Data gram Congestion Control Protocol (DCCP)

The Datagram Congestion Control Protocol (DCCP) is a message-oriented Transport Layerprotocol. DCCP implements reliable connection setup, teardown, ECN, congestion control, and feature negotiation. DCCP was published as RFC 4340, a proposed standard, by the IETF in March, 2006. Linux had an implementation of DCCP first released in Linux kernel version 2.6.14 (released 28-Oct-2005).

DCCP provides a way to gain access to congestion control mechanisms without having to implement them at the Application Layer. It allows for flow-based semantics like in TCP, but does not provide reliable in-order delivery. Sequenced delivery within multiple streams as in SCTP is not available in DCCP.

DCCP is useful for applications with timing constraints on the delivery of data that may become useless to the receiver if reliable in-order delivery combined with congestion avoidance is used. Such applications might include streaming media and Internet telephony. Such applications have either settled for TCP or used UDP and implemented their own congestion control mechanisms (or no congestion control at all).

A DCCP connection contains acknowledgment traffic as well as data traffic. Acknowledgments 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.

DCCP has the option to have very long (48-bit) sequence numbers corresponding to a packet ID (rather than a byte ID as in TCP). The long length of the sequence numbers is intended to guard against "some blind attacks, such as the injection of DCCP-Resets into the connection.

Almost all internet applications like the streaming media and internet telephone favour reliability than time. This factor makes the TCP factor a less preferred choice. Even the UDP network cannot make up to this level as it is in short of the congestion control. These congested controlled networks are usually causes great risk factors for the use of high bandwidth UDP applications. So naturally there was need for designing a congestion-controlled unreliable transport protocol. The result, Data gram Congestion Control Protocol or DCCP gets added to UDP like foundation the minimum mechanisms necessary to congestion control. The resulting protocol sheds light on how congestion control support interacts with unreliable transport, how modern network constraints impact protocol design, and how TCP reliable byte stream semantics intertwine with its other mechanisms, including congestion control.