Packet reordering inside the Sprint backbone

In this paper we study the magnitude and causes of packet reordering in the Internet using data collected at a POP on the Sprint IP Backbone. We develop a methodology that uses TCP packet-level traces to infer the cause for reordering without the need of the complete TCP connection information (i.e. both data and acknowledgement paths). We classify reordering in two classes depending on the cause of reordering: i) router design or routing changes and ii) retransmission due to the fast retransmit algorithm or to the retransmit timeout. In contrast with what has been reported in previous studies, our analysis shows that reordering occurs in the backbone with a relatively low frequency.