transport protocol design for wireless sensor network

8/10/2019 Transport Protocol Design for Wireless Sensor Network

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TRANSPORT PROTOCOL DESIGN FORWIRELESS SENSOR NETWORK


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OUTLINETransport protocol

Performance metrics

Congestion controlCongestion Detection

Congestion NotificationCongestion Mitigation & Avoidance

Loss RecoveryLoss Detection & Notification

Retransmission Recovery


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Transport protocol

Runs over the network layerEnd-to-end messsage transmisson

Provide functions:-

Orderely transmission

Flow & Congestion Control

Loss recovery

QOS


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Performance Metrics1. Energy Efficiency :

Factors affecting energy efficiency:-Packet lossRetransmission distanceControl messages

2. Reliability:For different applications , different levels of reliabilitymay be required. According to packet loss 2 types ofreliabilty can be classified:-

Packet reliability : Application is loss sensitive & requiresuccessful transmission of each packet.Eg:- downstreamcode distribution or queries.

Event reliability : Requirement of loss-tolerant applicationsthat allow certain packet loss. Eg:-sensor nodes with digital

camera can be used to send images to the sink


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3. QOS : For some delay-sensitive applications a network

must guarantee real - time data transmission. someapplications are loss sensitive and cannot standpacket loss or require a very small packet - loss ratio.Therefore, a transport protocol may need to supporttraditional QoS in terms of throughput, packetdelivery latency, and packet - loss ratio.

4. Fairness: Sensor nodes are usually scattered in ageographical area to collect information.In order to letthe sink have full information on the entire sensedarea, a transport protocol should provide fairbandwidth allocation among all sensor nodes so thatthe sink can get the same number of packets from

each sensor node during a period of time.


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Congestion Control Mainly two reasons that result in congestion in a WSN:

packet arrival rate exceeding the packet service ratecontention, interference, and the bit error rate on a link

In a WSN, congestion has a direct impact on energy efficiencyand application QoS.

Congestion can cause: buffer overflow queuing delay and higher packet loss degrade reliability and application QoS

Three mechanisms that can deal with this problem:-1. congestion detection

2. congestion notification and

3. congestion mitigation and avoidance


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Congestion DetectionIn TCP, congestion is observed or inferred at the end

nodes based on a timeout or redundantacknowledgment.

In a WSN, however, it is preferred to use proactive

mechanisms. A common mechanism for congestion detection is to

use

queue length,

packet service time, or

the ratio of packet service time over packetinterarrival time at the intermediate nodes


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Congestion Notification Propagate the congestion information from the congested node

to its upstream nodes or the source nodes that contribute to

congestion.The information can be transmitted using, for example, a single

binary bit, called congestion notification (CN) bit.

2 approaches used to disseminate congestion information :- Explicit congestion notification :-uses special control messagesto notify the involved sensor nodes of congestion information an intermediate sensor node will broadcast a suppressionmessage upstream toward the source when it perceives

congestion. Implicit congestion notification :-does not need any additionalcontrol message to propagate congestion information. This approach usually piggybacks congestion information on

normal data packets


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Congestion Mitigation and Avoidance 2 general approaches to mitigate and avoid congestion:

Network resource management :- Tries to increase network resources (e.g., bandwidth) In a WSN, power control and multiple radio interfaces can beused to increase bandwidth and mitigate congestion

Traffic control :- Controlling congestion through adjusting the traffic rate atsource nodes or intermediates nodes Approach is helpful to saving network resources, and is more

feasible and efficient when exact adjustment of networkresources becomes difficult According to the control behavior ,there are two generalapproaches for traffic control in WSNs: end - to - end hop - by - hop.


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Loss Recovery

Loss recovery is more active and energy efficient, andcan be performed at both the link layer and thetransport layer.

At the link layer, loss recovery is performed on a hop-

by-hop basis, while at the transport it is usually doneon an end - to - end basis.

Loss recovery approach consist of 2 phases:

Loss detection and notification, andRetransmission recovery


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Loss Detection and Notification. Packet loss can be far more common in WSNs than in

wired networks

Common mechanism is to include a sequencenumber in each packet header. The continuity of

sequence numbers can be used to detect packet loss.Loss detection and notification can be performed at:-

end - to end :- end points (destination or source)are responsible for loss detection and notification asin TCP. hop - by hop :- intermediate nodes detect andnotify packet loss.


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end - to - end approach is not very effective for WSNsbecause 1. the control messages that are used for end - to -

end loss detection requires a return path consistingof several hops, which is not energy efficient

2. control messages travel through multiple hops andcould be lost with a high probability due to eitherlink errors or congestion

3. the end - to - end loss detection approachinevitably leads to end - to - end retransmissionsfor loss recovery & that consumes more energythan hop - by - hop retransmission


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hop - by - hop approach , can further be categorized

into-

Receiver based packet loss detection : a receiver inferspacket loss when it observes out - of - sequence packetarrivals.

Sender based packet loss detection: the sender detectspacket loss either on a timer - based or overhearing

mechanism.


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Retransmission RecoveryRetransmission of lost or damaged packets can also beperformed by

End - to - end: Source performs the retransmission & anintermediate node that intercepts loss notification searches its localbuffer. If it finds a copy of the lost packet in the buffer, it retransmits it.Otherwise, it relays the loss information upstream to otherintermediate nodes. The hop number between cache point & loss point can be referredto as retransmission distance . The retransmission distance is anindication of retransmission efficiency in terms of energy consumedin the process of retransmission. Used to preferred if 100% packet reliability is required

Hop - by hop : more energy efficient Allows application - dependent variable reliability levels Cannot assure message delivery in the presence of a nodefailure.


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THANKS

transport protocol design for wireless sensor network

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