Sentence:  One straightforward way of taking advantage of these similarities to provide more data for training the model parameters is to use the same Gaussian distributions to represent all the states of all models, with only the mixture weights being state-specific. Thus the distribution parameters are <WSD>tied</WSD> across the different states, and this type of model is often referred to as a <WSD>tied</WSD> mixture. 
Meaning of the word marked with <WSD> tags:  Closely connected or associated.