Message delivery rate vs document size

Figure 4.5 shows a comparison between the numbers of documents received by both protocols with documents of size 64KB. The proposed CDDPP protocol proves to be more efficient in document delivery. As the number of documents created is more than the documents received by either protocol, it can be seen that CDDPP protocol received 91% of the documents. The greedy protocol however, is less efficient in this regard as it receives only 48%. In the beginning of the simulation the rate for documents received by either protocol is much lower, the reason is that it takes time for documents to disseminate in the network. The number of documents received by the greedy protocol (98%) is higher than CDDPP protocol (52%) in the beginning of the simulation, i.e. up to 3000 sec; since greedy protocol enthusiastically searches and stores more documents regardless of relativity to the interests, for that reason it is able to obtain more documents. Another point to be noted is the limited space available in each host‘s repository creates frequent updates as the space quickly fills up in the beginning of the simulation. When there is no space to store a newer document, the node looks for the least recently used document and removes

Table 4-1: Parameters used for simulation

Mobility model Random Waypoint Mobility model

Number of nodes 100

Number of interest profile (keywords) 32

Repository size 10 MB

File size used 32KB, 64KB, 128KB, 256KB, 512KB

Simulation time 15000 s

Area 1000x1000 m

Spot area 100x100m

Spot velocity 2m/s

Normal velocity 3m/s

82 it from the repository. This technique for making more space obviously has a disadvantage of removing some documents before these are even shared on the network.

As time progresses in the simulation, the document delivery rate of the greedy protocol decreases due to the frequent updates of the repository as can be seen in Figure 4.6. Due to these updates many documents in the repository need to be removed to make way for newer documents thus decreasing the availability of a shared document. At the end of the simulation (15000 simulation seconds) the documents delivered for CDDPP surpasses the greedy protocol. The document delivery ratio for the CDDPP protocol is 90.7% compared to only 47.8% in the greedy protocol. Graphs showing comparison of greedy protocol and CDDPP protocol with various document sizes can be found in appendix A.

Figure 4-6: Comparison of Average number of repository updates for Greedy protocol and CDDPP protocol with 64KB document size

0 5 10 15 20 25 30 35 40 45 50 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 N um be r o f u pd at es

Simulation time steps (1000xsec)

CDDPP vs Greedy (Avg.) Repository updates with 64KB doc_size

CDDPP Greedy

83 Figure 4.7 shows the comparison of delivery rates for both protocols based on document size. The size of document is set to 64, 128, 256 and 512 Kilo bytes. It can be seen, with all document sizes the delivery rate is much higher, i.e. more than 80% for the CDDPP protocol, but is lower for the greedy protocol. The size of documents affects the delivery rate for documents using the greedy version of the protocol. Figure 4.8 shows number of documents delivered over time with 128 KB document size. The graph shows the difference in packets sent versus packets received using CDDPP and Greedy protocol. It can be seen that the number of repository updates continuously increase with greedy protocol compared with CDDPP, which shows that CDDPP protocol reduces the overall amount of number of updates required. Further results with different document sizes can be found in appendix A.

4.4 Summary

Users of Mobile Social Networks share data only if they are interested, therefore there is a need to create a content driven communication protocol for disconnected MANETs. This chapter presented a simple CDDPP protocol for data sharing in disconnected MANETs. The protocol is light weight and does not rely on costly methods for constructing and maintaining complex routes. The ability of a node in MANET to store, carry and forward documents has been exploited to allow users to announce their interest profiles, documents and share them. A node therefore successfully announces its documents stored in repository and shares them with other users. Documents thus stored are carried to other locations and are shared with other users having similar interest profiles. Simulation results shown in the previous section prove that the CDDPP protocol is effective in propagating documents between senders and interested receivers thus successfully disseminating and forwarding messages in single-hop connections in the network.

CDDPP protocol does not however consider data propagation over a multi-hop topology. It can be seen from simulation results that greedy protocol is more efficient in delivering documents to a larger set of users in the start of the simulation and is handicapped due to the limited repository size and the frequent updates of the repository to accommodate new documents. Moreover after two users have negotiated interest profiles, respective document lists are broadcasted to all neighbouring users, thus creating a flood of traffic. This inefficiency in the protocol design reduces the overall performance. The next chapter

84 presents an Opportunistic Routing Protocol (ORP) that extends the CDDPP protocol by addressing node discovery and data sharing over multiple hops. ORP solves the problem of flooding by applying an adaptive approach of selective multicast messages to neighbouring nodes over a multihop topology while utilizing the store-carry-forward transmission paradigm.

Figure ‎4-7: Comparison of Packets delivered over time between CDDPP and Greedy protocols along with repository updates.

85

Figure ‎4-8: Comparison of Delivery Rate for CDDPP and Greedy protocols

0% 20% 40% 60% 80% 100% 64 128 256 512 De liv ery Rat e %age Document Size in KB CDDPP Greedy

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Chapter 5