Acronym for Datagram Congestion Control Protocol.
DCCP is a transport level protocol (like TCP and UDP) which aims to solve many different congestion issues. This is useful for applications that don't need the data reliability/re-transmission of TCP, but want a session and want congestion control unlike UDP.
DCCP is a series of proposed standard RFCs (4340-4342)
The main reference page on the web for DCCP is here: http://www.read.cs.ucla.edu/dccp/
There is also a writeup at LWN.
Much of this page is shifting to http://linux-net.osdl.org/index.php/DCCP - that page is considered the definitive reference for the DCCP implementation for Linux.
DCCP is present in the LinuxKernel. This is being maintained by ArnaldoMelo at present. The history of this is that it draws from the code of Patrick McManus, Lulea and the WandGroup that IanMcDonald is part of. It was accepted into the LinuxKernel by LinusTorvalds in 2.6.14. It continues to evolve rapidly at time of writing (preparatory 2.6.20) and it usually pays to get the latest code from a Git tree.
The core DCCP stack was written by ArnaldoMelo using the Linux TCP implementation as a model, with DCCP being used as a way to identify code in the TCP implementation that could be made generic and shared with other INET transport level implementations. This resulted in the generalisation of code related to the minisockets representing both TCP_SYN_RECV/DCCP_RESPOND and TCP_TIME_WAIT/DCCP_TIME_WAIT status, code related to established/timewait/listen sockets (inet_lookup, inet_lookup_established, etc), the interface to get sock information (tcp_diag), and many other functions and data structures, with more expected to be generalised and eventually used by SCTP and any other INET transport protocols that may be introduced in the future.
The CCID3 code was, as IanMcDonald mentioned, drawn from the WandGroup, that in turn got it initially from the Lulea FreeBSD codebase and made it work in the core DCCP stack written by Patrick McManus. It was modified by ArnaldoMelo to fit Linux standards wrt list handling and several other aspects.
The CCID modular infrastructure was written to fit the CCID3 existing interface, but will probably be changed in the near future in the effort to have a generic CA (Congestion Avoidance) infrastructure shared with TCP (and others, who knows), continuing work on the existing TCP CA infrastructure put in place by Stephen Hemminger.
TcpDump now has DCCP support in the tree. There is TcpDump support available at http://wand.cs.waikato.ac.nz/iam4/dccp/tcpdump8.diff for older versions. This applies to many versions and at least the weekly build from CVS of tcpdump dated 22nd August 2005. Remember to run tcpdump(8) with a -s0 parameter to capture all data (or some other value) as the default size gets the base DCCP header, but not the options, in many cases.
Arnaldo writes: TIMEWAIT sockets are finally implemented and we have initial support for iproute2, so just enable INET_DIAG and if enabled as a module make sure it is load prior to using the iproute2 utilities, like ss.
The latest iproute2 version, available at: http://developer.osdl.org/dev/iproute2/download/iproute2-ss050901.tar.bz2 now includes DCCP support directly.
Then use it:
[root@qemu ~]# ./ss -dane State Recv-Q Send-Q Local Address:Port Peer Address:Port LISTEN 0 0 *:5001 *:* ino:730 sk:cfd503a0 ESTAB 0 0 127.0.0.1:5001 127.0.0.1:32770 ino:731 sk:cfd51480 ESTAB 0 0 127.0.0.1:32770 127.0.0.1:5001 ino:741 sk:cfd517e0 [root@qemu ~]# [root@qemu ~]# ./ss -dane State Recv-Q Send-Q Local Address:Port Peer Address:Port TIME-WAIT 0 0 127.0.0.1:32770 127.0.0.1:5001 timer:(timewait,59sec,0) ino:0 sk:cf12a620
The above listing was with the ttcp test.
http://www1.ietf.org/mail-archive/web/dccp/current/index.html - A discussion of the DCCP protocol by the IETF
http://firstname.lastname@example.org/ - a discussion of the Linux implementation of DCCP
There is a Todo list also which tracks the issues needing working on.
For sample code have a look at the applications ported or you can contact IanMcDonald
gcc ttcp_acme.c -o ttcp_acme -I ~/linuxsrc/dccpwork/include/
-#include <netinet/tfrc.h> +// #include <netinet/tfrc.h> +#include <linux/tfrc.h>
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