Page 742 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide
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FIGURE 11.3 Representation of the OSI model peer layer logical
channels
The message sent into the protocol stack at the Application layer (layer
7) is called the data stream. It retains the label of data stream (or
sometimes the label of protocol data unit [PDU] is applied) until it
reaches the Transport layer (layer 4), where it is called a segment (TCP
protocols) or a datagram (User Datagram Protocol [UDP] protocols).
In the Network layer (layer 3), it is called a packet. In the Data Link
layer (layer 2), it is called a frame. In the Physical layer (layer 1), the
data has been converted into bits for transmission over the physical
connection medium. Figure 11.4 shows how each layer changes the
data through this process.
