A WLAN topology can be an extension to an existing scalable LAN. The
best-built and managed scalable internetworks are typically designed in layers,
following a hierarchical model. By using hierarchical layers, the user can
break a large network into smaller pieces, which can each be dealt with
separately. To understand the importance of layering, consider the OSI
Reference Model. The OSI Reference Model is a layered model for understanding
and implementing computer communications. By dividing up the total network
functionality into smaller pieces, or layers, the OSI model simplifies the
tasks required for two computers to communicate. Activity 4.1.6a shows many of
the devices that exist in a typical enterprise environment. The devices are
shown at the highest layer of the OSI Model, on which they operate.
Hierarchical models for internetwork design also use layers, to simplify the
task required for internetworking. Each layer can be focused on specific
functions, thereby allowing the user to choose the right systems and features
for the layer. As a result, a hierarchical model simplifies the management of
the internetwork and allows the user to control the growth, without overlooking
the network requirements. The Cisco three-layer hierarchical model is shown in
Figure
.
The
traditional wired devices that are utilized include routers, switches, servers,
and printers. These devices are shown in Figures
through
, along with
their graphical icons. Developing technologies, such as voice over IP (VoIP),
can add additional capabilities to both wired and wireless LANs. IP phones and
the graphical icon are shown in Figure
. Finally,
network security devices such as firewalls, VPN devices, and intrusion
detection systems are becoming requirements for a secure LAN/WAN. A Cisco PIX
Security Appliance and its icon are pictured in Figure
.
All of
these devices must be considered when implementing a WLAN solution. This is
because the WLAN must seamlessly interoperate with the existing wired network.
WLAN security configuration will be covered later in the course. The wired LAN
will continue as a predominant portion of the complete and modern network
system.