Pre-Congestion Notification-based Flow Management in MPLS-based DiffServ Networks

Recent trends in applications require per-flow treatment instead of the packet-based treatment inherent in the present day Internet. This requirement is analogous to trying to make a phone call in a standard PSTN line or cellular network and either receiving a busy tone or call accept. This paper explores the potential of providing flow-based admission control and termination functionality to an MPLS-based DiffServ network by applying Pre-congestion notification (PCN). MPLS-based DiffServ networks are state of the art technologies used in many carrier backbones to provide Quality of Service for different traffic classes. The standard PCN scheme as developed by the IETF requires three code-points, one of which finds application in differentiating between PCN and non-PCN traffic, while the other two are used for PCN congestion marking to indicate admission control and flow termination, respectively. An MPLS-based DiffServ network on the other hand is limited as only two code-points are available. To overcome this limitation, we propose various schemes, namely: 1) one-codepoint signaling for admission control (AC), 2) one-codepoint signaling for flow termination (FT), and 3) one-codepoint signaling for 3 states (no congestion, AC and FT). The three schemes use the available code-point for different purposes and require different behaviors from the involved PCN nodes. We evaluate them using simulations. The results suggest that the third approach is able to effectively signal the three states without incurring much inaccuracy. The success rate with respect to the Quality of Experience (QoE) of existing flows, error recovery and throughput is not compromised either. To the best of our knowledge, this is the first known attempt to study the use of PCN in an MPLS-based DiffServ network.