n SONET revolution, bringing with it optically enabled IP, flexible architectures, and multiservice capabilities. This next-generation SONET environment is highly integrated for low cost and high density, guaranteeing simplified provisioning and integrated-packet services. Ethernet/RPR. Each technology has advantages and disadvantages yet all will play a major role in the metro market's growth. 33 Some of the questions being posed include the following: Will metro DWDM solve the metro band- width bottleneck? Will next-generation SONET be able to handle the data- centric Internet world? Will easy-to-use, low-cost Ethernet work its way out of the access and into the metro core market? The transition of the lower layers, particularly the physical layer of the network, is a complex task that must be undertaken diligently because all higher layers supporting telecom and data communications are dependent on it. Figures 1-8 through 1-12 show the current SONET-based architectures, evolving incumbents' archi- tectures, GbE/VLAN-based ELECs architectures, and two different evolv- ing architectures for next-generation carriers. Chapter 1 Figure 1-8 TYPICAL EXISTING NETWORK Architecture SINGLE ENTRY evolutions: existing Customer Building Metro Access Metro Core networks (subset). SONET SONET Core ATM Switches Copper/ Fiber SONET SONET Rings Optical Crossconnect Rings at at OC-12/48 (DSL, TDM, OC-3/12 Long Haul SONET Frame Relay, SONET Routers NX OC-3/12) TYPICAL EXISTING NETWORK DUAL ENTRY Customer Building Metro Access Metro Core SONET SONET Core ATM Switches SONET SONET Rings Optical Crossconnect Rings at at OC-12/48 (DSL, TDM, OC-3/12 Long Haul SONET Frame Relay, SONET Routers NX OC-3/12) TYPICAL EXISTING NETWORK DUAL ENTRY - STREAMLINED Customer Building Metro Access Metro Core SONET SONET Core ATM Switches Optical Crossconnect SONET Rings at OC-12/48 (DSL, TDM, Long Haul Frame Relay, SONET NX OC-3/12) SONET Routers Figure 1-13 depicts at a macroscopic level the migrations that are occur- ring from the point of view of a