The Enterprise Edge can have multiple WAN interconnections. Common connectivity modules include but are not limited to the Internet, the demilitarized zone (DMZ), and the WAN. Internet service providers (ISPs) offer many connectivity options for the Internet and DMZ modules of the Enterprise Edge. Internal WAN connectivity between an organization's headquarters and remote sites generally is across a service provider or carrier network. PSTN connectivity still exists for teleworkers and more recently because of the increasing use of VoIP offnet services.
WAN technologies such as Frame Relay exist for point-to-point (P2P) and multipoint WAN services. Service providers also offer full IP WAN solutions such as MPLS where the Enterprise Edge router interacts with service providers at Layer 3. Public WAN connections over the Internet are also available through the use of cable and/or DSL technologies. Typically, these services do not provide any guarantee of network availability, as do Frame Relay and MPLS network solutions.
Figure 5-2 illustrates the use of modules, or blocks, in the Enterprise Edge.
Figure 5-2 WAN Interconnections
Building Acces m k
Data Center / Server Farm
Data Center / Server Farm fll u
Remote Access _> VPN
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