ITRA: Inter-tier relationship architecture for end-to-end QoS. The importance of guaranteed end-to-end Quality of Service (QoS) increases as business-to-business interactions become increasingly sophisticated, lengthy, and involve more sites. The collaboration between tiers to supply functionality can be extended to provide QoS. In this paper, we focus on end-to-end availability. In multi-tier computation, support for transparent failovers is often required, even if failures occur in more than one tier at the same time. One of the obstacles in achieving a transparent failover is determining the status of outstanding operations, some of which span several tiers. Such determination of outstanding operations status upon failure requires collaboration of neighboring tiers. In this paper, we present Inter-Tier Relationship Architecture (ITRA). ITRA describes mechanisms, the role of each tier with respect to its predecessor and successor tiers, programming model and inter-tier relationship protocol. eServices following the ITRA architecture can collaborate to transparently recover from failures in multiple tiers, as well as better exploit mutual resources to provide the required availability and failover transparency aspects of an end-to-end QoS. We have exercised the architecture by mapping it to enterprise java beans and implemented a prototype.