1. PART I: IEEE 802.15.4, a novel MAC/Phy layer for the Zigbee stack A.G. Ruzzelli Adaptive Information Cluster (AIC) Group, University College Dublin, Ireland.

2. Summary  Wireless Sensor networks (WSNs)  Generality  Prototypes  Application Requirements  Zigbee generality  Overview of the stack  The components  The primitives  Zigbee NWK layer  The NWK layer architecture and services  The address assignment  The AODV protocol  IEEE 802.15.4  Generality  Superframe structure  Transmission modes  Association phase  Conclusion

3. Energy-Efficient Wireless Sensor Networks (WSNs) A large number of tiny wireless devices to sense the environment: –Sensor nodes Sensing unit (temp,pressur e, vibration, sound, etc.) Small processing unit Short range radio unit Small power unit (battery) Few more powerful devices to collect the data: –Gateways (or sinks or PAN coordinators) High processing unit Wireless comm. unitHigh power unit Wired comm. unit PDA, laptop, PC etc.

4. Some WSN applications Remote area monitoring Object location Industry machinery monitoring Disaster prevention Wireless medical systems Wind Response Of Golden Gate Bridge environmental data collection: temperature light, humidity, pressure, solar radiation. medical systems Monitoring nesting patterns of Storm Petrels.

5. Wireless sensor characteristics Sensors are battery operated for long unattended period:  Saving energy is a primary objective Sensors are of : Low cost Low processing capability  System strength based on sensor collaboration Large scale networks  Multihop communication WSN manager

6. WSN issues Large number of nodes  Scalability issues High dynamic condition (number and position of nodes might change)  Network Reactivity and Self-organization Power management  The network needs to be connected as long as possible System reliability  The wireless signal needs to cope with interference  Coordination among node communication Node synchronization (clock skew and offset)  To avoid sending to a sleeping node Robustness  Subject to environmental variability (harsh condition)  Complex interoperability of network devices

7. Sensor node prototypes Philips sand nodes Mica2 mote Eyes node prototype Tyndall sensor

8. General sensor node architecture: Any layer try to achieve the task using the smallest amount of energy possible Antenna Sensing devices Application Data interpolation Routing MAC Physical Sensing coverage Cross layer interaction Localization

9. The need of the Zigbee standard An exponential increase of the interest on WSNs No communication systems that addressed: –Energy efficiency; –Low cost devices; –Low data rate per node; –Very low duty cycle; –Scalability (e.g. issues with Bluetooth); WSN proprietary systems cause interoperability problems

10. Stack Reference Model IEEE 802.15.4 PHY IEEE 802.15.4 MAC (CPS) ZigBee NWK MAC (SSCS) 802.2 LLC IP APIUDP ZA1ZA2…ZA n IA1IA n Transmission & reception on the physical radio channel Channel access, PAN maintenance, reliable data transport Topology management, MAC management, routing, discovery protocol, security management Application interface designed using general profile End developer applications, designed using application profiles LLC= logical link control SSCS = Service specific convergence sublayer

11. Protocol Stack Features 8-bit microcontroller Full protocol stack < 32 KB Simple node-only stack ~ 4KB Coordinators require extra RAM –Node device database –Transaction table –Table of neighbours PHY LAYER MAC LAYER DATA LINK LAYER NETWORK LAYER APPLICATION INTERFACE APPLICATION Silicon ZigBee Stack Application Customer IEEE ZigBee Alliance

12. Z-NWK layer: The components Zigbee coordinator (ZC) Only one ZC present in the network Initiates the network formation (PAN ID, channel stack etc.) It acts as PAN coordinator with FFD capability It can act as a router to other nodes It acts as interface between the user and the network

13. Z-NWK layer: The components Zigbee router (ZR) Responsible for tree/mesh packet routing Associates/disassociates node to the network Coordinates communication to children nodes It is in RX mode when idle (no sleep mode implemeted) Maintains a table of neighbours

14. Z-NWK layer: The components Zigbee end device (ZED) It has reduced functionalities It has reduced duty cycle regulated by the parent ZR It can talk with the parent ZR only It cannot associate other nodes

15. Zigbee primitives and services Zigbee primitives are used to communicate between layers 4 primitive types are present: –Request/confirm –Indication/response Layers communicate through the entitities of the Service Access Point (SAP) e.g. NLDE-SAP = network layer data entity-SAP RequestConfirm ResponseIndication Lower layer Upper layer

16. Architecture of the Z-NWK layer ZigBee Device Types Stack Profile, Network Rules Network Management and Addressing Message Routing Route Discovery and Maintenance Security

17. Network formation modalities PAN coordinator Coordinator FFD End device RFD Star topology Tree topology Mesh topology

18. NWK Layer services Layer management entity LME allow requesting services and interfacing to other layers Layer data entity LDE Allow transmitting data SAP= Service access point

19. Network Initiation by ZCoordinator NLME_NETWORK_DISCOVERY.request –Performs an Active Scan –Looks for other ZigBee networks on the channel –Selects a compatible network Stack Profile

20. Network Association: ZR & ZED NLME_JOIN.request –Selects the highest acceptable router –Link Quality, with capacity –Associates with the router –Allocated an address on the network –Device authenticates with network NLME_START_ROUTER.request –Updates Beacon Payload –Depth, Capacity –Starts a router –Updates Association Permit Status

21. Transmitting data NLDE-DATA.request –Used by NHL for all data transmissions –Uni-casts and broadcasts –Accepts the following parameters –Destination Address –Radius –Discover Route NLDE-DATA.indication –Reports the receipt of a data transmission –Includes the following parameters –Source Address

22. IEEE addressing IEEE provides unique long address of 64bits for nodes that uses 802.15.4 Long addresses cause high data overhead if used for node communication Communication relies on not-unique short address of 16bits (65536 devices) Short adrresses are forged by the Zigbee address assignment procedure

23. Zigbee Tree-structure address assignment Router (FFD) at depth d+1 Cskip(d) = [1 + C m -R m -C m *R m ^(L m -d-1)]/(1-R m ) N-th end device (RFD) An = A parent + Cskip(d)R m +n Note: In order to assign addresses, it is necessary to know a priori maxDepth, maxRouter numbers and maxNumbChildren

24. Ad-Hoc on demand vector (AODV) routing Route discovery Find or update route between specific source and destination Started if no active route present in routing table Broadcast routing request (RREQ) packets Generates routing table entries for hops to source Endpoint router responds with Routing response (RREP) packet Routes generated for hops to destination Routing table entry generated in source device

25. The ADOV protocol Route discovery A routing table is required if a route already exists RREQ RREP 1 2 3 4 2 1 5 picture taken from “ZigBee” presentation by Jan Dohl et al.

26. THE IEEE 802.15.4 Defined by the IEEE for low-rate, wireless personal area networks (WPANs). Defines the physical layer “Phy” and the medium access control layer “MAC”. low-power spread spectrum signal at:

27. 868MHz / 915MHz PHY 2.4 GHz 868.3 MHz Channel 0 Channels 1-10 Channels 11-26 2.4835 GHz 928 MHz902 MHz 5 MHz 2 MHz 2.4 GHz PHY Operating Frequency Bands

28. Concurrent channel allocation An example of Frequency Channel allocation for device classes 2400 240124022403248124822483 2480 Bluetooth cannels IEEE 802.11b channel in North America and Europe IEEE 802.11b channel in Europe picture taken from ZigBee Specifications v1.0

29. IEEE 802.15.4: PHY layer 2400MHz Band specs 4 Bits per symbol DSSS with 32 Bit chips O-QPSK modulation Sine halfwave impulses Bit to Symbol QPSK Mod. Symbol to Chip Binary Data Medium picture taken from IEEE 802.15.4 Specification

30. PHY layer contd. General specs and services Error Vector Magnitude (EVM) < 35% -3dBm minimum transmit power (500µW) Receiver Energy Detection (ED) Link Quality Indication (LQI) Use ED & LQI to reduce TX-power Clear Channel Assessment (CCA) with 3 modes –Energy above threshold –Carrier sense only –Carrier sense with energy above threshold

31. Device types In conformity with Zigbee devices, IEEE802.15.4 are of 3 types: –PAN coordinator Act as network initiator Only one allowed in the network –Full functional devices FFDs That have all access control functionalities implemented (channel scan, beacon transmission, association etc.) –Reduced functional devices RFDs That can only talk to the FFD that associated them

32. IEEE 802.15.4: MAC layer Managing PANs Channel scanning (ED, active, passive, orphan) PAN ID conflict detection and resolution (in progress) Starting a PAN Sending beacons Device discovery Device association/disassociation Synchronization (beacon mode) Orphaned device realignment

33. Beacon/nonbeacon-enable modes Beacon-enabled mode: Beacons are broadcasted periodically by the FDD Beacons do not employ CSMA prior transmission Beacons contain info related to superframe length and GTS allocation details ACK is optional Nonbeacon-enabled mode: The MAC reduces to a simple unslotted CSMA-CA No Superframe No GTS ACK is optional

34. The superframe structure Becons, transmitted by FFDs, contain a superframe specification

35. IEEE 802.15.4 association phase FFD Coordinator RFD RFD: Broadcast Beacon request FFD: Superframe spec. RFD: Association req.. FFD: ACK with seq#. FFD: Broadcast standard timezone packet FFD: Broadcast standard data packet RFD: Data request FFD: ACK with seq#. FFD: Association response with short ID. RFD: ACK with seq#.

36. The IEEE802.15.4 chip IEEE802.15.4 is coded onto the chip CC2420 (partially hard coded) Zigbee licence must be bought separately Zigbee compliancy might be lost if some change to the code is made  NOT very suitable for research purposes

37. End of PART I

38. PART II: MERLIN over IEEE 802.15.4: routing capabilities without Zigbee A.G. Ruzzelli Adaptive Information Cluster (AIC) Group, University College Dublin, Ireland.

39. Network formation by the IEEE 802.15.4 MAC One PAN coordinator Zero or more coordinators Zero or more end devices First device starts the network as PAN coordinator A new device can detect all coordinators (both the PAN coordinator and coordinators) A device can join the network by associating with any coordinator in range After joining a device can volunteer as coordinator PAN coordinator Coordinator End device

40. Step 1: Starting a new network Device starts network scan ( MLME_SCAN ) Detects no network Starts new network as PAN coordinator ( MLME_START with PANCoordinator=TRUE ) If PANCoord then other devices in range can discover device 1 by means of a network scan 1 PAN coordinator Coordinator FFD End device RFD

41. Step 2: Second device joins the network Device 2 starts network scan ( MLME_SCAN ) Detects PAN coordinator device 1 Sends association request to device 1 ( MLME_ASSOCIATE ) Node2 is now and End device  Other devices cannot discover device 2 by means of a network scan PAN coordinator Coordinator FFD End device RFD 2 1 range

42. Step 3: Device 2 becomes a coordinator Device 2 starts serving as a coordinator of the existing network ( MLME_START with PANCoordinator=FALSE, PANId & channel parameters are ignored) Node2 is now Other devices in range can now discover device 2 by means of a network scan PAN coordinator Coordinator FFD End device RFD 2 1

43. Step 4: Device 3 joins the network Device 3 starts network scan ( MLME_SCAN ) Detects coordinator device 2 (assuming device 1 is not in range of device 3) Sends association request to device 2 ( MLME_ASSOCIATE ) Note: Other devices cannot discover device 3 by means of a network scan PAN coordinator Coordinator FFD End device RFD 2 1 3 range

44. Step 5: Device 4 joins the network Device 4 starts network scan ( MLME_SCAN ) Detects two coordinators: device 1 and device 2 (assuming device 1 and device 2 are in range of device 4) Sends association request to device 1 ( MLME_ASSOCIATE ) (alternatively it could join the network also through device 2) Note: Other devices cannot discover device 4 by means of a network scan PAN coordinator Coordinator FFD End device RFD 2 1 3 4 range

45. Step 6: Device 4 becomes a coordinator Device 4 starts serving as a coordinator of the existing network (MLME_START with PANCoordinator=FALSE, PANId & channel parameters are ignored) Note: Other devices in range can now discover device 4 by means of a network scan PAN coordinator Coordinator FFD End device RFD 2 1 3 4

46. Other devices can join in the same way IEEE 802.15.4 allows only direct (single hop) communication between two devices that are in range of each other. IEEE 802.15.4 leaves it to the higher layers to define how network-wide unique short MAC addresses are assigned by coordinators. Extended MAC addresses can be used instead of short addresses  High packet overhead PAN coordinator Coordinator FFD End device RFD 1 2 4 7 5 3 6 8 range

47. Other devices can join in the same way A networking protocol (e.g. ZigBee) on top of IEEE 802.15.4 is required to allow communication between nodes that are not in range of each other by routing of packets via intermediate nodes (multi hop). ZigBee defines how short NWK addresses are assigned to devices. The short NWK addresses are used also as short MAC addresses. PAN coordinator Coordinator FFD End device 1 2 4 7 5 3 6 8 range

48. Issue 1: The hidden association problem The IEEE 802.15.4 does NOT provide coordination between coordinators End devices (RFDs) can talk to its coordinator only  packet collisions might occur 1) Eg. Node9 transmitting to node2 might generate collision at node8 that is receiving from node11. 2) Eg. Either node10 and node7 transmission might prevent correct neighbouring node reception PAN coordinator Coordinator FFD End device RFD 1 2 4 7 5 3 6 8 range 10 9 11

49. Issue 2: Beacons are weak Beacons are more prone to collide as transmitted without CSMA If a beacon collides then no children RFD devices can transmit or receive. 2 3 8 10 9 11 1 4 7 Beacon Tx

50. Question Q.1 How can we avoid packet collisions? A.1 By using RTS/CTS/ACK –Cons1 We lose the 802.15.4 compliancy –Cons2: Results show a very long delay when associated to low node duty cycle 1 2 8 9 11 RTS CTS ACK PAN coordinator Coordinator FFD End device RFD

51. YES –1)You let all nodes become full functional devices (FFDs) PROS: –FFDs can perform carrier sensing before transmitting a packet –Any node is free to talk to any other node  peer-to-peer communication CONS: –IEEE 802.15.4 does not define any sleeping mode for FDDs  High energy consumption Can we at least mitigate collisions without lose the compliancy? PAN coordinator Coordinator End device 1 2 4 7 5 3 6 8 range 10 9 11 A sleeping scheduling for FFD devices is needed!

52. How all nodes can become FFDs void mlmeAssociateIndication(ADDRESS deviceAddress, BYTE capabilityInformation, BOOL securityUse, UINT8 aclEntry) {// We accept all association requests here. if( gAF_ApplInfo.appCoordinator == IAM_COORDINATOR || gAF_ApplInfo.appCoordinator == IAM_COORD_W_BEACON || gAF_ApplInfo.appCoordinator == IAM_ASSOCIATED_COORD ) //By Ruzzelli … void mlmeAssociateConfirm(WORD assocShortAddress, MAC_ENUM status) { if( status != SUCCESS ) return; if( assocShortAddress == 0xFFFD ) return; gAF_MyShortAddr = assocShortAddress; gAF_ApplInfo.appCoordinator = IAM_ASSOCIATED_COORD;//by Ruzzelli

53. TICOSS: TImezone COOrdinated Sleeping Scheduling for FFDs – We organize nodes in timezones (TZ) based on the number of hops to the PAN coordinator –We address nodes either –solely based on their TZ –using the short address provided by the Zigbee address procedure –We inject a sleeping scheduling table to coordinate FDDs’ activitiy PAN coordinator Coordinator End device 1 2 4 7 5 3 6 8 range 10 9 11 TZ 1 TZ 2

54. The origin of TICOSS TICOSS is derived from the routing characteristic of MERLIN [1] adapted to the IEEE 802.15.4 [1] Ruzzelli, A.G., O’Hare, G.M.P., O’Grady, M.J., Tynan, R., MERLIN: A synergetic integration of MAC and routing protocol for distributed sensor networks, In SECON06, Third Annual IEEE Communication Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks Reston, VA, USA, September 25-28, 2006 DESIGN goals: MAC+Routing integration into a simple architecture; No usage of handshake mechanisms; No specific node addressing  Upstream/downstream Multicast; Reduced latency along a very low energy consumption Increasing communication reliability while limiting packet overhead;

55. Timezone data traffic scheduling Upstream multicast: Packets are forwarded to lower zones Zone 2 Zone 3 Zone 1 Downstream multicast: Packets transmitted to higher zones Local broadcast: Packets reach all neighbours. No forwarding performed Sleeping

56. Global allocation Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8 Frame The allocation of further zones can be obtained by appending the same table. The allocation of further frames is obtained by flanking the same table.

57. Accessing the table Nodes in the same timezone contend the slot for local broadcast only once each 4 frametimes If Mod(FRAME#, NZONE) = Mod(myZone,NZONE) To access the current slot in the table: SLOT# = GlobalTime/SLOTTIME currentSlot = Mod(SLOT#, NSLOT) NZONE = 4 NSLOT =9

58. Nodes in the same zone share the same slot for activity Intra-zone transmission is regulated by IEEE 802.15.4 Inter-zone transmission is regulated by the scheduling TICOSS over 802.15.4 PAN coord

59. The network-wide unique address Recall that with TICOSS as a routing protocol, we can 1. Address nodes solely based on their TZ ( MULTICAST )  a node transmits data packets only specifying the timezone of the receiver PROS: –Avoid problems of address conflicts –Avoid issues of running out short addresses –Reduce the actual byte transmitted (for special transmission I can still use the long address) CONS: –multiple copy of the same msg sent can be generated   increase transmission overhead! –ACK not used (the original MERLIN version uses burst tone instead) 2. Use the Zigbee address assignment procedure to address a secific nodes ( UNICAST )  a node transmits data packets to the node with highest cost link function Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 A B PAN coord

60. Packet ACK In TICOSS, packet transmission can be: –Multicasted to higher or lower timezones No ACK is performed –Unicasted to a selected node that is chosen based on a tunable cost function Successful reception are ACK by transmitting back the IEEE802.15.4 sequence packet number

61. Routing characteristics (I) 3 small buffers of upstream, downstream and local broadcast are provided Packets organised in multiple msgs of the same data traffic type; Packets contain a msg-ID index of included msgs; Nodes, which lose the contention, keep on listening to the beginning of the transmitted packet then go into sleep; Nodes discard from their buffer the msgs already fowarded. Pro : Reduce overhead in transmission! Con : Small increase of node activity; Increase complexity. Channel contention messages Msg-index Discard msgs already forwarded from their queue P a c k e t Listen to the packet index Controlled multipath

62. Routing characteristics (II) Timezone maintenance Timezone update are sent periodically; Failed reception of timezone update from zone N-1 node to zone N node triggers a upstream multicast of Timezone Update request (TUR) –N-1 node/s reply  Connection reestablished N-1 failed  local broadcast TUR –At least one reply  change of zoen to N+1 N failed  downstream broadcast TUR 1 2 3 3 4 2 4 1 3 4 2 TUR 1 3 4 2 1 3 4 2 6 5

63. TICOSS/MERLIN analogy Similarities – Both protocols use same routing features; –Both protocols use a slotted CSMA to access the channel Differences –MERLIN is a proprietary integrated MAC and routing protocol, instead TICOSS uses the IEEE 802.15.4 MAC+Phy features, –MERLIN uses burst ACK to notify correct incorrect receptions, instead TICOSS has two ACK modalities: Multicast with ACK disabled Unicast with ACK enabled

64. MERLIN Assessment Simulation tool: OmNet++ Framework: EU EYES project Evaluation of MERLIN against SMAC+ESR Experiments: Philips Sand node implementation Evaluation of TICOSS in progress

65. Scenario and Setup Scenarios 5 nodes two-hops 70 nodes Random multihop Metrics: Energy consumption per RX packet Network lifetime E-to-E latency Total packet overhead % sleeping time Parameters: Duty cycle (acting on CW and frametime size) Low traffic conditions (12 packet/min) High traffic conditions (60 packet/min) Sources Forwarder Destinations

66. V-scheduling 0 50 100 150 200 250 300 0.40.60.811.21.41.61.82 Frametime (sec) Network Lifetime (days) V-Scheduling 1 Gateway 100 Nodes rand. Distributed. 800*500 area network Min signal strength(12 m) 50 msg/min sent by 5 rand. nodes Static network V scheduling Network lifetime. The network is considered to fail when 30% of nodes are depleted. Lifetime calculated for a linear depletion of 2 AA batteries. The network lifetime depends linearly on the frame length;

67. V scheduling setup time V scheduling can be setup in less than 10 seconds up to 250 nodes/100m^2 of network density.

68. End-to-end packet delay V-scheduling The controlled multiple path mechanism may cause a lower delay for nodes farther from the gateway; An increase of latency at the intersection of data traffic flows due to periodical stop of nodes activity that go into sleep. V-scheduling delay obtained for 2sec frametime length Frametime length should be based upon application requirements.

69. Low traffic 2-hops scenario

70. High traffic 2-hops scenario

71. Multihop scenario: Lifetime Note: These graphs have little relevance if not related to the EtoE latency

72. Multihop scenario: Latency/energy Given a certain sustainable latency, MERLIN consumes between 2 and 2.5 times less energy than SMAC+ESR

73. Total packet overhead The MAC routing integrated nature MERLIN results in a smaller packet overhead than SMAC+ ESR.

74. Conclusion PART I: –The Zigbee stack has been presented; –A focus on IEEE 802.15.4 has been given; PART II – We described how to build networking capabilities over IEEE 802.15.4 –We presented TICOSS, which is derived from the MERLIN protocol, as a tree-based routing layer –MERLIN simulated results have been presented

75. Thank you! www.csi.ucd.ie/researchwww.csi.ucd.ie/research (Prism LAB web site) www.adaptiveinformation.iewww.adaptiveinformation.ie (AIC project)

76. An application for TICOSS Sensor-based wireless medical systems

77. Appendix: MERLIN MAC features

78. Recall that Nodes in the same zone share the same slot for activity transmission in MERLIN (multicast) do not address a specific receiving node How can simultaneous transmission be handled? How can correct/incorrect receptions be notified? Intra-zone MAC features Zone N Zone N+1 Zone N-1

79. Burst tones can help Properties –Are signal impulse  Do not contain any coded information –Are robust  Several simultaneous burst can still be identified as one burst –They are shorter that a normal ACK Utilization Multicast: Bursts identify correct receptions BACK In transmission to the gateway Broadcast: Bursts identify reception errors BNACK In local broadcast

80. Asynchronous transmission Mechanism Tx1 Tx2 Tx1 CCA PreamblePacketPreamblePacket Listen Sleep Rando m Burst* * burstACK if local broadcast, burst NACK if multicast CCA Sleep Listen Transmit CCA Sleep Tc S l o t l e n g t h Tc Tx1 Tx2 Rx1 CCA Listen Sleep Rx2 Burst* Rx2

81. Disadvantages 1)MERLIN does not address a specific receiving node  multiple copy of the same msg sent can be generated   increase overhead! 2) Some collisions due to the Hidden Terminal Problem (HTP) Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 A B Zone 3 A B ?

82. Something more about the work that we do at the PRISM group:

83. Autonomic WSNs: Origin of autonomic computing by IBM Relieve human of the burden of managing large scale computer systems Autonomic WSNs properties: –Self healing –Self protection –Self configuration –Self optimization –Self managing

84. Agent technology for autonomic WSNs Agent properties: –Sense-deliberate-act cycle Sensing data is used as input for the decision making process –Mobility Useful characteristic of agents that well map onto WSNs Agent can migrate from one node to another processing data as it goes –Fault tolerance Agents can still take decision if some data are missing

85. An example: Network anomaly intervention Possible solution Multiple Notification messages (High energy consuming) Proposed solution: Migrating agent (Moderate energy consuming)

86. Contribution of autonomic computing to WSNs Self configuring nodes (1) can set up a network; (2) might not be well positioned but still work; (3) can evaluate network gaps; (4) can decide communication schedule. Self protection attribute –Migrating agents check channel condition and battery level before migrating Self healing –Repair network damage due to hash work condition –Negotiating new routes; –Activating redundant nodes; –Ask for replacement of damaged nodes. Self optimization –Quality of service –Network efficiency –Delay control and data prioritization

87. Intelligence-aided sensor network Opportunistic power management Intelligent coverage Intelligent routing

88. Opportunistic power management (1) Increase network longevity by deactivating redundant nodes: node hibernation Sensing Coverage: –All points within the sensed area need to be covered by at least 1 sensor. Traditionally, a point is covered if it is within the sensing range of a given sensor. Gateway Redundant based on sensor coverage

89. Intelligent sensing coverage It deals with the quality of sensory data provided to the application which is using it; Data sampling frequency at the node and surrounding nodes should be enough to have a certain detail of the phenomena of interest; Migrating agents control: –Sensor sampling rate by tuning it; –Might request an increase of node density in an area

90. Intelligent routing By interacting with different layers the agent can check several parameters A look-up table with neighbouring nodes parameters (RSSI, battery level, location) is provided Even with incomplete data an agent can figure out the best neighbours to which to forward the data to Antenna Routing MAC Physical Route managing Agent table