...except! If the server is processor-sharing/timeslicing. The results derived for timeslicing servers are surprisingly general in service distribution, and can

...except! If the server is processor-sharing/timeslicing. The results derived for timeslicing servers are surprisingly general in service distribution, and can be stated in product form like the networks of simple M/M/c servers you know. (Arrivals still need to be Poisson, but that's a fairly nice requirement in that many real-life arrivals actually look Poisson.)