Redes de Comunicação em Ambientes Industriais Aula 8

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1 Redes de Comuncação em Ambentes Industras Aula 8 Luís Almeda lda@det.ua.pt Electronc Systems Lab-IEETA / DET Unversdade de Avero Avero, Portugal RCAI 2005/2006 1

2 In the prevous epsode... Cooperaton models: Clent/Server, Producer/Consumer, Producer/Dstrbutor/Consumer, Publsher/Subscrber Manufacturng Message Specfcaton Goals Archtecture Objects and methods Clock synchronzaton IEEE 1588 SynUTC RCAI 2005/2006 2

3 Establshes the relatve order of message transmssons Related ssues: Constrants mposed by the MAC Fxed-prortes, Master-Slave, Token-passng, TDMA, FIFO queues, Table-based Support for global synchronsm Allows use of offsets On-lne or off-lne (table-based) schedulng Statc or dynamc schedulng RCAI 2005/2006 3

4 The traffc schedulng algorthm s essentally executed at the data lnk level (MAC and by local queung polces) network layer (routng queues) It can be dstrbuted (e.g. CAN), or centralzed n a partcular node (e.g. FTT-CAN, WorldFIP). RCAI 2005/2006 4

5 Resemblances wth task schedulng The problem of schedulng tasks n a processor, upon fully dstrbuton (one processor per task) s transformed n a message schedulng problem The network s now the bottleneck (.e. the resource to be scheduled) G(s) G(s) Network RCAI 2005/2006 5

6 Resemblances wth task schedulng Task model must be adapted adequately accordng to network protocol Tasks executon tme (C ) translates to message transmsson tme, or to transacton duraton when atomc Perod (T ), Deadlne (D ) and Prorty (P ) are smlar Offsets (O ) are supported on globally synchronzed systems, only D C t=0 O O + T O + kt tme RCAI 2005/2006 6

7 Resemblances wth task schedulng Non-preempton of message (packet) transmsson. Once transmsson starts cannot be nterrupted. Can be accounted for as a blockng term (B ) Ready Messages Bus tmelne B 1,3 B - Blockng Messages RCAI 2005/2006 7

8 Typcal schedulng model M {m (C,T,J,D,P,O ), =1..N} N ncomng streams Nonpreemptve scheduler Outgong traffc Problem: Can all tmng constrants be met? or Is the message set schedulable? Schedulablty Analyss Knowng the schedulng polcy and the arrval pattern of the ncomng flows allows determnng the departng pattern of the outgong flow RCAI 2005/2006 8

9 Schedulng Crtera Fxed Prortes Rate Monotonc (RM) Deadlne Monotonc (DM) Importance Dynamc Prortes Earlest Deadlne Frst (EDF) Least Laxty Frst (LLF) Frst Come Frst Served (FCFS) RCAI 2005/2006 9

10 Schedulablty Analyss Most typcal analyss focus on Bandwdth utlzaton U= Network nduced delay also referred to as worst-case response tme analyss. In statc table-based systems t s typcal to use branch and bound technques to optmze the schedule (e.g. wrt to jtter or precedences) N C T 1 RCAI 2005/

11 Schedulablty analyss based on utlzaton Rate Monotonc (RM): N 1 B + max < T 1..N T C 1/N N(2-1) Earlest Deadlne Frst (EDF): N C B + max < 1 T 1..N T 1 B = max (C ) l= j..n l Modfed Lu and Layland (1973) utlzatons bounds accountng for blockng RCAI 2005/

12 Schedulablty analyss based on utlzaton Gettng rd of the blockng wth nserted dle-tme Ready Messages Bus tmelne X n E 3 1 X Inserted dle-tme E Tck duraton Messages Non-Preemptve Blockng-Free Schedulng Model RM: EDF: C T ' C = C * E X max RCAI 2005/ N 1 N 1 + C <1 T < N(2 1/N E -1)

13 Schedulablty analyss based on network-nduced delay Maxmum network-nduced delay (Fxed Prortes) Bus Tmelne 6 crtcal nstant B I R 5 B Blockng I Busy wndow R Response tme of messages Rwc I = B = I + + C jn hp() I + Tj τ *C j RCAI 2005/

14 Schedulablty analyss based on network-nduced delay Maxmum network-nduced delay (Fxed Prortes) I (n + 1) = B untl + wth I (0) = B j n hp() I (n + 1) = I + I (n) + τ *C j Tj (n) or I (n + 1) > D C jn hp() Load generated up to t t + τ H (t) = B + *C j + C jn hp() Tj j Load hpe H (t) H (t) = t tme RCAI 2005/

15 Schedulablty analyss based on network-nduced delay crtcal nstant Maxmum network-nduced delay (Fxed Prortes) Wth nserted dle-tme we can use the Tmelne Analyss Consder the followng set of 9 varables wth perods gven by T 1 =1, T 2..5 =2, T 6..9 >3 Rwc t= Bus tmelne RCAI 2005/

16 Cyclc Table-Based Schedulng uc A table s bult off-lne wth a cyclc schedule At run-tme, the table s scanned to ntate transmssons accordng to schedule The table can be centralzed (e.g. WorldFIP) or dstrbuted (e.g. TTP/C) Applcable to perodc traffc MC MC = LCM(T ) uc = GCD(T ) Bus tmelne Schedule table uc = Mcro-Cycle MC = Macro-Cycle Perodc Messages: T Messages table RCAI 2005/

17 Cyclc Table-Based Schedulng Allows usng optmzaton technques (e.g. Branch and Bound, Smulated Annealng, Integer Lnear Programmng, Genetc Algorthms) to mprove schedule propertes (e.g. jtter, Rwc, precedences) RCAI 2005/

18 Smlartes wth server schedulng Typcally, controlled access networks allocate a fracton of bandwdth (server) to each node. Server-based analyss for processor schedulng can also be used n ths case, wth adequate adaptatons. e.g. a TDMA slot can be vewed as a server handlng the traffc from the respectve node. Messages from one node slot TDMA round RCAI 2005/

19 Smlartes wth server schedulng Submtted WC load H (t) A(t) Server avalablty H (t) = A(t) Transmsson request WCRT tme Hgher prorty messages from the same node RCAI 2005/

20 Constrants mposed by the MAC Mnmum transmsson perod (e.g. TDMA round cycle, or mcrocycle n Master-Slave. Hgh jtter n Token-Passng systems, due to the rregularty of token arrvals. Blockng term n asynchronous systems (no offset,.e. phase, control). Dead nterval n pollng systems (e.g. Master-Slave, Token-Passng) to handle aperodc communcaton requests. Inserted dle-tme n synchronous systems wth varable sze data. RCAI 2005/

21 Summary: Traffc schedulng: Establshes the relatve order of the message transmssons Carred out essentally at Data Lnk or Network layers Dstrbuted/Centralzed Resembles task schedulng (adaptaton of the task model possble) Schedulng crtera: Fxed prortes (RM, DM, mportance/value) Dynamc prortes (EDF, LLF, FCFS) Schedulablty analyss: Utlzaton Response tme Tmelne Branch and bound (for statc table/based) RCAI 2005/

22 Summary: Smlartes wth server schedulng fracton of the network bandwdth allocated to each node MAC mposes constrants mnmum transmsson perod jtter blockng dead-nterval nserted dle-tme RCAI 2005/

Challenges of Flexible Real-Time Communication

Challenges of Flexible Real-Time Communication -1 - ARTIST2 Summer School 2008 n Europe Autrans (near Grenoble), France September 8-12, 8 2008 Challenges of Flexble Real-Tme Communcaton Lecturer: Lus Almeda Embedded Systems Lab IEETA Unversty of Avero,