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Johnathan Corgan
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Everything the release needs except the version number, which stays at 0.5.0-dev until the tag. The changelog entry covers only the work that is new on this line. The point release's forty-six entries arrived under their own heading with the forward merge and are left alone; the twenty that remained are regrouped by topic and eight more added for changes no entry covered. Three of those eight matter to someone upgrading. Five root modules and four re-exports left the public library surface and Node::connections narrowed, none of it recorded anywhere; the entry names what to use instead and distinguishes the removed connection-phase enum from the Noise type of the same name, which is a different type that still exists. Tracing targets moved, so an existing RUST_LOG filter stops matching rather than erroring. And the handshake resend interval key no longer governs the first resend, which is now a constant, though it still governs later ones. Seven more entries cover the work that landed after the first content pass was written: the experimental native datagram API, the fipsctl probe diagnostic, per-instance transport addressing, the app-owned UDP socket seam, and the connect, disconnect and path-MTU fixes. The four bug fixes among them all reach the deployed line, so the release notes no longer claim this release carries exactly one fix for a shipped bug; it carries four. There is no security section, because after the split every security entry belongs to the point release. The release notes say so plainly rather than leaving a reader upgrading across both releases to conclude this one carries no security work. The notes are organized by audience, since the release spans OpenWrt routers, embedders, FreeBSD, and the existing platforms, and a single list serves none of them. The native datagram API is given a section of its own rather than folded into the embedding seam: it is a client-facing API rather than a way to host a node, and its one rule with no Berkeley-socket counterpart, that the v1 wire carries no half-close, needs to be somewhere a client author will read it. FreeBSD is advertised as supported on x86_64 only, stated wherever the platform appears. Android is advertised as an embedding seam and not as a supported platform: a compile-gated library surface with no artifact and no host application guide. The configuration table rename is carried through every shipped file that taught the old spelling: nine documentation files, the OpenWrt sample config and a test generator, twenty-two sites in all. Guides written this same cycle were among them, which is how the omission was found. The documentation that arrived with the native API was checked for the same omission and was already clean. The compatibility tests keep the old spelling deliberately, since they exist to test the fold. The changelog section is the fold of master's [Unreleased], not a snapshot of it. An earlier version of this commit took a copy that then drifted, so each section ended up holding a bullet the other did not and re-folding them would have picked a winner silently. Both causes were fixed on master instead — the NixOS module had never been recorded there, and the pre-release batch of fixes was new — so [Unreleased] is a strict superset and this is a copy rather than a merge. [0.5.0] carries all forty-six bullets byte for byte, [Unreleased] is empty, and [0.4.2] is untouched, checked by hashing it against master's copy. The BLE work landed after the content pass and gets one summary entry in the changelog and one section in the release notes rather than nine bullets: the ble_available gate replacing target_os = "linux", packet-boundary recovery for stream-oriented backends, peer recognition by node identity instead of a rotating link address, the L2CAP PSM moving into the backend seam and onto the advertisement, the embedder-supplied Android radio, bounded probe retry, and inbound handshakes moved off the accept loop. The two release-notes copies no longer share their link paths. Relative links resolve from one directory only, so the seven written for docs/releases/ all 404ed from the root copy. The root copy now uses paths from the repository root and the versioned copy keeps the ../ form; both sets were resolved against the tree. The same two links are broken the same way in the v0.4.0 through v0.4.2 notes, left as shipped history. The contributor tallies are re-derived against maint..HEAD rather than adjusted: twenty commits from outside the project and 171 from me, with Arjen at fifteen and fr34aky at two. An earlier count of twelve and 138 was carried from a measurement taken three days before this content was written, and the BLE branch widened the gap after it. Arjen's NixOS flake module, the UDP sin6_scope_id fix and most of the BLE rework were uncredited, as was fr34aky's L2CAP PSM seam. They want one last re-derive at tag time if anything lands before the tag. A sweep of all 99 tracked markdown files against the tree corrected fifty-three of them. Four told the reader to run a build.sh that does not exist; the only harness builder is testing/scripts/build.sh. The BLE build prerequisites were described as optional on the strength of a probe that build.rs does not perform, and bluez was named a build prerequisite when libdbus-sys asks only for libdbus-1-dev and pkg-config and bluez is the runtime daemon. Link cost is the primary sort key in next-hop ranking, not reserved for future use; Ethernet runs on macOS as well as Linux; the BLE MTU is the L2CAP CoC MTU rather than a negotiated ATT_MTU; effective Ethernet MTU is 1497; the LAN discovery subsystem is src/mdns and eight citations still named a src/discovery that never existed here. The connectivity states in three tutorials were invented, and their jq filters matched nothing including healthy peers. One command filtered on a literal fd97: address prefix, which only the first byte of fixes, so it returned empty for all but one reader in 256 and every later step using the variable failed silently. transports.tor.advertise_on_nostr was undocumented despite being validated against node.rendezvous.nostr.enabled. The transport design document gains the BLE section it never had, written from the source: the backend cascade and its compile_error tripwire, the platform gate, the PSM advertisement wire layout and the byte budget that forces a 16-bit service-data key, and the probe and admission bounds. Three source files carried the same class of staleness and are corrected with the documentation: the OpenWrt ipk usage line and Makefile error text both named a packaging/openwrt that does not exist, and chaos.sh parsed --subnet without listing it. Folded in with the content commit, having been prepared alongside it: The three GitHub Action pins that had gone stale. Every third-party action is pinned to a commit SHA, nothing reports that a pin has aged, and re-resolving all ten against their tags found dorny/test-reporter@v2, taiki-e/install-action@v2 and vmactions/freebsd-vm@v1 had moved. The three install-action@nextest references stay unpinned, since that action reads the tool to install from the ref name. check-action-pins.sh passes at 75 references and all nine workflow files parse. The lockfile refresh, which is the mutating half of the dependency sweep. Thirty-six packages move to their latest semver-compatible versions and every one is transitive; nothing declared in Cargo.toml changes version. No advisory forces any of them. It was taken before the validation battery, because a gate run against a lockfile that later moves proves nothing about what ships. The sha2 0.10 to 0.11, hkdf 0.12 to 0.13 and bech32 0.11 to 0.12 majors, three of the four deferred at v0.4.0 for change surface rather than security. All three land with no source change. sha2 and hkdf must move together, since both depend on digest 0.11, and neither changes an algorithm. That matters because the chaining-key KDF in the Noise handshake is built on Hkdf::<Sha256>, where an output change would be a wire break rather than a compile error; no known-answer vectors exist for that path, so the wire-compatibility gate is what covers it. secp256k1 0.31 is deliberately absent, since nostr's own requirement would leave two copies of the ECC library in the tree. The README support matrix, rebuilt as one feature table broken out by Linux variety. A single Linux column hid that Debian, Ubuntu, Arch and NixOS are one glibc build differing in packaging, that OpenWrt is musl and drops BLE, and that Android is not a daemon platform. Transport rows sort by how many platforms carry them. A Native API row reads its platform set from the cfg gates. The installer row becomes a package format row naming the artifact, and only the .deb is exercised per release. Four changelog and release-note gaps the BLE re-walk found: a Bluetooth LE bullet stranded inside the released 0.4.2 section, a missing Fixed entry for the scan and probe loop counting a pool-refused connection as an established link, the unnamed embedder call that installs an application-owned radio, and the fact that stopping the transport now stops scanning as well as advertising. Three release-document gaps found walking the unsurveyed commits: the UDP reuse-flag fix stated in the direction opposite to the one it was made, with the silent second-daemon bind it prevents left unsaid; the corrected native-API socket paragraph carried into both release-note copies, which still named SOCK_SEQPACKET on FreeBSD and two kernels where three are handled; and the coordinate-cache hardening, which shipped with no text anywhere despite adding four operator-visible status fields. That last entry states plainly that the checks are mitigations and not a closure, since the coordinate is still not authenticated. Also folded in, the documentation pass that followed the content commit: A stage-pipeline diagram for the probe, embedded in the fipsctl reference under the five-stage list. It draws the five stages left to right with each stage's failure reasons below it, and the bypass that skips both lookup stages when the coordinates are cached or the target is a direct peer. Its branches come from the probe state machine rather than from the report, so the path stage is drawn as the one failure that does not stop the probe. A rewrite of the README's "What FIPS does" section. It now opens with what a machine running FIPS gets, rather than with the two deployment modes, and gives the self-organizing and permissionless property its own paragraph since it holds for both modes. A regrouping of the README's feature list into the mesh, getting traffic onto it, and running a node, with a bullet added for the native datagram API, which had none despite sitting in the support matrix. The Quick start now leads with the released packages rather than a source build. It also fixes a real defect: the package enables fips.service and fips-dns.service and starts neither on a fresh install, so .fips name resolution was silently dead until the next reboot and neither page said to start the service. A rewrite of the release notes. They opened with seven subsections of upgrade caveats and reached the first feature two hundred lines in; they now open with a summary of the release and elaborate below it in the same order. Android is stated as supported through an embedded crate rather than as a standalone daemon, consistently across all three documents. The OpenWrt pair is corrected: it is 802.11s between routers with FIPS supplying encryption, authentication and routing, plus a convention of an open !FIPS SSID a client joins over WiFi, not meshing over a router's own radios. The probe's path output is described as the least-common-ancestor walk, which is the worst-case fallback route rather than the route a packet takes. Detail that did not change what a reader does was cut from the notes and kept in the changelog.
225 lines
9.5 KiB
Markdown
225 lines
9.5 KiB
Markdown
# Metrics Measurement Protocol (MMP)
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The Metrics Measurement Protocol provides per-link and per-session
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quality metrics — SRTT, loss, jitter, goodput, ETX, and one-way delay
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trend — using only counter and timestamp fields already present in
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the FMP and FSP wire formats. No additional probing traffic is
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required. The same algorithms and report message format are used at
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both layers; only the routing scope and configuration namespace
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differ.
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This document is the canonical home for the MMP design. For the
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link-layer instance's role inside FMP, see
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[fips-mesh-layer.md](fips-mesh-layer.md). For the session-layer
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instance's role inside FSP, see
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[fips-session-layer.md](fips-session-layer.md). For the byte-level
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SenderReport and ReceiverReport layouts, see
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[../reference/wire-formats.md](../reference/wire-formats.md).
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## Two Layers, One Protocol
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MMP runs at two layers:
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- **Link-layer MMP**: One instance per active FMP peer link. Reports
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are exchanged peer-to-peer between direct neighbors and measure the
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quality of that single hop.
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- **Session-layer MMP**: One instance per established FSP session.
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Reports are encrypted end-to-end and forwarded through every transit
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link, measuring end-to-end quality independent of hop count.
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The algorithms (SRTT estimation, jitter computation, loss inference,
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ETX) are identical at both layers. The differences are configuration
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namespace, report intervals, and routing scope. See
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[Layer Differences](#layer-differences) below.
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## Metrics Tracked
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MMP computes the following metrics from the per-frame counter and
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timestamp fields:
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- **SRTT** — Smoothed round-trip time (Jacobson/RFC 6298, α=1/8).
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Derived from timestamp-echo in ReceiverReports with dwell-time
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compensation.
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- **Loss rate** — Bidirectional loss inferred from counter gaps.
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Tracked as both instantaneous (per-interval) and long-term EWMA.
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- **Jitter** — Interarrival jitter (RFC 3550 algorithm) in
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microseconds.
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- **Goodput** — Bytes per second of payload data (excludes MMP
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reports).
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- **OWD trend** — One-way delay trend (µs/s, signed). Indicates
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congestion buildup before loss occurs.
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- **ETX** — Expected Transmission Count, computed from bidirectional
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delivery ratios. Used in cost-based parent selection via
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`link_cost = etx * (1.0 + srtt_ms / 100.0)`, and in bloom-filter
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candidate ranking inside `find_next_hop()` (the same `link_cost`
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is the primary key when choosing among bloom-filter peers, with
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tree distance as the tie-breaker).
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- **Dual EWMA trends** — Short-term (α=1/4) and long-term (α=1/32)
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trend indicators for both RTT and loss, enabling change detection.
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Session-layer MMP additionally tracks the observed forward-path MTU;
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see [fips-mtu.md](fips-mtu.md) for the end-to-end path-MTU mechanism.
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## Operating Modes
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MMP supports three modes:
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| Mode | Reports Exchanged | Metrics Available |
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| ---- | ----------------- | ----------------- |
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| **Full** (default) | SenderReport + ReceiverReport | All metrics including RTT, loss, jitter, goodput, OWD trend |
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| **Lightweight** | ReceiverReport only | Loss (from counter gaps), jitter, OWD trend. No RTT. |
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| **Minimal** | None | Spin bit and CE echo flags only. No computed metrics. |
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The mode is configured per layer (`node.mmp.mode` and
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`node.session_mmp.mode`).
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## Report Scheduling
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Reports are sent at RTT-adaptive intervals computed as
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`clamp(2 × SRTT, low, high)`. A cold-start interval is used until SRTT
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has converged.
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| Layer | Adaptive bounds | Cold-start |
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| ----- | --------------- | ---------- |
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| Link | `[1s, 5s]` | 200 ms (first 5 samples) |
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| Session | `[500ms, 10s]` | 1 s |
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The session-layer bounds are higher because session reports are
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encrypted and forwarded through every transit link, so bandwidth cost
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is proportional to path length.
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## Spin Bit and RTT
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The SP (spin bit) flag in the FMP inner header follows the QUIC spin
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bit pattern: reflected on receive, toggled on send when the reflected
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value matches the last sent value. The spin bit state machine runs
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for TX reflection, but **RTT samples from the spin bit are
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discarded**. In a mesh protocol where frames are sent irregularly
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(tree announces, bloom filters, MMP reports on different timers),
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inter-frame processing delays inflate spin bit RTT measurements
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unpredictably. Timestamp-echo from ReceiverReports (with dwell-time
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compensation) is the sole SRTT source.
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Duplicate or regressed ReceiverReports are ignored before any RTT, loss,
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goodput, or ETX update. If receiver-side dwell time exceeds the wire
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field, the report keeps its counters but sends a zero timestamp echo so
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the sender cannot form an invalid RTT sample.
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The spin bit lives in the link-layer FMP inner header, so this
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mechanism applies to link-layer MMP only. Session-layer MMP carries
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its spin bit in the FSP encrypted inner header but uses it the same
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way: reflected for diagnostic visibility, not used for SRTT.
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## ECN Congestion Signaling
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The CE (Congestion Experienced) flag (bit 1 in the FMP flags byte)
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provides hop-by-hop congestion signaling through the mesh. Transit
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nodes detect congestion on outgoing links and set CE on forwarded
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packets; once set, the flag stays set for all subsequent hops to the
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destination.
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**Congestion detection** triggers on any of:
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- Outgoing link MMP loss rate ≥ `node.ecn.loss_threshold` (default 5%)
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- Outgoing link MMP ETX ≥ `node.ecn.etx_threshold` (default 3.0)
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- Kernel receive buffer drops detected on any local transport (via
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`SO_RXQ_OVFL` on UDP)
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**CE relay**: The forwarding path computes
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`outgoing_ce = incoming_ce || local_congestion`. Once CE is set on a
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packet, it remains set for the rest of the forward path.
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**IPv6 ECN-CE marking**: When a CE-flagged DataPacket arrives at its
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final destination, the IPv6 Traffic Class ECN bits are marked CE
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(0b11) before TUN delivery — but only for ECN-capable packets (ECT(0)
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or ECT(1)). Not-ECT packets are never marked per RFC 3168. The host
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TCP stack then echoes ECE in ACKs, triggering sender cwnd reduction
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through standard congestion control.
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**Session-layer tracking**: The `ecn_ce_count` field in MMP
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ReceiverReports tracks CE-flagged packets received per link, providing
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end-to-end visibility into congestion propagation.
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ECN signaling is a link-layer mechanism. Session-layer MMP only
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observes the CE counter as part of the report stream; CE marking is
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not generated end-to-end. Tuning parameters live under `node.ecn.*`
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in [../reference/configuration.md](../reference/configuration.md).
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## Send Failure Backoff (Session Layer Only)
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When a session MMP report cannot be delivered (destination unreachable,
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no route), the sender applies exponential backoff to the probe
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interval — a standard distributed-systems pattern for transient
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failure handling:
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- Each consecutive failure doubles the interval: 2x, 4x, 8x, 16x, 32x
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- Backoff caps at 32x the base interval (5 consecutive failures)
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- A successful send resets to the normal SRTT-based interval
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- Debug logging is suppressed after 3 consecutive failures; a summary
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is logged when the destination becomes reachable again
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This prevents wasted CPU and log noise when a session's remote
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endpoint has departed the network but the local session has not yet
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timed out. Link-layer MMP has no equivalent — link-layer reports are
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peer-to-peer over an authenticated link, so delivery failure is
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indistinguishable from link death and the link-liveness mechanism
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takes over.
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## Layer Differences
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| Aspect | Link layer | Session layer |
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| ------ | ---------- | ------------- |
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| Routing scope | Peer-to-peer (one hop) | End-to-end (forwarded through every hop) |
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| Configuration namespace | `node.mmp.*` | `node.session_mmp.*` |
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| Report bounds | `[1s, 5s]` | `[500ms, 10s]` |
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| Cold-start interval | 200 ms (first 5 samples) | 1 s |
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| Bandwidth cost | One link | Proportional to path length |
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| Send-failure backoff | Not applicable | Yes |
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| Path-MTU echo | Not applicable | PathMtuNotification (see [fips-mtu.md](fips-mtu.md)) |
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| Idle-timeout interaction | None | Reports do **not** reset session idle timer |
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## Idle Timeout Interaction (Session Layer Only)
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MMP reports (SenderReport, ReceiverReport) and PathMtuNotification do
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**not** reset the session idle timer. Only application data
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(DataPacket, type 0x10) resets `last_activity`. This ensures sessions
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with no application traffic tear down after
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`node.session.idle_timeout_secs` (default 90s), while MMP continues
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providing measurement data up to the teardown moment.
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## Operator Logging
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Both layers emit periodic metrics at debug level, so `node.log_level`
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(or `RUST_LOG`) must be set to `debug` to see them. The interval is
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`node.mmp.log_interval_secs` for link-layer (default 30s) and
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`node.session_mmp.log_interval_secs` for session-layer (default 30s).
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Link-layer:
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```text
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MMP link metrics peer=node-b rtt=2.3ms loss=0.2% jitter=0.1ms goodput=76.0MB/s tx_pkts=1234 rx_pkts=5678
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```
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Session-layer:
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```text
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MMP session metrics session=npub1tdwa...84le rtt=4.3ms loss=0.6% jitter=0.2ms goodput=71.3MB/s mtu=1472 tx_pkts=1234 rx_pkts=5678
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```
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Teardown logs include final SRTT, loss rate, jitter, ETX, goodput,
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and cumulative tx/rx packet and byte counts.
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## See also
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- [fips-mesh-layer.md](fips-mesh-layer.md) — link-layer MMP integration
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inside FMP
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- [fips-session-layer.md](fips-session-layer.md) — session-layer MMP
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integration inside FSP
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- [fips-mtu.md](fips-mtu.md) — PathMtuNotification, the session-only
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end-to-end path-MTU echo
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- [../reference/wire-formats.md](../reference/wire-formats.md) —
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SenderReport (0x01 / 0x11) and ReceiverReport (0x02 / 0x12) byte
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layouts
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- [../reference/configuration.md](../reference/configuration.md) —
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full `node.mmp.*`, `node.session_mmp.*`, and `node.ecn.*` knob tables
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