The OSI Network Model

Open System Interconnection or OSI models were created to serve as tools that could be used to describe the various hardware and software components that can be found in a network system.

Over the year we have learned that this is particularly useful for educational purposes, and in expressing the full details of the things that need to occur for a network application to be successful.

Ads

This particular model consists of seven separate layers, with the hardware placed at the very bottom, and the software located at the top.

The arrow identifies that a message originating in an application program in the column listed as #1 must make its way through all of the other layers contained in both of the computers in order to make it to the destination application in the column listed as #2.

This process could easily be compared to that of reading an email. Imagine Column #1 and #2 as computers when exploring the figure below:

The first layer, which is clear labeled as the physical layer, is used to describe components like that of internal voltage levels, it is also used to define the timing for the conduction of single fragments.

The next layer is the Data Link, which is the second layer that is listed in the example above, this often relates to the sending of a small amount of data, this could be and often is a byte, it is also often used for the task of error corrections.

The Network layer follows the Data Link layer, this defines how to transport the message through and within the network. If you can stop an moment and think of this layer as one working with an internet connection, it is easy to imagine that it would be used to add the correct network address.

Next we have the Transport layer, this layer is designed to divide small amounts of the data into smaller sets, or if needed it even severs to recombine them into a larger more complete set. The Transport layer also deals with data integrity; this process often involves a checksum.

Following the Transport layer we find the Session layer, this next layer is related to issues that go further or are more complicated then a single set of data.

More to the point the layer is meant to address resuming transmissions like those that have been prematurely interrupted or even some how corrupted by some kind of outside influence. This layer also often makes long term connections to other remote machines.

Following the Session layer is where we find the Presentation layer. This layer acts as an application interface so that syntax formats and codes are consistent with two networked or connected machines.

The Presentation layer Ialso designed to provide sub-routines as well, these are often what the user may call on to access their network functions, and perform some functions like encrypting data, or even compressing their data.

Finally we have the Application layer. This layer is where the actual user programs can be found. In a computer this could be as simple as a web browser surprisingly enough, or it could serve as a ladder logic program on a PLC.

Network Model Tips

After reading this article it is not hard to see the big differences between the Hierarchical Model and the Network Model. The network model is by far more complicated and deals with larger amounts of information that can be related in various and complicated ways.

This model is more useful due to the fact that the data can have many-to-many relationships, not restricting in to a single parent to a child structure. This is how the Hierarchical Model works with data.

Though the Network model has been officially replaced by the more accommodating Relational Model, for me it is not hard to imagine how it can still be used today, and may very well still be being used by PCs around the globe when I think of the Network Model in relation to how we email one another.

Ads

After reviewing the information and investigating the facts of the Network model I have come to the conclusion that it is a sound and relatively helpful model if not a bit complicated.

Its one major downfall being that the data must be predefined; this adds restrictions and is why a more suitable model was needed for more advanced data. Ultimately this one restriction lead to the model’s untimely replacement with in the world of data analysis.

First Page: Network Model