Case Study | Network Sales and Services Handbook (Cisco Press Networking Technology)

The following (two) case studies illustrate the network hierarchical model first from the customer perspective, and then from the network NSP perspective.

Figure 14-12 illustrates a customer LAN/WAN internetwork architecture.

Figure 14-12. Enterprise Customer LAN/WAN Architecture

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The following list details the hierarchy found in this LAN/WAN internetwork:

Core functionality is represented by the WAN; providing site interconnectivity through Frame Relay, ATM, or IP VPN.
Site X represents a remote office LAN, with severs, workstations, and a WAN router. Distribution and access functionality is represented by the WAN router.
Site Y represents a medium site, using a LAN switch (for example, Cisco 3550/4000 Series Switches) to interconnect multiple LAN segments, as well as enabling WAN connectivity (through the WAN router). Distribution functionality is provided by the WAN router and access functionality is provided by the LAN switch in place. These LAN switches also can provide distribution functionality within the CAN/LAN environment.
Site Z represents a large site, also using a LAN switch (such as Cisco 3550/4000/6000 Series Switches) to interconnect multiple LAN segments, as well as enabling WAN connectivity (through the WAN router). Distribution functionality is provided by the WAN router and access functionality is provided by the LAN switch in place. These LAN switches also can provide distribution functionality within the CAN/LAN environment.

Figure 14-13 illustrates a NSP architecture.

Figure 14-13. NSP Architecture

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The three-tiered hierarchy of this network is defined in the following list:

Core functionality is represented by the WAN switches in the core of the NSP's network backbone. These WAN switches are interconnected with high-speed dedicated lines, such as an OC-48/192 (2.5 Gbps/10 Gbps) SONET implementation or DWDM 2.5 Gbps/10 Gbps wavelengths.
Distribution functionality is represented by the network edge routers/switches, connected to two core switches for link redundancy.
Access functionality is represented by the customer WAN router.