## 2 Relevant Work  
Due to the ever-increasing pace of IoT and WSN deployment in the real-world, many authors have proposed prioritization schemes for dealing with heterogeneous traffic. Some of the recent schemes are reviewed in this section. Traffic Priority-based Channel Access Technique (TP-CAT) is proposed for improving the delay for critical data in healthcare scenarios [24]. The scheme is developed over 802.15.6 and aims at reducing the transmission delay as well as user conflicts for the critical data. Separate algorithms for dealing with data of low and high thresholds have been developed. Furthermore, the protocols are made efficient through introducing a novel back-off scheme named as Random Overlapping Back-off value Avoidance (ROBA) which ensures selection of random value by the nodes during back-off process. Although the protocol could efficiently reduce access delay for the critical data, the interruption of ongoing transmission is not considered. Data Prioritization and Capacity Assignment (DPCA) analyses the capacity of each routing path and ensures delivering high priority data in the presence of congestion [25]. The novel contribution of the scheme is to analyze the capacity of routing path and network in conjunction with the priority of data. In case the network is congested, the data of higher priority is ensured to be transmitted to the sink, whereas that of lower priority is discarded. On the other hand, efficient resource usage is also guaranteed as in case the network is not totally consumed, the bandwidth could be assigned to the lower priority data instead of waiting for the high priority data. The drawbacks of this work include that the testbed implementation or simulation of the scheme is not provided, and preemption of ongoing transmission is not discussed. Traffic-Adaptive Priority-based MAC (TAP-MAC) proposed an adaptive super-frame structure in order to provide the nodes with regular and emergency data with optimal channel access [5]. The channel access period (CAP) has been divided into two categories, where CAP1 is reserved for the emergency and CAP2 can be accessed by both the emergency and normal traffic. TAP-MAC hence improves the chances for channel access for the emergency traffic as it would have shorter contention window values, however, since the CAP is partially shared with low priority traffic, there is a certain probability that the nodes with low priority data would win the channel even in the presence of emergency traffic. Moreover, no mechanism has been suggested to interrupt the ongoing transmission of normal traffic. Urg-MAC has been specifically developed for dealing with the urgency challenges in Wireless Multimedia Sensor Networks [15]. Various mechanisms for offering priority to the urgent traffic have been implemented at the application and link layers. The traffic is divided and subdivided into different categories of real-time and non-real-time and the mechanisms of traffic rate adjustment, contention window adaptation, duty-cycle reduction and multimedia message passing have been applied. Although the protocol integrated some of the famous prioritization schemes for offering priority to the urgent traffic, the interruption of ongoing transmission is still not possible. A priority guaranteed MAC protocol has been developed in [26] specifically for improving the network lifetime for Wireless Body Area Networks (WBAN). The protocol categorizes the traffic into different priorities and uses the modified frame structure of 802.15.4 to efficiently manage the transmission of prioritized traffic. Furthermore, the novel component of wakeup radio has also been used in this work. Although the protocol achieves energy efficiency and reduced delay for the prioritized traffic, no mechanism to interrupt the ongoing transmission on radio has been proposed. Also, the protocol design relies on the wakeup radio which is not embedded with majority of the sensor motes today.