A three-stage network is operated in strictly nonblocking manner in accordance with the invention includes an input stage having r
1 switches and n
1 inlet links for each of r
1 switches, an output stage having r
2 switches and n
2 outlet links for each of r
2 switches. The network also has a middle stage of m switches, and each middle switch has at least one link connected to each input switch for a total of at least r
1 first internal links and at least one link connected to each output switch for a total of at least r
2 second internal links, if m≧s*MIN(n
1,n
2) where
- s=2 when r2=[9,11],
- s=3 when r2=[25,48],
- s=4 when r2=[49,99],
- s=5 when r2=[100,154],
- s=6 when r2=[155,224], and
- s=7 when r2=[225,278].
In one embodiment, each multicast connection is set up through such a three-stage network by use of at most s middle stage switches. When the number of input stage r1 switches is equal to the number of output stage r2 switches, and r1=r2=r, and also when the number of inlet links in each input switch n1 is equal to the number of outlet links in each output switch n2, and n1=n2=n1 a three-stage network is operated in strictly nonblocking manner in accordance with the invention if m≧s*n where
s=2 when r=[9,11]; s=3 when r=[25,48]; s=4 when r=[49,99]; s=5 when r=[100,154]; s=6 when r=[155,224]; and s=7 when r=[225,278]. In one embodiment, each multicast connection is set up through such a three-stage network by use of at most s middle stage switches.