CONTI'20041 Event Management in Distributed Control Systems Gheorghe Sebestyen Technical University of Cluj-Napoca Computers Department

CONTI'20042 Content Introduction – goals and motivations Event management in a distributed environment An Event management service model Analytical evaluation of the reaction time to events Conclusions

CONTI'20043 Events in control systems control systems: event-driven – reactive systems time-driven – time (clock ticks) drives the system event handling in single computer systems:  Input/Output pooling  Interrupts + ISRs in distributed systems  not a trivial task

CONTI'20044 Events in Distributed control problems concerning events: detection, notification, ordering actions (tasks) triggering as response to events evaluation of time delays between event and action proposed solutions: MMS (Manufacturing Message Specification)  Virtual devices + Event objects ROOM (Real-time Object Oriented Model)  Interface objects for I/O and signaling operations

CONTI'20045 A system model based on Distributed services Distributed system = a collection of autonomous and distributed services For a distributed control system: data acquisition service resource management service supervision and control service time and synchronization service event management service

CONTI'20046 A fully distributed Event management service Network interface Local event manager Application Network node Network interface Local event manager Application Network node Network interface Local event manager Application Network node.... Industrial Network Global Event Management Service

CONTI'20047 The Event Management service Functions: definition and configuration of data structures that describe and store events detection of conditions that trigger events dynamic event logging event notification mechanisms task scheduling based on the pending events- event messaging event ordering and synchronization mechanisms remote access to event objects unique time reference for event time-stamping

CONTI'20048 Components of a Local Event Manager Event server Event detector Event database Process variables Task scheduler Time service Resource management Network interface Control Application Local Event Manager

CONTI'20049 Evaluation of the reaction-time to events The computational model: tasks are statically allocated to network nodes every node has a task scheduler that use the Rate Monotonic scheduling algorithm; this algorithm is optimal for a single computer system tasks communicate through messages, on the network messages are scheduled with a TDMA (Time Division Multiple Access) algorithm, which means that every node has a predefined time slice for communication a task or message is delayed by its predecessor (message or task) in the transaction

CONTI' T he reaction time for a task without communication: r i = C i +  (  r i /T j  ) j=>prior where: r i – the reaction time of task “i” C i – the execution time of task “i” T j – the period of a task “j” that have a higher priority than task “i” if communication is involved: r i = J i +w i where:J i – the launching jitter, caused by the predecessor message w i – the reaction time caused by the task scheduling algorithm

CONTI' T he reaction time for a task (cont.) w i = C i +  (  (J j +w i )/T j  * C j ) j=>prior a recursive formula r i (k+1) = C i +  (  r i (k)/T j  * C j ) j=>prior

CONTI' Delivery time of a message r m =  (1 + I m )/S  * T TDMA where: r m – the delivery time of message “m” I m – the number of messages that have higher priority than message “m” and which may be launched before message “m” S – number of messages that can be transmitted by a node in its time slice of a TDMA period T TDMA – the TDMA protocol’s period The term I m may be evaluated with the following expression: I m =   (J j +r m )/T j  j=>prior where: J j – the delay (jitter) caused by the task that generate the message T j – the period of a message “j” that have a higher priority than message “m”

CONTI' Iterative computation R 1 (m+1) =  RM ( J 1(m) ) R 2 (m+1) =  RM ( J 2(m) ) …….. R n (m+1) =  RM ( J n(m) ) R ret(m+1) =  TDMA (J ret(m) ) J 1(m+1) =  1 (R ret(m+1) ) J 2(m+1) =  2 (R ret(m+1) ) …….. J n(m+1) =  n (R ret(m+1) ) J ret(m+1) =  ret (R 1(m+1), R 2(m+1),… R n(m+1) )

CONTI' Conclusions event management is a critical task in any control system distributed control systems require special event detection, notification and ordering mechanisms the service-based event management approach is proper for a distributed environment a scalable, reliable and fault-tolerance solution the reaction time of a distributed system can be evaluated with an analytical method