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.

Improved Packet Reordering Metrics Status of This MemoThis memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. IESG NoteThe content of this RFC was at one time considered by the IETF, and therefore it may resemble a current IETF work in progress or a published IETF work. The IETF standard for reordering metrics is RFC 4737. The metrics in this document were not adopted for inclusion in RFC 4737. This RFC is not a candidate for any level of Internet Standard. The IETF disclaims any knowledge of the fitness of this RFC for any purpose and in particular notes that the decision to publish is not based on IETF review for such things as security, congestion control, or inappropriate interaction with deployed protocols. The RFC Editor has chosen to publish this document at its discretion. Readers of this RFC should exercise caution in evaluating its value for implementation and deployment. See RFC 3932 for more information. AbstractThis document presents two improved metrics for packet reordering, namely, Reorder Density (RD) and Reorder Buffer-occupancy Density (RBD). A threshold is used to clearly define when a packet is considered lost, to bound computational complexity at O(N), and to keep the memory requirement for evaluation independent of N, where N is the length of the packet sequence. RD is a comprehensive metric that captures the characteristics of reordering, while RBD evaluates the sequences from the point of view of recovery from reordering.

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-Packet reordering is an inevitable phenomenon on the Internet. An ideal metric for packet reordering should capture reordering accurately, provide insight into nature of reordering, and help in evaluation and analysis of reordering leading to mitigation of its adverse effects. Proposed metrics for packet reordering, namely, Reorder Density, Reorder Bufferoccupancy Density, Reordering Extent, and n-Reordering, overcome to various degrees the deficiencies of percentage reordering in capturing the nature and extent of reordering. These metrics vary widely in areas such as evaluation complexity, measurement technique, usage, and in the definition used for packet reordering itself. Metrics for reordering are evaluated using a framework consisting of a set of both essential and desirable attributes of reorder metrics. The attributes include the ability to capture reordering, sensitivity to lost and duplicate packets in reorder measurements, usefulness, simplicity, and evaluation complexity. Finally, the characterization of packet reordering using these metrics is discussed, using sets of measurements carried over the Internet.

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