 protocol architecture (a more detailed protocol stack is included at the end of Chapter 3, "Traditional SONET Architectures"). Some of these migration steps are more likely than others: IP over ATM to IP over SONET ATM traditionally provided connection-oriented virtual channels. A mechanism exists in ATM for Advances and Opportunities in Next-Generation SONET Figure 1-9 INCUMBENTS, EMERGING NETWORKS Architecture SINGLE ENTRY evolutions: Customer Building Metro Access Metro Core incumbents (subset). Optical Switch Copper/ Optical Fiber Switch Optical Crossconnect Mesh or xDSL, TDM, Long Haul Frame Relay, Ethernet Routers NX OC-3/12 Optical Access Optical Switch Switch INCUMBENTS, EMERGING NETWORKS DUAL ENTRY Customer Building Metro Access Metro Core Optical Optical Switch Switch Optical Crossconnect Mesh or xDSL, TDM, Long Haul Frame Relay, Ethernet Routers NX OC-3/12 Optical Access Optical Switch Switch INCUMBENTS, EMERGING NETWORKS DUAL ENTRY - STREAMLINED Customer Building Metro Access Metro Core Optical Optical Switch Switch Optical Crossconnect xDSL, TDM, Long Haul Frame Relay, Ethernet Optical Routers NX OC-3/12 Optical Switch Switch supporting QoS. SONET/SDH provides for TDM circuit transport and grooming. Protection and restoration (within 50 ms) are also provided by SONET. The OTN supports the transmission of one or more (SONET) optical channels over a fiber pair. When more than one channel is supported, a WDM technique is needed. For sometime now, ATM has been in the process of being replaced/eliminated from very Chapter 1 Figure 1-10 EVOLVING ELEC/VLAN MODEL (HIGH END) Architecture SINGLE ENTRY evolutions: GbE Customer Building Metro Access Metro Core VLAN ELECs (subset). Optical Ethernet Switch Switch Optical Copper/ Switch Fiber Optical Crossconnect ::::: Services: Ethernet Long Haul Ethernet Switch Routers Ethernet Optical Switch Switch EVOLVING ELEC/VLAN MODEL (HIGH END) DUAL ENTRY Customer Building Metro Access Metro Core Ethernet Optical Optical Switch Switch Switch Optical Crossconnect Services: