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Hybrid Diffusion for ICS Traffic (HAI 21.03) — Project Report
工业控制系统流量混合扩散生成（HAI 21.03）— 项目报告
1. Project Goal / 项目目标
Build a hybrid diffusion-based generator for ICS traffic features, focusing on mixed continuous + discrete feature sequences. The output is feature-level sequences, not raw packets. The generator should preserve:
- Distributional fidelity (continuous ranges + discrete frequencies)
- Temporal consistency (time correlation and sequence structure)
- Field/logic consistency for discrete protocol-like columns
构建一个用于 ICS 流量特征的混合扩散生成模型，处理连续+离散混合特征序列。输出为特征级序列而非原始报文。生成结果需要保持：
- 分布一致性（连续值范围 + 离散频率）
- 时序一致性（时间相关性与序列结构）
- 字段/逻辑一致性（离散字段语义）
2. Data and Scope / 数据与范围
Dataset used in current implementation: HAI 21.03 (CSV feature traces).
当前实现使用数据集： HAI 21.03（CSV 特征序列）。
Data path (default in config):
dataset/hai/hai-21.03/train*.csv.gz
特征拆分（固定 schema）： example/feature_split.json
- Continuous features: sensor/process values
- Discrete features: binary/low-cardinality status/flag fields
timeis excluded from modeling
3. End-to-End Pipeline / 端到端流程
One command pipeline:
python example/run_all.py --device cuda
Pipeline stages:
- Prepare data (
example/prepare_data.py) - Train temporal backbone (
example/train.py, stage 1) - Train diffusion on residuals (
example/train.py, stage 2) - Generate samples (
example/export_samples.py) - Evaluate (
example/evaluate_generated.py)
一键流程对应：数据准备 → 时序骨干训练 → 残差扩散训练 → 采样导出 → 评估。
4. Technical Architecture / 技术架构
4.1 Hybrid Diffusion Model (Core) / 混合扩散模型（核心）
Defined in example/hybrid_diffusion.py.
Inputs:
- Continuous projection
- Discrete embeddings
- Time embedding (sinusoidal)
- Positional embedding (sequence index)
- Optional condition embedding (
file_id)
Backbone (configurable):
- GRU (sequence modeling)
- Transformer encoder (self‑attention)
- Post LayerNorm + residual MLP
Outputs:
- Continuous head: predicts target (
epsorx0) - Discrete heads: logits per discrete column
连续分支： Gaussian diffusion 离散分支： Mask diffusion
4.2 Stage-1 Temporal Model (GRU) / 第一阶段时序模型（GRU）
A separate GRU models the trend backbone of continuous features. It is trained first using teacher forcing to predict the next step.
独立的 GRU 先学习连续特征的趋势骨架，使用 teacher forcing 进行逐步预测。
Trend definition:
trend = GRU(x)
residual = x - trend
5. Diffusion Formulations / 扩散形式
5.1 Continuous Diffusion / 连续扩散
Forward process on residuals:
r_t = sqrt(a_bar_t) * r + sqrt(1 - a_bar_t) * eps
Targets supported:
- eps prediction
- x0 prediction (default)
Current config:
"cont_target": "x0"
5.2 Discrete Diffusion / 离散扩散
Mask diffusion with cosine schedule:
p(t) = 0.5 * (1 - cos(pi * t / T))
Mask-only cross-entropy is computed on masked positions.
6. Loss Design / 损失设计
Total loss:
L = λ * L_cont + (1 − λ) * L_disc
6.1 Continuous Loss / 连续损失
epstarget: MSE(eps_pred, eps)x0target: MSE(x0_pred, x0)- Optional inverse-variance weighting:
cont_loss_weighting = "inv_std" - Optional SNR-weighted loss: reweights MSE by SNR to stabilize diffusion training
6.2 Discrete Loss / 离散损失
Cross-entropy on masked positions only.
6.3 Temporal Loss / 时序损失
Stage‑1 GRU predicts next step:
L_temporal = MSE(pred_next, x[:,1:])
6.4 Residual Alignment Losses / 残差对齐损失
- Quantile loss on residuals to align distribution tails.
- Residual mean/std penalty to reduce drift and improve KS.
7. Data Processing / 数据处理
Defined in example/data_utils.py + example/prepare_data.py.
Key steps:
- Streaming mean/std/min/max + int-like detection
- Optional log1p transform for heavy-tailed continuous columns
- Optional quantile transform (TabDDPM-style) for continuous columns (skips extra standardization)
- Discrete vocab + most frequent token
- Windowed batching with shuffle buffer
8. Sampling & Export / 采样与导出
Defined in:
example/sample.pyexample/export_samples.py
Export process:
- Generate trend using temporal GRU
- Diffusion generates residuals
- Output:
trend + residual - De-normalize continuous values
- Inverse quantile transform (if enabled; no extra de-standardization)
- Bound to observed min/max (clamp or sigmoid mapping)
- Restore discrete tokens from vocab
- Write to CSV
9. Evaluation / 评估指标
Defined in example/evaluate_generated.py.
Metrics (with reference):
- KS statistic (continuous distribution)
- Quantile diffs (q05/q25/q50/q75/q95)
- Lag‑1 correlation diff (temporal structure)
- Discrete JSD over vocab frequency
- Invalid token counts
指标汇总与对比脚本： example/summary_metrics.py
- 输出 avg_ks / avg_jsd / avg_lag1_diff
- 追加记录到
example/results/metrics_history.csv - 如果存在上一次记录，输出 delta（新旧对比）
分布诊断脚本（逐特征 KS/CDF）： example/diagnose_ks.py
- 输出
example/results/ks_per_feature.csv（每个连续特征 KS） - 输出
example/results/cdf_<feature>.svg（真实 vs 生成 CDF） - 统计生成数据是否堆积在边界（gen_frac_at_min / gen_frac_at_max）
Recent run (user-reported, Windows):
- avg_ks 0.7096 / avg_jsd 0.03318 / avg_lag1_diff 0.18984
10. Automation / 自动化
example/run_all.py runs all stages with config-driven paths.
example/run_compare.py can run a baseline vs temporal config and compute metric deltas.
11. Key Engineering Decisions / 关键工程决策
- Mixed-type diffusion: continuous + discrete split
- Two-stage training: temporal backbone first, diffusion on residuals
- Switchable backbone: GRU vs Transformer encoder for the diffusion model
- Positional + time embeddings for stability
- Optional inverse-variance weighting for continuous loss
- Log1p transforms for heavy-tailed signals
12. Code Map (Key Files) / 代码索引
- Core model:
example/hybrid_diffusion.py - Training:
example/train.py - Temporal GRU:
example/hybrid_diffusion.py(TemporalGRUGenerator) - Data prep:
example/prepare_data.py - Data utilities:
example/data_utils.py - Sampling:
example/sample.py - Export:
example/export_samples.py - Evaluation:
example/evaluate_generated.py - Pipeline:
example/run_all.py - Config:
example/config.json
13. Known Issues / Current Limitations / 已知问题
- KS may remain high → continuous distribution mismatch
- Lag‑1 may fluctuate → distribution vs temporal trade-off
- Continuous loss may dominate → needs careful weighting
- Transformer backbone may change stability; needs systematic comparison
14. Suggested Next Steps / 下一步建议
- Compare GRU vs Transformer backbone using
run_compare.py - Explore v‑prediction for continuous branch
- Strengthen discrete diffusion (e.g., D3PM-style transitions)
15. Summary / 总结
This project implements a two-stage hybrid diffusion model for ICS feature sequences: a GRU-based temporal backbone first models sequence trends, then diffusion learns residual corrections. The pipeline covers data prep, two-stage training, sampling, export, and evaluation. The main research challenge remains in balancing distributional fidelity (KS) and temporal consistency (lag‑1).
本项目实现了两阶段混合扩散模型：先用 GRU 时序骨干学习趋势，再用扩散学习残差校正。系统包含完整训练与评估流程。主要挑战仍是分布对齐（KS）与时序一致性（lag‑1）之间的平衡。