 local exchange) switch. Some users are serviced by xDSL, and these lines terminate on a DSL access multiplexer (DSLAM). The DSLAM links back to the local exchange for regular voice traffic, which is diverted out over the PSTN, and it also has connections into the packet-based backbone (which could be a core or backbone network based on IP, ATM, Frame Relay, or MPLS) for data traffic. Some users have dialup modems that terminate on remote access devices; through digital access cross-connects and routers, they use private lines to access their corporate facilities to work with internal LANs and resources. Customers who have optical networks have a series of multiplexers onsite that multiplex sub- optical carrier levels up to levels that can be introduced into an SDH/SONET Chapter 10 Next-Generation Networks End Office Tandem Edge Network Dialup Modems Router/Switch Class 5 Switch ATM/FR Switch DSL Modem Core Router DSLAM Ethernet/ATM/ HFC Plant IP Switch Cable Modem Private Line Enterprise SONET Networks Switch Frame Relay Enterprise Edge Switch Networks Enterprise ATM Edge Switch Networks Enterprise IP Edge Router Networks Figure 10.4 Today's networks add/drop multiplexer to carry that traffic through the SDH/SONET ring, or today they may even have connections directly into DWDM systems. Customers also have Frame Relay, ATM, and IP switches and routers that interface into comple- mentary equipment within the carrier network. Between the access and the edge is a plethora of different equipment, requiring different interfaces; different provi- sioning, billing, and network management systems; and different personnel to han- dle customer service and technical support and maintenance. The core network is increasingly becoming optical. Therefore, there is access into the high-speed optical multiplexers via routers or switches, and then those opti- cal carrier levels in the SDH/SONET hierarchy are further multiplexed via DWDM systems to take advantage of the inherent bandwidth available in those fibers. The broadband a