## 1 Introduction  
In our daily lives, wireless home automation networks (WHANs) promise an important role, as the devices in common use can easily be connected with each other to enhance user comfort and to allow efficient home management. The potential of such wireless devices increases further as the connection to the Internet becomes possible for them. WHANs present a strong alternative to wired networks for home automation systems, and they have been a target of several standardization efforts [1,2]. Among these efforts, ZigBee has been considered as a strong candidate to be adopted for WHANs [3]. The ZigBee protocol stack has been the subject of several performance studies [4, 5, 6, 7], some of which focus on the use of ZigBee for WHANs [8,9]. Various detailed evaluations have been carried out for specific ZigBee layers [10, 11, 12]. On the other hand, ZigBee has been defined on the basis of components developed and widely studied by the research community. However, these components have been considered separately. In fact, a holistic evaluation of the ZigBee protocol stack, which is vital to observe the overall performance of the specification, is not publicly available in the literature. The generic ZigBee specification [13] defines a set of protocol mechanisms and parameters, the latter with default and allowed values. Moreover, for specific application types, ZigBee defines application profiles. One of these is the ZigBee Home Automation (HA) profile [14], which includes specific settings for WHAN scenarios. A trivial and mainly the common way of configuring the network parameters and mechanisms in a deployment is to keep their default settings from the specifications. Hence, it is crucial to understand the potential performance gains that can be achieved by tuning the settings of the protocol stack. Therefore, an evaluation of the default and the allowed settings defined in the ZigBee specification and HA profile is needed. In this paper, we study the end-to-end network performance of ZigBee WHANs following a holistic approach, which considers parameter settings and mechanism designs from different protocol stack layers. The goal behind these evaluations is to quantify possible performance improvements through the tuning of these settings and, also, to provide a future direction for the evolution of the ZigBee specifications. Performance evaluations are done: (i) for the default protocol stack configuration, which corresponds to using the default settings of the investigated parameters and mechanisms; (ii) for various alternative configurations that are also compliant with the ZigBee specifications; and (iii) for alternative settings that do not disrupt the ZigBee architecture, but are however not compliant with the specifications. For the study, we run various application scenarios that have been derived according to the ZigBee HA profile and Internet Engineering Task Force (IETF) specifications for home automation [1]. Experiments are carried out on a testbed of 57 nodes, where different network conditions are defined and evaluated. Specifically, we define different network topologies and consider the effect of the transmit power setting in these. We also define different types of traffic generation models along with varying corresponding loads. Moreover, we partially randomize the source and destination nodes for a given traffic load to devise the average behavior of the evaluated approaches. The investigated performance metrics are end-to-end packet delivery ratio (PDR), end-to-end delay and energy efficiency, which are three common and crucial network performance criteria for WHANs. These metrics are evaluated for various combinations of settings of key network parameters and mechanisms from different stack layers. Based on the findings from our experiments, we proposetwo new protocol stack configurations, namely the Recommended-Compliantconfiguration and the Recommended-Unrestricted configuration.