Group communications (multicast) are foreseen to be one of the most critical yet challenging technologies to meet the exponentially growing demands for data distribution in a large variety of applications of the Internet (grid computing, video-conferencing, web applications, distributed simulations). When reliability is required, there is no straightforward solutions and meeting the objectives of reliable multicast is not an easy task. Active networks open a new perspective in providing more efficient solutions for the problem of reliability. In this context, routers are able to perform customized computations (services) on the packets flowing through them. In this paper, we propose a new service consisting in an early loss detection service to be deployed into routers. We also show how the loss detection service can improve the performances (in term of the recovery delays) of an active reliable multicast protocol such as DyRAM making it more suitable for applications requiring low latencies.