Transaction based web services that demand realtime performance guarantees, such as on-line auctions, stock trading and real-time database servers generally require a higher level of security and performance compared to normal web services. To improve server throughput of servers for such applications under heavy loads or under denial of service attacks, it is necessary to service requests differentially, giving preference to on-going or imminent client requests. We show how such facilities can be efficiently implemented on an active network adapter based gateway that controls accesses to a pool of backend servers. Using an experimental prototype based around a dual-ported active NIC, we show how a differentiated service policy can be implemented on such a gateway to bound the server response time and to improve server throughputs under heavy loads.