Although many classical IP geolocation algorithms are suitable to rich-connected networks,their performances are seriously affected in poor-connected networks with weak delay-distance correlation. This paper tries to improve the performances of classical IP geolocation algorithms by finding rich-connected sub-networks inside poor-connected networks. First,a new delay-distance correlation model(RTD-Corr model)is proposed. It builds the relationship between delay-distance correlation and actual network factors such as the tortuosity of the network path and the ratio of propagation delay. Second,based on the RTD-Corr model and actual network characteristics,this paper discusses about how to find rich-connected networks inside China Internet which is a typical actual poor-connected network. Then we find rich-connected sub-networks of China Internet through a large-scale network measurement which covers three major ISPs and thirty provinces. At last,based on the founded rich-connected sub-networks,we modify two classical IP geolocation algorithms and the experiments in China Internet show that their accuracy is significantly increased.
