1. Hongchao Zhou, Xiaohong Guan, Chengjie Wu
RTMC: Reliable Transport with Memory Consideration in Wireless Sensor Networks
Hongchao Zhou, Xiaohong Guan, Chengjie Wu

2. Reliable Transport with Memory Consideration Experiments
Outline
Background
Reliable Transport with Memory Consideration
Experiments
Simulation and Comparison
2019/5/19

3. Wireless sensor networks
Wireless sensor networks (WSN) consist of many resource constrained sensor nodes with limited computational capability, communication radius and memory space.
The availability of low-cost hardware such as CMOS cameras and microphones enables sensor nodes to capture images or audio from environment, and increases the requirement of reliable file transport.
Image
Audio
Video
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4. Problems and Challenges
Requirement: the files to be transmitted generally divided into multiple segments to avoid high packet error rate.
Problem: How to send all the multiple segments from a source to the sink via multiple unreliable hops?
Challenges
unreliable links in WSN and conflict in transmissions from different nodes may cause packet loss
limited memory of relay sensor nodes with possible overflow may also cause packets loss.
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5. Existing Methods
Node-by-node: One relay node receives all the segments and then re-transmit all the segments to the next hop.
Possible large delivery latency
Significant memory requirement
TCP is widely used to provide end-to-end reliability and congestion control in Internet.
End-to-end retransmission is not appropriate in wireless systems with high packet-loss rate.
End-to-end congestion control may have a tardy response and cannot adapt to the rapid change of channel capacity in WSN.
Control Messages may lost.
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6. A reliable transport protocol:
A reliable transport protocol in WSN should
hop-by-hop retransmission
hop-by-hop congestion control
100% reliability (some segments may very important)
make good use of bandwidth
Reliable Transport with Memory Consideration (RTMC)
2019/5/19

7. Reliable Transport with Memory Consideration Experiments
Outline
Background
Reliable Transport with Memory Consideration
Experiments
Simulation and Comparison
2019/5/19

8. RTMC
Basic Ideas:
If the local node knows that its next hop can store m extra segments, then it can send m segments without any negotiations.
If the local node does not know whether one segment is received by the next hop, it can not remove this segment.
Variable Definition
segment_length : the number of segments to transport
BL :maximal number of segments (small integer)
local_free :extra segments can be stored in the local node
next_free :extra segments can be stored in the next hop
rec_segments : the IDs of the received last BL segments
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9. RTMC Packets: Initial Packet:
Ask the next hop to participate into the current transport.
local_free, rec_segments, segment_length
Data Packet: …
Send a segment to the next hop
local_free, rec_segments, segment_id, content
Requiring Packet:
Ask the last hop to send a data packet.
local_free, rec_segments I 1 2 R
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10. RTMC An instance to demonstrate that how RTMC works. BL=3
segment_length=9
hops =3
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11. Example by RTMC Beginning Send initial packets 1 1 2 2 3 3 4 4 5 5 6 67 4 7 5 8 5 8 9 6 6 9
source
sink A B I
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12. RTMC instance Beginning
If A does not receive any response from B, an initial message should be retransmitted. 1 1 2 2 3 3 4 4 5 5 6 6 4 4 7 7 5 8 5 8 9 6 6 9
source
sink A B I I
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13. RTMC instance Transporting
Receive a data packet from the last hop node.
local_free
rec_segments 1 2 2
6-4-3
7-6-4
7-6-4 5 1 6 2 2 2 7 3 6 2 2 8 4 2 6 7 7 9
source
sink A B 7
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14. RTMC instance Transporting Hear a data packet from the next hop node.
local_free
rec_segments 1 2
7-6-4
7-6-4 5
next_free=2 1 6
ready to
transmit 2 2 2 7 3 6 2 2 8 4 2 6 7 7 9
source
sink A B 7
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15. RTMC instance Transporting
Special case: A is empty but source thinks that A is full, due to packets loss. A should send Requiring packets to source periodically until memory is not empty.
next_free=0
next_free=2 1 3
7-6-4
7-6-4 5 1 6
ready to
transmit 2 2 2 7 3 2 7 2 8 4 2 6 2 9
source
sink A B R
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16. RTMC instance
Ending
For a node, if (1) its memory is empty and (2) it has received all of the segments, then the transport is finished of this node.
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17. Reliable Transport with Memory Consideration Experiments
Outline
Background
Reliable Transport with Memory Consideration
Experiments
Simulation and Comparison
2019/5/19

18. Experiment Scenario Mica2, 19.2kbps, 10K image file, 100segments
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19. Experiment result without congestion
Time (s)
Segment sequence No.
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20. Experiment result with congestion
G was turned on 20seconds later
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21. Experiment result with congestion
Time (s)
Segment sequence No.
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22. Reliable Transport with Memory Consideration Experiments
Outline
Background
Reliable Transport with Memory Consideration
Experiments
Simulation and Comparison
2019/5/19

23. Comparison
SEA
A receiver sends back an acknowledge after receiving a packet.
The sender retransmits the packet if it does not receive the acknowledge.
Each node can store no more than 10 segments
RTMC
Each node can store 5 segments
Simulation
5 nodes, TDMA (one message for RTMC, one message and one acknowledge for SEA). p p p p
source
sink
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24. Simulation Result Transport time (periods) Packet success rate p
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25. Simulation Result
Packets transmitted
Packet success rate p
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26. Conclusions
RTMC can get 100% reliability due to hop-by-hop retransmission and congestion control mechanism.
RTMC can use channel effectively and has low delivery latency, since the transmission rate can quickly change with the traffic change in the network.
RTMC costs less energy, since the number of retransmission packets is reduced.
Both experiment and simulation results support these conclusions
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27. Thank you
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