chapter 3 controlled epidemic routing...
TRANSCRIPT
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CHAPTER 3
CONTROLLED EPIDEMIC ROUTING WITH
MESSAGE FERRY
3.1 INTRODUCTION
There are a number of applications like disaster recovery scenarios,
remote village communications where nodes are disconnected. For delivering
packets in such scenarios, a number of protocols have been developed such as
Epidemic routing protocol, Message ferrying protocol etc., Epidemic routing
protocol delivers a packet only when connectivity occurs between destination
node and any one of the nodes which carries the source packet. But Message
Ferry needs more buffer space to carry the messages between nodes and also
needs direct connectivity (i.e., online collaboration) between nodes and the
ferry. If message ferry needs to cover a huge area and if nodes are mobile,
then the probability of delivering the packet is less. It also takes more time to
deliver the packets. Thus a new protocol namely, Controlled Epidemic
Routing with Message Ferry (CMF) is developed which combines both
Message Ferry and Epidemic routing Schemes.
In this proposed system, deployed area is divided into a number of
clusters. Each node must belong to any one of the clusters called node’s
native cluster. In this scheme, the ferry carries the messages for the
disconnected nodes which are located in the same/different cluster. But,
regular nodes carry messages only for the nodes which belong to its native
cluster. Whenever the source has a packet to send, it checks its route to a
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Message Ferry Regular Node
Ferry’s Route
Cluster 1
Cluster 2
Cluster 3
S
D
destination. If the route is found, then it delivers it. Otherwise, it delivers the
packet to the ferry. The ferry periodically checks if there is any route to a
destination is available for the packet stored in its buffer. If the ferry finds the
route, then it delivers the packet to its destination. If the ferry does not find a
route to a destination, it propagates the packet to the destination’s native
cluster using epidemic routing protocol whenever it visits that cluster.
Epidemic routing protocol is applied only to a single cluster, not to the entire
deployed area. This improves the probability of delivering the packet to the
correct destination with minimum resource utilization. Figures 3.1 to 3.5
highlight the operation of Controlled Epidemic routing with Message ferry.
Figure 3.1 Message delivery at time t0 using CMF
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Message Ferry Regular Node
Ferry’s Route
Cluster 1
Cluster 2
Cluster 3
S
D
S - Source D - Destination
message ready to transmit
route available to destination
deliver the packet to destination
deliver the packet to ferry
wait for ferry’s arrival
No
Yes
Figure 3.2 Message delivery at time t1 using CMF
Figure 3.3 Node operation in CMF
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broadcast periodic beacon
any node within comm. range
route exists for a buffered packet
deliver the packet to destination
remove delivered packet from the buffer
destination node’s native cluster
propagate the packet in the cluster
No
Yes
No
Yes
Yes
No
Figure 3.4 Ferry operation in CMF (delivering packet to the nodes)
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Figure 3.5 Ferry operation in CMF (receiving packet from the node)
broadcast periodic beacon
any packet for a ferry ?
ferry’s buffer full?
remove propagated packet from the buffer
remove least recently received packet
No
Yes
No
Yes
Yes
No
buffer space for new packet available?
buffer newly received packet
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3.2 ROUTE LENGTH AND CLUSTER CONNECTIVITY
Let us assume that speed of the message ferry is X meter/sec. Let
nMM ,...,1 be the set of n meeting points for the message ferry. Waiting time
at each meeting point iM is iW . If the distance between meeting point iM and
jM is ijd meters, then the route length of the message ferry is calculated as
1)1(342312 ............ nnn dddddd meters. The time taken to complete
one round, excluding waiting time by the ferry, is secXdt . The total time
taken by the ferry to complete one round, when considering waiting time at
each meeting point, is n
iiW
Xdt
11 . Once in the duration of 1t , the ferry
creates regular connectivity between partitions. There is no restriction on the
route length of the ferry.
3.3 RESULT ANALYSIS
Figures 3.6 to 3.15 show the performance improvement of CMF
over ER.
Figure 3.6 Number of nodes vs Delivery probability (CMF and ER)
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Figure 3.7 Mobility speed vs Delivery probability (CMF and ER)
Figure 3.8 Transmit speed vs Delivery probability (CMF and ER)
Figure 3.9 Transmission range vs Delivery probability (CMF and ER)
Speed (m/s)
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Figure 3.10 Buffer size vs Delivery probability (CMF and ER)
Figure 3.11 Number of messages vs Delivery probability (CMF and ER)
Figure 3.12 Mobility speed vs Average latency (CMF and ER)
Speed (m/s)
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Figure 3.13 Mobility speed vs Overhead ratio (CMF and ER)
Figure 3.14 Mobility speed vs Average buffer time (CMF and ER)
Figure 3.15 Mobility speed vs Average hop-count (CMF and ER)
Speed (m/s)
Speed (m/s)
Speed (m/s)
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Tables 3.1 to 3.3 illustrate that the improved performance of CMF
over ER for varying parameters like node density, message density, mobility
speed etc.
Table 3.1 Delivery rate of CMF
Varying Parameters Delivery rate in ER Delivery rate in CMF
No.of nodes (10 to 300) 6.51% to 32.25% 16.12% to 42.01%
Mobility Speed (0.1m/s to 40m/s) 14.41% to 28.83% 32.69% to 61.66%
No.of Messages (50 to 2000) 27.95% to 46% 30.4% to 50%
Tr. Range (10 to 500m) 4.16% to 30.76% 4.46% to 64.93%
Tr.Speed (50 to 300KBps) 24.67% to 29.42% 23.33% to 32.84%
Buffer Size (10 to 100MB) 11% to 37.44% 23.63% to 51.11%
Table 3.2 Average end-to-end latency of CMF
Varying ParametersEnd-to-End Latency
in ER End-to-End Latency
in CMF
No.of nodes (10 to 300) 2871.0198s to 5911.91s 4159.4938s to 6458.65s
Mobility Speed (0.1m/s to 40m/s)
916.016s to 5844.0608s 2147.0499s to 5984.9409s
No.of Messages (50 to 2000) 1649.6826s to 3413s 2532.33s to 4772.8545s
Tr. Range (10 to 500m) 511.0699s to 6414.9s 1439.1007s to 5682.27s
Tr.Speed (50 to 300KBps) 5857.4475s to 6790.3934s 5852.1 to 6889.60s
Buffer Size (10 to 100MB) 5342.1662s to 6011.0461s 2322.7296s to 2827.5984s
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Table 3.3 Average overhead ratio of CMF
Varying ParametersOverhead ratio
in ER Overhead ratio
in CMF
No.of nodes (10 to 300) 5.6364 to 899.5991 2.9633 to 866
Mobility Speed (0.1m/s to 40m/s) 57.6023 to 149.4433 32.3617 to 77.9963
No.of Messages (50 to 2000) 39.9349 to 89.7005 14.6782 to 68.8667
Tr. Range (10 to 500m) 32.2857 to 753.9266 8.8 to 204.034
Tr.Speed (50 to 300KBps) 28.9699 to 98.4475 25.6178 to 81.6495
Buffer Size (10 to 100MB) 52.2976 to 102.3475 67.3924 to 130.5157
Obviously, Message Ferry shows improvement and a better
performance than that of epidemic routing protocol. Epidemic suffers from an
inability to deliver messages to recipients that are in other disconnected
cluster. In this protocol, message is propagated only to the accessible hosts
until the TTL of the message expires. When TTL of the message expires, the
message will be dropped. One reason for message dropping is that the
recipient remains in the same disconnected cluster for a long duration of time
which is greater than that of TTL of the message. In the new scheme,
message is carried by Message Ferries and it creates regular connectivity
between clusters. Until the completion of the first visit of all the clusters after
receiving the message, the ferry did not find a route to a destination. So the
message is propagated to all the accessible hosts in the destination’s native
cluster. This increases the probability of delivering the packet from 10% to 34% and reduces overhead and average latency.
When the buffer size is small, the probability of message dropping
will be high and the number of messages exchanged also will be low. At the
other end, as buffer size increases, the number of message drops will be
reduced due to overflow. This will improve delivery ratio. In general, as the
buffer space increases, the data delivery ratio also increases. On the other
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hand, with a limited buffer space, new packets may replace the old
undelivered ones. This results in packet drops and low delivery ratio.
Epidemic routing protocol propagates the packet to all the accessible hosts.
Here all the hosts in the network are required to exchange the message for all
the remaining nodes in the network. Hence all the nodes need more buffer
space. If the number of nodes is increased, then the nodes need to have more
buffer space. In the new protocol, propagation of the message is done only
within the native cluster of the destination. Hence nodes in the new scheme
may require a small buffer space than that of epidemic routing protocol. But
for both the protocols, the delivery ratio depends on the buffer space for a
certain limit.
If the destination is in the same cluster as the source or if a route
exists between source and destination then the message is delivered more or
less immediately in both the protocols. Consider the situation that the
destination is in another cluster which is disconnected from the source cluster.
In this situation, whenever connectivity occurs due to mobility of the node
before the lifetime of the packet expires is only delivered in epidemic routing
protocol. If delivery is more important than any other metric, the node has to
wait for connectivity. This increases delay time. But in the new scheme, the
ferry makes connectivity between clusters periodically. As a result, this reduces delivery delay.
3.4 CONCLUSION
The results of this scheme clearly show that in all instances, CMF
improves delivery rate from 10% to 15% which is more than ER for varying
number of nodes from 10 to 300. Certainly, CMF improves delivery rate from
15% to 30% for varying mobility speed of the nodes. Further analysis
indicates that CMF’s relative performance is better than that of ER in terms of
delivery rate, average end-to-end latency and overhead ratio for varying
transmit speed, transmit range, number of messages and buffer space.