5/16/2023 0 Comments And yet it moves switch portMoving down the line, the Internet Layer would receive the Transport Layer’s PDU, encapsulate it with the source and destination IP addresses, then send the entire packet to the appropriate recipient. Once received by the Transport Layer (most common would be the use of TCP to ensure proper message delivery), this layer encapsulates the Application Layer’s PDU with the source and destination ports. When that layer’s PDU is sent to the next layer (following the TCP/IP model, it would be Transport Layer but OSI has a few intermediary layers), the PDU is known as a segment if TCP is used as the Transport protocol or datagram if UDP is used instead. Since we start on the Application Layer, there is only that layer’s payload data. Each subsequent layer encapsulates the previous layer’s PDU with that layer’s respective headers and is then sent to the next layer. Data on any layer is referred to as a protocol data unit (PDU). If a user is using a web browser, they’ll be making HTTP requests, email usage would entail IMAP/POP3/SMTP, etc. Since this payload is made at the Application Layer (Layer 7 of OSI, Layer 4 of TCP/IP Model), think of it as that application’s way of formatting the data by means of the specified protocol. When conducting network-based activities, actions are carried out by the underlying operating system (OS) and includes the need to transform a user’s request into a network-appropriate format.Īfter a request is made, it is transformed by the underlying OS into a payload or data (refer to Figure 1 Data unit column values). All the processing that a computer does is in the background and automatic, fortunately, as the technical details can get a tad complicated. Whether browsing the web, checking emails, or listening to the latest episode of The 443 Podcast, typical usage entails clicking and typing. Figure 1: OSI Model depicting its seven layers with example objects in each layer, as well as their data units and functionįigure 2: Comparing and contrasting the OSI Model vs TCP/IP Model.Īs an average user, the most common way of interacting with a computer would be via an application. Figure 1 depicts the OSI model, Figure 2 compares and contrasts the OSI model with the TCP/IP suite. Regardless which model you reference, the core concept is the same in that they both separate the duties of transmitting data into different layers. ![]() There are two main models that are accepted: the Open Systems Interconnection (OSI) model separates duties into seven distinct layers and the TCP/IP model does so in four distinct layers. That is, what happens when a user on a network node communicates with another networked node. Building on the Networking Basics article previously written and a high-level overview of How Servers Serve Content, I wanted to write about how data actually moves over a network.
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