The OSI model is a tool used to provide a standard set of
rules for communication across multivendor hardware. Each
layer of the OSI model has a function it must accomplish,
but the method to perform this function is left to the devel-
oper. As data flows down each of the layers, encapsulation
takes place allowing for reassembly of the data on the re-
ceiving machine. Each layer is responsible in part for the
complete data transfer from the source host to the destina-
tion host. Knowing the OSI model will help in troubleshoot-
ing Cisco networks.
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Scenario Lab 1.1
You have been asked to begin a large design and implemen-
tation project with Network Solutions, Inc. (a fictional com-
pany). However, before you are allowed to proceed, the
project manager wants to be sure that you are the correct
person for the job. This person asks you to list the layers of
the OSI model and describe in brief the functions of each
layer. Can you prove you are the correct person for the job?
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By working through this chapter, you should have sufficient
knowledge to answer these exam objectives:
• Identify and describe the functions of each of the seven
layers of the OSI reference model.
• Describe data link addresses and network addresses
and identify the key differences between them.
• Define and describe the function of a MAC address.
• Identify at least three reasons why the industry uses a
• Define and explain the five conversion steps of data
• Define flow control and describe the three basic meth-
ods used in networking.
• List the key internetworking functions of the OSI Net-
work layer and how they are performed in a router.
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1.The technology used to connect multiple computers to-
gether in a single office is called:
2.Connecting multiple networks together using an out-
side carrier’s signal, such as the telephone service is
3.Why should we use layered models in a network archi-
tecture? (select all that apply)
a.It tells us exactly how to perform a specific func-
b.It allows us to take a complex method and break
it into smaller, more manageable methods.
c.A change to one layer has no affect on any other
d.A change to one layer affects all other layers.
e.It restricts us to using only one network vendor.
f.It makes troubleshooting networks easier by being
able to locate the exact layer causing the problem.
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