Open System Interconnect or OSI is one of the old network models based on which the most initial data transmission pathway or flow was formed. OSI model is quite the foundation and other network models such as 4-layer models were innovated later. TCP/IP is based on the 4-layer model which is for data transfer over the internet even now. The OSI model is still, however, useful with regards to study and visualization of data flow over a network. It comprises seven layers through which a data packet is transferred to reach its destination in a network. It is helpful in terms of understanding networking concepts, troubleshooting real-time issues, and various network devices and their compatibility with specific network layer. These seven layers are discussed at length in this post.
Get Introduced to the 7 Layers of the OSI Model
As mentioned, there are seven layers in this model which offers an insight into how a data packet traverses through them to reach the destination address. In this case, we must start from the seventh layer which is the topmost layer and the first layer is the bottom most one.
- Layer 7 or Application Layer: This can be called a web browser level layer as various browsers such as Google Chrome and Internet Explorer function on this layer. This is the layer where humans can access and communicate with the network, and data transmission happens in terms of a user to computer or network communication, which may be in the form or emails. The data packet or message is received on this layer, which indicates a computer or network to human communication. HTTP, SNMP, and DNS are a few widely used protocols for data transfer on this layer.
- Layer 6 or Presentation Layer: This OSI model layer encodes and decodes the data based on the destination where it is to be sent. It interprets and converts the syntax, which means from a natural language in an email to a digital one. This is because two devices or networks where data transfer happens may be dissimilar. So, this layer prepares the data to be transferred over to the sessions layer.
- Layer 5 or Session Layer: This layer opens up a session facilitating two networks or devices to communicate with each other. The session is disconnected once the data is transferred to the next layer.
- Layer 4 or Transport Layer: This layer accepts the data more towards the receiving end and breaks into smaller pieces when transmitting to the next layer. It can also restructure the data back to its original format. This layer looks into the flow and speed of transmission depending upon the network speed, signal strength, and connectivity.
- Layer 3 or Network Layer: This OSI model layer is important, as it decides the path for the data packets to traverse and reach the right destination. Also, it searches for the shortest and the best possible path from several paths a server has. Here, it uses what we know as the IP address. This layer performs another function of breaking down the data packets into smaller ones and again restructuring them into their original form at the receiving end. There are different network devices which operate on this layer including 10 Gigabit Ethernet switches and various PoE devices.
- Layer 2 or Data Link Layer: This is the most crucial and complex OSI model layer. It has two sub layers- Media Access Control (MAC) and Logical Link Control (LLC), wherein LLC is the upper and MAC is the lower layer within the data link layer. LLC detects the network protocols, arranges the data frames in a logical sequence, and identifies and fixes errors if any. MAC connects to physical devices for data transmission and reception. Various PoE devices, managed and unmanaged switches operate at this layer.
- Layer 1 or Physical Layer: This is the OSI model layer where cabling, network nodes, connectors, adapters, and wiring come into the picture. This layer sends binary data packets to the physical layer of the receiving computer or device in the network
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