# Novel Extensions to Enhance Scalability and Reliability of the IEEE 802.15.4-DSME Protocol
## 2 Related Work  
Several works addressed the features and performance of the IEEE 802.15.4 standard. For instance, the works in [15; 16] address the real-time capabilities of IEEE 802.15.4, while in [5; 17] multichannel approaches to improve the protocol scalability were proposed. Recently, thanks to its ability to cope with timing and reliability requirements, the DSME protocol is gaining ground over the plain IEEE 802.15.4 for general industrial and commercial applications. Consequently, several researchers showed high interest in assessing the protocol and in devising solutions to further improve its performance. As far as interference mitigation is concerned, a DSME device in channel adaptation mode switches to another available channel if the received signal quality is less than a threshold value [18; 19]. The work in [19] considered a single interfering IEEE 802.11b (WiFi) source and evaluated the error frame rate introduced in a DSME network, for different traffic loads and power levels of the WiFi transmission. As the simulation results show, the frame error rate cannot exceed 25% in DSME, since a WiFi channel can overlap with at most four (out of 16) of the channels used in DSME. Hence, DSME can exploit the channels that are not affected by WiFi transmissions to communicate without interference. Other approaches in the literature, such as [20], propose a new superframe structure in order to mitigate the problems of WiFi and ZigBee interference. As far as throughput and energy consumption are concerned, the assessment in [18] shows that the DSME protocol with the CAP reduction enabled performs better than the plain IEEE 802.15.4 protocol. The works in [21; 22] introduce some enhancements for DSME to reduce both the energy consumption of the end nodes during the CAP and the network discovery time. In [23] the authors propose a novel DSME access scheme that divides the network nodes in multiple subsets, each one associated with a CAP slot in the beacon interval. During each CAP slot, only the nodes in the related subset perform channel contention. This way, the probability of collision between transmitting nodes is reduced and a lower number or retransmissions are required. In addition, an improved slot allocation scheme for CFP section is adopted. When a GTS transmission fails, the next CAP slot within the multi-superframe is used for retransmission. The proposed access scheme can reduce delay and power consumption. However, it is intended only for a star topology (not for a mesh topology). The work in [24] addresses the integration of RPL (IPv6 Routing Protocol for Low Power and Lossy Networks) and proposes Symphony for DSME, a dynamic GTS schedulingalgorithm that integrates RPL over DSME to provide a QoS efficient schedule for GTS placement. However, this approach implies that the network schedule is repeated periodically. Thus, every time a cyclic-scheduling allocation problem needs to be solved. In addition, the devices must implement the protocol stack proposed in [24]. A new DSME implementation, called openDSME, is presented in [25]. The authors also propose a method for traffic-aware and decentralized slot scheduling in order to realize scalable IWSNs. It is a versatile solution, as it does not require routing information and therefore it can be used with any routing protocol. The works in [26; 27] propose a scheduling algorithm, implemented using RPL integration and OpenDSME, which changes dynamically the multi-superframe structure as a function of the current number of network nodes, in order to reduce transmission delays. The work in [28] proposes a DSME-based distributed scheduling algorithm for mobility support that adaptively assigns GTSs based on the network traffic of each node, thus improving the network reliability and timeliness.