7. Application Layer - Data
6. Presentation Layer - Data
5. Session Layer - Data
4. Transport Layer - Segments
3. Network - Packet
2. Data Link - Frame
1. Physical - Bit
A Protocol Data Unit (PDU) is a unit of data specified in a protocol of a given layer of the OSI model. Each layer has its own PDU: at the Application layer, it's called a message; at the Transport layer, it's a segment (or datagram in UDP); at the Network layer, it's a packet; at the Data Link layer, it's a frame; and at the Physical layer, it's a bit or symbol. These PDUs help in managing and encapsulating data as it traverses through the layers of the OSI model.
Application layer: Data Presentation layer: Data Session layer: Data Transport layer: Segment (TCP) or Datagram (UDP) Network layer: Packet Data Link layer: Frame Physical layer: Bit
A layered network, or a network layer, is the set up of how data is sent over a network. Each layer has it's own responsibility by either capturing the data or routing it to a computer on the network.
The OSI model has seven layers whereby each layer has its function. The Data Link Layer is responsible for addressing data messages so that they reach their destination correctly.
What are two functions of the data link layer? (Choose two.) It segments and reorders the data. It exchanges data between programs that are running on the source and destination hosts. ***It controls how data is placed onto the media. It generates signals to represent the bits in each frame. ***It encapsulates each packet with a header and a trailer to transfer it across the local media. ============================ 1. Data Link layer do not reorder data - this is the job of Transport Layer 2. Programs are at Aplication Layer 4. Physical Layer generate signals
By encapsulation process data is put in a nutshell with all basic protocol information at each and every OSI layer. During this phase of network layer each layer conveys and exchange information to its neighboring layer. This is done utilizing Protocol Data Units.
physical layer
In the OSI model, encapsulation occurs as data is passed down through the layers. At the Application layer (Layer 7), data is created and then passed to the Presentation layer (Layer 6) for formatting. The Session layer (Layer 5) manages sessions, while the Transport layer (Layer 4) adds headers for segmentation and reliability. As data moves down to the Network layer (Layer 3), it receives IP addressing, followed by the Data Link layer (Layer 2), which adds MAC addressing and framing, and finally, the Physical layer (Layer 1) transmits the raw bits over the physical medium. Each layer adds its own header (and sometimes footer) to the data, forming a protocol data unit (PDU) specific to that layer.
The PDU (protocol data unit) @ transport layer (e.g. TCP or UDP) is called as 'segment' .
Protocol layers may be defined in such a way that the communications within a layer is independent of the operation of the layer being being used. This is known as "peer-to-peer" communication and is an important goal of the OSI Reference Model. Each layer provides a protocol to communicate with its peer. When a packet is transmitted by a layer, a header consisting of Protocol Control Information (PCI) is added to the data to be sent. In OSI terminology, the packet data (also known as the Payload) is called a Protocol Data Unit (PDU). The packet so-formed, called a Service Data Unit (SDU) is passed via a service access point to the layer below. This is sent using the service of the next lower protocol layer.
Packets
Layer 2 or the 'Data' layer of the OSI model encapsulates either 'bits' from the physical layer (1)- moving up the TCP stack or 'Packets' from the Network layer (3)- going down the the stack. 7 - Application Layer DATA 6 - Presentation Layer DATA 5 - Session Layer DATA 4 - Transport Layer SEGMENT 3 - Network Layer PACKET 2 - Data Layer (Incorporating LLC and MAC) FRAME 1 - Physical Layer BIT A good nmemonic for remembering the data encapsulation in the OSI model is 'Don't Some Peolple Fry Bacon' - Data, Segments, Packets, Bits.