To sustain a large-scale overlay network, knowledge about network characteristics is indispensable. However, the collection of such information is often a burden on the developers: why should they struggle to obtain the information even though it is not their intended purpose? As one solution to this problem, this paper presents N-TAP, a distributed measurement infrastructure. N-TAP is an independent service for overlay network applications that provides network characteristics. N-TAP itself forms the measurement overlay network on which measurement nodes can cooperate in measurement activity. Consequently, overlay network applications can take full advantage of novel measurement methodologies. Through a discussion on the problems of distributed measurement, in this paper we explore the capabilities and the future direction of N-TAP.