Reorder buffer-occupancy density and its application for measurement and evaluation of packet reordering

Increasing internal parallelism within nodes due to increase in links speeds, and external parallelism among the links due to QoS, ad hoc routing in wireless, etc., point to a significant increase in packet reordering. Application performance degrades considerably due to out-of-order arrivals as well. The concept of “Reorder Buffer-occupancy Density” (RBD) is defined, which provides the statistics of occupancy of a buffer used to recover from reordering. RBD also captures and measures reordering effectively, helps relate causes of reordering to observations, and allows the development of models for packet reordering. A formal representation and analysis of reordering is presented along with the derivation of RBD models for basic reordering patterns, such as independent, overlapping and embedded reordering. Measurements associate most of the packet reordering occurrences in the Internet to such patterns. The RBD models for these patterns are used to build a buffer-occupancy model, using as an example a scenario associated with traffic splitting or bandwidth aggregation. Such models can aid in determining the resource requirements for mitigating effects due to reordering, as well as performance characteristics of underlying network. Developed models are verified using measurements on emulated networks.