1. REAL TIME COMMUNICATION IN WIRELESS SENSOR NETWORKS BY ZILLE HUMA KAMAL

2. CS 691 - WMU - WSNR WHAT IS A REAL TIME SYSTEM (RTS) “A real time system is one in which the correctness of the computations not only depends on their logical correctness, but also on the time at which the result is produced” [St]

3. CS 691 - WMU - WSNR CLASSIFICATION OF RTS 2 Categories of RTS: –A Hard RTS is one in which one or more activities must never miss a deadline or timing constraints, otherwise the system fails or results in catastrophe. [St] –A Soft RTS is one that has timing constraints, but occasionally missing them has negligible effects, as application requirements as a whole continue to be met. [St]

4. TERM AND DEFINITIONS Task – executable entity Job – instance of a task Release Time – time at which task becomes ready to run and job is released Period – time between releases of two instances of the same task Deadline – relative time at which a job should complete execution Execution Time/ Run Time – time taken to complete execution without interruption Frame – discrete unit of time [CZSB]

5. CS 691 - WMU - WSNR WIRELESS SENSOR NETWORKS CHARACHTERISTICS –An instance of MANET –Resource constraint – energy and storage capacity –Limited range for communication and sensing –Frequent network topology changes –Individual entities are not critical, aggregation of results is necessary for effectiveness and accuracy

6. CS 691 - WMU - WSNR RTS IN WSN Two types of communication groups are inherently formed –Local Coordination – to aggregate results –Sensor-Base Communication – to send results to base station This introduces contention on the communication channel, thus the main schedulable resource is the communication channel

7. CS 691 - WMU - WSNR RAP A Real-Time communication architecture Sensing/Control Application Coordination Service Query/Event Service Location Addressed Protocol Geographic Forwarding Velocity Monotonic Scheduling Prioritize MAC Query/Event Service APIs RAP

8. CS 691 - WMU - WSNR APIs Issue Query - query name - attribute list - area - timing constraints, e.g. period, deadline - querier location

9. CS 691 - WMU - WSNR APIs Event Registration - event name - area - query

10. CS 691 - WMU - WSNR Example register_event{ virus_found(0,0,100,100), query{ virus.count, area=(X event-1,Y event-1,X event+1,Y event+1 ), period=1.5, deadline=5, base=(100,100) } };

11. CS 691 - WMU - WSNR LAP Location Addressed Protocol - transport layer - connectionless - no IP/ID addressing, location based addressing - three types of communication »unicast »area multicast »area anycast

12. CS 691 - WMU - WSNR LAP Unicast Message is delivered to node closest to destination, e.g when sensors send query results back to base station Area Multicast Message is delivered to every node in a specified area, e.g when base station sends query to an area, or for local coordination Area Anycast Message is delivered to at least one node in the specified area, e.g when base station wants to send a query to an area, the node which receives it can start the initiation process

13. CS 691 - WMU - WSNR GF Greedy algorithm A packet is forwarded to a neighbor only if: (1) the neighbor node has the shortest distance to the packet’s destination among all immediate neighbors AND (2) the neighbor node is closer to the destination than the forwarding node If these conditions not satisfied, GPSR is used instead of GF

14. CS 691 - WMU - WSNR VMS Deadline aware Distance aware Deadline aware Distance aware Packet scheduling policy –2 types of packet scheduling policies –Static Velocity Monotonic –Dynamic Velocity Monotonic

15. CS 691 - WMU - WSNR VMS SVM –Requested velocity is fixed at each hop V = dis(x 0, y 0, x d, y d )/D DVM –Requested velocity changes at each hop and reflects the time the packet has spent in the network v i = dis(x 0, y 0, x d, y d )/(D-T i ) v 0 = dis(x 0, y 0, x d, y d )/D

16. CS 691 - WMU - WSNR Priority Queues various FIFO queues, one for each priority Advantage – per packet overhead decreases, ordering of each packet is not required Disadvantage – more storage capacity required single FIFO queue, with priority ordering Advantage – reflects order of packets requested Disadvantage – greater number of packets lost

17. CS 691 - WMU - WSNR MAC PRIORITIZATION Extensions to 802.11 –Initial wait time after idle –Backoff Increase Function Initial wait time after idle DIFS = BASE_DIFS * PRIORITY Backoff Increase Function CW = CW * (2+(PRIORITY-1)/MAX_PRIORITY)

18. CS 691 - WMU - WSNR EXPERIMENTATION Overall deadline miss ratio of DSR and GF with deadlines (5,10)

19. CS 691 - WMU - WSNR EXPERMENTATION Overall deadline miss ratio

20. CS 691 - WMU - WSNR EXPERIMENTATION Miss ratio vs distance between source and destination (Deadline: (5:10) s; Rates: (0.8, 0.36)/s)

21. REAL TIME COMMUNICATIONS IN WIRELESS SENSOR NETWORK NOW PRESENTING SPEED BY Zille Huma Kamal

22. CS 691 - WMU - WSNR UNFAVORABLE Despite the simplicity of RAP and the high miss deadline ratio it serves, RAP does not guarantee for soft or hard real time communication systems. Therefore, our search for a Real Time Communication protocol is unsatisfied.

23. CS 691 - WMU - WSNR TO END THE SEARCH SPEED is a real time communication protocol which guarantees end to end soft real time communication We will discuss the components of SPEED and then relate SPEED to other existing protocols for MANETS, ad-hoc networks and real-time communication systems.

24. CS 691 - WMU - WSNR COMPONENTS OF SPEED API Neighbor Beacon Exchange Delay Estimation Stateless Non-deterministic Geographic Forwarding(SNGF) Neighborhood Feedback Loop(NFL) Backpressure Rerouting Void Avoidance Last mile processing

25. CS 691 - WMU - WSNR API & PACKET FORMAT UnicatSend(Global_ID, packet) AreaMulticastSend(position, radius, packet) AreaAnycastSend(position, radius, packet) SpeedReceive( ) SPEED packet format: PacketTypeGlobal_IDDestinationAreaTTLPayload

26. CS 691 - WMU - WSNR Neighbor Beacon Exchange Periodic beacons – exchange location information In static or slow moving sensor networks – very low beaconing rate Further reduce overhead – piggybacking, include ID on data packets, so that you are using the existing packets and not introducing more traffic

27. CS 691 - WMU - WSNR NEIGHBOR TABLE Through beaconing each node is capable of maintaining a Neighbor Table (NT) In addition to location beacons, you have delay estimation beacons and backpressure rerouting beacons Neighbor_IDPositionSendToDelayExpireTime ……………… ……………… ……………… ………………

28. CS 691 - WMU - WSNR DELAY ESTIMATION Single Hop Delay – delay across one router Sender - timestamps when packet leaves node and then waits for acknowledgement from receiver. Receiver – in acknowledgment packet sends the time taken to process the acknowledgment Sender – after receiving the acknowledgment, calculates round trip time as timestamp – ACK time – ACK processing time

29. CS 691 - WMU - WSNR DELAY ESTIMATION This round trip delay time is aggregate with previous delay times via EWMA Since delay estimation expensive – SPEED only invokes delay estimation when round trip delay for an individual case exceeds a predetermined threshold value

30. CS 691 - WMU - WSNR BACK-PRESSURE REROUTING Routing layer adaptation to congestion Beacon format When congestion occurs, node sends back- pressure beacon to sender with AvgSendToDelay equal to infinity IDDestinationAvgSendToDelay

31. CS 691 - WMU - WSNR SNGF - TERMINOLOGY Ns i = {all nodes within radio range of node i } FS i (destination) = {x | x  Ns i and it is closer to the destination than node i } Relay Speed

32. CS 691 - WMU - WSNR SNGF – FORWARDING CONDITIONS Only if node belongs to FS i (destination) FS i (destination) into 2 categories: –FS1 i (destination)of nodes with relay speed > S setpoint –FS2 i (destination) of nodes with relay speed < S setpoint –Forwarding node is always from FS1 i (destination) If no node in FS1 i (destination) then call Neighborhood Feedback Loop (NFL) and decide whether to drop packet or not

33. CS 691 - WMU - WSNR NFL - TERMINOLOGY Miss = when packet delivered at neighbor with relay speed < S setpoint or any packet loss due to collision Miss ratio calculation

34. CS 691 - WMU - WSNR NFL MAC layer adaptation to avoid congestion

35. CS 691 - WMU - WSNR VOID AVOIDANCE By using backpressure rerouting Only guarantees to find a path if a greedy path exists

36. CS 691 - WMU - WSNR LAST MILE PROCESS For AreaMulticast and AreaAnycast – TTL manipulation For Unicast

37. CS 691 - WMU - WSNR EXPERIMENTATION - CONGESTION

38. CS 691 - WMU - WSNR EXPERIMENTATION - CONGESTION

39. CS 691 - WMU - WSNR EXPERIMENTATION – E2E DEADLINE MISS RATIO

40. CS 691 - WMU - WSNR EXPERIMENTATION – E2E DEADLINE MISS RATIO

41. CS 691 - WMU - WSNR EXPERIMENTATION - COST

42. CS 691 - WMU - WSNR EXPERIMENTATION - COST

43. CS 691 - WMU - WSNR EXPERIMENTATION – ENERGY CONSUMPTION

44. CS 691 - WMU - WSNR EXPERIMENTATION – TRAFFIC BALANCING

45. CS 691 - WMU - WSNR REFERENCES [CZSB] M Caccamo, L.Y Zhang, L Sha, G Buttazzo, “An Implicit Access Protocol for Wireless Sensor Networks,”Proceedings of IEEE Real-Time Systems Symposium, Austin, TX, Dec 2002. http://www.cs.wustl.edu/~venkita/publications/class/implicit edf.pdf

46. CS 691 - WMU - WSNR REFERENCES [HSLA] T He, J.A Stankovic, C Lu, T Abdelzaher, “SPEED: A Stateless Protocol for Real-Time Communication in Sensor Networks,” Department of Computer Science, University of Virginia and Department of Computer Science and Engineering, Washington University in St Louis http://www.cs.virginia.edu/~stankovic/psfiles/SPEED_ICDCS.pdf

47. CS 691 - WMU - WSNR REFERENCES [LBASH] C Lu, B.M Blum, T.F Abdelzaher, J.A Stankovic, T He, “RAP: A Real-Time Communication Architecture For Large-Scale Wireless Sensor Networks,” Department of Computer Science, University of Virginia www.cs.virginia.edu/~stankovic/psfiles/rtas02-rap.pdf [P] T. F Piatkowski, “Citation and acknowledgment guide,” Department of Computer Science, Western Michigan University, Aug, 2000 www.cs.wmich.edu/~piat/citationAckGuide.pdf

48. CS 691 - WMU - WSNR REFERENCES [Sp] “Delay Analysis,” Sprint, 2003 http://ipmon.sprintlabs.com/delaystat/ [St] D.B Stewart, “Introduction to Real Time,” Embedded.com, Nov 1, 2001 www.embedded.com/story/OEG20011016S0120