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FTRP: A Fault Tolerant Reliable Protocol for Wireless Sensor Networks

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Wireless sensor networks operate in very challenging environments that make them prone to different types of faults. Hence, there is a high need for a reliable protocol that offers an acceptable functionality in the presence of faults. In this paper, we propose the Fault Tolerant Reliable Protocol (FTRP), a novel routing protocol designed to be used in wireless sensor networks. FTRP offers fault tolerance reliability for packet exchange, as well as adaptation for dynamic network changes. The key concept in this protocol is the use of node logical clustering. The protocol delegates the routing ownership to the cluster heads, where the fault tolerance functionally is implemented. FTRP utilizes cluster head nodes along with cluster head groups as intermediate storage for transient packets. In addition, FTRP utilizes broadcast in its routing messages communication. This technique substantially reduces the message overhead as compared to classical flooding mechanisms. FTRP manipulates Time to Live (TTL) values for the various routing messages in addition to utilizing jitters in messages transmission. FTRP performance has been evaluated through extensive simulations. Aggregate Throughput, Packet Delivery Ratio and End-to-End delay have been used as performance metrics. The results obtained showed that FTRP ensures high Throughput, high Packet Delivery Ratio, and acceptable End-to-End delay in the presence of changing networking conditions. FTRP performs well in dense and sparse networks while nodes are mobile. Stationary simulations represented the worst-case behavior. This is attributed to synchronized nodes, where nodes send similar messages at the same time.
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FTRP: A Fault Tolerant Reliable Protocol for Wireless Sensor Networks
Islam Ahmed Moursy, Mohamed Nazih ElDerini
Computer and Systems Engineering Department
Faculty of Engineering, Alexandria University
Alexandria, Egypt
e-mail: {islam.moursy, elderini}@alexu.edu.eg
Magdy Abd-Elazim Ahmed
Vice Dean for Graduate Studies and Research
Faculty of Engineering Alexandria University
Alexandria, Egypt
e-mail: magdy@alexu.edu.eg
Abstract Wireless sensor networks operate in very
challenging environments that make them prone to different
types of faults. Hence, there is a high need for a reliable
protocol that offers an acceptable functionality in the presence
of faults. In this paper, we propose the Fault Tolerant Reliable
Protocol (FTRP), a novel routing protocol designed to be used
in wireless sensor networks. FTRP offers fault tolerance
reliability for packet exchange, as well as adaptation for
dynamic network changes. The key concept in this protocol is
the use of node logical clustering. The protocol delegates the
routing ownership to the cluster heads, where the fault
tolerance functionally is implemented. FTRP utilizes cluster
head nodes along with cluster head groups as intermediate
storage for transient packets. In addition, FTRP utilizes
broadcast in its routing messages communication. This
technique substantially reduces the message overhead as
compared to classical flooding mechanisms. FTRP manipulates
Time to Live (TTL) values for the various routing messages in
addition to utilizing jitters in messages transmission. FTRP
performance has been evaluated through extensive
simulations. Aggregate Throughput, Packet Delivery Ratio and
End-to-End delay have been used as performance metrics. The
results obtained showed that FTRP ensures high Throughput,
high Packet Delivery Ratio, and acceptable End-to-End delay
in the presence of changing networking conditions. FTRP
performs well in dense and sparse networks while nodes are
mobile. Stationary simulations represented the worst-case
behavior. This is attributed to synchronized nodes, where
nodes send similar messages at the same time.
Keywords-fault tolerance; proactive routing; wireless sensor
networks ; NS-3.
I. INTRODUCTION
Wireless Sensors Networks (WSNs) continue to present a
lot of interest in both the research domain as well as the
industry [1]. WSNs are highly adaptive to various domains,
including - but not limited to - energy control systems,
environmental monitoring, security, surveillance, health
applications, area monitoring and Internet of Things [2].
Typical WSNs are networks composed of a large number
of sensor nodes. Each node is equipped with sensors to
detect various attributes of the surrounding environment.
WSNs are built to operate for prolonged time and even in a
hostile environment, which increases the need for fault
tolerant reliable communication protocols [3].
There are many research papers on routing protocols.
However, only few are adopted by the industry. The
Institute of Electrical and Electronics Engineers (IEEE) had
adapted the topic and introduced Low-Rate Wireless
Personal Area Network (Lr-WPAN) [4] as a standard Media
Access Control (MAC) layer for WSNs, which opens a
great opportunity for WSNs. This paper introduces a new
fault tolerant reliable routing protocol for WSNs, which is
efficient under mobility conditions.
Mahmoud et al. [5] introduced a novel three-dimensional
reference model for research in WSN reliability. The model
categorizes WSN protocols into one of two techniques,
which are retransmission or redundancy. Reliability is
ensured within those techniques either by using a hop-by-
hop or an end-to-end method to recover the lost data while
maintaining either packet or event level reliability. Chouikhi
et al. [6] classify fault tolerance techniques according to the
time at which the fault tolerance is triggered (before or after
the fault occurrence). According to this, these techniques are
classified as preventive or curative. Hence, the proposed
protocol is classified as a proactive protocol that is
retransmission based, connection oriented (end-to-end), with
packet level reliability and utilizing a curative technique to
achieve fault tolerance.
Fault Tolerant Reliable Protocol (FTRP) operates as a
table driven proactive protocol [7]. FTRP regularly
exchanges topology information with selected nodes of the
network. Initially, nodes are in learning mode and broadcast
a status of not being in a sensor domain in preparation to
join one. If no answer is received, the nodes stay in that
state until an answer is received. If an answer is received,
the node evaluates the answer depending on its source and
its included attributes. A cluster then begins to form
according to the proposed protocol.
After cluster formation, Cluster Member (CM) nodes
send data messages to their designated cluster head (CH).
The CH, in turn, decides how many copies of the message to
be retained until an acknowledgment (ACK) is received
from the destination. The CH stores that message in the
cluster head group (CHG) according to the protocol-defined
parameters. The proposed protocol utilizes the following
main techniques:
A. Retransmission-based reliability
Retransmission is the traditional way of ensuring
reliability [5]. This is achieved by allowing the sender node
to wait for an ACK for its previously sent packets. In case
no ACK is received, the packet is considered lost and
retransmission takes place to ensure reliability. FTRP
implementation relieves the responsibility of packet storage
and retransmission to higher entity nodes (CHs, CHGs or
Sinks), as will be elaborated in Section III.
B. End-to-End (connection-oriented) reliability
End-to-End reliability is a connection-oriented scheme
for achieving reliability in which only the two
communicating end nodes (source and destination) are
responsible for ensuring reliability. FTRP implementation
expands the end-to-end reliability by relieving the source
node from this task, and transferring it to the CH. The CH
determines, according to the replicas parameters, which
CHGs to be used as storage. Whenever the destination node
receives the packets, it broadcasts a message only processed
by CHs or CHGs to release their locally stored
corresponding replicas.
C. Packet level reliability
Packet level reliability ensures that all the packets
carrying sensed data from all the related nodes are reliably
transported to their destinations.
The rest of the paper is organized as follows. In Section II,
the most relevant related works are presented. In Section III,
the relevant FTRP protocol operations are detailed. The
performance analysis of the FTRP protocol is presented in
Section IV. Finally, Section VI concludes the paper and lists
ongoing and future work.
II. RELATED WORK
In this section, we review literature work addressing the
same elements as our protocol, namely retransmission
based, connection oriented (end-to-end) and packet level
reliability.
Iyer et al. [8] proposed the Sensor Transmission Control
Protocol (STCP), an end-to-end reliability protocol with a
congestion control mechanism that is sink-centric. STCP
dynamically controls the application data flow by utilizing a
controlled variable reliability mechanism where the
application type controls the throughput. Reliability is
maintained by using ACK or Negative Acknowledgement
(NACK) as end-to-end retransmission mechanisms. Packets
are cached locally in each node until an ACK is received
from the Sink.
Whenever the Sink receives information about congested
paths, the Sink directs the downstream-congested nodes to
select alternative paths. Reliability in STCP is achieved
through connection-oriented explicit ACKs, which involves
only the end nodes. STCP is considered scalable for a large
number of nodes with high hop counts from a source node
to the Sink.
STCP nodes are prone to huge end-to-end delay time [5],
which results in high latency and cache overflow.
Marchi et al. [9] proposed a Distributed Transport for
Sensor Networks (DTSN). DTSN is non-sink centric, end-
to-end and an energy oriented packet reliability protocol.
DTSN is based on two mechanisms, full and differential
reliability mechanisms. Full reliability is achieved via
retransmission based explicit ACKs, while differential
reliability is performed independently. In the full reliability
mechanism, the source node keeps transmitting the packets
until the number of transmitted packets equals the size of
the acknowledgement window. An explicit
acknowledgement request is issued from the source node to
the destination to confirm message delivery. If the sequence
of the packets is in order, an ACK is sent. These packets are
then removed from the buffer of the source node. If a
NACK is received then retransmission of the missing
sequence of packets is performed. The key contribution of
DTSN is the integration of mechanisms involved in
achieving reliability, such as partial buffering at the source
and intermediate nodes and the utilization of erasure coding.
However, DTSN does not provide details on how the
reliability level is maintained when network conditions
change.
III. FTRP OPERATIONS
A. Protocol Overview
FTRP operations utilize a simple messaging system to
communicate different protocol statuses to the participating
nodes. This messaging system is used to transition the node
from one state to another in order to form a logical grouping
of nodes referenced later as a cluster. FTRP tries to
overcome the issues in STCP [8] by utilizing a distributed
cache rather than preserving the cache at the sender node.
This approach allows the cluster head to control the amount
of cache allocated and where to store the data packet. FTRP
introduces a retry count for locally cached entries.
Whenever a packet entry reaches its max retry count, (the
default is six retires), it is flushed out of the cache to
overcome cache overflow. In fact, FTRP is well suited for a
changing environment, where its messages update the
network paths and handle nodes failure well.
FTRP communicates using a unified packet format for all
data related to the protocol. This provides an easy way to
combine different messages in a single packet transmission.
These packets are encapsulated into User Datagram Protocol
(UDP) [10] datagrams. On the other hand, FTRP messages
contain a sequence number, which is incremented for each
message. In such case, the recipient of a control message is
able to identify which information is more recent and to
ignore those older unprocessed messages.
B. Definitions of main nodes status
1) Sink: The Sink is the central node of the network,
having information about all nodes. Usually, it is connected
to a wired network and it has access to the wireless sensor
domain.
2) Cluster Head (CH): The Cluster Head can be
regarded as a Sink, but for a subset of nodes. It is
responsible for relaying all information from and to the
nodes controlled under its domain.
3) Cluster Head Group (CHG): CHGs are normal
nodes selected by the CH as per the protocol parameters to
act as local cluster storage for messages in transient.
4) Cluster Member (CM): CMs are normal nodes
composing the cluster and are managed by the respective
CH.
5) Cluster Bridge Head (CBH): If the CH is far away
from the Sink, the CBH is the node within another cluster
that links the cluster with the nearest CH.
6) Learning: Initially, a node is not in a cluster or it
does not know route to a Sink.
7) Swarm: A node has identified another node that is
not in its domain and it has knowledge of other nodes
(nonsink).
8) Discovered: A discovered node is a node that is
discovered from either a Sink or another cluster.
The life cycle begins with a node in a Learning state. A
few nodes who have knowledge of their respective existence
can form a swarm. Few swarm nodes can then transition to a
discovered state upon sensing a nearby Sink. Figure 1
depicts the state transition for nodes in FTRP.
Figure 1. FTRP State Transition Diagram
The Sink nominates a discovered node to be a CH. The
CH can request nearby nodes for association as CMs. Few
CMs can then be nominated as CHGs, as per the predefined
configuration parameters of the protocol.
C. FTRP Messaging System
1) Hello Message (HELLO)
A nonsink node lifecycle begins in a Learning state,
where it periodically broadcasts a hello message exposing
its status and other parameters. Hello messages have their
Time to Live (TTL) [11] value set to one, in order not to
flood the whole network. A Hello message is populated with
the sending node known attributes, and its known existing
members, if any. Hello messages are broadcasted as keep
alive periodically. The behavior of each node is different
upon receiving a Hello message, according to the receiving
node status. A Sink node receiving a Hello message checks
if the incoming node has not yet joined a domain, and if it is
not a member of any other cluster. In that case, the Sink
sends an association request. If the node had already been
identified in a domain yet had not joined any cluster, the
Sink will not take any action. This mechanism is adopted in
order to control the allocation of CHs and to allow the
network clustering formation to converge by favoring the
node to join a cluster than to promote it to a new CH. The
Sink will ignore any Hellos from other Sinks and will
update the information received from any other CH.
2) Association Message (ASC)
ASCs are used to instruct nodes to join a cluster or
domain. Only the Sink and the CHs are allowed to send
association to other nodes. ASC messages have two classes.
a) A regular association:
A regular association messages have their TTL value
set to one, so that association does not flood the network.
b) A Broadcasted Association (ASCb)
A broadcasted association messages have their TTL
value set to 255 in order for a CH to be nominated when it
has no direct link to the Sink. It uses its nearest CBH to
reach the Sink through the distress Save-Our-Ship (SOS)
mechanism.
A node populates the ASC message with its members.
Having that, members of a Sink are the CHs known to that
Sink and members of a CH are those nodes under the CH
control as fault tolerance domain.
3) Control Message (CTL)
CTLs are used as decision-making mechanism and out of
band, status updates of different protocol aspects. It has the
following subclasses:
a) Reject CH promotion
Reject CH promotion is issued in the case when a Sink
at some point in time decided to promote a CM to CH
however, this CM was earlier acquired by another CH. In
that case, rejecting the CH promotion is favored so that the
CH ID pool is not depleted too fast. In return, the CM issues
a Reject CH Promotion control message to notify the Sink
to release the allocated CH ID.
b) Members check
A swarm node that was nominated to be CM or CH
knows about the existence of other swam nodes whom with
which a swarm was formed. This swarm must be checked
against a high entity node (Sink in case the node is CH or
CH in case the node is CM). The receiving node (Sink or
CH) checks the incoming member list for local existence in
its data structures, and then replies to the sender node with a
Release swarm members message for those members the
higher entity does not know about.
c) Release swarm members
When this message is received, the node drops the
sending node from its local base as swarm, and sends them
swarm release notify control message.
d) Swarm release notify
This message is processed by swarm to drop the
sender from its local base.
e) Swarm SOS
Whenever the swarm is about to drop its last member, it
issues swarm SOS to the sender of the release notify so that
the sender is treated as bridgehead and relays the SOS to the
Sink. The Sink will then send an ASCb, with its TTL value
set to 255, to this swarm node to be nominated as new CH.
f) Fault Tolerant message release (FT_Release)
Whenever a node successfully receives its data packet, it
sends this message in broadcast mode, i.e., its TTL value set
to 255, to notify CHs and CHGs to release the local copies
of the messages considered for fault tolerance.
D. Routing function and fault tolerance
The default routing or forwarding scheme for a node is to
direct the outgoing packets to its master (CH in case of a
node, and a Sink in case of a CH). The scheme below also
applies in case the CH or Sink is initiating a packet send.
Upon the reception of a forward request, the routing
function checks local parameters for replica count and then
stores the message in the CHGs accordingly. Then, finally,
the packet is forwarded normally.
CHs and CHGs are using a timed queue to store the
packets. The receiving node, upon successful reception of a
packet, generates an FT_Release message having the packet
unique identification. Each receiving CHG, CH or Sink
accepts this message and removes the requested message
(if it exists) from its local queue. Upon the expiry of the
queue timer, the local fault tolerance queue is checked for
packets that had not exceeded their retry time, and those
packets are resent. Packets having expired retry time are
removed from the queue and are considered undeliverable
due to unreachable destination.
IV. SIMULATION AND PERFORMANCE
EVALUATION
A. Assumptions
The simulation model is based on the following
assumptions:
The Sink has infinite power source, while nodes have
not.
Each node can behave as both a client and a router.
Each node has a single interface running the FTRP
protocol on that interface.
The nodes have the same capabilities, i.e., same
coverage area and same antenna.
The nodes are randomly placed.
The nodes follow a 2d-walk mobility pattern in
mobility scenarios and follow a constant position
model for stationary simulations.
The nodes can either receive or transmit at a time.
There is no turn around time between transmitting
and receiving. Nodes can switch between transmit
and receive instantly.
Mobility is uncorrelated among the nodes and links
fail independently.
B. Performance metrics
The following performance metrics are used to analyze
the behavior of FTRP.
1) Aggregate Throughput
This is the sum of the throughputs in the uplink and the
downlink.
2) Packet Delivery Ratio(PDR)
This is the number of successfully delivered packets
divided by the total number of transmitted packets
3) End-to-End Delay (E-2-E)
This is the sum of time taken for packets transmitted
from sources to destinations divided by the total number of
received packets.
C. Simulation Environment
The FTRP routing model is built using NS-3 network
Simulator [12] on top of IEEE 802.11 MAC model of NS-3.
Due to simulator limitations, model parameters have been
tuned to match the 802.15.4 MAC layer.
TABLE 1 PARAMETERS FOR SIMULATION MODEL
Simulation Parameter
Value
Simulator
NS-3 (version 3.25)
Operating system
Linux (Ubuntu 14.04)
Simulation time
50 secs
Simulation Area
100m x 100m
Number of nodes
20 for sparse , 40 for dense
Node transmission range
50 meters
Movement model (for
mobility tests)
Random Walk 2d Mobility Model
Stationary model (for no
mobility tests)
Constant Position Mobility Model
Nodes Position allocator
Random Disc Position Allocator
Speed of mobile nodes
1m/sec and 2m/sec
Traffic type
CBR
Data payload
512 bytes
Packet rates
20 p/sec to 80 p/sec
MAC Layer
802.11 DCF with RTS/CTS
Radio Frequency
2.4 GHz
Radio Channel rate
2Mbps
Propagation loss model
Friis Propagation Loss Model
Propagation Delay Model
Constant speed propagation delay
model
The Random 2d-walk model [13] was adopted for driving
mobile clients. In the Random 2d-walk mobility model,
each instance moves with a speed and direction chosen
randomly until either a fixed distance has been walked or
until a fixed amount of time has passed. If a node hits one of
the boundaries (specified by a rectangle) of the model, it
rebounds on the boundary with a reflexive angle and speed.
This model is often identified as a Brownian motion model.
The speed is varied from no mobility using a constant
position model, 1m/sec to 2 m/sec. Table 1 depicts the
parameters set for the simulation model that is common for
all our simulations.
D. Results and analysis
FTRP is simulated using various networking scenarios
with the help of the NS-3 simulator. The scenarios and
results along with detailed analysis are presented in the
following sections.
1) Scenario I
In this scenario, we analyze the performance of FTRP in
terms of throughput, PDR and E-2-E delay in a sparse
network comprising of 20 nodes. The simulation is
performed by varying the number of data packets sent per
second, while maintaining a constant number of flows and
system load. Number of packets per flow ranged from 20
packets/sec to 80 packets/sec. The simulation was repeated
using no mobility model, 1m/sec and 2 m/sec walking
models. Other parameters considered for simulations are the
same as shown in Table 1.
Figure 2 depicts PDR against increasing traffic load in a
sparse network. It is observed that increasing the data rate
beyond 280 kb/s causes PDR to begin to drop, although not
significant.
Figure 2. PDR in a sparse network
As per our simulation parameters, a data rate of 240 kb/s
corresponds to 60 packets/sec and a data rate of 280 kb/s
corresponds to 70 packets/sec. Mobile nodes achieve a good
PDR with regard to the maximum data rate supported by Lr-
WPAN [4] standard, which are 250 kb/s (approximately 63
packets/sec). While nodes are stationary, the obtained PDR
results fall to above 94% at the target data rate of 60
packets/sec, which is acceptable.
Figure 3 depicts Aggregate throughput against increasing
traffic load in a sparse network. It is observed that the
throughput increases as the data rate increases. Both low
and high mobility scenarios achieve good throughput as data
rate increases even for data rates above the targeted 250
kb/s. The stationary nodes performance is lower than that of
mobile ones, which can be attributed to the nodes
synchronized states.
Figure 3. Aggregate Throughput in a sparse network
Figure 4 depicts E-2-E delay against increasing traffic
load in a sparse network. It is observed that, as the data rate
increases, the E-2-E delay increases significantly in a
stationary scenario. The E-2-E delay increases within
acceptable range for mobile scenarios.
Figure 4. End to End Delay in a sparse network
The increase in E-2-E delay is expected due to the
introduction of fault tolerance mechanism, which uses store
and forward. In the stationary scenario, the increase is
significant and can be justified by the nature of FTRP being
too communicative. In the stationary scenario, the collision
rate of packets can increase, while mobility helps to
decrease collision. This can be attributed to the variations of
node states. This variation reduces messages exchanged,
reduces collisions and maintains good E-2-E delay.
2) Scenario II
In this scenario, we analyze the performance of FTRP in
terms of throughput, PDR and E-2-E delay in a dense
network composed of 40 nodes. The simulation is
performed by varying the number of data packets sent per
second, while maintaining a constant number of flows and
system load. The number of packets varied per flow ranged
from 20 packets/sec to 80 packets/sec. The simulation was
repeated using no mobility model, 1m/sec and 2m/sec
walking models. Other parameters considered for
simulations are the same as depicted in Table 1. Scenario II
results emphasize the results of scenario I. It is found that in
a dense network with no mobility, PDR drops, Aggregate
Throughput tends to saturate early and E-2-E delay
increases significantly. In mobility scenarios, PDR is within
acceptable ranges at 70 packet/sec rate, the Aggregate
Throughput increases and E-2-E delay is within acceptable
ranges. Figure 5 depicts PDR against increasing traffic load
in a dense network.
Figure 5. PDR in a dense network
It is observed that, while nodes are mobile, the PDR is
almost the same. However, for data rates higher than 260
kb/s (65 packets/sec) higher mobility nodes PDR tends to
saturate while for less mobile nodes PDR tends to decrease.
Stationary nodes are the worst performer, result which can
be attributed to synchronized nodes states.
Figure 6 depicts Aggregate Throughput against
increasing traffic load in a dense network. It is observed
that, while nodes are mobile, the throughput is almost the
same. However, for data rates higher than 250 kb/s, higher
mobility nodes’ throughput tends to increase while for less
mobile nodes throughput tends to saturate.
Stationary nodes are the worst performer, which can be
attributed to synchronized nodes states.
Figure 6. Aggregate Throughput ina dense network
Figure 7 depicts E-2-E delay against increasing traffic
load in a dense network. It is observed that, while nodes are
mobile, E-2-E is almost the same and for data rates higher
than 250 kb/s all mobile nodes’ E-2-E tends to increase.
Stationary nodes are the worst performer, which is directly
linked to the fault tolerance function, in which, for every
sent packet, an ACK for reception is needed to consider a
packet is delivered. This increases the time when a packet is
considered successfully delivered.
Figure 7. End to End Delay in dense network
The ACK packet as well might get lost due to network
collisions and synchronized nodes states, which in turn will
cause the source node to resend the packet and wait for
another ACK. This significantly affects the E-2-E delay for
FTRP.
V. CONCLUSION
This paper introduced a novel reliable fault tolerant
routing protocol, FTRP, for wireless sensors networks.
FTRP creates a communication path between source and
destination nodes and forwards packets on that path.
FTRP performance has been evaluated through extensive
simulations using NS-3. Aggregate throughput, Packet
Delivery Ratio and End-to-End delay have been used as
performance metrics. In terms of Packet Delivery Ratio and
Aggregate throughput, FTRP is an excellent performer in all
mobility scenarios, whether the network is sparse or dense.
In stationary scenarios, FTRP performed well in sparse
networks; however, in dense networks, FTRP’s performance
had degraded, still remaining in an acceptable range. In
terms of End-to-end delay, FTRP is considered a good
performer in all mobility scenarios where the network is
sparse. In the sparse stationary scenario, FTRP is still
considered a good performer. However, in dense stationary
scenarios, FTRPs performance is considered as worst-case
behavior, which can be attributed to synchronized nodes
states that occur when nodes send similar messages at the
same time.
There are times when properly receiving a network
message carrying crucial information is more important than
other costs, such as, but not limited to, energy or delay. That
makes FTRP suitable for a wide range of WSNs application
domains, such as military applications by monitoring
soldiers’ biological data and supplies while on the battle
field as well as battle damage assessment. FTRP can also be
used in health applications by tracking and monitoring
doctors and patients inside a hospital and elderly assistance,
in addition to a wide range of geo-fencing, environmental
monitoring, resource monitoring, production lines
monitoring, agriculture and animals tracking.
FTRP should be avoided in dense stationary deployments
such as, but not limited to, scenarios where a high
application response is critical and life endangering, such as
biohazards detection or within intensive care units.
As future work, we plan to improve the performance of
FTRP in stationary scenarios. The FTRP performance was
evaluated through simulations. We plan to extend the FTRP
implementation in a WSN operating system to compare the
complexity of a real system against the simulation results.
The effect of varying the number of attempts to retransmit a
non-delivered packet (max retry count) should be
investigated. Furthermore, the energy efficiency has to be
evaluated for various FTRP operations.
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... However, since the multipath routing and opportunistic routing exploit a large number of nodes to improve packet delivery ratio, the decrease of participating nodes might degrade the performance of them. To improve reliability, reliable routing based on a learning algorithms [17,18] have been recently proposed. In these schemes, a source node selects an arbitrary node in every packet transmission to the destination according to the appraisals of each path, from the source node to the destination in the learning phase. ...
... In the learning algorithm [19], a node constructs the best routing path through machine learning. In the fault tolerant reliable protocol (FTRP) [17], the nodes are in learning mode and broadcast a status of not being in a sensor domain in preparation to join one. If the node has not yet joined a domain and if it is not a member of the cluster, the node receives an answer from the sink node to be a cluster head. ...
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