Reorder Density (RD): A Formal, Comprehensive Metric for Packet Reordering

The increase in link speeds, increased parallelism within routers and switches, QoS support and load balancing among links, all point to future networks with increased packet reordering. Unchecked, packet reordering will have a significant detrimental effect on the end-to-end performance, while resources required for dealing with packet reordering at routers and end-nodes will grow considerably. A formal analysis of packet reordering is carried out and Reorder Density (RD) metric is defined for measurement and characterization of packet reordering. RD captures the amount and degree of reordering, and can be used to define the reorder response of networks under stationary conditions. Properties of RD are derived, and it is shown that the reorder response of the network formed by cascading two subnets is equal to the convolution of the reorder responses of individual subnets. Packet reordering over the Internet is measured and used to validate the derivations.