better understanding of the OSI model and how it works effectively. So, what are the pros and cons of this approach?
5 benefits of the OSI model
- Network support – There is only one place to begin, and this is with the broad network support you can expect. This is because the OSI model is generic on default, and so it is supported by a whole host of devices and manufacturers. The vast majority of computer networks today use OSI as their standard model.
- Layer changes do not impact other layers – Every layer in the OSI model is separate from the other layers. As a consequence, any layer changes will not impact other layers. This is typically the case, but there are some exceptions, for example, if there are changes to the layer interface.
- Troubleshooting – As every layer in the OSI model is separated from one and other, troubleshooting is made even easier. If there is any sort of failure, the network administrator could identify the issue more successfully by looking at every layer. This means that you do not waste time evaluating the full network.
- The model is flexible – Another benefit to consider is the flexibility of the OSI model because it can work with both connectionless and connection-based services. If there is a scenario whereby you need to maintain reliability, then it is possible to utilize connection-based services. On the flip side, if you are worried about the speed of data transmission, connectionless services will be the better option to go for.
- Layer identification – Every layer in the OSI model is assigned the task of interfaces, protocols, and services. Yet the OSI model is able to clearly distinguish the task in every layer. As a consequence, all of the devices work with the OSI model and are able to support one and other.
5 cons of the OSI model
- Practical implementation is almost not possible – Because the OSI model is completely theoretical, practical implementation is incredibly difficult. Furthermore, the cost of implementation tends to be very high, so this can be a significant barrier.
- Collaboration problems exist – Another drawback is that there are some complications while working collaboratively. Every layer in the OSI model is not going to be able to work in parallel. Unless the data is passed from the layer before, the OSI layers are not able to work.
- The OSI model has a complex structure – In terms of structure, the OSI model is complex, especially when you compare it to the likes of the TCP/IP model. This is because there are different layers present, which have not been optimized. For instance, network layer functions and data link functions are not carried out by the same layer. Furthermore, this means there can be service duplications, which is when more than one layer ends up processing the same task.
- The OSI model can fall short of practical expectations – There are a lot of people that feel that when you put the OSI model into practice, it does not live up to expectations. This is something that was highlighted in the former point when we discussed the issue of duplication.
- Adaptation levels aren’t as strong as you may expect – Finally, a lot of companies were reluctant to use the OSI model to begin with because the TCP/IP model was so popular. The adaptation rates for the TCP/IP model have outperformed the OSI model, and this is largely because the former was first to the party, meaning more businesses decided to go down this route and they were not ready to accept change when the OSI model came about.
Final words about the OSI model
So there you have it: everything you need to know about the OSI model. As you can see, there are pros and cons associated with this computer network language. However, it is widely used around the world and enables us to carry out collaboration activities that we probably don’t even think twice about.