Despite years of research and development, pioneering deployments of multihop wireless networks have not proven successful. The performance of routing and transport is often unstable due to contention-induced packet losses, especially when the network is large and the offered load is high. In this paper we propose RAIN, a reliable wireless network architecture for large-scale multihop wireless networks. A RAIN network enforces contention control by limiting the queue length at intermediate wireless routers to the minimum. To keep the queue short a RAIN network enforces congestion control through in-network implicit back-pressure. RAIN congestion control is built on wireless datalink layer mechanisms, e.g., mandatory per-frame acknowledgement and inter-frame backoff in popular CSMA/CA wireless transceivers, therefore very efficient and effective compared with those defined at the network or transport layer for the wired Internet. As a result of the built-in contention and congestion control, RAIN presents the end hosts a highly reliable network service model, even more reliable than that of the wired Internet. The end hosts only need to deal with packet losses due to router or routing failures. Therefore, the transport protocol can be significantly simplified. This is in stark contrast to the existing approach of adding more and more complexity to adapt TCP for multihop wireless networks. We propose the details of RAIN datalink layer protocol, and a simple transport protocol at the end hosts.