In content-based publish/subscribe(CBPS) system, the efficient cooperation to obtain CBPS services among peer nodes is a fundamental issue over structured P2P network. Moreover, the peer nodes change their status freely that makes efficient cooperation an intricate task to achieve. In this paper, we present ECOOP which is a novel solution to address this problem in Distributed Hash Table (DHT) based CBPS systems. We also present the new underlying DHT overlay network as Stable-Chord. The main objective of this paper is to ensure the overlay nodes are stable, i.e., stable Rendezvous Nodes (RN) and intermediate nodes. All the participating unstable nodes in CBPS systems only work either subscriber or publisher. Furthermore, our scheme, ECOOP, maintains stable event delivery paths on overlay network and is based on three main contributions: Rendezvous nodes selection, subscription management, and event publication & delivery. Eventually, our scheme maximizes the event delivery ratio and minimizes the transfer traffic overhead,
