## 2 Background  
The IPv6 over the TSCH mode of IEEE 802.15.4e (6 TiSCH) protocol has been developed to integrate the IPv6 infrastructure with the underlying low-power IEEE 802.15.4e TSCH network [5, 6]. It constructs and manages schedules based on TSCH network requirements, ensuring standardized communication between devices. For industrial Low-Power and Lossy Networks (LLNs) operating in a critical environment, it guarantees reliable, secured [7], and deterministic operations [8]. The 6 TiSCH uses an existing IPv6 upper stack that includes an IPv6 over Low-Power Wireless Personal Area Networks (6 LoWPAN) header compression layer, IPv6 Routing Protocol for LLNs (RPL), and Constrained Application Protocol (CoAP) lightweight application layer as shown in Figure 2.  
The wide deployment in industrial LLNs consists of a set of routers that are interconnected with resource-constrained devices. To meet routing requirements in such network scenarios, the RPL routing protocol has been developed [9]. It organizes the network into a Destination Oriented Directed Acyclic Graph (DODAG) with several source nodes and a root node. The LLN may consist of multiple DODAGs created for a network and may run multiple instances of RPL concurrently. It builds a DODAG network route by keeping less signal overhead and specifies an objective function that enables the QoS requirements for specific applications. RPL isolates routing optimization from packet processing and forwarding operations. Routing optimization aims to achieve bounded latency while satisfying given constraints. In RPL, each node selects its parent node based on the optimized path to ensure root reachability [10]. Figure 2: Layered architecture of the 6 TiSCH protocol stack, integrating the IEEE 802.15.4e TSCH MAC layer with IPv6 protocols like 6 LoWPAN, RPL, and CoAP. 6 TiSCH defines the Operation Sublayer (6 top), which enables distributed scheduling by negotiating the required number of cells between neighbors. It adds and/or removes cells within a slotframe as per traffic and topology needs. Additionally, it monitors the performance of each cell and relocates underperforming cells as needed. The 6P requests and responses are sent via Information Elements (IEs) that are encapsulated within the 6P packet. When a node sends an ADD REQUEST, it includes a list of required cells by specifying their [_timeOffset_, _channelOffset_] coordinates and the desired cell count. Upon receiving the ADD REQUEST, the neighbor node selects appropriate cells and replies with a RESPONSE containing the selected cell list. Cell negotiation is managed using either a 2-step or 3-step transaction. In the 2-step process, the sender directly selects cells for addition, deletion, or relocation. In the 3-step process, the receiver responds with a list of selected cells after evaluating the request. Any node can initiate a DELETE request to remove an allocated cell from the schedule. Various 6 TiSCH Scheduling Functions (SFs) are being developed to ensure deterministic operations in dynamic IIoT networks. These are broadly categorized based on their cell allocation approaches, which include centralized, distributed, and autonomous. The centralized schedulers rely on a single central unit to generate and manage the schedule for the entire network. This approach is well-suited for networks with fixed traffic patterns and low node density. However, the centralized mechanism becomes ineffective in dynamic network topologies with high node density and unstable data traffic [11]. The distributed scheduling approach utilizes cell negotiation to allocate cells between node pairs based on traffic and topology requirements. Both centralized and distributed schedulers experience signal overhead in dynamic networks. In contrast, the autonomous scheduling approach is becoming more attractive due to its low signal overhead and improved QoS [12]. It avoids both cell negotiation and centralized schedule management; instead, it uses the node's MAC addresses to allocate cells within a slotframe.