The demand for more bandwidth is clearly driven by IP-based applications and consequently service providers are looking at infrastructure that best supports such applications. It has become clear that a packet-centric infrastructure is preferred, and such technologies are therefore displacing technologies like SONET/SDH, ATM and Frame Relay in new build-outs due to the high cost and lack of flexibility associated with these legacy technologies. Ethernet is rapidly becoming the transport technology of choice in access and metro networks because the worldwide deployment of LANs together with standardization has driven the price down considerably. In recent years data has surpassed circuit-switched voice and TDM leased lines as the predominant traffic on telecommunications networks. As result, carriers have increasingly deployed IP routers and Ethernet switches to handle the rapid growth in data traffic. Nevertheless, a large customer base will continue to use TDM service. Carriers face the challenge of supporting such services over IP/Ethernet networks which are not optimized for constant bit rate traffic - such as voice, T1/E1 and T3/E3 - that continues to provide the largest portion of telecom carrier revenues.