Next, we present the results taken with 20 sensor nodes forming a multi-hop network. Table 2 shows the overall results taken for 4 test cases each running for 12 hours.
Resource Mean RTT
(Standard Deviation) # of bytesCON/ACK /r 331.32 ms (4.03 ms) 70/77 bytes /rt 61.16 ms (3.74 ms) 71/96 bytes OF0 MRHOF Mean RTT 549.11 ms 362.43 ms Std. Deviation 4216.26 ms 733.02 ms Retransmissions 46 15 Packet losses 0 0
Table 2: CoAP performance when using OF0 and MRHOF
Table 2 shows that using MRHOF leads to lower values for the mean RTT and that fewer packets are lost and retransmitted when compared to OF0.
Figure 2 shows one instance of a routing topology when using the OF0. This topology is created using the /rt details. The analysis of the routing topologies at different time instances shows higher numbers of single-hop connections to the RPL root node, when using MRHOF. Those higher numbers of single-hop connections lead to lower RTT values and less retransmission compared to the use of OF0.
Figure 2: Routing topology of multi-hop network (Objective function of RPL: OF0)
default routes to root
direct routes to neighbour nodes Table 1: Single-Hop Evaluation
Thomas Pötsch, M.Sc.
The Efficiency of Machine-to-Machine Protocols in Current and Future Mobile Networks for Logistical Processes E-mail: [email protected]
Country: Germany Start: 01.05.2012
Supervisor: Prof. Dr. rer. nat. Carmelita Görg Faculty: Physics / Electrical Engineering Research Group: Communication Networks References
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[2] Kuladinithi, K.; Bergmann, O.; Pötsch, T.; Becker, M.; Görg, C.: Im- plementation of CoAP and its Application in Transport Logistics. In: Proceedings of the Workshop of Extending the Internet to Low power and Lossy Networks (IP+SN 2011). Chicago U.S.A. 2011.
[3] Becker, M.; Pötsch, T.; Kuladinithi, K.; Görg, C.: Deployment of CoAP in Transport Logistics. In: Proceedings of the 36th IEEE Conference on Local Computer Networks (LCN). Bonn Germany 2011.
[4] Winter, T.; Thubert, P.; Brandt, A. et al.: IPv6 Routing Protocol for Low power and Lossy Networks. Internet-Draft (work in progress). URL: http://tools.ietf.org/ html/draft-ietf-roll-rpl-19, Date of access 29.08.2012.
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[7] Shelby, Z.; Hartke, K.; Bormann, C.; Frank, B.: Constrained Application Protocol (CoAP). Internet-Draft (work in progress). URL: http:// tools.ietf. org/ html/ draft-ietf-core-coap-11, Date of access 18.09.2012. [8] Fielding, R.: Architectural Styles and the Design of Network-based Soft-
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.
When using OF0, the number of two-hop connections exceeds the number of single-hop connections to the RPL root node. Since the OF0 algorithm considers only the individual link quality between a node and its neighbors (and their rank) to determine a parent, this algorithm tends to construct more two-hop connections than MRHOF. For example, Figure 2 shows a two-hop connection bet- ween node fec0::12 and the RPL root node (notified in the figure as
PppRouter) over node fec0::11 when using OF0, whereas the node
fec0::12 selects a direct connection to the RPL root node when using MRHOF. This means MRHOF sees that the direct connecti- vity to the PppRouter is better than using a 2 hop path over node fec0::11. Furthermore, the ETX metric, based on the individual link quality, varies frequently and child nodes with OF0 start to switch between different parents. This causes instability of routes resulting in higher packet losses in the network and triggering retransmis- sions at the CoAP layer. In contrast to OF0, MRHOF shows a more stable connectivity due to choosing a parent considering the quality of the complete path.
Conclusion
The main objective of the experiments was to evaluate the CoAP protocol in combination with the other lower layer IETF protocols which are planned to be deployed for M2M communication in logistical applications for supervision of the environmental condi- tions during transport. The resources of the CoAP protocol, which should be deployed in the Intelligent Container project, have been implemented and tested. The results of the experiments show that RPL performs better when using the MRHOF objective function instead of OF0. Furthermore, the results presented here show the feasibility of deploying CoAP, RPL (with MRHOF) and 6LoWPAN protocols together in the project, though care has to be taken to adapt the parameters of CoAP to the protocols/settings that have been chosen in the lower layers.
Acknowledgments
This research project (’The Intelligent Container’) is supported by the Federal Ministry of Education and Research, Germany, under reference number 01IA10001.
Kurztitel des Artikels
Production Engineering Collaborative Business in Enterprise Networks 49
Introduction >>> Today‘s business has rapidly changed and has
become more competitive. Companies more and more realized the effective role of supply networks to compete in the global market and networked economy. Since a supply network is considered as the collaboration between suppliers and an OEM with the objective to realize a product, the management of quality, cost and time is not the issue of one single organization any more [1].
Time plays an important role for every participant of a supply network because of the need to ensure internal efficiency, and because of external pressure of time based competition [2]. Quan- tities, delivery times, due dates, start times, etc., in the network may change at any time. Hence, the supply network is a dynamic system where these quantities are changing continually. Conse- quently, supply network systems must be updated accordingly so that decisions are based on dynamic information [3]. Nowadays, a company in the supply network can outsource different functions and signifies different degrees of commitment and integration between the company and the contractor. Outsourcing in the supply network creates a new source of uncertainty in delivery time and other quantities and qualities factors. This uncertainty has an impact on supply network performance by affecting delivery time reliability [4]. The importance of delivery time as a strategic weapon has been recognised in the arena of global competition [5] [6]. The strategic importance of delivery time uncertainty (DTU) has been recognised (introduced) by many researchers and practitioners, and it has emerged as a key competitive factor in a supply network. Thus, many manufacturers are adopting the use of delivery-time guarantees as part of their market positioning strategy [7].