Digital communication network with a moderator station election process

• US 5,471,461 A
• Filed: 04/28/1993
• Issued: 11/28/1995
• Est. Priority Date: 04/28/1993
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Lucak, Mark A., Kucharski, Paul, Engdahl, Jonathan R., Gee, David J.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US08/054,581
• Time in Patent Office: 944 Days
• Field of Search: 370/17, 370/85.1, 370/79, 370/85.2, 370/85.6, 370/91, 370/92, 370/94.1, 370/119, 375/121, 340/825.06, 340/825.07, 340/825.22, 340/825.31, 371/69.1, 395/325
• US Class Current: 370/252
• CPC Class Codes: G05B 19/0421 Multiprocessor system
• 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 12/407 with decentralised control
• CPC Class Codes: H04L 41/00 Arrangements for maintenance, administration or management of data switching networks, e.g. of packet switching networks

Abstract

A moderator on a communication network periodically transmits a set of parameters for a protocol that is used to communicate over the network. Each node on the network compares the set of protocol parameters from the moderator to a set of parameters stored in that node. If the sets of parameters at a given node do not match, that given node ceases transmitting messages over the network until either the set of protocol parameters from the moderator match the stored set of parameters, or a matching set of parameters is stored in the node. Typically the active node that is assigned the lowest numerical network address functions as the moderator. However, an automatic process is utilized to prevent a node with a non-matching set of the protocol parameters from becoming the moderator for more than a brief period of time. An override procedure is provided to force all the nodes on the network to adopt a common set of protocol parameters in the event that the automatic process fails.

Claims

1. In a communication network having a plurality of nodes connected to a medium with each node being assigned a unique network address within a range of numerical values, and wherein one of the plurality of nodes is designated as a moderator which periodically transmits a set of communication protocol parameter values over the medium, a method by which a given node determines whether to function as the moderator comprising:

receiving messages sent by other nodes over the medium, each message including an identification of the network address from which the message originated;

determining from received messages whether another node is assigned a network address that is closer to one extreme of the range of numerical values than a network address assigned to the given node; and

functioning as the moderator by periodically transmitting communication protocol parameter values, when the given node has a network address that is closer to the one extreme of the range of numerical values than all other nodes which are sending messages over the medium.

2. The method as recited in claim 1 wherein the given node determines whether another node is assigned a network address with a lower numerical value than the network address assigned to the given node in said determining step, and the given node assumes operation as the moderator in said functioning step when the given node has a network address that is lower in numerical value than the network addresses of all other nodes which are sending messages over the medium.

3. The method as recited in claim 1, wherein when the given node is not functioning as the moderator, the method for the given node further comprises the steps of:

receiving the communication protocol parameter values transmitted over the medium by an existing moderator;

comparing the communication protocol parameter values transmitted by said existing moderator to a group of communication protocol parameter values stored in the given node; and

wherein the given node is permitted to transmit over the medium only when the communication protocol parameter values received from said existing moderator match the group of communication protocol parameter values stored in the given node.

4. The method as recited in claim 3 further comprising the steps of:

receiving a control message transmitted over the medium by a candidate moderator node, the control message including a new set of communication protocol parameters and a unique parameter value that forces the given node to accept the candidate moderator node as the moderator; and

responding to the control message containing the unique parameter value by storing the new set of communication protocol parameter values as the group of communication protocol parameter values for use in communicating over the network.

5. The method as recited in claim 3 further comprising:

another node transmitting communication protocol parameter values over the medium in a control message containing a special network address that is reserved from assignment to a node; and

the given node responding to the control message by storing the communication protocol parameter values as the group of communication protocol parameter values for use in communicating over the network.

6. The method as recited in claim 5 wherein the special network address is address zero.

7. The method as recited in claim 1 in which the step of functioning as the moderator further comprises transmitting a new set of communication protocol parameter values over the medium in a control message containing a unique parameter value that forces other nodes to accept the given node as the moderator.

8. In a communication network having a plurality of nodes connected to a medium with each node being assigned a unique numerical network address, and wherein one of the plurality of nodes is designated as a moderator which periodically transmits a set of communication protocol parameter values over the medium, a method performed by a given node comprising steps of:

receiving the set of communication protocol parameter values transmitted over the medium by the moderator;

storing the received set of communication protocol parameter values;

utilizing the stored set of communication protocol parameter values to transmit messages over the medium receiving messages sent by other nodes over the medium, each message including an identification of the network address from which the message originated;

determining from received messages whether another node is assigned a network address with a lower numerical value than the network address assigned to the given node; and

the given node functioning as the moderator by periodically transmitting communication protocol parameter values, when no other node that is sending messages over the medium has a lower numerical network address than the given node.

9. In a communication network having a plurality of nodes connected to a medium with each node being assigned a unique numerical network address, and wherein one of the .plurality of nodes is designated as a moderator which periodically transmits a set of communication protocol parameter values over the medium, a method performed by a given node comprising steps of:

receiving the set of communication protocol parameter values transmitted over the medium by the moderator;

storing the received set of communication protocol parameter values;

utilizing the stored set of communication protocol parameter values to transmit messages over the medium utilizing a user interface terminal connected to the network for determining a network address to use by performing steps including;

(a) receiving the set of communication protocol parameter values transmitted over the medium by the moderator;

(b) determining from the set of communication protocol parameter values a maximum address that is allowed to be used on the network;

(c) selecting the maximum address as a terminal address;

(d) listening to activity on the network to detect whether the terminal address, that was selected, is being used by another node; and

(e) if the terminal address is being used by another node, decrementing the terminal address and returning to step (d), otherwise using the terminal address to communicate over the network medium.

10. The method as recited in claim 9 in which step (e) is modified such that said user interface terminal ceases returning to step (d) and thereby fails to join the network, if the terminal address is decremented below a predefined value.

11. In a communication network having a plurality of nodes connected to exchange messages over a medium with each node being assigned a unique network address, and each message including an identification of the network address from which the message originated, and wherein a moderator node periodically transmits moderator messages over the medium, a method by which a given node determines whether to function as the moderator node comprising:

(a) receiving a first moderator message containing a first set of protocol parameter values transmitted over the medium by the moderator node;

(b) comparing the first set of protocol parameter values transmitted by the moderator node to a second set of protocol parameter values stored in the given node;

(c) disabling transmission of messages over the medium by the given node when the first and second sets of protocol parameter values are not substantially identical;

(d) while transmission of messages from the given node continues to be disabled, monitoring the medium for transmission of messages by other nodes, and upon detecting that no messages are being sent over the medium for a defined period of time, starting a timer to time a watch interval;

(e) if a second moderator message containing a third set of protocol parameter values is received by the given node during said watch interval, and the third set of protocol parameter values contained in said second moderator message do not match the second set of protocol parameter values stored in the given node, terminating the first timer and returning to step (d);

(f) when the first timer times out, determining from activity on the medium whether another node is assigned a network address with a lower numerical value than the network address assigned to the given node;

(g) functioning as the moderator node by periodically transmitting further moderator messages which contain further protocol parameter values, when no other node that is sending messages over the medium has a lower numerical network address than the given node; and

(h) functioning as a non-moderator node when another node is sending messages over the medium that have a lower numerical network address than the given node.

12. The method as recited in claim 11 further comprising upon powering up, the given node transmitting configuration data to other nodes on the network with which the given node is to communicate.

13. The method as recited in claim 11 further comprising upon powering up, the given node receiving the second set of protocol parameter values from another node on the network with which the given node is to communicate;

and storing the second set of protocol parameter values into a memory.

14. The method as recited in claim 11 further comprising after disabling transmission of messages over the medium, the given node enables transmission of messages over the medium upon consecutively receiving a predefined number of first sets of protocol parameter values each of which matches the second set of protocol parameter values.

15. In a communication network having a plurality of nodes connected to a medium with each node being assigned a unique numerical network address, each message including an identification of the network address from which the message originated, and wherein one of the plurality of nodes is designated as a moderator node which periodically transmits moderator messages over the medium, a method by which a given node determines whether to function as the moderator node comprising:

if the given node is not functioning as the moderator, the given node performs steps of;

(a) receiving a first moderator message containing a first set of protocol parameter values transmitted over the medium by an existing moderator node,

(b) comparing the first set of protocol parameter values transmitted by said existing moderator to a second set of protocol parameter values stored in the given node,

(c) disabling transmission of messages over the medium by the given node when the first and second sets of protocol parameter values are not substantially identical,

(d) while transmission of messages from the given node continues to be disabled, monitoring the medium for transmission of messages by other nodes, and upon detecting that no messages are being sent over the medium for a first period of time, starting a first timer to time a first interval,

(e) if a second moderator message containing a third set of protocol parameter values is received by the given node during the first interval, and the third set of protocol parameter values contained in said second moderator message do not match the second set of protocol parameter values stored in the given node, terminating the first timer and returning to step (d),

(f) when the first timer times out, determining from activity on the medium whether another node is assigned a network address with a lower numerical value than the network address assigned to the given node,

(g) functioning as the moderator node by periodically transmitting further moderator messages which contain further protocol parameter values, when no other node that is sending messages over the medium has a lower numerical network address than the given node, and

(h) functioning as a non-moderator node when another node is sending messages over the medium that have a lower numerical network address than the given node; and

if the given node is functioning as the moderator node, the given node performs steps of;

(i) upon detecting that only moderator messages are being sent over the medium for a second period of time, disabling transmission of messages over the medium and starting a second timer to time a second interval that is longer than the first interval,

(j) if a third moderator message containing a fourth set of protocol parameter values is received by the given node during the second interval and the fourth set of protocol parameter values contained in said third moderator message do not match the second set of protocol parameter values stored in the given node, terminating the second timer and entering step (d) as a non-moderator node, and otherwise

(k) when the second timer times out, determining from activity on the medium whether another node is assigned a network address with a lower numerical value than the network address assigned to the given node,

(l) functioning again as the moderator node by periodically transmitting further moderator messages which contain further protocol parameter values, if no other node that is sending messages over the medium has a lower numerical network address than the given node, and

(m) functioning as a non-moderator node when another node is sending messages over the medium that have a lower numerical network address than the given node.