When you have an MPLS network, there are a few ways that your traffic is divided for Class of Service treatment.  One common approach is at the carrier edge router.  Another approach, is based on tagging at your own network using DiffServ, which is then picked up by the carrier edge router.

DiffServ can support up to 64 classes, while the MPLS shim label supports 8 classes, which may or may not be supported by a carrier. 

Real Time Voice is configured with the EF queue, which will have the highest priority.

Video and High Priority Data is configured with the AF4, AF41, AF42 or AF43 queues.  The AF4 is typically used for video.  AF41/42/43 are usually used for critical business applications such as SAP, Siebel, PeopleSoft or Point-of-Sale (POS) traffic.

Priority Data is configured with AF3.

The fourth CoS level is configured with AF2.  This is used for Telnet, Extranet Web applications and general data applications.

The fifth CoS level is configured with AF1.  This is for non-interactive applications that are insensitive to drops and run in the background, such as content distribution and database synchronization.

Best effort is the lowest class of service and is configured with BE.  This works fine for FTP, database synchronization, email and web surfing.  This is also the default for any traffic that is not otherwise configured with one of the about DSCP labels.

Using traffic engineering, you can get better performance out of your MPLS network without spending money on unnecessary bandwidth.