Apparatus and method for communicating between nodes in a network

• US 5,117,430 A
• Filed: 02/08/1991
• Issued: 05/26/1992
• Est. Priority Date: 02/08/1991
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Berglund, Neil C.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): BLUM, RUSSELL
• Application Number:
  US07/652,760
• Time in Patent Office: 473 Days
• Field of Search: 370/94.3, 370/85.1, 370/85.2, 370/85.3, 370/85.9, 370/85.8, 370/95.2, 340/825.02, 340/825.5, 340/825.51, 340/825.06, 340/825.08
• US Class Current: 370/408
• CPC Class Codes: H04L 12/403 with centralised control, e.g. polling
• CPC Class Codes: H04L 12/4035 in which slots of a TDMA packet structure are assigned based on a contention resolution carried out at a master unit TDM/TDMA multiplex systems per se H04J3/1694; hybrid switching systems H04L12/64
• CPC Class Codes: H04L 12/44 Star or tree networks

Abstract

A plurality of nodes in a network are connected in a tree arrangement. A master control node is at the root of the tree. Each connection between a parent node and a child node in the tree consists of only one pair of wires, over which data bits are transmitted serially. To avoid contention, communications are always initiated by the parent node. The child node detects the end of message when no more data is received for a set timeout period. The child node then has a specified time interval for response to the communication, during which interval it has control of the line. After the end of the interval, control reverts to the parent. If a message has been received from the child within that time, normal status is resumed; oterwise, the parent retries the message or takes other error recovery actions. In the preferred embodiment, the network is used to monitor power conditions at a plurality of nodes in a computer system.

Claims

1. A communications network apparatus, comprising:

a master node and a plurality of subject nodes;

a plurality of connections running between nodes, each said connection comprising a single serial data signal carrier connected a pair of nodes, wherein one of said pair of nodes is a parent node with respect to the other of said pair of nodes, and the other of said pair of nodes is a child node with respect to said parent node, wherein said plurality of connections connect said master node and said plurality of subject nodes in a tree configuration, said tree having said master node at its root, wherein each of said plurality of subject nodes is connected to one or more nodes, one and only one of which is its parent;

means in said master node and in each of said plurality of subject nodes for transmitting and receiving messages comprising serial data on said connections;

end of message detection means in said master node and in each of said plurality of subject nodes for determining that a message being received has ended, wherein said end of message detection means determines that a message has ended when no more serial data is received on said connection for a predefined timeout period; and

collision avoidance means in said master node and in each of said plurality of subject nodes for determining when said node is entitled to initiate transmission of a message on said connections, wherein said means permits a child node to initiate transmission of a message to its parent only during a predefined interval following the occurrence of a predefined event, and said means prevents a parent node from transmitting a message to said child during said predefined interval.

2. The communications network apparatus of claim 1, wherein said collision avoidance means determines that the child node is entitled to initiate transmission of a message during a predetermined interval following the receipt of a message from another node.

3. The communications network apparatus of claim 1, further comprising transmission timeout means in said master node and in each of said plurality of subject nodes for aborting transmission of a message, said message comprising a plurality of predefined units of data transmitted serially, if a predefined timeout period has elapsed since transmission of the previous unit of data of said message.

4. The communications network apparatus of claim 1, wherein at least one of said subject nodes is connected, by one of said plurality of connections, to a child node of said subject node.

5. The communications network apparatus of claim 4, wherein:

said master node comprises means for initiating a broadcast message to be transmitted to every subject node in said network; and

each subject node in said network being connected by at least one of said connections to a child node comprises means for re-transmitting said broadcast message to each node which is a child node of said subject node.

6. The communications network apparatus of claim 4, further comprising transmission timeout means in said master node and in each of said plurality of subject nodes for aborting transmission of a message, said message comprising a plurality of predefined units of data transmitted serially, if a predefined timeout period has elapsed since transmission of the previous unit of data of said message.

7. The communications network apparatus of claim 1, wherein said subject nodes comprise means for monitoring the status of one or more devices and reporting said status to said master node.

8. The communications network apparatus of claim 1, wherein said serial data signal carrier is a pair of wires running between said pair of nodes.

9. A subject node in a communication network, wherein said network comprises a master node, a plurality of subject nodes and a plurality of connections running between nodes, each said connection comprising a single serial data signal carrier connecting a pair of nodes, wherein one of said pair of nodes is a parent node with respect to the other of said pair of nodes, and the other of said pair of nodes is a child node with respect to said parent node, wherein said plurality of connections connect said master node and said plurality of subject nodes in a tree configuration, said tree having said master node at its root, wherein each of said plurality of subject nodes is connected to one or more nodes, one and only one of which is its parent, said subject node comprising:

means for coupling at least one of said plurality of connections to said subject node;

means for transmitting and receiving messages comprising serial data on said connection coupled to said subject node;

end of message detection means for determining that a message being received has ended, wherein said end of message detection means determines that a message has ended when no more serial data is received on said connection for a predetermined timeout period;

collision avoidance means for determining which node of the pair of nodes connected by said connection is entitled to initiate transmission of a message on said connection, wherein said means permits said child node to initiate transmission of a message to its parent only during a predefined interval following the occurrence of a predefined event, and said means prevent said parent node from transmitting a message to said child during said predefined interval.

10. The subject node in a communications network of claim 9, further comprising transmission timeout means for aborting transmission of a message, said message comprising a plurality of predefined units of data transmitted serially, if a predefined timeout period has elapsed since transmission of the previous predefined unit of data in said message.

11. The subject node in a communications network of claim 9, wherein said serial data signal carrier is a pair of wires running between said pair of nodes.

12. The subject node in a communications network of claim 9, wherein said collision avoidance means permits said subject node to initiate transmission of a message to its parent only during a predefined interval following the receipt of a message from said parent.

13. The subject node in a communications network of claim 12, further comprising transmission timeout means for aborting transmission of a message, said message comprising a plurality of predefined units of data transmitted serially, if a predefined timeout period has elapsed since transmission of the previous predefined unit of data in said message.

14. The subject node in a communications network of claim 13, further comprising means for monitoring power availability status of a device in a computer system.

15. The subject node in a communications network of claim 13, further comprising means for receiving a program for executing in said subject node from said network.

16. The subject node in a communications network of claim 9, further comprising means for transmitting and receiving messages comprising serial data on at least two of said plurality of connections, wherein at least one of said plurality of connections runs to a child node of said subject node.

17. The subject node in a communications network of claim 16, further comprising transmission timeout means for aborting transmission of a message, said message comprising a plurality of predefined units of data transmitted serially, if a predefined timeout period has elapsed since transmission of the previous predefined unit of data in said message.

18. The subject node in a communications network of claim 16, wherein:

said master node comprises means for initiating a broadcast message to be transmitted to every node in said network other than said master node; and

said subject node comprises means for re-transmitting said broadcast message to each node which is a child node of said subject node.

19. The subject node in a communications network of claim 18, further comprising:

means for broadcasting a message to a plurality of child nodes attached to said subject node simultaneously; and

means for ignoring responsive messages received from said child nodes when said responsive messages are received in response to a message which is broadcast to a plurality of child nodes simultaneously.

20. The subject node in a communications network of claim 18, further comprising means for receiving a program for executing in said subject node from said network.

21. The subject node in a communications network of claim 18, further comprising means for monitoring power availability status of a rack used for housing devices in a computer system.

22. A method in a subject node for communicating betwen nodes in a network, wherein said network comprises a plurality of nodes and a plurality of connections running between nodes, each said connection comprising a single serial data signal carrier connecting a pair of nodes, wherein one of said pair of nodes is a parent node with respect to the other of said pair of nodes, and the other of said pair of nodes is a child node with respect to said parent node, wherein said plurality of connections connect said plurality of nodes in a tree configuration, said tree having a master node at its root, wherein said subject node is not said master node, and wherein each of said plurality of nodes other than said master node is connected to one or more nodes, one and only one of which is its parent, said method comprising the steps of:

waiting in idle mode for a message from another node of said network, wherein said subject node is enabled to receive data on said network while performing said step of waiting in idle mode but does not transmit data on said network while performing said step of waiting in idle mode;

resetting an end of message timer whenever a predefined unit of data is received from another node of said network;

predetermining that a message has ended when said end of message timer times out;

setting a process timer for response to said message when said message has ended;

processing a responsive message to said message; and

transmitting said responsive message to the parent node of said subject node if said process timer has not timed out.

23. The method of claim 22, wherein said step of transmitting a responsive message comprises the steps of:

resetting a transmit timer whenever a predefined unit of data is transmitted to said parent node; and

aborting transmission of said message if said transmit timer times out before said message has been transmitted in its entirety.