physical network implements several network services required by the network application the operation of the sn layer may be reduced on the other hand as described above if the underlying physical network does not implement some or all network services required by the application it is the sn layer 39 s duty to adapt and implement them let there be a complex network application implementing a true distributed control network application and whose operation requires a hybrid network comprising subnetworks utilizing several dissimilar network communication protocols and media a true distributed control network application requires several network services for its successful operation which are described in detail in the aforementioned co pending patent documents if said required services including acknowledged and unacknowledged datagram services and multicast and broadcast services among others are not implemented by the underlying physical network the sn layer will implement them fig2 illustrates an exemplary hypothetical hybrid network implementing a true distributed control system in which a plurality of network router nodes 12 14 16 and 18 are connected to an internet 10 said routers serve as connection links between internet 10 and subnetworks 20 22 24 26 which use dissimilar communication protocols and or media in fig2 subnetwork 20 is of hypothetical type iii e g through a wireless medium subnetworks 22 and 26 are of hypothetical type ii e g using lontalk protocol and subnetwork 24 is of hypothetical type i e g using rudp ip over ethernet there are two further components.