 such applications have often either settled for TCP or used User Datagram Protocol (UDP) and implemented their own congestion-control mechanisms, or have no congestion control at all.While being useful for these applications, DCCP can also serve as a general congestion-control mechanism for UDP-based applications, by adding, as needed, mechanisms for reliable or in-order delivery on top of UDP/DCCP.In this context, DCCP allows the use of different, but generally TCP-friendly congestion-control mechanisms.