*Â Â Technical Summary
The Datagram Congestion Control Protocol (DCCP) is a transport
protocol that provides bidirectional unicast connections of
congestion-controlled unreliable datagrams.Â DCCP is suitable for
applications that transfer fairly large amounts of data, but can
benefit from control over the tradeoff between timeliness and
reliability.Â TCP is not well-suited for these applications, since
reliable in-order delivery and congestion control can cause
arbitrarily long delays.Â UDP avoids long delays, but UDP applications
that implement congestion control must do so on their own.Â DCCP
provides built-in congestion control, including ECN support, for
unreliable datagram flows, avoiding the arbitrary delays associated
with TCP.Â It also implements mechanisms for reporting loss, reliable
connection setup, teardown, and feature negotiation.Â The congestion
control mechanisms are defined in Congestion Control Profile
documents, known as CCIDs.
Â Â Â Â *Â Â Working Group Summary
There is a strong working group consensus to develop this protocol.
The applicability of DCCP to interactive real-time multimedia flows has
been somewhat controversial in the working group. The DCCP protocol
specification has been developed with just two initial congestion control
profiles, companions to this publication, draft-ietf-dccp-ccid2, and
draft-ietf-dccp-ccid3. However, the modular nature of the protocol
enables the core specification to be completed while work proceeds
on congestion control profiles for interactive real-time applications.
There is clear and strong support for applying DCCP to non-realtime
streaming and growing interest in other applications as well.
Â Â Â Â *Â Â Protocol Quality
DCCP has received extensive transport and cross-disciplinary review.
Written "expert reviews" were conducted by Eric Rescorla (a security
expert), Magnus Westerlund (a multimedia expert and AVT wg chair), and
Greg Minshall (a TCP expert), generating many detailed comments and
substantive improvements in the protocol.Â The expert review was
followed by a working group "design review" at IETF-57 where the
working group and invited experts -- Magnus Westerlund (multimedia),
Steve Bellovin (security), and Rob Austein (architecture) -- walked
through the spec in detail resulting in additional comments and
substantive changes.Â Additionally, formal modeling was performed
showing that DCCP is deadlock-free.Â The protocol is as mature as is
possible without significant implementation experience.Â The three
known implementations were started early in the life of the
specification and one (from ICIR) resulted in some relatively major
changes to the spec.Â Recently, it has become known that Kame FreeBSD
contains an implementation of DCCP, albeit not matching the final
version of the spec.Â It is expected that feedback from implementors
and users will result in further improvements and revisions.
The IESG review of the specification was done by Allison Mankin.
The WG Chair shepherd was Aaron Falk.