Post on 15-Jan-2016
transcript
An Overview of the Web over Wireless GroupWeb over Wireless GroupUC, Berkeley
GroupProf. Pravin Varaiya
Researchers: Dr. Anuj PuriBaris Dundar
Graduate Students:Mustafa ErgenSinem ColeriDuke LeeXuanming DongRahul JainMohit AgarwalAmit Mahajan
Under Graduate Students:Jeff KoYan Li http://wow.eecs.berkeley.edu
Research FocusCellular networksAd Hoc wireless networksSensor networksApplications
Cellular Networks
Current Cellular newtorksGeographical area divided into cellsBase station (BS) in each cellPrimary traffic is voice What will future wireless networks look like?Primary traffic is dataCellular + Wireless LANs
Heterogeneous Wireless Networks802.11 Wireless LANsUpto 50 MbpsUnlicensed spectrumCheap and easy to set upHot spot coverage with wireless LANsMobility between networksApplications
Ad Hoc Wireless NetworksWireless token ringDSDV routingGeographical routingWTPSensor Networks
Wireless Token Ring ProtocolMultiple rings Station with token transmits Deterministic bounds on access time Adjacent rings transmit on different channels Basic operations of join and leave to allow mobility
DSDV - Wireless RoutersCheaper/better performance cellular networksAd Hoc wireless networksInternetWireless Router
Geographical Routing AlgorithmAll nodes know their positions Packet for a destination postion Use geographical information in routingi.e, route to neighbor nearest to the destination
Geographicalnetwork
Transport Layer (WTP)UDP: Connectionless but unreliableTCP: Connection oriented and reliableWTP: Connectionless and reliableUsed by WAP (Wireless application protocol) as a transaction protocol for cell phonesOptimized for wireless links for short messagesDoesnt use congestion controlSmall WTP headersMessage based protocol
Network ArchitecturePhysical LayerData LinkMACNetwork LayerTransport LayerToken ring, bluetooth 802.11, SeedexGeographic routing,DSDV, QOS, TBRF,STARATCP/UDP/WTPMobilityManagementOFDM
Mobility and Internetworking Among NetworksInternetGeographicRoutingSensor Networks802.11TokenRingDSDV
TechnologyWireless Token Ring DSDV routing Geographical routing and WTP Mobile IPFast HandoffMEWLANASensor Networks
WIRELESS TOKEN RING PROTOCOL
The Wireless Token Ring Protocol (WTRP) is a medium access control protocol for wireless networks in mission critical systems. It supports quality of service in terms of bounded latency and reserved bandwidth. The token passing defines the transmission order, and each token is forced to give up the token after a specified amount of time.Each ring has unique ring id based on unique MAC address of one of the stations of the ring. (The station is called the owner of the ring). When owner leaves the ring, another station elects itself to be the owner of the ring.Introduction
Descriptions (Operations)Joining: Stations periodically invite other nodes to join the ring by broadcasting the available resources left in the mediumLeaving: When B wants to leave, it requests A to connect to its successor, C. If A does not have connection with C, then it connects to the next node in terms of the transmission order of the ring.
Descriptions (Management)Ring Recovery Able to recover quickly by keeping information about topology of the ring, recovers from multiple simultaneous faults by taking increasingly drastic actionsToken Recovery Multiple token is deleted using unique priority of token based on generation sequence number and token ring address pair.
WTRP Deliverables
WTRP USER-SPACE
WTRS-WTR Simulator
Performance Analysis
Performance Analysis
DSDV Routing
DSDV Routing ProtocolBased on Bellman-Ford algorithm Use sequence number to avoid loop-forming and make convergence fastThe sequence number must be originated by the destination nodeThere is a trade off between the stability and the convergence speed of the routing table
System Architecture
Socket Layer
TCP
UDP
IP
IEEE 802.11 MAC Layer
ARP
Kernel Routing
Layer
Zebra Daemon
DSDV Daemon
Linux Kernel
IEEE 802.11
Network Interface
DSDV Router
RIB
Events of DSDV Protocol1.TimersPeriodical updates (30-second) Random offset timer (at most 30-second)Timeout (30-second)garbage-collection (120-second)2.Input processing Request Responseresponse to a specific queryregular updatestriggered updates triggered by a metric change3.Output Processing by input processing when a request is receivedby the periodical routing updateby triggered updates caused by changed route metric
How does the DSDV Daemon workDSDV_Daemon(){Detect network interfaces and copy required information;Read configure file and initialize all variables and routing table;Create a UDP socket for DSDV routing messages;Send hello message to all neighbors;Install signal handlers for different kinds of timers;Loop for events (select())Different timers:Input processing:Output processing:Other system events:Loop end}
Geographical Routing
OverviewGeographical Routing using partial information for Wireless Ad Hoc Networks, R. Jain, A. Puri and R. Sengupta
A routing protocol for wireless ad hoc networks using information about geographical location of nodes.
ArchitectureMulti-threaded Location Advertisement ProtocolGeographic Routing ProtocolRoute Discovery ProtocolRouting Table Update Daemon
Assumes the presence of a GPS system at each node in the network
When a node receives data packet :
Check_final_destinationif (final_destination is a neighbor)forward the packetelsecheck the routing table, find the closest neighbor to this destination and then forward the packet to that neighborGeographical Routing Protocol
If a node can not send a packet to a destination because of a physical barrier it will use a DFS type of algorithm in order to find an alternate route to the destination.When the route discovery packet reaches the final destination, the destination node will send the packet back to the sender and this way the sender will discover the route to that specific destinationRoute Discovery Protocol
Packet FormatEth. HeaderGeog. HeaderData (if any)Route advertisement and route discovery packets dont need the data field (i.e. length field in the geographic header is equal to the length of the geographic header)Length field for Data packets is equal to the length of geographic header + length of dataWTP Hdr
Geographic HeaderSrc Loc + MACDst Loc + MACChecksum Location: UTM Location of the node MAC: MAC Addr of the node Checksum: checksum over the header Packet Len: length of the packet Seq: Sequence number Opts: options (TBD)p.lenseqopts
The Universal Transverse Mercator projection andgrid system was adopted by the U.S. Army in 1947for designating rectangular coordinates on largescale military maps. UTM is currently used by theUnited States and NATO armed forces.
Why UTM?Supported by all GPS receiversSimpler to use than latitude and longitude.UTM Coordinates
Demo Scenario MAC Filter Transport Layer WTP
DstGwCCBB
DstGwAABBCC
DstGwAABB
DstGwAABBCB
WOW Mobile IP
OverviewIP Mobility Support, C. Perkins, RFC 2002ProtocolsTunneling (HA FA)Registration (MA - FA - HA)Agent Advertisement (FA)
Mobile IPCorrespondent Host 10.0.1.4Home Agent 10.0.1.2Foreign Agent #1 10.0.2.2 & 11.0.1.2Foreign Agent #2 10.0.3.2 & 11.0.1.310.0.2.0 subnet10.0.3.0 subnet10.0.1.0 subnetRouter 10.0.1.110.0.2.110.0.3.1
RegistrationMobile needs to make the home agent aware of its present location i.e, the care of addressUsing UDPRegistration request (mobile -> home)Registration reply (home -> mobile) contains duration of validity (~100 seconds)What if UDP packet is dropped!!Request sent again after reasonable time
TunnelingEncapsulation is done for redirectionHome agent tunnels the packet to the care of addressDestination foreign agent de-tunnels the packet and transmits it to the mobilePackets from mobile to correspondent host go directly (with source IP as original (fixed) IP of the mobile node)
MA SoftwareListens the Agent Advertisement broadcasts sent by the FAsRegisters with FAs automatically depending on S/N over the link , signal qualities, BERThe bandwidth available on the linkThe encryption provided on the networkThe cost
Demo SetupCorrespondent Host 10.0.1.4Home Agent 10.0.1.2Foreign Agent #1 10.0.2.2 & 11.0.1.2Foreign Agent #2 10.0.3.2 & 11.0.1.310.0.2.0 subnet10.0.3.0 subnet10.0.1.0 subnetRouter 10.0.1.110.0.2.110.0.3.1CH: Netmeeting (video + audio)Mobile: OpenH323 Client
Intra-Domain Handoff DFA
Takes packet from HA or CH.
Decapsulates and checks its visitor list.
Sends the packet to the related branches according to Location FA table. FA
If it is an adjacent FA, buffer the packets.
Else send the packet to the related branches according to Location FA table.FAST HANDOFF with position based routing
FAST HANDOFF
FAST HANDOFFS with GPS for MOBILE IP
Motivation for Fast Handoff in Mobile IP Previous Work on Fast HandoffLocation Based Fast Mobile IP ProtocolProtocol DescriptionControl MessagesSecuritySimulation and ImplementationSystem Extensions Conclusion
Outline
Primary Aim of Mobile IPRobust communication between mobile users
Major Problem in Mobile IPAchieving QoS requirements of real-time applicationsSolution:High bandwidth through smaller cells
Motivation
Small Wireless CellsAdvantage:More number of users Diameter of cell decreases by Nnumber of cells in a certain area increases by Nnumber of available channels increases by NDisadvantage:Mobile host crosses cells more oftenMore number of handoffs
Motivation
HA
CH
Time Diagram of a Hand_off
Basic Mobile IP Handoff
Previous Work on Fast Handoff
Basic Mobile IP
Performs basic functionsTransparency and Handoff SupportNot optimized for handoff
Previous Work on Fast Handoff
Optimization in Mobile IP Hand-off
Through domainsDecreases overhead by localization of registrationStill suffers from delay and packet loss in intra-domain handoff Leaves inter-domain movement to the basic Mobile IP
Through multi-cast addressesAssigning multi-cast address to current access point and handoff targetsManual determination of handoff targetsRequires continuous messaging to learn about new multi-cast addressesMulti-cast address conflicts
Location Based Fast Mobile IP Protocol
Goals of the Protocol:
Support uninterrupted operation of real-time applicationsLower Handoff Delay, less Packet LossDecrease messaging burden of fast handoffAvoid manual configuration for fast handoffAvoid possible address conflicts
Location Based Fast Mobile IP Protocol
Structure of the internet
Intra-domain Uses geographical information . Finds adjacent FAs of the current attached FA. Send the datagram to the adjacent FAs besides current FA. Reduces handoff time and packet loss.
Inter-domain Gives HA functionality to a DFA Local Home Agent (LHA). Does not bother HA for movements within a geographical radius . Reduces handoff time and control messaging. Distribute HA database dynamically.
Location Based Fast Mobile IP Protocol
Intra-Domain Handoff Example
Soda Hall 3rd Floor
Intra-Domain Handoff
Internet
HA
DFA
FA
MH
FA
CH
FA
DFA
Takes packet from HA or CH.
Decapsulates packet and checks its visitor list.
Sends the packet to the related branchesaccording to Location FA table. FA
If it is current FA, send the packet to MN.
Else If it is an adjacent FA, buffer the packets.
Else send the packet to the related branches according to Location FA table.
Inter-Domain Handoff
Current inter-domain handoff compared to our system
Fast Inter-domain handoff necessary due toIncrease in the battery power of laptop computersTiling of the world into small wireless cells
Inter-Domain Handoff
Current inter-domain handoff compared to our system
Procedure of Inter-domain handoff in Basic Mobile IP:MH sends registration request to a FA in a new domainFA sends request to DFADFA sends request to HAHA sends registration reply to MHDisadvantage of Basic Mobile IP:Delay and packet loss due to wasteful trip of registration messages
Inter-Domain Handoff
Current inter-domain handoff compared to our system
Procedure of Fast Inter-domain handoff:MH sends registration request to a FA in a new domainFA sends request to DFADFA sends request to HA or local home agentHA or local home agent sends registration reply to MHAdvantage of Fast Inter-Domain Handoff:Decrease in delay and packet loss due to registration
Inter-Domain Handoff
How do we decide whether to register to a local home agent or HA ?
Register to old LHA instead of HA as long as DFA of MH is inside the circle
Angled1: Distance between LHA (DFA) and HAd2: Distance between LHA and Current DFAR : Movement range without changing LHA
Messaging: Registration Messages
TYPE
CODE
LIFETIME
HOME ADDRESS
TARGETED DOMAIN FOREIGN AGENT ADDRESS
IDENTIFICATION
LOCAL HOME AGENT IP ADDRESS
LOCAL HOME AGENT GEOGRAPHICAL LOCATION
OTHER EXTENSIONS
Registration Request Format
Registration Reply Format
Messaging: Location Advertisement Messages
Aim:Eliminate manual configurationDistribute the location of each FA to other FAs inside domain
Content:Location and CoA of the FA that it originates
Procedure:Every FA advertises its CoA and position to its neighborsEvery router sends the incoming LAM to its neighbors
Security
Uses security features of current Mobile IP(IPSec etc)
Requires security association between DFAs
New FA delivers buffered datagram to MH only after finishing secure registration
Simulation: Intra-Domain Handoff
Intra- Domain Handoff Scenario
Packet audio sourcePacket inter-arrival time: 20msAverage packet size: 200bytesConstant traffic to MH
Handoff Time = Discovery Time + Registration Time
Maximum Discovery Time = Beacon Period
Link: 2 Mbps, 4ms
Simulation: Intra-Domain Handoff
Human ear can tolerate approximately 200 ms delay at maximum*We achieved 141ms max inter-arrival time*
Link: 2 Mbps, 4ms5 Mobile NodeBuffer Size 10
Simulation: Intra-Domain Handoff
Simulation: Inter-Domain Handoff
Distance Number of nodes in between Delay
Inter- Domain Handoff Scenario
= arcsin 1/5
Simulation: Inter-Domain Handoff
Implementation: Intra-Domain Handoff
HA SoftwareTwo threadsRegistration protocolListens for UDP registration requestsUpdates Binding Table upon requestTunneling ProtocolListens to traffic in home networkSends packets for MH to its current CoA
Implementation: Intra-Domain Handoff
DFA, FA SoftwareProcess 1: Agent Advertisement ProtocolSends out agent advertisements periodicallyProcess 2Thread1: Registration ProtocolUpdates Binding Table upon registrationSends all buffered packets if anyThread 2: Tunneling ProtocolSends packets to handoff targetsBuffers incoming packets if adjacent FA
Implementation: Intra-Domain Handoff
MH SoftwareThread1: Listening threadListens for MAC layer packets to get the source address and sequence number of last packetThread 2: Registration ProtocolListens for agent advertisement messagesRegisters to new FA
Implementation: Intra-Domain Handoff
Basic Mobile IPUnrecoverable throughput decrease during handoffLonger handoff period
Our Fast MIP schemeDecrease in throughput compensated by sending the packets missed during handoffShorter handoff period
Implementation: Intra-Domain Handoff
Basic Mobile IPNumber of lost packets is constant for the same sending rateNo buffer used Number of lost packets increases as sending rate increases
Our Fast MIP schemePacket loss can be eliminated by choosing enough buffer size.Required buffer size increases as sending rate increases
System Extensions
Determining the location of indoor access points (FAs).
GPS support for only outdoor settingsLocation support for indoor environments viaUse of infrared signals (Active Badge Location System)Use of concurrent radio and ultrasonic signals (Cricket)
System Extensions
Roaming at the boundary of the domain
Introductory message to adjacent DFA with CoA and locationForwarding of packets to handoff targets by adjacent DFA
FA
FA
FA
FA
FA
FA
Domain A
Domain B
DFA
DFA
System Extensions
Avoiding Ping-pong effect
Registration to new access point like a registration updatePackets are already in new FA
FA
FA
MH
DataRegistration
time
Conclusion
Goal QoS for Wireless Real Time ApplicationDistributing Home Agent FunctionalityIntra-domain Handoff Sends packets to handoff targetsInter-domain Handoff Geographical Boundary and Local Home AgentMessaging SecuritySimulationRegistration time, Packet inter-arrival timeImplementationInstantaneous throughput, Buffer sizeSystem extensions
Hierarchical structure can be formed with a messaging which works with very large period or a change in the structure of the network
MEWLANAMobile Enriched Wireless Local Area Network Architecture
MEWLANA-Mobile IP Enriched Wireless Local Area Network Architecture
Introduction
Mobile IP & Ad-Hoc Networks OverviewMotivationNetwork Architecture
Protocol
Previous Work -MIPMANET -on demand routingMEWLANA-TD - table driven routingMEWLANA-RD - root driven routing (mesh networks)
Performance AnalysisConclusion
Mobile IP & Ad-Hoc Networks
Mobile IPRetain a fixed IP identity while moving.Mobile Node (MN)Home Agent (HA)Foreign Agent (FA)Correspondent Host (CH)Agent AdvertisementRegistrationTunneling
Ad-Hoc Network No network infrastructure.Special routing protocol
Motivation
Mobile IP in Ad hoc NetworkHigh cost for building a large number of bases.Total throughput limited by the number of cells in the area.High power consumption of mobile stations having the same transmission range as bases. Ad hoc networks are limited to be small scale.
The number of bases or the transmission ranges of both mobile stations can be reduced.Connections are still allowed without base stations.Multiple packets can be simultaneously transmitted within a cell. Paths are less vulnerable than the ones in ad hoc networks because the bases can help reduce the wireless hop count.
Motivation
Does this new architecture impose new traffic characteristics?Inside traffic, Outside Traffic
Can we classify the environment based on the traffic characteristics?Small or large size ad hoc networkIntensity of inside and outside traffic
Does using one kind of ad hoc routing give optimum result in all environments?
Motivation
Intensity of outside traffic = constant
A conference
Big Size NetworkHigh Inside Traffic
A subway
Big Size NetworkNegligible Inside Traffic
A rescue mission
Small Size NetworkHigh Inside Traffic
Example
Network Architecture
Ad Hoc Routing Protocols
Table Driven Routing DSDV,
On Demand RoutingAODV,
Route Driven Routing TBBR (Tree Based Bidirectional Routing)
Tree Based Bidirectional Routing
MESH NETWORK
Root : Foreign AgentBranches: Mobile NodesRoot periodically initiates protocolBidirectional RoutesRoutes FA to MN and MN to FA
Protocol-Main Components
Discovering Base StationUnicast or Broadcast
Registration MechanismInform the HA of the current location of the mobile.
Tunneling Mechanism from HA to FA
Delivery from FA to mobile FA keeps a table Gateway mobile MAC address and Source IP address pair.
Gateway Mobiles
Beacon: Agent Advertisement Message (modified ICMP)
Domain specific info: DNS, CoA, hop count, source address.
MN duplicates the beacon : hop count ++
Hop count is to limit the serviced nodes and a decision mechanism
MN`s new access point = CoA
Mobile establish the route to the FA
Protocol-Agent Discovery
Protocol-Registration & Tunneling
Normal Mobile IP Registration
Registration Request: MN4->MN3->MN2->MN1->FA->HA Registration Reply: HA->FA->MN1->MN2->MN3->MN4 Periodic registration update.
Ethernet Header FA addr. HA addr. MN addr. CH addr. Packet
MN addr. CH addr. Packet
Ethernet Header MN addr. CH addr. Packet
Gateway Mobile Node MAC Address
Decapsulating at FA
Sending to MN at FA
Encapsulating at HA
Tunneling
Protocol-Hop Count
Lifetime of agent advertisement = # of hop countChange access point by considering hop count.
A
B
C
D
E
F
FA
FA2
MN1
MN2
Ad hoc Domain
Protocol-OVERHEAD
MIPO: Mobile IP OverheadBeacon Flooding
AHRO: Ad Hoc Routing Overhead Routing Table Formation
NHIT: Number of Hops for Inside Traffic Wireless bandwidth usage
Previous Work-MIPMANET
Designed with on demand routing
Agent AdvertisementBeacon Flooding
Ad Hoc RoutingAODVCreate route before sending
High MIPOAHRO depends on traffic and sizeNHIT depends on traffic and size
MEWLANA-TD
Designed with table driven routing
Agent Advertisement: Dynamic BeaconingInitiate advertisement when the routing table changes
Ad Hoc RoutingDSDV- route table exchange
MEWLANA-TD
Dynamic BeaconingThere exists a route for each node
Low MIPOAHRO depends on sizeNHIT depends on size and traffic
Sheet1
DestinationNext Hop
MN1MN2MN2
MN3MN2
MN4MN2
FAFA
*FA
MN2MN1MN1
MN3MN3
MN4MN3
FAMN1
*MN1
MN3MN4MN4
MN2MN2
MN1MN2
FAMN2
*MN2
MN4MN3MN3
MN2MN3
MN1MN3
FAMN3
*MN3
Table 1 : Routing Tables
MEWLANA-RD
Depth Level Number (DLN): Hop Count -> eliminate loopRoutes (1) From mobile to FA : Beacon Routes (2) From FA to mobiles: Multi Hop Registration Request
MEWLANA-RD
Multi Hop Registration Request Mechanism
MEWLANA-RD
Beacon floodingCreate treePerformance degradation in inside trafficIf in different tree, connect with Mobile IP
High MIPONo AHROHigher NHIT
Empirical Classification
Low
High
Small
Large
Intensity level of Inside traffic
Ad Hoc network size
MIPMANET
MEWLANA-RD
MEWLANA-TD
III
II
I
IV
Simulation Parameters
NS-2
CBR Source : 1-1010 packets per second512bytesBeacon Period: 1 sec.Nodes:{4,8,32,64,128}PF: Performance Factor B=C=D=1A is a scaling factor
Simulation
Performance Factor
Conclusion
Classification of the environmentSize and traffic intensity
MEWLANA-TD : Small size and High inside trafficDynamic Beaconing
MEWLANA-RD: Large size and Low inside trafficEliminate Ad hoc Routing Protocol Overhead
MIPMANET : Large size and High inside trafficDemand routing protocol when there is a need.
Reference
Royer, C. Toh, A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks IEEE Personal Communications, Vol. 6, No.2, pp.46-55, April 1999.
Broch J., Maltx D. ,Johnson D.,Hu Y.,Jetcheva J., A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols, The fourth annual ACM/IEEE International conference on Mobile computing and networking, October 25-30, 1998, Dallas, TX USA
Ulf Jonsson, Fredrik Alriksson, Tony Larsson, Per Johansson, Gerald Q. Maquire Jr. MIPMANET-Mobile IP for Mobile Ad Hoc Networks, MOBIHOC 2000.
Hui Lei and Charles E. Perkins, Ad hoc networking with Mobile IP in Proceedings of 2nd European Personal Mobile Communication Conference, Sept. 1997.
SENSOR NETWORKS
Scheduling and Positioning Problems for Sensor Networks
Outline
Introduction PositioningScheduling Wireless NetworksWireless Tree Networks
Parking Garage Problem
A sensor node at each parking spotA sensor node determines whether a car is present and informs the BSBS has global knowledge of state of the garageGuide cars to empty spotsCharging for time used
Energy consumption in sensor nodes
Some comparisons:Bluetooth:~40 mW power consumption2 mW tx output-80 dbm receiver sensitivityRange ~ 10m802.11:~ 1 W power consumption30 mW tx output-82 dbm receiver sensitivityRange ~ 25-100m1 AAA battery has about:1000 mW Hour of energy
Asymmetric Communication
BS have lots of energy and processing powerSensor nodes have little energy and processing powerUse BS to coordinate sensor nodesSensor nodes collect and send data to BSBS communicates directly with sensors. Sensors send data over multiple hops
Received Power and Positioning
Fact: Received power is corelated with locations of sender and receiverCellular Models:Average_Rx_Power (in dB) = -10 a log(R) + N(0,b)Indoor Models:Average_Rx_Power = M(t,r) + N(0,b)
Bayesian Inference
K transmitters at fixed known locationsProblem: determine location of receiverRandom Variables:R1, , Rk received powers from the k transmittersX location of the receiverGiven: P(Ri = a | X = x)
Bayesian Inference (cont.)
Determine:P(X = x | R1=a1, R2=a2, , Rk=ak) = P(R=a|X=x)P(X=x)/R(R=a)Assuming independence:P(R=a|X=x) = P(R1=a1|X=x)P(Rk=ak|X=x)Maximum likelihood:argmax_{x} P(R=a|X=x)
Positioning when Tx have unknown positions
Random Variables:Y1, , Yk unknown locations of nodes R[i,j] - received power at node i from node jWe know: P( R[i,j] | Yi, Yj)Compute: P( Yi | R )
Scheduling in Wireless Networks
Paths of flows fixed through the wireless networkFluid flow/discrete packetsWireless constraintsConstraint graph: C = (E,F) where F \subset E x EProblem: empty the network
Scheduling in Wireless Networks (cont.)
Each node i has x(i) amount of trafficEach link l has t(l) amount of trafficGeneralized graph coloring of links
Greedy Policy
Greedy Policy: choose the maximum number of nodes to be fired.Is this a good policy ?
A Schedule
Schedule periodically announced by the BSOnly receivers and transmitters need to be on during a time slot
TimeSenderReceiver
01,24,5
12,35,6
23,48,9
Other Issues
Determining a schedule based on demand pattern or data collection patternSynchronizing the nodes
Wireless Tree Networks
Traffic light:BS calculates the number of cars waiting from the number of cars passed through each sensorRequirements:Generate packets in each node almost at the same time for a better estimate of the # of cars between each sensorMinimize the period each sensor sends the data to BS without overloading networkGuarantee the arrival of packets within a specific deadline
Wireless Tree Networks
Parking garage:BS determines free spaces from the packets received from sensor nodesRequirements:Guarantee the arrival of packets within a specific deadlineMinimize the period each sensor sends the data to BS without overloading network
Wireless Tree Networks
How can we achieve these requirements?Assumptions:BS has full knowledge of the networkEvery node knows its parent in the treeBS announces the scheduleNodes synchronized by BSDefn: Frame is the duration of time of length equal to the packet generation period at each node
Wireless Tree Networks
How can we achieve these requirements?Procedure:Each node generate one packet at the beginning of the frameEach nodes packet is guaranteed to reach BS until the end of the frameAdvantages:Each packet is generated at the same time(traffic light)Maximum delay to reach BS is bounded by frame lengthPacket generation rate is low enough not to overload the networkExactly one packet from each sensor node reaches BS(fair, otherwise some scheme like Alec Woos scheme required