The Datagram Congestion Control Protocol (DCCP) has been proposed as a transport protocol which supports real-time traffic. In this paper, we focus on the use of DCCP/CCID3 (Congestion Control ID 3) over a Diff- Serv/AF class. This class of service is used to build services that provide only a minimum throughput guarantee without any delay or jitter restrictions. This minimum throughput guarantee is called the target rate. In this context, the throughput obtained by DCCP/CCID3 mainly depends on RTT and loss probability. As a result, the application does not always get the negotiated target rate. To cope with this problem, we propose to evaluate a simple adaptation of the CCID3 congestion control mechanism, allowing the application to reach its target rate whatever the RTT value of the application?s flow is. As this adaptation can be seen as an extension to the DCCP with CCID3 congestion control, we call it gDCCP for guaranteed DCCP. Results from simulations are presented to illustrate the improvements of the proposed modification in various situations. Finally, we investigate the deployment of this proposal in terms of security.