Towards an Open Source Implementation of the IEEE 802.15.4 DSME Link Layer Maximilian K¨ ostler * , Florian Kauer † , Tobias L¨ ubkert ‡ and Volker Turau § Institute of Telematics, Hamburg University of Technology Am Schwarzenberg-Campus 3, 21073 Hamburg, Germany * maximilian.koestler@tuhh.de, † florian.kauer@tuhh.de, ‡ tobias.luebkert@tuhh.de, § turau@tuhh.de Abstract—Reliable wireless solutions for large-scale automa- tion are a major challenge today. The IEEE 802.15.4 standard forms the basis for many open and proprietary implementa- tions. To reflect current state-of-the-art techniques, the IEEE has amended standard 802.15.4 with new MAC-layers such as TSCH, which resembles WirelessHART, and the Deterministic and Synchronous Multi-Channel Extension (DSME). This paper introduces openDSME, our implementation of IEEE 802.15.4 DSME. DSME aims at preventing packet collisions through slot reservation in networks where conventional CSMA/CA is not reliable enough. In this document, we will outline core features of DSME and openDSME, and present details of our implemen- tation. Additionally, current research efforts on connected topics will be highlighted. Index Terms—Wireless Mesh Networks, IEEE 802.15.4 Link Layer, Reliability I. I NTRODUCTION Employing wireless networks in industrial environments helps to reduce costs and increases flexibility. Especially the installation costs can be reduced significantly [1]. The IEEE 802.15.4 standard has gained a lot of attention since it promises to allow for energy-efficient and low-cost wireless sensor and actuator networks. However, communication over a shared medium leads to the problem of message colli- sions when using contention based channel access methods such as Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA). Such collisions decrease the reliability of the network, especially in very large and dense networks [2]. Since reliability, however, is a fundamental requirement for industrial applications it is essential to provide a better coordination of the transceivers to decrease the number of packet colli- sions. The recent IEEE 802.15.4-2015 standard offers multiple possibilities to use Time Division Multiple Access (TDMA) schemes to access a range of channels. A promising extension presented in this standard is DSME that provides TDMA over multiple hops using a distributed slot allocation mechanism. We develop openDSME as an implementation of this standard including the associated services and interfaces 1 . This allows for the evaluation of DSME under realistic conditions. Instead of providing just another full-stack operating system for wire- less sensor networks, openDSME provides convenient adaption layers to plug it into existing stacks for seamless evaluation of DSME in existing hard- and software environments. These 1 The development of openDSME takes place at http://www.opendsme.org/ layers have already been created for OMNET++/INET [3] as well as for CometOS [4]. A. Limitations of Standard IEEE 802.15.4 In standard IEEE 802.15.4 [5], devices primarily commu- nicate via CSMA/CA. Additionally, communication with the network’s Personal Area Network (PAN) coordinator may be managed using previously reserved slots, called Guaranteed Time Slots (GTSs). In mesh networks, however, the utilisation of such slots would only be possible for a few devices situated in the vicinity of the PAN coordinator. In dense mesh networks with many devices, the available shared medium limits the maximum number of participants, since from a certain number of devices upwards, no further collision-free messages can be sent. For such networks, a bet- ter spatial reuse is required. IEEE 802.15.4 DSME attempts to offer a solution for these problems. It extends the use of GTSs to all devices in the network and opens multiple channels for slot allocation. Of course, this makes coordinating the slots and avoiding inconsistencies in the slot schedules much harder. Because of this, DSME provides its own handshake protocol to allow for distributed slot allocation. Since devices mainly broadcast messages during this procedure, nodes in the neighbourhood can overhear the handshake and will not use the respective slots for their communication. B. State of the Art Research on a combination of TDMA and Frequency Di- vision Multiple Access (FDMA) as proposed for DSME has already been performed in [6] and [7]. Researchers previously have pursued this concept of reservation-based communication in the context of IEEE 802.11. That work precedes the current DSME standard. [8] and [9] propose protocols that use a dedicated control channel to allocate the other channels for data transfer. Both protocols have been designed to implement IEEE 802.11 ad hoc networks. [9] requires two transceivers per device to allow parallel listening to the control channel while transmitting or receiving data. The Hop-Reservation Multiple Access (HRMA) protocol introduced in [8] only relies on a single transceiver but requires time synchronisation. Later protocols do not require a separate channel for control information [6], [7]. This change increases the maximum network throughput because every channel can be used for data transmission now. Both [6] and [7] have been based on