Current data-centers employ admission control mechanism to maintain low response time and high throughput under overloaded scenarios. Existing mechanisms use internal (on the overloaded server) or external (on the front-end proxies) approaches. External admission control is preferred since it can be performed transparently without any modifications to the overloaded servers and global decisions can be made based on the load information of all the back-end servers. However, this external approach is bound to use TCP/IP communication protocol to get the load information from the back-end servers and rely on coarse-grained load monitoring due to the overheads associated with fine-grained monitoring. In this paper, we provide a fine-grained external admission control mechanism by leveraging the one-sided RDMA feature of modern interconnects and consequently provide response time guarantees and overload control in the multi-tiered data-center environment. Our design is implemented over InfiniBand-based clusters working in conjunction with Apache based servers. Experimental evaluations with single file, world cup and zipf traces show that our admission control can improve the response time by up to 28%, 17% and 23%, respectively, as compared to performing TCP/IP-based admission control. The improvement become 51%, 36% and 42%, respectively, when comparing to the base performance without any admission control. Further, our evaluations alsoshow that RDMA-based admission control can provide better QoS guarantees than the TCP/IP-based admission control and no admission control approaches.