There is a distinct need to move towards providing service differentiation (diff-serv) in the Internet. Today's best-effort service model is not geared to support various levels of service to different users and the pricing of such services. The differentiated services architecture being developed in the IETF provides a framework within IPv4 to enable development of these features. The architecture distinguishes boundary nodes from interior nodes. Boundary nodes perform control plane functions such as policy, contracting, accounting and traffic conditioning (including metering, shaping, marking) whereas interior nodes need only implement a set of forwarding behaviors known as ``per-hop behaviors'' (PHBs). The PHBs at interior nodes are applied to traffic aggregates which are created at the boundary nodes and labeled using the DS field in IPv4 or IPv6 headers. Observe that per-flow state information is no longer needed at interior routers to provide service differentiation -- it can be (partially) inferred from the DS-field (or labels in MPLS which is used as an index to a table of PHBs.
The following paper examines the performance of TCP over this service and proposes design of TCP-friendly building blocks as a generic technique to boost performance.
Feroz Azeem, Amit Rao, Shivkumar Kalyanaraman, TCP-Friendly Traffic Conditioners for Differentiated Services , March 1999.