This document summarizes a research paper that proposes optimizations to caching-based wireless sensor network transport protocols. It introduces DTSN, an existing caching-based protocol, and then proposes three mechanisms to enhance it: 1) an improved NACK repair mechanism, 2) adaptive MAC retry limits based on frame error rates, and 3) optimization of the transmission window size. The mechanisms are evaluated through simulation and shown to significantly improve goodput and energy efficiency compared to DTSN and TCP, especially at higher frame error rates. Future work is noted to study more dynamic networks and congestion effects.

1. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
On the Optimization and Comparative
Evaluation of a Reliable and Efficient
Caching-Based WSN Transport Protocol
Nestor M. C. Tiglao, António M. Grilo
INESC-ID/Instituto Superior Técnico
Lisbon, Portugal
6 March 2013
DRCN 2013, Budapest, Hungary

2. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Outline
1 Introduction
2 Related work
Caching-based WSN Transport
DTSN
3 Proposed Mechanisms
NACK Repair
Adaptive MAC Retry
Transmission Window Optimization
4 Performance Evaluation
5 Conclusion

3. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Wireless Sensor Network
Composed of small, resource-constrained wireless devices
Multi-hop operation
Transport protocol: reliability, congestion control,
energy-efficiency

4. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Motivation
Develop simple mechanisms that can be implemented in
constrained devices (i.e., O(1) complexity)
Explore novel approaches in the transport layer
Leverage on intermediate caching to improve performance

5. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Caching-based Transport Protocols
Pump Slowly, Fetch Quickly (PSFQ, 2002)
sink-to-sensor, hop-by-hop reliability, designed for code
update, uses broadcast
Reliable Multi-Segment Transport (RSMT, 2003)
end-to-end reliability, uses NACKs, timer-driver loss
detection
Distributed TCP Caching (DTC, 2004)
caching TCP segments and retransmitting segments
local in case of packet loss
TCP Support for Sensor Networks (TSS, 2007)
not forward a cached TCP segment until the next-hop
has received all previous segments (backpressure)
Distributed Transport for Sensor Networks (DTSN, 2007)

6. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
DTSN
Enhanced DTSN
Basic DTSN

7. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Cross-Layer Approach

8. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Enhanced NACK Repair Mechanism
RNACK Procedure
procedure pkt_recv(pkt)
...
if (!rpending_ && seqno! =next_) then
repseqno_ ← seqno
rpending_ ← 1 ⊲ raise Repair Pending
Send RNACK (seqno)
else
do nothing
end if
if (rpending_ && seqno==repseqno_) then
rpending_ ← 0 ⊲ clear Repair Pending
next_ ← maxseen_ + 1 ⊲ update next_
end if
if (seqno > maxseen_) then
maxseen_ ← seqno
end if
⊲ update maxseen_ Example of the Enhanced NACK
... Repair Mechanism
end procedure

9. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Adaptive MAC Retry Limit
log Π − log p
r ← max 3, ⌊ ⌋
log p
R = 1−Π
Π is the Frame Error Rate(FER)
p is the physical layer frame error rate
r is the MAC retry limit MAC retry limit value, r, for
R is the desired MAC layer reliability various MAC reliability levels
60 R FER≤0.3 FER=0.5 FER=0.7
Π=0.8
50
Π=0.9 80% 3 3 4
Π=0.95
90% 3 3 6
40
95% 3 4 8
30
r
20
10
0
0 0.2 0.4 0.6 0.8 1
FER

10. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Transmission Window Optimization
Dynamic Window
Additive Increase Multiplicative, Decrease (AIMD)
algorithm (cwnd in TCP)
inefficient in wireless networks
Fixed Window
n
based on the bandwidth-delay product, i.e., W = 4
where n = number of hops
How about caching-based protocols?

11. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Setup
Simulation Parameters
Parameter Value
Network topology Linear chain
Packet size 500 bytes
Number of packets(pktno) 500
DTSN EAR interval 200 msec
Routing protocol
MAC protocol
Static
802.11b
Scenario 1: Global Hotspot
MAC retry limit (default) 3 (default)
PHY error model Binary Symmetric Channel
Max. simulation time 2,000 seconds
Simulator ns-2.31
Assumptions:
Routing topology is stable
Cross-layer information is Scenario 2: Localized Hotspot
available

12. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
DTSN Transmission Window Optimization
Goodput
AWopt = [CS , CS + ∆], ∆ = 10
FER=0 FER=0.1 FER=0.3 FER=0.5 FER=0.7 FER=0 FER=0.1 FER=0.3 FER=0.5 FER=0.7
140 140
120 120
Goodput (in packets/sec)
Goodput (in packets/sec)
100 100
80 80
60 60
40 40
20 20
0 0
2 8 10 20 30 40 50 2 8 10 20 30 40 50
Acknowledgment Window (AW) (in packets) Acknowledgment Window (AW) (in packets)
(a) CS=10 (b) CS=20
Scenario 1 – Goodput, as a function of AW

13. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
DTSN Transmission Window Optimization
Transmission Cost
Ndata + Nack + Nnack + Nmack
tx_cost =
pktno
FER=0 FER=0.1 FER=0.3 FER=0.5 FER=0.7 FER=0 FER=0.1 FER=0.3 FER=0.5 FER=0.7
250 250
200 200
Transmission Cost
Transmission Cost
150 150
100 100
50 50
0 0
2 8 10 20 30 40 50 2 8 10 20 30 40 50
Acknowledgment Window (AW) (in packets) Acknowledgment Window (AW) (in packets)
(a) CS=10 (b) CS=20
Scenario 1 – Transmission Cost, as a function of AW

14. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Performance Analysis
Protocols considered:
DTPA – The DTPA protocol, W = BDP(n) + 3
DTPA-CWL – The DTPA protocol, W = BDP(n)
DTSN+ – The DTSN protocol with the proposed
enhanced NACK repair and adaptive MAC retry limit
mechanisms
TCP− – The TCP protocol without the RTO exponential
backoff

15. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Performance Analysis
Goodput
Scenario 1 Scenario 2
140 140
DTPA−BDP DTPA−BDP
DTPA DTPA
120 − 120 −
TCP TCP
+ +
DTSN DTSN
Goodput (in packets/sec)
Goodput (in packets/sec)
100 100
80 80
60 60
40 40
20 20
0 0
0 0.10 0.30 0.50 0.70 0 0.10 0.30 0.50 0.70
Frame Error Rate Frame Error Rate
Performance Gain of DTSN+ Performance Gain of DTSN+
FER DTPA-CWL DTPA TCP− FER DTPA-CWL DTPA TCP−
0 96% 129% 88% 0 96% 129% 88%
0.10 51% 138% 59% 0.10 87% 135% 81%
0.30 71% 75% 137% 0.30 67% 123% 69%
0.50 720% 723% 1221% 0.50 100% 92% 239%
0.70 ∞ ∞ ∞ 0.70 346% 266% 883%

16. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Performance Analysis
Transmission Cost
Scenario 1 Scenario 2
160 160
DTPA−BDP DTPA−BDP
140 DTPA 140 DTPA
− −
TCP TCP
+ +
120 DTSN 120 DTSN
Transmission Cost
Transmission Cost
100 100
80 80
60 60
40 40
20 20
0 0
0 0.10 0.30 0.50 0.70 0 0.10 0.30 0.50 0.70
Frame Error Rate Frame Error Rate
Performance Gain of DTSN+ Performance Gain of DTSN+
FER DTPA-CWL DTPA TCP− FER DTPA-CWL DTPA TCP−
0 29% 58% 29% 0 29% 58% 29%
0.10 20% 65% 21% 0.10 28% 60% 28%
0.30 19% 54% 19% 0.30 23% 63% 22%
0.50 39% 54% 49% 0.50 25% 57% 25%
0.70 ∞ ∞ ∞ 0.70 31% 48% 49%

17. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Performance Analysis
TCP cwnd Evolution
FER=0 FER=0.1
10 10
8 8
cwnd (in pkt)
cwnd (in pkt)
6 6
4 4
2 2
0 0
100 110 120 130 100 110 120 130
Time (in sec) Time (in sec)
FER=0.3 FER=0.5
10 10
8 8
cwnd (in pkt)
cwnd (in pkt)
6 6
4 4
2 2
0 0
100 110 120 130 100 110 120 130
Time (in sec) Time (in sec)
FER=0.7
10
8
cwnd (in pkt)
6
4
2
0
100 110 120 130
Time (in sec)
Scenario 1 – Evolution of TCP cwnd

18. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Performance Analysis
Packet Reception
500 500
450 450
400 400
350 350
Sequence Number
Sequence Number
300 300
250 250
200 200
150 150
DTPA−CWL DTPA−CWL
100 DTPA 100 DTPA
50 TCP− 50 TCP−
DTSN+ DTSN+
0 0
100 102 104 106 108 110 100 105 110 115
Time (in seconds) Time (in seconds)
(a) FER=0 (b) FER=0.1
500 500
450 450
400 400
350 350
Sequence Number
Sequence Number
300 300
250 250
200 200
150 150
DTPA−CWL DTPA−CWL
100 DTPA 100 DTPA
− −
50 TCP 50 TCP
DTSN+ DTSN+
0 0
100 105 110 115 120 125 130 100 150 200 250 300 350
Time (in seconds) Time (in seconds)
(c) FER=0.3 (d) FER=0.5
Scenario 1 – Packet Reception

19. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
Conclusion
Transmission window and loss recovery semantics for
caching-based transport mechanisms need to be optimized
We have proposed the following mechanisms
enhanced NACK recovery
adaptive MAC retry limit
optimal DTSN transmission window
DTSN+ significantly outperforms TCP and DTPA in
terms of goodput and energy-efficiency
Future work
consider more complex and dynamic network scenarios
study performance in presence of network congestion

20. Introduction Related work Proposed Mechanisms Performance Evaluation Conclusion
References
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End
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