Switching Technologies
13
F I G U R E 1 . 4
The OSI model and the layer functions
The OSI model is the cornerstone for application developers to write and
create networked applications that run on an internetwork. What is impor-
tant to network engineers and technicians is the encapsulation of data as it
is transmitted on a network.
Data Encapsulation
Data encapsulation
is the process by which the information in a protocol is
wrapped, or contained, in the data section of another protocol. In the OSI
reference model, each layer encapsulates the layer immediately above it as
the data flows down the protocol stack.
The logical communication that happens at each layer of the OSI refer-
ence model doesn't involve many physical connections because the informa-
tion each protocol needs to send is encapsulated in the layer of protocol
information beneath it. This encapsulation produces a set of data called a
packet (see Figure 1.5).
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