Experiences with class of service (CoS) translations in IP/MPLS networks

This paper presents some experiences with class of service (CoS) translation in IP and MPLS based networks. IP provides CoS in the form of eight priority classes that can be used to distinguish between a variety of traffic types. Since most of the layer-2 technologies provide support for strict QoS, an appropriate translation from the coarse grained IP CoS to the fine-grained layer-2 QoS is fundamental to obtaining desired end-to-end throughput. Multiprotocol label switching (MPLS), residing in between IP and layer-2 in the protocol stack, provides an interface to translate IP CoS to appropriate layer-2 QoS. This paper presents some of the results obtained by using MPLS CoS with relative and fixed bandwidth allocation to MPLS classes. Experiments were conducted to observe the effects of per-CoS weighted fair queuing (WFQ) and class based queueing (CBQ) inside the MPLS cloud on fixed size high bandwidth traffic and bursty traffic. It was found that MPLS CoS did relative allocation of bandwidth and prevented starvation of lower priority flows inside the MPLS core. This paper also discusses some of the experiments conducted to evaluate the effects of improper CoS mapping, as a packet traverses multiple networks.