The Cost of Installing a 6TiSCH Schedule
Scheduling in an IEEE802.15.4e TSCH (6TiSCH) low-power wireless mesh network can be done in a centralized or distributed way. When using centralized scheduling, a scheduler computes a communication schedule, which then needs to be installed into the netwo
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Abstract. Scheduling in an IEEE802.15.4e TSCH (6TiSCH) low-power wireless mesh network can be done in a centralized or distributed way. When using centralized scheduling, a scheduler computes a communication schedule, which then needs to be installed into the network. This can be done using standards such CoAP and CoMI, or using a custom protocol such as OCARI. In this paper, we compute the number of messages installing and updating the schedule takes, using both approaches, on a realistic example scenario. The cost of using today’s standards is high. In some cases, a standards-based solution requires approximately 4 times more messages to be transmitted in the network, than when using a custom protocol. This paper makes three simple recommended changes to the standards which, when integrated, reduce the cost of a standardsbased solution by 18 % to 74 %. Since they are still being developed, these recommendations can easily be integrated into the standards. Keywords: Low-power wireless mesh networks TSCH · 6TiSCH · CoAP · CoMI · OCARI
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IEEE802.15.4e
Introduction
Industrial low-power wireless mesh network applications have strong requirements in terms of latency, energy efficiency and reliability. To cope with these requirements, the IEEE802.15.4e amendment [7] introduces the Time Slotted Channel Hopping (TSCH) mode. In a TSCH network, nodes are synchronized, and time is cut into timeslots, each typically 10 ms long. All communication is orchestrated by a communication schedule, which indicates to each node what to do in each slot: transmit, listen or sleep. This schedule can be built to enable collision-free communication, yielding predictable behavior, ultra-high reliability and years of battery lifetime. A schedule consists of a number of timeslots which continuously repeat over time. An example schedule is depicted in Fig. 2 with 9 timeslots and 3 logical channels. The index of a timeslot (the x-axis of the matrix in Fig. 2) is called slotOffset. The channelOffset represents the communication channel (the y-axis of the matrix in Fig. 2). Building the schedule consists in assigning a source node, a destination node and a channel to cells in the schedule. Installing the schedule into the network means indicating to each node the list of cells it is involved in, either c Springer International Publishing Switzerland 2016 N. Mitton et al. (Eds.): ADHOC-NOW 2016, LNCS 9724, pp. 17–31, 2016. DOI: 10.1007/978-3-319-40509-4 2
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Fig. 1. Logical network topology. chan. \ slot 0 1 2
0 4→1 3→1 5→2
1 2→1 10→3 6→4
2 4→1 3→1 2→1
3 2→1 11→3 12→4
4 4→1 3→1 9→2
5 2→1 10→3 5→4
6 4→1 3→1 8→2
7 2→1 7→3
8 3→1
Fig. 2. Schedule computed by MODESA for 12 nodes. chan. \ slot 0 1 2
0 4→1 3→1 2→1
1 2→1 10→3 5→4
2 4→1 3→1 9→2
3 2→1 11→3 6→4
4 4→1 3→1 8→2
5 2→1 12→4 10→3
6 4→1 3→1 13→2
7 2→1 5→4 7→3
8 4→1 3→1
Fig. 3. Updated schedule after node 13 is added. The black cells are the ones that differ from the schedule for 12 nodes.
as transmitter or as rec
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