3. Careful Resume の CC phases
| Phase | Role | Key exits or actions |
|---|---|---|
| Observing | Save CC parameters for a Remote Endpoint | MUST NOT retain more than one set; SHOULD update or replace later observations |
| Reconnaissance | Confirm the saved path while using normal CC | stop on congestion, path change, expired Lifetime, reused saved_cwnd, or minimum RTT <= saved_rtt / 2 |
| Unvalidated | Tentatively jump CWND using paced transmission | jump_cwnd <= Min(max_jump, saved_cwnd/2); all packets MUST use pacing based on current RTT |
| Validating | Check whether unvalidated packets arrived without congestion | enter Safe Retreat on packet loss or ECN-CE; exit after last unvalidated packet is acknowledged |
| Safe Retreat | Recover safely after congestion from unvalidated packets | delete saved parameters; CWND <= PipeSize/2; CWND MUST NOT increase; ssthresh <= PipeSize * Beta |
saved parameters が期限切れ, path mismatch, congestion, saved_cwnd reuse, minimum RTT <= saved_rtt / 2 の場合, sender は Careful Resume を停止して normal CC に戻る。