The Open Systems Interconnection (OSI) Model in Action
What is the OSI model? — OSI stands for Open Systems Interconnection. It’s a conceptual framework that splits the functions of a networking system into 7 layers that are easy to understand.
The Seven OSI Layers — The layers include the Physical Layer, Data Link Layer, Network Layer, Transport Layer, Session Layer, Presentation Layer, and lastly, the application layer.
Let’s explore email, which lives in the Application Layer of the OSI model, to get a better idea of how all the layers come together. To find out all of the layers of the OSI Model, click here (backlink)
- Specifically, the Application Layer is the email client, such as Microsoft Outlook, which users use to send data.
- At the Presentation Layer, the data gets converted into ASCII format and goes through the process of compression and encryption.
- Then, in the Session Layer, a session is started, and here, a header is added to label it. Then a connection is established between nodes.
- The Transport Layer is where the message is split into segments and transmission via the Transmission Control Protocol (TCP), and then the source and destination ports are added.
- At the Network Layer, the best physical routing path for the data segments is determined, and the right headers are also added. The segments that were created in the previous later are converted into data packets.
- Those data packets are passed on to the Data Link Layer, which converts the packets into frames and contributes the physical address of the node.
- It is at the Physical Layer that the data packets are received at the physical medium for transmission.
Unless you’re an administrator or IT professional, you likely won’t be thinking of the OSI model all too often, but it’s good information to know of regardless. Because of the way the OSI model distinctly separates the technical work across different layers, it makes it easier to isolate and troubleshoot the issues plaguing your network connection.
It also allows administrators and IT professionals to determine what type of software and hardware to use and informs manufacturing so that they’re able to create devices that can communicate with other devices built with the OSI model in mind. It’s also just a secure model for transmitting data.
How to troubleshoot a network issue using the OSI model
Unsurprisingly, most issues that plague network connections happen at the Physical Layer, Data-Link Layer, and Network Layer. For this reason, a good rule of thumb is to start your investigation here before proceeding to the other layers.
- Check to see that all physical devices related to your network are plugged in and working; it’s not uncommon that damaged cabling is the culprit of network problems. If you have a wireless connection to your network, the cause of the problem is likely to be excessive signal attenuation or wireless interference.
- If all your physical components are working properly and you’re still experiencing issues, it’s time to check the Data Link Layer. You can do so by verifying that all the VLAN and switch configurations are working properly; if those are good, move on to see if there are IP address conflicts—try to remove any duplicate IP addresses. Next, check the STP to make sure it’s functioning properly.
- Moving onto the Network Layer, this is where most routing and network addressing issues live. Make sure that your networking devices are not damaged, have the wrong configurations, are authenticated, and that you have enough network bandwidth.
- At the Transport Layer, network issues typically come from ports that are damaged or blocked. Disabling quality of service (QoS) may resolve the issue, but otherwise, you’ll want to make sure that none of your firewalls are blocking TCP/UDP ports.
- It’s rare that the network issue originates from the Session and Presentation layers because they play a less crucial role in keeping the network up and running.
- Finally, at the Application Layer, you’ll find that network issues are often related to the DNS, most of which can be fixed by using the “nslookip” command. You can also try using the “tcpdump” command, which filters TCP/IP packets and analyzes network packages.
The broader impact of the OSI model
Some argue that the OSI model is obsolete because of its more theoretical layer, but because the model helps frame discussions of protocol and helps contrast various technologies, it’s likely to remain relevant for a long time to come.
- OSI Model Use-Cases — While IT professionals and administrators are the ones who will engage with the OSI model most, it’s still useful to end-users and business people alike not just because of how it can help with network troubleshooting but also for how it breaks down network communication in an easy to understand way.
- Troubleshooting with the OSI Model — The OSI model helps with troubleshooting network issues by making it easy to investigate the problem step by step, analyzing the critical components of each layer, starting at the physical and then moving all the way up to the Application Layer. Network issues rarely stem from the Session or Presentation layers.
Managing your business’s Network Services
Understanding the OSI model can certainly help with DIY network troubleshooting, but that’s probably not a responsibility you want to deal with on top of managing the day-to-day of your business.
While it’s great to be able to handle your own network troubles, why not off-load that task to us with our Network & Wireless Connections service?
After all, a functioning network is a crucial component of your business’s IT security. Your network is the primary piece of infrastructure that facilitates access and delivers connectivity to all your servers, files, devices, and more.
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