Improvement in packet-reordering with limited re-sequencing buffers: An analysis

Packet reordering is a common, and an unavoidable network phenomenon. Recovery from reordering requires re-sequencing buffers, e.g., at transport or application layer at the end nodes. Input or output buffers are used in high-performance routers to mitigate reordering due to massive internal parallelism. Reordering caused by multi-path routing in sensor networks has to be dealt with at nodes with limited buffers. Yet, no formal techniques exist to analyze or predict the improvement in packet order achievable with limited re-sequencing buffers. A theoretical foundation for analysis of the impact on packet reordering under different re-sequencing buffer availabilities is presented. Analytical relationships for variation of Reorder Density (RD) and Reorder Buffer occupancy Density (RBD), two measures of packet reordering, are provided as packet streams pass through re-sequencing buffers. Simulations driven by Internet measurement traces are used to verify the analytical results. The model provides an overall perspective of the impact of re-sequencing buffers and allows for buffer allocation to meet bounds related to packet reordering.