Local area network with message priority

• US 5,353,287 A
• Filed: 03/25/1992
• Issued: 10/04/1994
• Est. Priority Date: 03/25/1992
• Status: Expired due to Term

• Current Assignee: Alcatel Network Systems India Limited (Nokia Corporation)
• Original Assignee: Alcatel Network Systems India Limited (Nokia Corporation)
• Inventors: Mathews, Cecil, Kuddes, David W., Mazzola, Anthony J.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HSU, ALPUS
• Application Number:
  US07/857,353
• Time in Patent Office: 923 Days
• Field of Search: 370/60, 370/85.1, 370/85.2, 370/85.3, 370/85.6, 370/85.13, 370/85.14, 370/94.1, 370/94.3, 340/825.5, 340/825.51, 371/32, 371/33
• US Class Current: 370/448
• CPC Class Codes: H04L 12/4015 by scheduling the transmission of messages at the communication node
• CPC Class Codes: H04L 12/413 with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]

Abstract

A message priority scheme for use in local areas networks (LANS) operating in accordance with carrier sense, multiple access/collision detect (CSMA/CD) bus access protocol. A LAN station having a high priority message to send ignores the carrier sense signal, and thereby obtains immediate bus access. If the high priority message collides with another message already on the bus, both messages are subject to a backoff period. However, the backoff period for a high priority message is guaranteed to be less than that of a low priority message for a certain number of re-transmission attempts. An intermediate priority status is assigned to a message that previously had a high priority status, after a certain number of transmission attempts. The intermediate priority message is deprived of its ability to transmit while ignoring the carrier sense signal, but retains its shorter backoff period.

Claims

1. A method for adding a message priority scheme to a local area network station control unit operating in accordance with carrier sense, multiple access with collision detect (CSMA/CD) bus access protocol, comprising the steps of:

generating a carrier sense signal in response to a carrier to inhibit transmission of a message;

disabling said carrier sense signal when said message is a high priority message;

transmitting said high priority message while said carrier sense signal is disabled;

generating a collision detect signal in response to a collision between said high priority message and another message;

inhibiting a re-transmission of said high priority message for a high priority backoff period in response to said collision detect signal;

re-transmitting said high priority message, in response to said collision detect signal, after said high priority backoff period has elapsed;

updating a count value in response to said collision detect signal;

repeating the collision detect signal generating, inhibiting, re-transmitting and updating steps until either no collision occurs or said count value equals a predetermined number;

re-enabling said carrier sense signal;

prohibiting transmission of messages while said carrier sense signal is generated; and

re-transmitting said high priority message when said count value equals said predetermined number, when said high priority backoff period has elapsed, and generation of said carrier sense signal has ceased.

2. A control unit for adding a two-level message priority scheme to a local area network bus operating in accordance with carrier sense, multiple access with collision detect (CSMA/CD) bus access protocol, comprising:

an interface for detecting a collision of messages on the local area network bus and generating a collision detect signal in response to said collision, and for detecting a carrier on the bus and generating a carrier sense signal in response to said carrier;

a controller for executing CSMA/CD tasks, wherein said controller receives said collision detect signal from said interface and delivers a request to send a signal to said interface when a message is ready for transmission or re-transmission on said bus;

means for selecting between a standard backoff multiple and a low priority backoff multiple of longer duration than said standard backoff multiple, said means for selecting being in communication with said controller;

said controller further operable to calculate a backoff period said controller waits before delivering a second request to said interface to re-transmit said message, said controller uses said standard backoff multiple to calculate said backoff period if said message is a high priority message and said controller uses said low priority backoff multiple if said message is a low priority message; and

a priority unit for receiving said carrier sense signal from said interface and for delivering said carrier sense signal to said controller, wherein said priority unit further comprises means for disabling said carrier sense signal to said controller to allow said high priority message to be transmitted, said high priority message is re-transmitted on said bus if a collision with another message on said bus is not detected by said interface, wherein said priority unit further comprises means for counting the number of times said high priority message is re-transmitted while said carrier sense signal is being disabled, and means for re-enabling said carrier sense signal to said controller in response to said counting means counting to a predetermined number.

3. A method for adding a message priority scheme to multiple local area network station control units operating in accordance with carrier sense, multiple access with collision detect (CSMA/CD) bus access protocol, comprising the steps of:

generating a carrier sense signal in response to a carrier;

determining whether a message to be transmitted on said bus is a high priority message or a low priority message;

if said message is a high priority message,

disabling said carrier sense signal;

transmitting said high priority message; and

determining whether said high priority message collides with another message;

if a collision occurs, then performing the steps of;

inhibiting a re-transmission of said high priority message;

waiting for a high priority backoff period to elapse;

re-transmitting said high priority message;

determining if said re-transmitted high priority message collides with another message;

adjusting a count value in response to said collision;

repeating the steps of inhibiting, waiting, re-transmitting, determining, and adjusting until either said count value equals a predetermined number or no collision of said re-transmitted high priority message occurs;

re-enabling said carrier sense signal;

if said count value equals said predetermined number, then re-transmitting said high priority message, after said high priority backoff period elapses, as an intermediate priority message subject to said carrier sense signal;

if said message is a low priority message,

transmitting said low priority message subject to said carrier sense signal;

determining if said low priority message has collided with another message;

if a collision occurs,

waiting for a low priority backoff period to elapse; and

re-transmitting said low priority message subject to said carrier sense signal.

4. A control unit for adding a message priority scheme to a local area network bus operating in accordance with carrier sense, multiple access with collision detect (CSMA/CD) bus access protocol, comprising:

a processor for generating messages incorporating higher level message protocols;

an interface for detecting a collision of messages on the local area network bus and generating a collision detect signal in response to said collision, and for detecting a carrier on the bus and generating a carrier sense signal in response to said carrier;

a controller for executing CSMA/CD tasks, wherein said controller has means for receiving said collision detect signal from said interface, means for delivering a request to send a signal to said interface when a message generated by said processor is ready for transmission, and means for calculating different backoff periods for high and low priority messages; and

a priority unit, controlled by said processor via address and data lines, for receiving said carrier sense signal from said interface and for delivering said carrier sense signal to said controller, wherein said priority unit further comprising a logic gate unit for disabling said carrier sense signal from said controller when a high priority message is to be transmitted, wherein said priority unit further comprises means for initiating re-transmission of said high.priority message if said high priority message has a collision with another message on the local area network bus and a counter unit for re-enabling said carrier sense signal after a certain number of re-transmission attempts for said high priority message, such that said high priority message is transmitted subject to said carrier sense signal but with a high priority backoff period.

5. A method for adding a message priority scheme to multiple local area network station control units operating in accordance with carrier sense, multiple access with collision detect (CSMA/CD) bus access protocol, comprising the steps of:

sensing a carrier on a bus;

detecting a collision between multiple messages on said bus;

generating from a network interface a carrier sense signal in response to said carrier and a collision detect signal in response to said collision;

generating a request to send a signal with a network controller when a message is to be transmitted on said bus;

coupling said carrier sense signal from said network interface to said network controller via a priority control unit;

coupling said collision detect signal from said network interface to said network controller and to said priority control unit;

coupling said request to send signal from said network controller to said network interface and to said priority control unit;

transmitting high priority messages and low priority messages from said network controller;

disabling said carrier sense signal between said priority control unit and said network controller during transmission of high priority messages;

inhibiting a re-transmission of said high priority messages in response to said collision detect signal;

calculating, in response to said collision detect signal, a backoff period which is longer for a low priority message than for a high priority message;

if said message is a low priority message, re-transmitting, after said backoff period has elapsed, said low priority message when said carrier sense signal ceases to be generated;

if said message is high priority message, re-transmitting, after said backoff period has elapsed, said high priority message;

counting, in response to said collision detect signal and said request to send signal, the number of times that transmission of said high priority message is attempted while said carrier sense signal is disabled;

repeating the step of re-transmitting said high priority message, in response to said collision detect signal and said request to send signal, until either the number of times equals a predetermined number or no collision is detected;

re-enabling said carrier sense signal when the number of times equals said predetermined number; and

if transmission of said message without detecting a collision has not occurred, re-transmitting said message subject to said backoff period and said carrier sense signal.

6. A message priority unit for use within a local area network (LAN) control unit coupled to a bus operating in accordance with carrier sense, multiple access with collision detect (CSMA/CD) bus access protocol, comprising:

a logic gate unit operable to receive a carrier sense signal from an interface, said carrier sense signal indicates a signal on the bus to which the interface is coupled, said logic gate unit further operable to couple said carrier sense signal to a controller operable to execute CSMA/CD tasks and control said interface, said logic gate unit further operable to disable said carrier sense signal to said controller when the control unit sends a high priority message; and

a counter unit operable to receive a collision detect signal from said interface, said collision detect signal indicative of a collision between said high priority message and another signal on the bus, said counter further operable to count, in response to said collision detect signal, the number of times said high priority message is re-transmitted while said carrier sense signal is being disabled.