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Minimization of the total completion time for asynchronous transmission in a packet data-transmission system

100%

Piórkowski A. , Werewka J.

2010

tom Vol. 20, no 2

391-400

The minimization of the total completion time for asynchronous transmission in distributed systems is discussed. Attention is focused on the problem of message scheduling on part of the sender. Messages to be sent form a queue, and the order in which they are to be sent has to be first established. The methods of scheduling messages, which minimize the factor of the total completion time, are presented herein. The message-scheduling problem becomes considerably complicated when the stream of data transmitted between the sender and the receiver is organized into packets. A scheduling rule, according to which the shortest messages (SPT-Shortest Processing Time) are selected as the first to be sent, has been proven to be appropriate for the proposed model. A heuristic algorithm for scheduling messages with real-time constraints is proposed. The performance of the scheduling algorithm is experimentally evaluated. The results of the study show the possibility of improving the total completion time from a few to ten percent, depending on the characteristics of the sender. Thus, the practicability of the method has been proved.

Badania eksperymentalne magistral miejscowych dla wybranych metod szeregowania wiadomości

80%

Żaba S.

tom Vol. 50, z. 2

261-286

W artykule przedstawiono właściwości i prametry czasowe trzech wybranych magistral miejscowych: PROFIBUS FMS, CAN i InterBus-S. Prezentowane wyniki uzyskano na podstawie badań, polegających na sprawdzeniu dotrzymania ograniczeń czasowych dla wiadomości w rozproszonym systemie czasu rzeczywistego z magistralą miejscową przy założeniu, że wiadomości szeregowane są przy użyciu metod szeregowania : FIFO, GRMS, EDF. Badania przeprowadzone były dla najgorszego przypadku, tzn. zostało założone, że w chwili t = 0 zostały aktywowane wszystkie zadania w systemie. Uwzględniono także czasy blokowania wiadomości. Wyniki badań zaprezentowano w postaci graficznej i tabelarycznej.

In this paper properties and time parameters of three fieldbuses PROFIBUS FMS, CAN, InterBus are presented as the result of research based on checking of RT - constraint fulfilment of messages in distributed real time system based on fieldbus. Research was done for FIFO method and real time methods scheduling GRMS and EDF. Tests were performed for the worst case - it was assumed that all messages in system were activated in instant zero. The message blocking is also considered. Results of testing were obtain by using computer algorithms created by author. On the basis of performing tests we can draw conclusions as follow: * FIFO method is very simple and requires small calculating time, bul its performance are the least from among priorities method, * Dynamic methods have better performance than static priority for each fieldbus (except for CAN fieldbus, becouse there is impossible to apply dynamic method to this fieldbus), * InterBus-S fieldbus has the best effects for transmitting 1 or 2 bytes data length, CAN fieldbus has the best effects for transmitting 3 to 8 bytes data length and PROFIBUS FMS fieldbus has the best effects for transmitting massages with data length above 8 bytes.