When we speak about service (the tertiary economical sector), we always use les services in French. Now about the rest of the sentence (efficace, un), keep in mind we are referring to the network = le réseau, which is indeed singular. (It is an efficient network = C'est un réseau efficace)
What is a "service network"? I see a thread suggesting "service" has to do with the customer service industry, but I can't apply that definition here and make sense out of this sentence.
In a recent sentence we learned about "le service DES transports", but here we have "un reseau DE services". In both cases, de(s) refers to a plural object. So why the difference? What's the rule on when to use de and when to use des?