 BLSR depends only on the aggregate eastbound or westbound traffic at the busiest node. When implementing the same ring as a UPSR, the aggregate of all services transported by the entire ring must be taken into account. Synergies with ATM ATM is a transport technology that evolved in the 1990s that can be used for multimedia and data services. ATM offers band- Traditional SONET Architectures Node-to-Adjacent- Figure 3-51 Hub Pattern Uniform Mesh Pattern Node Pattern Ring traffic patterns. Dashed lines denote traffic flow Figure 3-52 BLSR capacity analysis. Capacity Relative to a UPSR Distributed Mesh Traffic Pattern (Typical) (UPSR capacity) 100% All Traffic Hubbed Number of Nodes width efficiency, scalability, and service transparency for data, voice, video, and multimedia applications. To date, ATM has been extensively deployed in enterprise data networks, especially WANs with large amounts of bursty traffic. In these environments, the statistical multiplexing capabilities of ATM network elements allow the efficient transport of bursty data with- out unacceptable underutilization of facilities during off-peak periods. When distributing data embedded in ATM payloads among various WAN sites, two-fiber BLSRs offer two major advantages: A level of survivability that meets the most demanding reliability objects for mission-critical applications Efficient sharing of a common STS-3c ATM payload among multiple locations Chapter 3 The latter benefit is illustrated in the example ATM network that appears in Figure 3-53. As shown, a two-fiber BLSR links each site in the network. The ring's capability to reuse bandwidth is employed to deliver the same STS-3c concatenated SONET payload (STS-3c Payload A) to each location. This traffic routing enables the ATM network element at each site to efficiently pack traffic into a common payload through statistical multi- plexing. Thus, one economical STS-3c channel can replace an expensive arrangement of dedicated channels linking each site with every other site. Transporting Extra 