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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.