Network comprising a plurality of network nodes for media access checks

1. A network comprising a plurality of intercoupled network nodes, characterized in that the network nodes, controlled by a respective bus guardian, send messages during an assigned time slot and receive messages outside this time slot, in that each network node contains a test signal generator which delivers a test signal outside the assigned time slot, and in that each network node contains a test signal detector which, after receiving a test signal from at least another network node outside the time slot, detects that there is a defective circuit portion in the assigned network node and/or in at least another network node, the test signal detector is also provided for directly receiving the test signal of the assigned test signal generator and in that a control unit in a network node

receives and evaluates the detection results of the test signal detector and

establishes that a circuit portion in the assigned network node is defective when only during the assigned time slot the assigned test signal generator and another network node deliver a test signal and

establishes that a circuit portion in at least another network node is defective when during the assigned and the other time slot at least another network node delivers a test signal.

2. A network as claimed in claim 1 , characterized in that the control unit blocks the output of the network node in case of a defective circuit portion in the assigned network node.

3. A network as claimed in claim 1 , characterized in that the control unit in a network node establishes that the assigned test signal generator is defective when during the assigned and the other time slot a test signal is delivered neither by the assigned test signal generator nor by another network node.

4. A network comprising a plurality of intercoupled network nodes, characterized in that the network nodes, controlled by a respective bus guardian, send messages during an assigned time slot and receive messages outside this time slot,

in that each network node contains a test signal generator which delivers a test signal outside the assigned time slot, and in that each network node contains a test signal detector which, after receiving a test signal from at least another network node outside the time slot, detects that there is a defective circuit portion in the assigned network node and/or in at least another network node, in that at least part of the network nodes are directly intercoupled via at least one star node,

in that the star node comprises a plurality of star interfaces which are assigned to at least one network node,

in that a respective star interface in dependence on a pilot signal transfers a message from the assigned network node to the other star interfaces or from another star interface to at least one of the assigned network nodes,

in that more than one star interface are assigned to at least one network node, of which only one interface transfers messages in dependence on the status of the assigned network node.

5. A network as claimed in claim 4 , characterized in that each network node includes a pilot signal generator which generates either a pilot signal which indicates the whole assigned time slot or the beginning and end of the time slot.

6. A network as claimed in claim 5 , characterized in that the pilot signal generator is also used as a test signal generator.

7. A network as claimed in claim 4 , characterized in that the test signal detector also detects the pilot signal generated during the assigned time slot.