Osi Model Questions Long
In the OSI (Open Systems Interconnection) Model, protocol data units (PDUs) are used to encapsulate and transport data between different layers of the model. PDUs are essentially the packets or frames that carry information from one layer to another.
Each layer in the OSI Model has its own specific PDU format, which is defined by the protocols used at that layer. These PDUs are created and processed at each layer as data is passed down or up the protocol stack.
Let's go through the different layers of the OSI Model and their corresponding PDUs:
1. Physical Layer: The PDU at this layer is called a bit. It represents the raw binary data transmitted over the physical medium, such as electrical or optical signals.
2. Data Link Layer: The PDU at this layer is called a frame. It includes the physical address (MAC address) of the source and destination devices, as well as error detection and correction mechanisms.
3. Network Layer: The PDU at this layer is called a packet. It contains the logical address (IP address) of the source and destination devices, as well as routing information and other network-related data.
4. Transport Layer: The PDU at this layer is called a segment (for TCP) or a datagram (for UDP). It includes the source and destination port numbers, sequence numbers, and other transport-related information.
5. Session Layer: The PDU at this layer is called a message. It represents the data exchanged between applications or processes running on different devices.
6. Presentation Layer: The PDU at this layer is called a message. It is responsible for data formatting, encryption, and compression, ensuring that the data is presented in a format that can be understood by the receiving application.
7. Application Layer: The PDU at this layer is called a message. It represents the data generated by the application itself, such as an email, web page, or file.
Each layer in the OSI Model adds its own header (and sometimes trailer) to the PDU received from the layer above, forming a new PDU specific to that layer. This process is known as encapsulation. When the data is transmitted, the PDUs are passed down the layers of the sending device and then passed up the layers of the receiving device, with each layer removing its own header and processing the data as necessary.
In summary, PDUs in the OSI Model are the packets or frames that carry data between different layers. Each layer has its own specific PDU format, and these PDUs are created, processed, and encapsulated as data is passed through the protocol stack.