21-EFT.WP.Metrology.Sync v1.0 | Chapter 4 — Measurement Links & Timestamps (Hardware / Software / Hybrid)

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Chapter 4 — Measurement Links & Timestamps (Hardware / Software / Hybrid)

One-line objective: Define a traceable timestamping discipline for network measurement links—unifying HW/SW/hybrid capture points, delay decomposition, and uncertainty publication—so that offset/skew/J and T_arr-related quantities have consistent, compliant interpretations across devices and domains.

I. Scope & Objects

1. Applicable systems
   • Ethernet/fiber PTP/NTP links supporting PHY/MAC/NIC hardware timestamps, kernel/user software timestamps, and hybrids that fuse the two.
   • Boundary (BC) / Transparent (TC) devices, server NICs, virtualized/container stacks, and TSN contexts.
2. Inputs
   • Packets & events: Sync/Follow_Up/Delay_Req/Delay_Resp or NTP four-timestamp sequences, accumulated correctionField, switch residence_time.
   • Capabilities & conditions: ts_point ∈ {phy_ingress, mac_rx, nic_rx, kernel_rx, userland}, line_rate, L_frame, driver/firmware versions, IRQ & scheduler policy.
   • References & constraints: tau_mono, ts, budgets for offset/skew/J, dual-form T_arr thresholds.
3. Outputs
   • Standardized timestamps: ts_std(p) with provenance ts_point, calibration bias, and uncertainty U(ts_std).
   • Link-delay breakdown: t_ser, t_prop, t_mac, t_phy, t_fifo, t_dma, t_irq, t_sched with u(•).
   • Manifests & contracts: manifest.sync.ts.*, assertion outcomes, and signature.

II. Terminology & Variables

1. Capture points & link
   • ts_point ∈ {phy_ingress, mac_rx, nic_rx, kernel_rx, userland}.
   • Components: t_ser = L_bits / R_bps, t_prop (medium), t_mac / t_phy (sublayer processing), t_fifo (NIC queues), t_dma, t_irq, t_sched.
   • Total: t_link = t_ser + t_prop + t_mac + t_phy + t_fifo + t_dma + t_irq + t_sched.
2. PTP/NTP four timestamps
   • T1 (master egress), T2 (slave ingress), T3 (slave egress), T4 (master ingress).
   • CF12 (forward correctionField sum), CF34 (reverse sum), t_res (per-TC residence_time).
   • delay_rt, asym.
3. Uncertainty & release
   • u(x) (standard uncertainty), U = k * u_c (expanded), check_dim(expr).
   • Time base: compute on tau_mono, publish on ts, and record offset/skew/J.

*III. Axioms P604- **

• P604-1 (Traceable single point): Each packet has exactly one authoritative ts_point; fusion aids estimation/correction but never rewrites provenance.
• P604-2 (Hardware-first): Prefer HW timestamps; without HW, SW capture must publish full link breakdown and U.
• P604-3 (Lexical delay breakdown): Record t_link components in a fixed order; omitted items set to zero and annotated.
• P604-4 (Conservative correctionField merge): Sum all intermediate-device correctionField and t_res into the estimator—no double-subtraction.
• P604-5 (Dual-form mandatory): For path/arrival metrics, compute both T_arr forms and record delta_form.
• P604-6 (Dimensional integrity): Validate all time/rate/length units via check_dim before computation.
• P604-7 (Unified time base): Do all stats/windowing on tau_mono, publish on ts, and attach offset/skew/J.
• P604-8 (Virtualization explicit): Split t_irq/t_sched by host/guest attribution in virtualized setups.
• P604-9 (Signed replay): manifest.sync.ts.* must be replayable with hash_sha256(blob) and signature.

*IV. Minimal Equations S604- **

• S604-1 (Serialization & insertion overhead)
  t_ser = ( L_bits + preamble_bits + ifg_bits ) / R_bps
• S604-2 (Software capture bias)
  ts_sw = ts_hw + t_dma + t_irq + t_sched + t_syscall + eps_sw
  bias_sw = E[ ts_sw - ts_hw ]
• S604-3 (Corrected four-timestamp pair)
  T2' = T2 - CF12
  T4' = T4 - CF34
• S604-4 (Offset & round-trip delay with asymmetry)
  offset = ( ( T2' - T1 ) + ( T3 - T4' ) ) / 2 - asym
  delay_rt = ( ( T2' - T1 ) + ( T4' - T3 ) ) / 2
• S604-5 (Hybrid normalization)
  ts_std(p) = ts(p) - bias(p) where bias(phy/mac)=0, bias(nic)=t_fifo, bias(kernel)=t_dma + t_irq + t_sched + t_syscall
• S604-6 (Total timestamp uncertainty)
  u^2(ts_std) = ∑ u^2(component)，U = k * sqrt( u^2(ts_std) )
• S604-7 (Dual-form delta)
  delta_form = | ( 1 / c_ref ) * ( ∫ n_eff d ell ) - ( ∫ ( n_eff / c_ref ) d ell ) |

V. Metrology Flow M60-4 (Measurement Link & Timestamps)

1. Capability probe & policy set
   • Enumerate interface/driver capabilities; determine ts_point; record line_rate, L_bits; detect correctionField and two-step Follow_Up.
   • Fix precedence: phy/mac > nic > kernel > userland.
2. Link decomposition & baseline calibration
   • Compute t_ser; estimate t_prop (medium/length); read NIC/DMA knobs to estimate t_fifo/t_dma.
   • Measure bias_sw via loopback/fixtures; derive ts_std calibration mapping.
3. Four-timestamp acquisition & correction
   • Extract T1..T4 and CF12/CF34; compute offset/delay_rt via S604-3/4; log t_res.
   • Publish ts_std and u(•); all computations on tau_mono.
4. Virtualization & hybrid fusion
   • Attribute t_irq/t_sched to host/guest; add paravirt correction if needed.
   • Anchor on ts_hw; use ts_sw to improve coverage when HW timestamps drop.
5. Dual-form arrival in parallel
   For propagation scenarios, compute both T_arr forms and delta_form; on breach, trigger path discovery or medium-parameter review.
6. Persist & sign
   Emit manifest.sync.ts.*: ts_point, ts_std, bias, U, t_link breakdown, offset, delay_rt, asym, delta_form, plus TraceID/signature.

VI. Contracts & Assertions C60-4*

• C60-41 (Single capture point): unique(ts_point | iface).
• C60-42 (Dimensional integrity): check_dim(t_ser) = [T], check_dim(offset) = [T], etc.
• C60-43 (Monotonicity & jitter): non_decreasing(ts_std); J(ts_std)_p99 ≤ J_max.
• C60-44 (Bias stability): | bias_sw - bias_sw_ref | ≤ bias_tol.
• C60-45 (RTT & asymmetry gates): delay_rt ≤ delay_max, |asym| ≤ asym_max.
• C60-46 (correctionField integrity): sums of CF/t_res consistent; missing_CF_rate ≤ tol_cf_miss.
• C60-47 (Dual-form delta): delta_form ≤ tol_Tarr.
• C60-48 (Virtualization annotations): when VMs exist, publish t_irq_host/guest, t_sched_host/guest.

VII. Implementation Bindings I60- (Timestamps & Link Layer)*

• discover_ts_capabilities(iface) -> {ts_point, features}
• estimate_serialization(L_bits, R_bps) -> t_ser
• measure_sw_bias(loopback_cfg) -> bias_sw, U
• correct_with_cfield(T1,T2,T3,T4, CF12,CF34) -> {T2', T4'}
• compute_offset_delay(T1,T2',T3,T4', asym) -> {offset, delay_rt}
• decompose_link(ds, nic_meta) -> {t_ser..t_sched, U}
• fuse_timestamps(ts_hw, ts_sw, policy) -> ts_std
• emit_ts_manifest(results, meta) -> manifest.sync.ts
• Invariants: sum(u^2)_components ≈ u^2(ts_std); announce_loss_rate ≤ tol_loss; delta_form ≤ tol_Tarr.

VIII. Cross-References

• Time-base & Allan-family noise, MTIE/tdev: EFT.WP.Metrology.TimeBase v1.0 Chapters 7 & 14.
• Synchronization baseline & BMCA: this volume Chapters 2 & 3.
• Cleaning compliance & manifests: Methods.Cleaning v1.0 Chapter 10 and Appendix C.
• Statistical uncertainty propagation: Methods.CrossStats v1.0 Appendix E.

IX. Quality SLIs & Risk Control

1. SLIs
   • ts_bias_p50/p95/p99, ts_jitter_p95/p99, missing_hw_ts_rate, cf_miss_rate, offset_p99, delay_rt_p99, asym_p95.
   • Component shares & drift rates for t_dma/t_irq/t_sched in t_link_breakdown.
   • delta_form_p99 and manifest coverage.
2. Risk actions
   • When bias drift breaches thresholds, auto recalibrate and degrade to HW capture; rising cf_miss_rate triggers path probing and TC health checks.
   • Under virtualization load, constrain/isolated irq/sched; if offset_p99 exceeds budget, downweight servo or switch upstream.

Summary