18-04-2011, 11:55 AM
PRESENTED BY
ZILLE HUMA KAMAL
[attachment=12291]
REAL TIME COMMUNICATION IN WIRELESS SENSOR NETWORKS
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]
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]
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]
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
– 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
RAP
• A Real-Time communication architecture
APIs
• Issue Query
- query name
- attribute list
- area
- timing constraints, e.g. period, deadline
- querier location
APIs
• Event Registration
- event name
- area
- query
• Example
register_event{
virus_found(0,0,100,100),
query{
virus.count,
area=(Xevent-1 ,Yevent-1,Xevent+1,Yevent+1),
period=1.5, deadline=5,
base=(100,100)
}
};
LAP
• Location Addressed Protocol
- transport layer
- connectionless
- no IP/ID addressing, location based addressing
- three types of communication
» unicast
» area multicast
» area anycast
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
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
• VMS Deadline aware
Distance aware
• Deadline aware
• Distance aware
• Packet scheduling policy
– 2 types of packet scheduling policies
– Static Velocity Monotonic
– Dynamic Velocity Monotonic
• VMS
• SVM
– Requested velocity is fixed at each hop
V = dis(x0, y0, xd, yd)/D
• DVM
– Requested velocity changes at each hop and reflects the time the packet has spent in the network
vi = dis(x0, y0, xd, yd)/(D-Ti)
v0 = dis(x0, y0, xd, yd)/D
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
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
• EXPERIMENTATION
• EXPERMENTATION
• EXPERIMENTATION
• REAL TIME COMMUNICATIONS IN WIRELESS SENSOR NETWORK
• NOW PRESENTING SPEED
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.
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.
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
API & PACKET FORMAT
• UnicatSend(Global_ID, packet)
• AreaMulticastSend(position, radius, packet)
• AreaAnycastSend(position, radius, packet)
• SpeedReceive( )
SPEED packet format:
• 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
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
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
ZILLE HUMA KAMAL
[attachment=12291]
REAL TIME COMMUNICATION IN WIRELESS SENSOR NETWORKS
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]
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]
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]
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
– 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
RAP
• A Real-Time communication architecture
APIs
• Issue Query
- query name
- attribute list
- area
- timing constraints, e.g. period, deadline
- querier location
APIs
• Event Registration
- event name
- area
- query
• Example
register_event{
virus_found(0,0,100,100),
query{
virus.count,
area=(Xevent-1 ,Yevent-1,Xevent+1,Yevent+1),
period=1.5, deadline=5,
base=(100,100)
}
};
LAP
• Location Addressed Protocol
- transport layer
- connectionless
- no IP/ID addressing, location based addressing
- three types of communication
» unicast
» area multicast
» area anycast
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
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
• VMS Deadline aware
Distance aware
• Deadline aware
• Distance aware
• Packet scheduling policy
– 2 types of packet scheduling policies
– Static Velocity Monotonic
– Dynamic Velocity Monotonic
• VMS
• SVM
– Requested velocity is fixed at each hop
V = dis(x0, y0, xd, yd)/D
• DVM
– Requested velocity changes at each hop and reflects the time the packet has spent in the network
vi = dis(x0, y0, xd, yd)/(D-Ti)
v0 = dis(x0, y0, xd, yd)/D
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
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
• EXPERIMENTATION
• EXPERMENTATION
• EXPERIMENTATION
• REAL TIME COMMUNICATIONS IN WIRELESS SENSOR NETWORK
• NOW PRESENTING SPEED
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.
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.
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
API & PACKET FORMAT
• UnicatSend(Global_ID, packet)
• AreaMulticastSend(position, radius, packet)
• AreaAnycastSend(position, radius, packet)
• SpeedReceive( )
SPEED packet format:
• 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
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
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