HPPD: A Hop-count Probabilistic Packet Dropper

Network applications and users have very diverse service expectations and requirements, demanding for provisioning of different levels of quality of service on the Internet. Packet loss rate differentiation has been an active research topic. However, the existing packet dropping schemes for loss rate differentiation have not considered an important issue, that is, the retransmission overhead of dropped packets. In this paper, we design a hop-count based probabilistic packet dropper (HPPD) for congestion mitigation and loss rate differentiation. HPPD aims to meet a two-fold objective by two-dimensional loss rate differentiation: one is the congestion mitigation that aims to reduce congestion in the first place by dropping intra-class packets differently based on their maturity levels to reduce retransmission cost; the other is inter-class proportional loss rate differentiation. The maturity level of a packet, the number of hops travelled, is inferred from its time-to-live value in the IP header. We propose an intra-class nth-root proportional dropping scheme, where n is a controllable parameter trading off dropping fairness for congestion mitigation. Simulation results show that HPPD can significantly mitigate the congestion by reducing the retransmission overhead of dropped packets and achieve the proportional loss rate differentiation at the same time.