# Efficient Route Management Method for Mobile Nodes in 6 TiSCH Network
## 3 Efficient Route Management Method for Mobile Nodes in 6 TiSCH Network
### Mobile--Root Node Fixed-Path Construction Techniques  
Each node in a 6 TiSCH network allocates or removes cells using the 6 top protocol after synchronization. If the preferred parent node is changed because of the movement of the moving node, the cell with the previous parent node must be released, and the cell negotiation process with the preferred parent node must go through again. In this process, packet omission occurs, and latency occurs during the process of reallocating cells. In addition, the moving nodes move while connected to the network and send and receive sensor data with the stationary nodes, which requires the root node to request the data it needs. Therefore, to transfer packets from a moving node to a root node and minimize latency in response to the transmitted packets, we propose a moving-root node down traffic fixed-path construction technique. The path of mobile root node fixation is formed in three processes. First, when a new node participates in the network and sends a DAO message to the root node, the root node collects the MAC addresses of the nodes participating in the network. We discriminate between stationary and moving nodes by adding a moving flag from the DAO message. If a DAO message is received from the root node and this DAO message is not a moving node, the slot and channel offsets are stored in automatic cells using the hash value of the MAC address of the node that sent the DAO. This is the basis for assigning a moving node fixed path when forming a moving-root node fixed-path. The root node assigns a move-root node fixed-path initiation cell to a location that minimizes the impact on existing schedules based on the cell information it has. The root node stores shared and automatic cells, as shown in Figure 3. In Figure 3, a shared cell is a dedicated cell that can send/receive EB, DAO, or DIO control messages, and the alphabet of the automatic cell represents a node participating in the network that is stored in the root node. An automatic cell is a value stored by the root node to allocate the Tx cells of a moving node in a fixed path to the root node, and no communication occurs in that cell. If we receive a DAO message from the root node and determine from this DAO message that the node currently participating in the network is a moving node, we check the number of cells allocated to each slot offset, regardless of the channel offset. This allows us to assign a dedicated path with the shortest latency from the root node to the moving node. As shown in Figure 4, one cell is allocated for slot offset 1, one cell for slot offset 2, one cell for slot offset 3, one cell for slot offset 4, 0 cells for slot offset 5, one cell for slot offset 6, and 0 cells for slot offset 7. If this is expressed as an array starting with slot offset zero and up to slot offset length, it can be expressed as [1, 1, 1, 1, 1, 0, 1, 0, 0]. The slot offset of 0 was calculated to be 1. This assigns the Tx cell of the root node to the slot offset starting slot with the most consecutive zeros. This requires a move-root node fixed-path to build a packet transmission path that starts with the shortest delay from the root node to the moving node, because each node must be assigned to a continuous slot offset, minimizing the effect of the schedule between the existing stop nodes. Figure 4: Cell allocation process. Figure 3: Cell information stored on the root node. Mobile--allocating Tx cells from the root node in the root node fixed path results in the cell negotiation process of the 6 Top protocol from the root node to the moving node. Cells are allocated between root nodes A and B through the cell negotiation process of the 6 Top protocol. Node B allows Tx cells on node B to allocate data passed from node E at slot offset 8 where 1 is greater than the Rx cell slot offset of node E, 7, in order to have minimum latency.