Data encapsulation at each layer of the OSI reference model

Data encapsulation at each layer of the OSI reference model
Application
Presentation
Session
Transport
Network
Data Link
Physical
Segment
PDU
Packet
Frame
Bits
TCP header Upper-layer data
IP header Data
LLC header Data
MAC header Data
0101110101001000010
Upper-layer data
FCS
FCS
390
Chapter 12 
The Campus Network
Looking at Figure 12.5, you can follow the data down through the OSI reference model as
it’s encapsulated at each layer. Cisco courses typically focus only on layers 2 through 4.
Each layer communicates only with its peer layer on the receiving host, and they exchange protocol
data units (PDUs). The PDUs are attached to the data at each layer as it traverses down the
model and is read only by its peer on the receiving side. Each layer has a specific name for the PDU,
as shown in Table 12.1.