rchitecture is an increasingly complicated arena. Many differ- ent alternatives in the network have been engineered to support specific voice, The Next-Generation Network Infrastructure data, or video applications, meeting certain performance characteristics and cost characteristics. When we add up all the different platforms and networks we have, it's quite a costly environment and one that is difficult to maintain and manage cohesively. By building the overlay networks and separating access and transport functions, carriers manage to add capacity and new services without interrupting their existing services. However, the downside of this system is that the new ser- vices rarely use the same provisioning management and troubleshooting systems as the old network. These operations and management costs can amount to as much as half of the carrier's total cost to provide a service. The Three-Tiered Architecture The broadband architecture has three tiers. The first tier involves the access switches; it is the outer tier, associated with delivering broadband to a customer. The second tier involves the edge switches and is associated with protocol and data service integration. The third tier, the inner tier, involves the core switches and han- dles transmission of high-speed packet data throughout the backbone. Figure 10.5 shows the components that comprise these three tiers, and the following sections describe them. Intelligent Network AIN, SS7 Voice and Mobile Network Network Multiservice Voice Satellite Switching Network ATM/IP/MPLS Access Multiservice Multiservice Optical Core Backbone Wireless Frame Relay Network Switching Switching Multiservice Enterprise Network Media Router-Based Server Farm IP Network Network Figure 10.5 A multiservice network Chapter 10 Next-Generation Networks The Outer Tier: The Broadband Access Tier Access tier devices include leg- acy network infrastructure devices such as Class 5 local exchanges and digital loop carriers. The access tier also includes DSLAMs, which are designed to concen