MPLS-Enabled Applications: Emerging Developments and New Technologies

4.3. APPLICATION SCENARIOS

The DiffServ-TE solution is the product of the TEWG Working Group in the IETF.^[] In [RFC3564], the Working Group documented a few application scenarios that cannot be solved using DiffServ or TE alone. These scenarios form the basis for the requirements that led to the development of the DiffServ-TE solution and are presented in this section. The scenarios show why per-traffic-type behavior is necessary.

^[] The TEWG finished all its work items and has been closed.

4.3.1. Limiting the proportion of traffic from a particular class on a link

The first scenario involves a network with two types of traffic: voice and data. The goal is to maintain good quality for the voice traffic, which in practical terms means low jitter, delay and loss, while at the same time servicing the data traffic. The DiffServ solution for this scenario is to map the voice traffic to a per-hop behavior (PHB) that guarantees low delay and loss, such as the expedited-forwarding (EF) PHB.

The problem is that DiffServ alone cannot give the required guarantees for the following reason. The delay encountered by the voice traffic is the sum of the propagation delay experienced by the packet as it traverses the network and of the queuing and transmission delays incurred at each hop. The propagation and transmission delays are effectively constant; therefore, in order to enforce a small jitter on the overall delay, the queuing delay must be minimized. A short queuing delay requires a short ...