Active Probing using Packet Quartets

摘要

A significant proportion of link bandwidth measurement methods are based on IP's ability to control the number of hops a packet can traverse along a route via the time-to-live (TTL) field of the IF header. A new delay variation based path model is introduced and used to analyse the fundamental networking effects underlying these methods. Insight from the model allows new link estimation methods to be derived and analysed. A new method family based on packet quartets: a combination of two packet pairs each comprising a probe following a pacesetter packet, where the TTL of the pacesetter is limited and the end-to-end delay variation of the probes is measured, is introduced. The methods provide 'pathchar-like' rate estimates over multiple links without relying on the delivery of ICMP messages, with reduced invasiveness and other advantages. The methods are demonstrated using simulations, and measurements on two different network routes are used for illustration and comparison against available tools (pathchar and clink). A comprehensive analysis of practical issues affecting the accuracy of the methods, such as link layer headers, is provided. Particular attention is paid to the consequences of 'invisible' hops: nodes where the TTL is not decreased.