What Is Layer 4?

Layer 4 is the layer you're looking for. It's the layer that ensures your data gets where it needs to go and gets what you need when you want it. It's also responsible for error recovery, flow control, and end-to-end transparency. It's unclear what we mean by "transparency," think about how much easier it is for you to email someone on your network than off of it. Your packets don't have to be routed through multiple networks or ISPs—they go directly from one endpoint to another. Layer 4 is like the chocolate chips in your cookie dough. It's not the central part of your cookie, but it makes it all work. A connection-oriented data stream is one service offered by layer 4. Flow control, multiplexing, and data reliability are other services provided by layer 4. The OSI model relies on layers for data and communication services. Layer 4 handles connections between hosts. In layperson's terms, layer 4 ensures that sending an email from one computer to another gets there in one piece! Layer 4 is like the delivery guy. It's responsible for getting your data from Point A to Point B, but it doesn't care about anything else. Layer 4 is the layer that has to deal with the actual raw data, and it does this by dividing it up into smaller chunks called packets. Each packet contains a header with the source and destination addresses, process information, and other packet-handling details. Layer 4 is to deliver these packets from one place to another, and that's all it cares about! It doesn't care if you're sending a picture of your cat or an email with your bank account information; Layer 4 wants to ensure that all your data gets where it needs to go in one piece.