“…It is confirmed by a number of works that the spectral expansion method is better than the matrix geometric method in a number of aspects [5,32,33,39]. It is observed that the spectral expansion method is proved to be a mature technique for the performance analysis of various problems [5-17, 20-25, 27, 28, 31, 32, 38, 39, 49-51, 53, 54, 52, 58].…”