Recently Ethernet-over-SONET/SDH becomes an important topic due to massive growth of data traffic. In this paper, we propose a bandwidth efficient architecture that can transport 4 gigabit Ethernets and 20 fast Ethernets over OC-48 SONET connection. It includes a cross connect UTOPIA interface to aggregate traffic, a switch block capable of flexible and resilient LCAS member mapping, and an enhanced LCAS module that refines VCAT granularity into one-third of VC-3 (STS-1) so as to achieve 97% bandwidth efficiency in worst case. Moreover, we improve the performance of LCAS bandwidth management by modifying its control packet to achieve constant refresh time. In the end, we present a novel mapping scheme that eliminates the need of differential delay compensation memory for UDP/IP applications.