Enterprise Composite Network Model

The Enterprise Composite Model (see Figure 1-3) is broken into three large sections:
Enterprise Campus—Switches that make up a LAN
Enterprise Edge—The portion of the enterprise network connected to the larger world.
Service Provider Edge—The different public networks that are attached

The Enterprise Composite Model

The Enterprise Edge, shown in the following figure, details the connections from the campus to the WAN and includes:
E-commerce
Internet connectivity
Remote access
WAN

The Service Provider Edge is just a list of the public networks that facilitate wide-area connectivity and include:
Internet service provider (ISP)
Public switched telephone network (PSTN)
Frame Relay, ATM, and PPP