Message protocol for efficient transmission of vital directives on a guideway
A method for delivering and maintaining mandatory directives data from a central office server to an on-board system. Mandatory directives include the enforceable train control data required for a train operating on controlled track. The method enables the on-board system and the central server to exchange data in a vital manner, in part by checking for any inconsistency between i) the on-board system's data as previously transmitted and ii) the required data as represented by both a transmitted set of data identifiers and an associated error correction code.
1. A method comprising:
receiving, by an on-board system situated on a train, a first message containing a set of mandatory train directives that comprise train control data for the train;
subsequent to receiving the set of mandatory train directives, receiving a plurality of regularly-transmitted heartbeat messages at a train; wherein a heartbeat message from the plurality includes i) a current set of data identifiers and ii) error detection code associated with the current set of data identifiers; wherein the heartbeat message from the plurality does not include the train control data; and wherein the error detection code comprises a smaller data set than the set of mandatory train directives;
comparing, for a discrepancy, the error detection code in each heartbeat message, when received, against a copy of the mandatory train directives that is stored in the onboard system; and
altering a normal operating mode of the train to a relatively more restrictive operating mode when a discrepancy is identified.
2. The method of claim 1 wherein the set of mandatory train directives is received once during a trip of the train.
3. The method of claim 2 , wherein the set of mandatory train directives is received at the origin of the trip.
4. The method of claim 1 further comprising transmitting a message comprising a report of a session failure when one of the heartbeat messages is not received when expected per a transmission schedule.
5. The method of claim 4 further comprising altering the normal operating mode of the train when one of the heartbeat messages is not received.
6. The method of claim 1 further comprising transmitting a message comprising a report of a discrepancy when such discrepancy is identified.
7. The method of claim 6 further comprising receiving, after transmitting the report of the discrepancy, updated data pertaining to the discrepancy in the copy of the mandatory train directives.
8. The method of claim 1 further comprising receiving a directive to return to the normal operating mode after the discrepancy is corrected.
9. The method of claim 1 wherein the train control data comprises wayside status.
10. The method of claim 1 wherein the error detection code comprises a cyclical redundancy check.
11. A method comprising:
transmitting, by a server that is separate from a train, a first message containing a set of mandatory train directives that comprise train control data for the train, to an onboard system situated on the train; and
transmitting, on a periodic basis and subsequent to the first message, a heartbeat message to the train, wherein the heartbeat message contains error detection code associated with the vital train control data, wherein the error detection code comprises a smaller data set than the set of mandatory train directives, and wherein the heartbeat message does not include the train control data.
12. The method of claim 11 further comprising receiving a message pertaining to a session failure when:
(a) there is a discrepancy between the error detection code received by the on-board system and a copy of the mandatory train directives that is stored in the on-board system; or
(b) the train does not receive the heartbeat message.
13. The method of claim 12 further comprising initiating a synchronization sequence upon receipt of the message pertaining to session failure, wherein the synchronization sequence updates the copy of the mandatory train directives.