12
Chapter 1
The Campus Network
Enterprise Services
Enterprise services
are defined as services that are provided to all users on the
internetwork. Layer 3 switches or routers are required in this scenario
because an enterprise service must be close to the core and would probably
be based in its own subnet. Examples of these services include Internet
access, e-mail, and possibly videoconferencing. When servers that host enter-
prise services are placed close to the backbone, all users would be the same
distance from the servers, but all user data would have to cross the backbone
to get to the services.
Switching Technologies
S
witching technologies are crucial to the new network design.
Because the prices on layer 2 switching have been dropping dramatically, it
is easier to justify the cost of buying switches for your entire network. This
doesn't mean that every business can afford switch ports for all users, but it
does allow for a cost-effective upgrade solution when the time comes.
To understand switching technologies and how routers and switches
work together, you must understand the Open Systems Interconnection
(OSI) model. This section will give you a general overview of the OSI model
and the devices that are specified at each layer.
For more detailed information about the OSI model, please see
CCNA: Cisco
Certified Network Associate Study Guide
, by Todd Lammle (Sybex, 2000).
You'll need a basic understanding of the OSI model to fully understand dis-
cussions in which it is included throughout the rest of the book.
Open Systems Interconnection (OSI) Model
As you probably already know, the OSI model has seven layers, each of
which specifies functions that allow data to be transmitted from host to host
on an internetwork. Figure 1.4 shows the OSI model and the functions of
each layer.
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