Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In [3] and [4], the authors introduce the idea of Early Application Identification and classify traffic flows by looking only at the lengths of the first packets in a flow; classification is performed by using clustering techniques such as K-means, Hidden Markov Models (HMM) and Gaussian Mixture Models (GMM).
Category: