With the advent of data services and the requirement for greater bandwidth and application flexibility, service providers must architect their next-generation networks to be data-friendly while being more costeffective.Many technologies are accessible to engineer the nextgeneration network. One approach gaining traction is the concept of deploying a carrier-grade Ethernet-centric access network with a converged MPLS core network（metro and long haul）. This architecture will support both the next-generation Ethernet and IP services, as well as legacy（leased line, FR and ATM）services with pseudowires. Typically, service providers are not in a position to deploy a “greenfield” nextgeneration network without considerations for the existing legacy transport network. This paper will describe the co-existence and interworking between the legacy transport networks（PDH and SONET/SDH）and nextgeneration converged networks（Ethernet-centric access network with a converged MPLS metro/long haul network）.
