To optimize overlay networks on the Internet, it is useful to estimate the qualities of each overlay link. Existing tools for measuring link qualities send probe packets from one end of the network to the other, but this requires the execution of measurement software at both end nodes. Besides, these tools need to send many probe packets to measure quality accurately, and this can disrupt other communication. In this paper, we propose a technique based on supervised learning for estimating link quality based on the quality observed for other similar links. Since our technique does not require sending probe packets, we can quickly estimate the qualities of many links without disrupting other communication or wasting processing time at many nodes. Through experiments on PlanetLab, the proposed method showed better performance on path latency estimation than the estimating results based on path length.

It is well known that algebraic specification methods are promising for specifying programs and for verifying their various properties formally. In this paper, an algebraic specification of information transfer procedures of high-level data link control (HDLC) procedures is presented and some of the main properties of the specification are shown. First, we introduce abstract states, state transition functions, and output functions corresponding to elementary notions extracted from the description of HDLC procedures in ISO 3309-1979 (E) and ISO 4335-1979 (E). Second, we show axioms which represent the relations between the values of functions before and after the state transitions. Then, it is proved that the specification is ``consistent,'' ``sufficiently complete,'' and ``nonredundant.'' Also it is shown that an implementation which realizes the specification is naturally derived. In the last section, verification of various properties of HDLC procedures is formulated in the same framework as the algebraic specification, and some verification examples are presented.