New feature negotiation options, new resync mechanism, PAWS (48-bit sequence number option), DCCP-Move uses a Mobility ID, many other changes.
Address some reviewer comments, including: Specify how the Loss Window is arranged. Ignored can contain multiple option data bytes. Refine the Ack Vector Consistency tables. CC mechanisms must treat Data Dropped like ECN Marked unless otherwise specified. Adjust MTU discovery.
(Minor revision) Include Acknowledgement Number in Identification options, and force it to be valid. Bad DCCP-Moves are ignored, not reset, to avoid leaking information to attackers.
Change when packets are "received" for purposes of acknowledgement, due to ECN Nonce verification problems. (New definition is much better.) Replace Data Discarded, Receive Buffer Drops, and Buffer Closed with new Data Dropped option. Clarify timeouts and retransmissions. Change Identification option: only the Sequence Number is included in the MD5 Regime's hash. Add Payload Checksum and Elapsed Time options. Add Middlebox Considerations and Design Motivation sections. The 4-bit Reserved field in the DCCP generic header is available for use by CCIDs. Other changes.
Add Identification mechanism, replacing old Challenge mechanism; Identification is much less vulnerable to attack. Add discussion of DCCP and RTP. Clarify when packets are "received" for purposes of acknowledgement, partial checksums, and what ECN-incapable endpoints should use for the ECN nonce. Support Data Discarded on more packets. Mention wrapped sequence numbers for future work. Wording.
Clarify discussion on TCP friendliness, specify DCCP-Reset Reasons, replace Identify Yourself and Connection Proof with Challenge and Challenge Response, replace Buffer Closed Drops with Buffer Closed, allow use of Data Discarded on packets other than DCCP-Response, add discussion on Ack Vector state constraints, wording, acknowledgements.
Minor changes in CCID 3 discussion.
Changed name of protocol; renamed options; new state diagram; new Loss Window and Connection Nonce options/features address sequence number validity; Slow Receiver option; DCCP checksum includes a pseudoheader; Move packet format changed; added explanation of acks-of-acks.