## 1 Introduction  
Wireless sensor networks (WSNs) are considered to be appealing event-based systems that achieve both densely deployed sensor nodes and the perception of a certain physical sensation. The key objective is to consistently sense the event features while utilizing minimal energy resources, processing and storage capabilities [1, 2]. To achieve this objective, a substantial amount of research has been conducted to develop the cooperative networking protocols needed to accomplish the necessary communication while achieving maximum energy efficiency. Most of the communication protocols for WSNs are individually designed and developed for different layers, _i.e._, the physical, medium access control, network and transport layers. These communication protocols have achieved significant improvements in terms of the different parameters correlated with each of the individual layers. However, these protocols experience several challenges when combined for multiple layers; these challenges include additional energy consumption, QoS, mobility, scalability, uniformity, data redundancy, congestion, lack of robustness, reliability and insufficient coverage. Furthermore, the limited battery life and extreme operating conditions can cause node failure [3], which wastes additional energy [4]. Considering these challenges faced by WSNs, a multi-layered network design, _i.e._, a cross-layer paradigm, is considered to be the most promising substitute and has attracted increasing interest from the research community in recent years. There are a few cross-layer protocols for maintaining high standards of communication, particularly coverage, but the issues of high energy consumption and improving the QoS have not been properly resolved [4]. With the proper placement of a mobile infrastructure, a wide area can be covered compared with an infrastructure-based network deploying the same number of sensors [5]. However, the key services' energy efficiency and the QoS provision are hurdles for robust WSNs. Detailed studies in [6, 7, 8] show that the cross-layered approaches could result in substantial savings in terms of energy efficiency. As a result, several cross-layered approaches have been designed and implemented [9, 10, 11, 12, 13]. A review of these approaches reveals that they either provide logical and analytical results without any proper communication protocol design or accomplish cross-layer support only within a restricted scope, e.g., MAC and routing layers. There is still much to be gained by reconsidering the features and functionalities of the protocol layers in an integrated manner to introduce communication paradigms for efficient and reliable communication while saving energy and improving the QoS provisioning in WSNs. To handle these issues, this paper introduces modular energy-efficient and robust paradigms that improve the energy efficiency and QoS provisioning. These paradigms involve the O-MAC protocol with the PT model to build a hybrid approach by incorporating the medium access control with the network. The O-MAC protocol involves the features of time division multiple access (TDMA) and carrier sense multiple access (CSMA). The O-MAC maintains the trade-off between energy efficiency and time management by introducing an optimized data frame format model. The optimized data frame format (ODFF) replaces the existing IEEE 802.15.4 data frame format model by modifying the existingfeatures and incorporating new features, e.g., a reduction in the size of the existing preamble, which helps to save energy and improve the QoS parameters. The new features also include the anycast addressing methodology and automatic buffering because the anycast methodology helps to select the particular nodes in the 1-hop neighborhood to avoid the overhearing problem and thus reduces the additional energy consumed in the 1-hop neighborhood; furthermore, automatic buffering helps to reduce the data storage wait time.