A mechanism which uses keyed verification sequences at the link layer of a protocol to control access to data transport facilities of a local area network is described.
The local area network itself has been described previously. For purposes of this discussion, its salient features are these: the transmission plant has the physical topology of a tree. Network nodes (users) are connected at some of the leaves. All transmissions from any node proceed up the tree to its root. At the root is equipment referred to as the Data Channel Access Module (DCAM). This rebroadcasts transmissions received at the root back down the tree toward the leaves. The network itself contains no switches; the selection of appropriate data from the rebroadcast datastream is amongst the functions assigned to a microprocessor at each of the network nodes.
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