Abstract: This paper discusses the application of wireless sensor networks in road traffic. Based on the special characteristics of strip topology, a two-level routing protocol is proposed. The upper-level node sends routing requests to establish routes, while the lower-level nodes maintain local routes. The lower-level network is divided into clustered structures without cluster heads based on geographical location. Practical application shows that this routing protocol is simple, easy to implement, and has low overhead in strip topology. Keywords: banded topology, hierarchical network, no cluster head, wireless sensor network Abstract: The application of wireless sensor network in traffic is discussed. Based on the particularity of banded topology, the network is divided into two hierarchies. The higher hierarchical nodes send requests to find the routing, while the lower hierarchical nodes maintain the route table. The lower hierarchical network is separated into multiple clusters without a cluster head based on the node's location. The application results indicate that this routing protocol for banded topology is simple, easily implemented, and low-cost. Keywords: banded topology, hierarchical network, no cluster head, wireless sensor network 0 Introduction Wireless sensor network technology is currently at the forefront of computer network research and has the potential to develop into a new, huge, high-tech market. Today, academic research institutions funded by the US military, multinational corporations, and the world's largest IT suppliers have all included sensor networks in their R&D plans and are actively developing them. With the in-depth research and widespread application of wireless sensor networks, they will gradually penetrate into all aspects of human life. Wireless sensor networks (WSNs) hold immense promise for applications in intelligent transportation. In road traffic, SSNs exhibit a unique network topology: a strip-shaped topology. This paper, considering the characteristics of WSNs, studies easily implemented network routing protocols suitable for strip-shaped topologies. 1. Network Structure and Routing Analysis Existing routing technologies are limited and cannot be directly applied to sensor networks. Furthermore, networking and communication protocols designed for mobile Ad Hoc networks are generally unsuitable for sensor networks. One key reason is the different scalability requirements. For mobile Ad Hoc networks, scalability is not a significant issue compared to node mobility; however, sensor networks require support for large-scale networks, with weak or nonexistent node mobility, making extending network lifetime the primary concern. This dictates different optimization objectives for the two types of networks. Therefore, it is necessary to study sensor network routing protocols tailored to the characteristics of traffic information data collection and transmission in traffic demonstration projects, focusing on improving scalability, reducing power consumption, and adapting to changes in network topology. [1] As shown in Figure 1, the network of the strip topology is a tree-like chain structure. Using the concept of hierarchical network [1], the network is divided into two layers. The bottom layer is where sensor nodes collect environmental parameters, and the top layer is where the network converges or the management center of the local small network. The information of the local area is collected and transmitted to the higher layer network after data fusion. Due to the special nature of the strip network, the bottom layer network is divided into multiple clusters according to geographical location. The reasonable cluster structure is to divide the clusters according to the direction of the chain and not to specify the cluster head. Therefore, the bottom layer network can also be called a hierarchical network without a cluster head. Under normal circumstances, the nodes between different clusters do not communicate with each other. The information collected by all nodes is transmitted to the upper layer network through the nodes of the cluster. [align=center] Figure 1 Topology diagram of the strip structure[/align] As shown in Figure 1, the bottom layer is divided into three clusters: M, N, and P. The number of members in the cluster can be arbitrarily expanded in the strip area. The upper layer network node B can move at high speed [2]. Such a strip structure network has its own special characteristics in route establishment and maintenance. Since the bottom layer nodes do not need to move or move slowly within a certain range, the purpose is to transmit the collected information to the upper layer moving nodes. Therefore, the underlying network routing adopts a table-driven approach. The upper-layer network nodes establish the routes for the entire network, but the task of maintaining the routes is completed by the local nodes. 2. Routing Protocol for Strip Network Structure 2.1 Route Establishment The idea of ​​the route establishment process is that the upper-layer nodes broadcast route request packets (RREQ) throughout the entire network. After receiving the RREQ, the lower-layer nodes update their neighbor lists and routing tables, and then forward the RREQ in the same broadcast manner, but only forward RREQs within the same cluster. The local nodes establish routes within the same cluster, but the neighbor lists they maintain include neighbor information for the entire network to record network connectivity. Borrowing the RREQ packet format from the AODV routing protocol, the protocol RREQ format is defined as shown in Table 1 [3,4]. Table 1 RREQ Packet Format Wherein, Packet Type: Used to indicate that the data packet is an RREQ packet, a broadcast packet; Source Address: The address of the node that initiates the RREQ, which should be the address of the upper-layer network node; Hop Count: The number of hops traversed from the source node to the node that receives the RREQ packet; Broadcast ID: A sequence number maintained by the source node, used to uniquely identify the RREQ packet. The routing table format maintained by the local node is shown in Table 2. Table 2 Routing Table Format Wherein, Destination Node: Records the destination node address, which should be the address of the upper-layer network node; Route Status: Indicates whether the route is valid; Next Hop: The address of the next-hop node from the local node to the destination node; Route Expiration Time: The point in time when the route is no longer valid. According to the role of different nodes in the route establishment process, the route establishment process is as follows: 1) Upper-layer mobile node: Broadcasts RREQ to the entire network to establish a route; receives data packets carrying information from nodes within each cluster. See node B in Figure 1. The broadcast ID and source address sequence uniquely identify the RREQ, used to determine whether a duplicate RREQ packet has been received. 2) Nodes that can communicate directly with the mobile node: After receiving the RREQ, they first update the neighbor list, then write the next hop from the local routing table to B, and update the routing table. As shown in Figure 1, M3, N3, and P3 are directly connected to B at this time, and are the exit points for other nodes within the three clusters to access the upper-layer node. 3) Other nodes in the underlying network: M3, N3, and P3 receive B's RREQ, update their routing tables, and then forward the RREQ via broadcast. At this point, nodes in different clusters will receive the forwarded RREQ from each other and use this information to update their local neighbor lists. For example, in Figure 1, N4 receives the RREQ forwarded by N3, and may also receive RREQs forwarded by M3 and P3. N4 uses this information to update its neighbor list. However, N4 updates its routing table with the RREQ forwarded by members of the same cluster, setting the next hop record in the routing table to N3's address, and then discards other received packets of the same RREQ. It then forwards the RREQ again via broadcast. The advantage of this approach is that broadcasting the RREQ within the same cluster establishes a route and records all neighbor nodes of the local node, including those in other clusters, while effectively avoiding the "broadcast storm" problem caused by RREQ throughout the network. Other nodes process the RREQ in the same way until the RREQ packets reach the maximum network radius. The route establishment process is shown in the flowchart in Figure 2. [align=center]Figure 2 Local Node Route Establishment Process[/align] 2.2 Route Maintenance In a strip topology, the number of neighboring nodes within the same cluster is limited. In most cases, only the left and right nodes are its neighbors. If a node runs out of energy, nodes within the cluster may disconnect, affecting the robustness and scalability of the network. As shown in Figure 3, node N4 no longer functions as a sensor node for some reason. Nodes to the right of N4 cannot transmit data to the destination node B according to the previously discovered route. Therefore, some measures must be taken to maintain network connectivity. Nodes also have neighboring nodes in other clusters and can continue transmitting data packets with the help of nodes in other clusters. [align=center]Figure 3. Routing Maintenance During Network Failure[/align] Due to the special nature of the strip topology, after a data packet finds the direction of the destination node (i.e., the route), it is passed down sequentially in a "relay" manner. Therefore, a point-to-point acknowledgment method is used instead of an end-to-end acknowledgment method. This allows nodes to know the status of the next node. When sending a data packet, if no acknowledgment packet is received from the next-hop node, it is resent once. If there is still no acknowledgment, it is considered that the next hop has failed, and another neighbor node within the same cluster is immediately selected from the neighbor list as the next-hop node. The cluster node is then responsible for transmitting the data packet. In Figure 3, after the data packet to the right of N5 is forwarded to N5, since N5 has not received an acknowledgment from N4, N5 needs to select one from the neighbor list as the next hop. If there is another neighbor node within the cluster (such as N3, which is also a neighbor of N5), it is selected first (note to avoid routing loops). If not, another neighbor within the cluster is selected. In the figure, N5 selects M5. N5 successfully delivers the data packet to a member within cluster M, which is then responsible for forwarding the data packet to the destination node. At this point, the next-hop field of N5's routing table is changed to M5, and the route expiration time is the expiration time of the neighboring node M5, until N5 receives the RREQ updated route forwarded by a node in the same cluster again. Simultaneously, N5 promptly notifies the upper-layer network of N4's fault information. The route maintenance process is shown in Figure 4 flowchart. [align=center] Figure 4 Local Node Route Maintenance Flowchart[/align] 3 Application and Practice of Strip Topology in Road Traffic Wireless sensor networks can achieve reliable data transmission over long distances. Sensor nodes self-organize into networks, quickly forming a relatively stable network topology. Wireless sensor networks in road traffic are a typical application of strip networks. In road traffic, wireless sensor networks (WSNs) have the following functions: rapid and reliable transmission of sensor data to user terminals; topology changes with the location of upper-layer nodes; strong dynamic changes in the network due to the shutdown or addition of nodes; unique node identification, with upper-layer aggregation of sensor information; and the ability to reproduce the network topology changes at the user terminal based on information received from upper-layer network nodes. For example, sensor nodes can be deployed along roadsides to collect road surface information. The upper-layer network can consist of independent, rapidly moving car nodes, allowing cars to receive information from the lower-layer network as needed, thus providing timely and accurate information about the road conditions ahead and behind. Cars can then transmit this information to the traffic control center via a higher-layer network. In this project, the RF chip chosen is the CC1100, with a frequency of 433MHz and a maximum effective range of approximately 150 meters. The processor is the LPC2210, and the operating system is the publicly available μC/OS II. Furthermore, due to the specific application environment of the project, noise from vehicles has a significant impact, necessitating strict control over the correctness of data packets. Practical application shows that this solution has a simple and easy-to-implement routing protocol with low routing overhead. 4. Conclusion This paper proposes a hierarchical network management method to address the unique characteristics of the strip topology of wireless sensor networks. The lower-level network adopts a clustering structure without cluster heads, which facilitates route establishment and maintenance. Research on network routing protocols for strip topologies has greatly promoted the application of sensor networks in road traffic, changing the current single-method approach to road information collection. Through data fusion processing of diverse traffic information collected by sensor networks, the accuracy and reliability of road traffic information are improved. The authors' innovation lies in dividing the network into two levels based on its unique strip topology, proposing an easily implemented clustering routing protocol without cluster heads. This mechanism involves upper-level mobile nodes establishing routes and lower-level nodes maintaining them. The routing protocol demonstrates ease of implementation, low overhead, and easy maintenance in road traffic applications. References: [1] Zhang Yue. Improvement of LEACH protocol group head algorithm for wireless sensor networks [J]. Microcomputer Information, 2006, 10: 183-185 [2] Jiang M, Li J, and Tay Y C. Cluster-Based Routing Protocol (CBRP). draft-ietf-manet-cbrp-spec-01.tex, Internet Draft, IETF, Aug. 1999 [3] Charles Perkins, Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computer, ACM SIGCOMM' 94 Conference on Communications Architectures, Protocols and Applications, 1994 [4] Charles E Perkins, Elizabeth M Belding-Royer, Samir R Das. Ad Hoc On-Demand Distance Vector Routing. Draft-ietf-manet-aodv-13.txt, 2003