[1] V. E. Beneš: 
Mathematical theory of connecting networks and telephone traffic. Academic Press, New York -London 1965. 
MR 0210516 
[2] V. E. Beneš: 
Semilattice characterization of nonblocking networks. Bell System Tech. J. 52 (1973), 697-706. 
MR 0332349 
[3] K. W. Cattermole: Graph theory and the telecommunications network. Bull. Institute Math. Applic. 11 (1975), 94-107.
[5] J. Nieminen: 
A classification of the vertices of an undirected communication graph G generating a congruence relation on G. Wiss. Z. TH Ilmenau 20 (1974), 55 - 62. 
MR 0357241 | 
Zbl 0275.05111 
[6] K. Takagi: 
Design of multi-stage link systems by means of optimum, channel graphs. Electr. and Comm. Japan 51-A, (1968), 4, 37-46. 
MR 0262014 
[7] D. A. Waller: 
Products of graph projections as a model for multistage communication networks. Electr. Lett. 12 (1976), 206-207. 
MR 0424439