MPLS (Multi-Protocol Label Switching)
MPLS is the latest WAN technology and appears to be the current or future plan of most WAN service providers. MPLS has many of the characteristics of ATM that allow services providers control over how traffic flows in their networks. This allows providers flexibility in how they offer services, and allows them to quickly adapt to new market needs for different services. Because MPLS allows providers this flexibility, many are offering services that include quality of service guarantees. This has led to the misconception that MPLS implies QoS, which it does not. Often a service provider will have built a good QoS offering on top of their MPLS implementation, but the details of this QoS implementation need to be understood to insure that real-time traffic gets the right treatment.
Service providers using MPLS create different classes of service by configuring their routers to either recognize bits in the MPLS tag, or by prioritizing specific routes based on their individual labels. For either method, there are a fixed number of classes, often eight or less. Thus there will again be some mapping that needs to be done between DiffServ markings and the specific traffic classes implemented by the MPLS core. Most MPLS-based WAN providers are using DiffServ to identify traffic classes. Work with your proposed MPLS-based vendor to understand how they map and support the different DiffServ markings into the classes of traffic they support, and understand the forwarding behavior they specify for each class in their network.