Module arq 

SRT ARQ (Automatic Repeat reQuest) reliability engine — draft-sharabayko-srt-01 §4.8 (Acknowledgement and Lost Packet Handling), §4.8.1 (Packet Acknowledgement — ACKs, ACKACKs), §4.8.2 (Packet Retransmission — NAKs), §4.10 (Round-Trip Time Estimation). Curated behavioural rules: specs/rules/srt-arq.md. The wire field layouts this module drives (ACK/NAK/ACKACK) are the existing crate::packet codecs — this module never re-encodes them, it only decides when to build one and what to do with one received.

Sans-IO, like the rest of this crate: Sender and Receiver never read a wall clock. All timing is driven by a caller-supplied now: core::time::Duration (elapsed time since a fixed epoch the caller owns) passed to tick/feed_data/on_data/on_ack/on_ackack.

Module map

• seq — wrap-safe 31-bit sequence-number arithmetic (not itself a srt-arq.md rule — the draft does not specify a comparison algorithm; see the module doc there for the resolution).
• rtt::RttEstimator — the rule 29-31 RTT/RTTVar EWMA, shared by both roles (rule 34: a socket’s RTT state is really one estimator usable by both a sender and a receiver path).
• Sender — send buffer, NAK-driven retransmit queue, ACK/ACKACK handling (rules 1, 3, 5, 7-10, 15-18, 23-24, 33).
• Receiver — loss detection, Full/Light ACK generation, periodic NAK, ACKACK-driven RTT measurement (rules 4, 8, 11-14, 21-22, 26-30, 32).

Non-goals (explicit follow-ups, not curated as ARQ rules here)

• TLPKTDROP fake-ACK skip handling (rule 13) — srt-tsbpd.md scope.
• RTO-based periodic retransmission without a NAK / congestion control (§5, FileCC) — srt-arq.md is explicit that the RTO formula is congestion-control scope, not curated there.
• Send-queue overflow / unsent-packet drop sizing (rules 19-20) — the latency-window math is §4.4/§4.5 scope.

Re-exports

pub use rtt::RttEstimator;

Modules

rtt

RTT / RTTVar EWMA estimation — draft-sharabayko-srt-01 §4.10 (Round-Trip Time Estimation), specs/rules/srt-arq.md rules 29-31.

seq

32-bit wrap-safe sequence-number arithmetic for SRT ARQ.

Structs

FeedOutcome

Outcome of one Receiver::feed_data call.

Receiver

ARQ receiver-side state (draft-sharabayko-srt-01 §4.8.1/§4.8.2/§4.10).

Sender

ARQ sender-side state (draft-sharabayko-srt-01 §4.8). See the module doc for the sans-IO contract.

Constants

FULL_ACK_PERIOD

Full ACK timer period — 10 milliseconds (specs/rules/srt-arq.md rule 11, quoting draft-sharabayko-srt-01 L2874-2876: “the ACK period or synchronization time interval SYN”).

LIGHT_ACK_THRESHOLD

Light-ACK packet-count threshold — 64 packets (specs/rules/srt-arq.md rule 12, L2877-2883): if this many packets have been sent/received within the Full ACK period, the receiver sends a Light ACK early.

NAK_INTERVAL_FLOOR

NAKInterval floor — 20 milliseconds (specs/rules/srt-arq.md rule 22, L2953-2960 / L3276): NAKInterval = max((RTT + 4*RTTVar) / 2, 20ms).