Continual Federated Learning for Network Intrusion Detection: An Open-Index Systematic Map

Abstract

Purpose: Continual federated learning (FCL) combines decentralized model updating with sequential adaptation, but network-intrusion studies use incompatible definitions of drift, retention, and evaluation. This open-index systematic map examines how such systems operationalize non-stationarity, preserve earlier knowledge, and report empirical and reproducibility evidence. Method: Eight queries were executed in OpenAlex, Crossref, and DBLP on 26 July 2026. The interfaces returned 8,819 records within documented result limits; deduplication left 3,075 unique records. The initial concept-block rule excluded 2,865 records. A rule-based sensitivity audit reclassified two false negatives, yielding 2,863 automatic exclusions and 212 records for title/abstract screening. Thirty-one database-derived and nine supplementary reports were sought; 24 were not retrieved. Sixteen full texts were assessed, two were excluded, and 14 primary studies were mapped. Results: The corpus comprised three studies from 2023, six from 2024, one from 2025, and four from the partial 2026 search year. Nine studies tested retention after later tasks or classes; five reported adaptation without a prior-task retention outcome. Within the nine retention-tested studies, replay-based designs most often reported favorable within-study stability results, but heterogeneous scenarios and comparators do not establish cross-study superiority. Only two studies reported standardized forgetting or backward transfer, two supplied study-specific code, and one tested malicious clients. Conclusion: The accessible open-index evidence supports FCL as a prototype strategy under constructed benchmark sequences. It does not establish cross-network robustness, formal privacy, or deployment-scale reliability. A targeted supplementary update on 27 July 2026 found no additional eligible, accessible full text. Interpretation is constrained by capped interfaces, single-reviewer screening, and 24 unretrieved reports.