When I first heard that switches have layers. I asked myself “Just like ogres?”. Unfortunately, the answer to that question is no, not like ogres. Layers, in networking terms, refer to the 7 different tiers of the OSI networking model. If you are just getting into networking and are on the first few steps to a networking associate certification, this is a great place to start reading about what, in the name of Cisco, is a networking layer.

The seven tiers of the OSI networking model, seen below, are a conceptual framework of the specific functions of networking equipment from the user interface or application layer (layer 7) to the physical data transfer (layer 1). Here they are in order from layer 1 to 7.

  • The Physical Layer
  • The Data Link Layer
  • The Network Layer
  • The Transport Layer
  • The Session Layer
  • The Presentation Layer
  • The Application Layer

The Application Layer Right now, this might be a bunch of random terms, but hopefully, after we dive into each of them a little bit further, we can walk away with some substantive networking knowledge. We will start with the large picture, then work our way down to the 1’s and 0’s, literally…

The Application Layer (Layer 7)

The layer where all the human-computer interaction occurs, and where applications access the network data. The application layer is responsible for manipulating the data on the screen to make it meaningful to the user. This layer is where the decision you make on your device starts the following chain of events in the networking model. The user can send data in many forms. For example: an email, a text message,  by accessing the internet through a web browser, a hypertext transfer protocol secure link (HTTPS), and other actions using a search engine.

The Presentation Layer (Layer 6)

Next, Layer 6, the presentation layer. This layer is responsible for preparing the data from and for the application layer. In more technical terms, it is responsible for translation, encryption, and the compression of data it receives from several devices. If the data needs to be encrypted or decoded, this layer will translate the data into legible data for the application layer or recode the data to be sent elsewhere.

The Session Layer (Layer 5)

Layer 5 is responsible for monitoring the communication between two devices, opening and closing the “sessions” as efficiently as possible. Think of the session layer as the security guard at the door of a data transfer, ensuring the right data comes in and out at the right time. The session layer also establishes data save checkpoints so that if there were to be a disconnect or crash, the session can resume from the checkpoint rather than from the beginning!

The Transport Layer (Layer 4)

Layer 4 deals with flow control. Managing the rate at which data is transmitted between devices, or through the metaphorical “security checkpoint”, to prevent congestion and ensure that the sender does not overwhelm the receiver. More specifically, layer 4 takes the data from the session layer, breaks it into segments, and then sends it to layer 3, where the data is reassembled into receivable “packages” called packets.

The Network Layer (Layer 3)

The Network layer is responsible for the boxing and unboxing of the packets. Or breaking up segments of information into network packets and reassembling them on the receiving end. Layer 3 also holds the responsibility of using a Internet Protocol address (IP) to route packets across the quickest path to the destination network.

The Data Link Layer (Layer 2)

I like to think of the data link layer as a post office of networking equipment. Just as the post office handles packages, the Data Link Layer handles packets! Layer 2 is responsible for the reliable transmission of data over a local area network. Ensuring that the packets are signed, sealed, and delivered to the intended recipient on the network. The data link layer also deals with issues such as framing, addressing, and error detection!

The Physical Layer (Layer 1)

Then finally, we have the “physical layer”. This layer is responsible for establishing the connection between the networking equipment and transmitting those important 1’s and 0’s that we know from our data. This connection can be tangible, in the form of ethernet console cables between devices. Or intangible, like the wireless technology that connects the devices.

A few things are important to remember, with this model. 1. Its important to know that a network switch does not operate at every layer of the OSI networking model. Depending on the brand, model, and targeted use case, most switches specialize in layer 2 or layer 3 protocols. The majority of switches use a physical ethernet cable to connect to their network putting them in layer 2. and Secondly, this system is fluid. Packets and information are constantly sent to and from different networks and checkpoints. Going from layer 1 to 7 and just as easily going from layer 7 to 1.

Here is the TL:DR:

The OSI networking model describes the the many different process of communication between networking gear. At the highest level of a user sending or initiating a message/action at the application level, to the little intangible 1’s and 0’s that ensure that these keystrokes I’m making get into your computer screen in a legible manner that forms this article! Data travels to and from each layer, set on the most efficient path from A to B, each layer performing checks and balances to ensure the puzzle is put together correctly on the users end.

In my humble opinion, networks can sometimes be a thing of mystery. Its not easy to understand the magic, but after a little dedication, and many analogies and metaphors, I hope it all starts to give a little bit of context to your everyday interactions with your network!

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