Modular Approach in Voice Network Design

Implementing voice requires deploying delay-sensitive services from end to end in all enterprise network modules. Use the modular approach to simplify design, implementation, and especially troubleshooting. Voice implementation requires some modifications to the existing enterprise network infrastructure in terms of performance, capacity, and availability because it is an end-to-end solution. For example, clients (IP phones) are located in the Building Access layer, and the call-processing manager is located in the Server Farm module; therefore, all modules in the enterprise network are involved in voice processing and must be adequately considered. Voice affects the various modules of the network as follows:

■ Building Access layer: IP phones and end-user computers are attached to Layer 2 switches here. Switches provide power to the IP phones and provide QoS packet classification and marking, which is essential for proper voice packet manipulation through the network.

■ Building Distribution layer: This layer performs packet reclassifications if the Building Access layer is unable to classify packets or is not within the trusted boundary. It aggregates Building Access layer switches (wiring closets) and provides redundant uplinks to the Campus Core layer.

■ Campus Core layer: The Campus Core layer forms the network's core. All enterprise network modules are attached to it; therefore, virtually all traffic between application servers and clients traverses the Campus Core. With the advent of wire-speed multilayer gigabit switching devices, LAN backbones have migrated to switched gigabit architectures that combine all the benefits of routing with wire-speed packet forwarding.

■ Server Farm module: This module includes multilayer switches with redundant connections to redundant Cisco Unified Communications Managers, which are essential for providing high availability and reliability.

■ Enterprise Edge: The Enterprise Edge extends IP telephony from the Enterprise Campus to remote locations via WANs, the PSTN, and the Internet.

Figure 3-22 shows the voice network solution in the Cisco Enterprise Architecture. It illustrates how a call is initiated on an IP phone, how the call setup goes through the Cisco Unified

Communications Manager, and how the end-to-end session between two IP phones is established.

Note that Cisco Unified Communications Manager is involved in only the call setup.

Figure 3-22 Voice Transport Example

Figure 3-22 Voice Transport Example

Calls destined for remote locations traverse the Enterprise Edge through the WAN and MAN and Site-to-Site VPN module or through the Remote Access and VPN module. Calls destined for public phone numbers on the PSTN are routed over the Enterprise Edge through the Remote Access and VPN module. Calls between IP phones traverse the Building Access, Building Distribution, and Campus Core layers, and the Server Farm module. Although call setup uses all these modules, speech employs only the Building Access, Building Distribution, and, in some cases, the Campus Core layers.

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