Method and apparatus for exchanging different classes of data during different time intervals

• US 5,553,095 A
• Filed: 04/28/1993
• Issued: 09/03/1996
• 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: Engdahl, Jonathan R., Lucak, Mark A., Gee, David J., Adams, Shawn L.
• Primary Examiner(s): Vu, Kim Yen
• Assistant Examiner(s): NGUYEN, ANH-VINH THI
• Application Number:
  US08/054,582
• Time in Patent Office: 1,224 Days
• Field of Search: 370/85.1, 370/85.15, 370/85.6, 370/85.7, 370/95.1, 370/110.1, 370/85.2, 370/85, 370/82, 375/288, 375/220, 375/222, 375/377
• US Class Current: 375/222
• CPC Class Codes: G05B 19/0421 Multiprocessor system
• CPC Class Codes: H04L 12/40013 Details regarding a bus controller
• CPC Class Codes: H04L 12/40026 Details regarding a bus guardian
• CPC Class Codes: H04L 12/40143 involving priority mechanisms hybrid switching fabrics H04L12/6402; intermediate storage or scheduling H04L49/90; time-division multiplex systems H04J3/00
• 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

Abstract

A digital communication network carries high and low priority data. The network stations that produce high priority data are assigned to a first group of stations and stations that produce low priority data are assigned to a second group with the two group not being mutually exclusive. Activity on the network is divided into periodic intervals of the same duration. Network control information, that defines how access to the medium, is determined is broadcast to all stations during a first segment of a periodic interval. The network control information defines the length of the periodic interval and of the periodic interval segments, and defines how many stations are in each group. Then during a second segment of the periodic interval, every station in the first group is afforded an opportunity, in a predefined order, to transmit high priority data over the medium. Stations in the second group are afforded an opportunity to transmit low priority data, when time remains after the first segment in a periodic interval before the network control information will be transmitted again. The specific station in the second group which is afforded an opportuinity to transmit first changes from periodic interval to periodic interval.

Claims

1. A station for a communication network in which activity is divided into periodic time intervals of equal duration, comprising:

a receiver coupled to the communication network to receive data therefrom;

a transmitter coupled to send data over the communication network;

an interface circuit connected to said receiver and said transmitter to exchange data with an external device; and

an access controller connected to said transmitter and to said receiver, and having a storage device to store network control information that is received from the communication network during a first segment of each periodic time interval, wherein when the network control information is revised from previous transmissions, the network control information further includes a countdown value designating a number of periodic intervals that must occur before the revised network control information is to be used in communicating over the communication network and said access controller further including means for temporarily storing the revised network control information, and for loading the revised information into said storage device for controlling network communications when a number of periodic intervals equal to the countdown value have occurred, the access controller performing a pair of functions comprising;

(a) enabling the transmitter to send data of a first class over the communication network during a second segment in each periodic time interval when data received from the network indicates that a preceding station in a predefined transmission order has finished transmitting, and enabling the transmitter to send data of a second class over the communication network during a third segment in a periodic time interval when an amount of time remaining in that periodic interval is at least as great as an amount of time required to send the data of the second class, and when either (1) the network control information indicates that the station is to transmit first during the third segment or (2) data received from the communication network indicates that a preceding station in a predetermined transmission order has finished transmitting data of the second class.

2. The station as recited in claim 1 wherein the storage device includes a first section to store a designation of the duration of the periodic interval, and a second section to store a designation of a duration of the first segment.

3. The station as recited in claim 1 wherein the storage device comprises a first section to store an indication of which stations are allowed to send data during the second segment, and a second section to store an indication of which stations are allowed to send data during the third segment.