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Datagram Congestion Control ProtocolThe Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol that is currently under development in the IETF. Applications that might make use of DCCP include those with timing constraints on the delivery of data such that reliable in-order delivery, when combined with congestion control, is likely to result in some information arriving at the receiver after it is no longer of use. Such applications might include streaming media and Internet telephony. Congestion control is the way that a network protocol discovers the available network capacity on a particular path. The primary motivation for the development of DCCP is to provide a way for such applications to gain access to standard congestion control mechanisms without having to implement them at the application layer. DCCP is intended for applications that require the flow-based semantics of TCP, but which do not want TCP's in-order delivery and reliability semantics, or which would like different congestion control dynamics than TCP. Similarly, DCCP is intended for applications that do not require features of SCTP such as sequenced delivery within multiple streams. To date most such applications have used either TCP, with the problems described above, or used UDP and implemented their own congestion control mechanisms (or no congestion control at all). The purpose of DCCP is to provide a standard way to implement congestion control and congestion control negotiation for such applications. One of the motivations for DCCP is to enable the use of ECN, along with conformant end-to-end congestion control, for applications that would otherwise be using UDP. In addition, DCCP implements reliable connection setup, teardown, and feature negotiation. A DCCP connection contains acknowledgement traffic as well as data traffic. Acknowledgements inform a sender whether its packets arrived, and whether they were ECN marked. Acks are transmitted as reliably as the congestion control mechanism in use requires, possibly completely reliably. External links
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