Today’s networks are constantly under attack from malicious intrusions. To tackle high‑dimensional, noisy and non‑linear traffic data, researchers have built a model that blends several techniques. First, a hybrid feature‑selection and kernel‑based dimensionality reduction method projects the data into a low‑dimensional space while preserving non‑linear separability. The reduced features are then encoded as colour images, where each hue encodes a distinct traffic characteristic. These images are fed to a convolutional neural network that is fine‑tuned via transfer learning: weights from a pre‑trained network are adapted to the new task, boosting multi‑class detection performance. Experiments on the UNSW‑NB15 and CICIDS 2017 datasets yield accuracies of 99.99% and 99.96%, with F1‑scores of 99.98% and 99.91%. The work shows how combining dimensionality reduction, visual representation and transfer learning can produce highly effective, real‑world‑ready intrusion detection systems.
The proposed model follows a multi‑stage pipeline. In the first stage, a hybrid filter‑wrapper feature selection algorithm employs mutual information and redundancy criteria to discard irrelevant or redundant variables. Next, kernel PCA with a Gaussian kernel reduces dimensionality while preserving non‑linear structures. The resulting low‑dimensional features are normalized and mapped to an RGB colour space via a semantic feature mapping that assigns each dimension to a colour channel, enabling complex patterns to be visualised as images. These 64×64 pixel images are processed by a CNN consisting of three conv‑batchnorm‑relu‑maxpool blocks followed by two fully connected layers with dropout. Transfer learning leverages weights from a ResNet‑18 pre‑trained on ImageNet; the first two blocks are frozen while the latter blocks are fine‑tuned on the intrusion dataset. An ensemble weighting scheme assigns higher importance to sub‑classifiers that achieve better precision on minority classes, boosting overall recall. Training uses the Adam optimizer with an initial learning rate of 1e‑4, reduced by a step scheduler every 10 epochs. The loss function is weighted cross‑entropy to counteract class imbalance. Five‑fold cross‑validation yields accuracy standard deviations below 0.05%, indicating high stability. Ablation studies confirm that each component—feature selection, kPCA, image mapping, and transfer learning—contributes significantly to the final performance.
