Datagram Congestion Control Protocol
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| Communication protocol | |
| Abbreviation | DCCP |
|---|---|
| Introduction | |
| OSI layer | Transport layer (4) |
| RFC(s) | Template:IETF RFC |
Template:IPstack In computer networking, the Datagram Congestion Control Protocol (DCCP) is a message-oriented transport layer protocol. DCCP implements reliable connection setup, teardown, Explicit Congestion Notification (ECN), congestion control, and feature negotiation. The IETF published DCCP as Template:IETF RFC, a proposed standard, in March 2006. Template:IETF RFC provides an introduction.
Operation
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 Transmission Control Protocol (TCP) but does not provide reliable in-order delivery. Sequenced delivery within multiple streams, as in the Stream Control Transmission Protocol (SCTP), is not available in DCCP. A DCCP connection contains acknowledgment traffic as well as data traffic. Acknowledgments inform a sender whether its packets have arrived, and whether they were marked by Explicit Congestion Notification (ECN). Acknowledgements are transmitted as reliably as the congestion control mechanism in use requires, possibly completely reliably.
DCCP has the option for 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 aims to guard against "some blind attacks, such as the injection of DCCP-Resets into the connection".[1]
Applications
DCCP is useful for applications with timing constraints on the delivery of data. Such applications include streaming media, multiplayer online games and Internet telephony. In such applications, old messages quickly become useless, so that getting new messages is preferred to resending lost messages. As of 2017[update] 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.
Implementations
The following operating systems implement DCCP:
- FreeBSD, version 5.1 [2] as patch
- Linux since version 2.6.14,[3] but marked deprecated since version 6.4 due to lack of maintenance and scheduled for removal in 2025.[4] Linux 6.16 drops DCCP.[5]
Userspace library:
- DCCP-TP Script error: No such module "webarchive". implementation is optimized for portability, but has had no changes since June 2008.[8]
- GoDCCP purpose of this implementation is to provide a standardized, portable NAT-friendly framework for peer-to-peer communications with flexible congestion control, depending on application.
Packet structure
The DCCP generic header takes different forms depending on the value of X, the Extended Sequence Numbers bit. If X is one, the Sequence Number field is 48 bits long, and the generic header takes 16 bytes, as follows. Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD If X is zero, only the low 24 bits of the Sequence Number are transmitted, and the generic header is 12 bytes long. Template:APHD Template:APHD Template:APHD Template:APHD Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
- Template:APHD
Current development
Similarly to the extension of TCP protocol adding multipath capability (MPTCP), a multipath extension of DCCP is under discussion at the IETF,[9] correspondingly denoted as MP-DCCP. First implementations have already been developed, tested, and presented in a collaborative approach between operators and academia[10] and are available as an open source solution.
See also
- Stream Control Transmission Protocol (SCTP)
- Transport layer § Comparison of transport layer protocols
References
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- ^ RFC 4340 section 7.6
- ^ Page Module:Citation/CS1/styles.css has no content."[dccp] FreeBSD implementation". www.ietf.org. Retrieved 18 April 2018.
- ^ Page Module:Citation/CS1/styles.css has no content."Linux gets DCCP [LWN.net]". lwn.net. Retrieved 18 April 2018.
- ^ Page Module:Citation/CS1/styles.css has no content."dccp: Print deprecation notice". kernel.org.
- ^ Page Module:Citation/CS1/styles.css has no content."Linux 6.16 Expected To Remove Datagram Congestion Control Protocol "DCCP" Networking". www.phoronix.com. Retrieved 15 April 2025.
- ^ Page Module:Citation/CS1/styles.css has no content."Linux 6.16 Expected To Remove Datagram Congestion Control Protocol "DCCP" Networking". www.phoronix.com. Retrieved 29 May 2025.
- ^ Page Module:Citation/CS1/styles.css has no content."Merge branch 'net-retire-dccp-socket'". git.kernel.org.
- ^ Page Module:Citation/CS1/styles.css has no content."Change log for the dccp-tp wiki, retrieved June 13, 2011". Archived from the original on October 4, 2011. Retrieved June 13, 2011.
- ^ Page Module:Citation/CS1/styles.css has no content.Amend, Markus; Brunstrom, Anna; Kassler, Aneas; Rakocevic, Veselin; Johnson, Stephen (9 November 2021). "DCCP Extensions for Multipath Operation with Multiple Addresses".
- ^ Page Module:Citation/CS1/styles.css has no content."Multipath extension for DCCP".
External links
Protocol specifications
- Template:IETF RFC — Datagram Congestion Control Protocol
- Template:IETF RFC — The Datagram Congestion Control Protocol (DCCP) Service Codes
- Template:IETF RFC — DCCP Simultaneous-Open Technique to Facilitate NAT/Middlebox Traversal
- Template:IETF RFC — RTP and the DCCP
- Template:IETF RFC — Datagram Transport Layer Security (DTLS) over DCCP
- Template:IETF RFC — Quick-Start for DCCP
- Template:IETF RFC — A Datagram Congestion Control Protocol UDP Encapsulation for NAT Traversal
Congestion control IDs
- Template:IETF RFC — Profile for DCCP Congestion Control ID 2: TCP-like Congestion Control
- Template:IETF RFC — Profile for DCCP Congestion Control ID 3: TCP-Friendly Rate Control (TFRC)
- Template:IETF RFC — Profile for DCCP Congestion Control ID 4: TCP-Friendly Rate Control for Small Packets (TFRC-SP)
Other information
- Template:IETF RFC — Problem Statement for the Datagram Congestion Control Protocol (DCCP)
- DCCP page from one of DCCP authors
- DCCP support in Linux
- Datagram Congestion Control Protocol (DCCP)
