 focus of carriers was on building core transport networks The Ultimate Guide to Building and Delivering OSS/BSS using SONET and then WDM technology at the physical layer (layer one). These technologies are a given in the core. The focus in the core now is on network layers above the physical layer. Currently a variety of core networks, often parallel, operate at layer 2 and above - TDM, FR, ATM, and Service providers spend a lot of money converting traffic to move around all the protocols. Until recently, ATM and FR were the few technologies could boast of delivering and supporting QoS-based services. However, the rapid growth in IP services and development of more capable IP QoS capabilities will allow much broader use of IP networks. Multi-protocol Label Switching has coupled ATM-style QoS capabilities with the routing flexibility of IP. This is fueling a tremendous interest in MPLS-based IP services, such as IP VPNs and DSL aggregation. The core network of the future might very well be an "outer core" of ATM switches connected to an "inner core" of optically connected, MPLS-enabled switch/routers. 1.4 QoS Guaranteed Service Delivery For years service providers have been trying to develop and deliver services that can be differentiated by their quality of service levels. Since IP networks were inherently best effort and connection-less, they used primarily ATM-based networks to deliver and guarantee QoS levels. To allow more and more types of traffic - voice, various types of data, video, etc. - to migrate and carry over the IP network, IP must support various service levels, such as guarantees regarding bandwidth, end-to-end delay, jitter and packet loss. Multiple IP QoS mechanisms are in place now to start implementing QoS- based services over IP networks that can scale to carrier-class. First came RSVP (Request reSerVation Protocol), a protocol that enables applications to setup reservations over the network for various services required. RSVP is essentially a signaling mechanism used for resource setup, in