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Network fault recovery by controllable switching of subnetworks
| Details |
Inventors: Rocco, Jr., A. Gregory;
Assignee: Massachusetts Institute of Technology (Cambridge, MA)
Primary Examiner: Evans; Arthur G.
Assistant Examiner: Barry; Lance L.
Attorney, Agent or Firm: Hamilton, Brook, Smith & Reynolds
A subring module for controlling the switching of a subring in and out of the main network of a token passing ring has a data detection circuit for detecting a token on the network. The subring module switches between two switch positions in response to an internal state machine. The first switch position incorporates the subring into the main network, and the second switch position isolates the subring from main network. The subring module has a state machine which responds to the detection of the token on the network to switch the subring out of the network when the network is down, and to switch the subring back into the network when both the subring and the main network are up again. When a number of subrings are present, each subring has its own module and state machine control. When the network goes down, the subrings switch out at different times depending on a hierarchial priority given to the subrings. The switching of the subrings back into the network is also controlled relative to a hierarchical priority. Thus, splitting and recombining of subrings of the the token passing ring can be arranged to proceed in any desired manner. The end result is that a defective subring is automatically isolated. |
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DETAILED DESCRIPTION A token passing ring of the present invention has a main network providing a serial communication path to a plurality of communication nodes.
A subring also provides a serial communication path to a plurality of communication nodes.
A subring module provides a switchable communication link between the subring and the main network.
In a first switch position, the subring module incorporates the communication path of the subring into the communication path of the main network.
In a second switch position, the subring module closes the communication paths of the subring and the network on themselves and isolates the communication path of the subring from the communication path of the main network.
Thus, while the switch is in the second position, the subring module completes the serial communication path of both the network and the subring such that each is an independent communication ring.
For controlling the switching of the subring module, a controller with a data detection circuit is provided which detects communication signals reaching the subring module.
In a preferred embodiment, the data detection circuit specifically detects tokens used in controlling traffic on the token passing ring.
The data detection circuit controls the subring module to switch the subring module from the first switch position to the second switch position if a required lower threshold frequency of tokens are not detected for a first selectable period of time.
The data detection circuit also controls the subring module to switch the subring module from the second switch position to the first switch position after a second selectable period of time if a required upper threshold frequency of tokens are detected on the subring.
With the data detection circuit of the controller detecting signals on the subring, the presence of the required upper threshold frequency of tokens indicates that the subring is not faulty and can be switched back into the network.
In the preferred embodiment, the first switch position of the subring module connects an input port of the subring to an output port of the main network, while connecting an input port of the main network to an output port of the subring
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