A method for recovering from link disruption in an OLSR-based wireless ad hoc network

Abstract

The application relates to a wireless self-organizing network link interruption recovery method based on OLSR, which comprises the following steps: running the OLSR routing protocol in each node in a network; performing link interruption detection, wherein a node judges whether a link is interrupted according to feedback information of a MAC layer in a data transmission process; performing link state updating, wherein if the node detects the link interruption, corresponding link information in a local link set and corresponding neighbor information in a neighbor set are updated, and a routing table is updated; after the node completes the link state updating, a HELLO message is sent and a link interruption message is broadcasted; global circuit breaking synchronization, wherein other nodes in the network receive the link interruption message, and corresponding interruption link information in a topology information base is updated; and local area topology refreshing, wherein the nodes in a specified range send the HELLO message triggered by the link interruption message. Compared with the prior art, the application can realize link interruption detection and rapid recovery, improve the reaction of the OLSR protocol, and improve the end-to-end packet delivery rate.

Description

Technical Field

[0001] This invention relates to the field of wireless ad hoc network routing technology, and in particular to a method for recovering wireless ad hoc network link interruptions based on OLSR. Background Technology

[0002] A Wireless Ad-Hoc Network (MANET) is a dynamic, multi-hop, mobile peer-to-peer network consisting of several to dozens of nodes, utilizing wireless communication. In essence, a MANET is a decentralized, multi-hop wireless network and a complex distributed network system. Its development history can be traced back to the Packet Radio Network (PRNET) supported by the DoD (DoD) in the 1970s. A new wave of research into mobile Ad Hoc networks began in the mid-1970s. With the development and maturation of wireless networking technologies, its applications have become increasingly widespread. Because MANETs are easy to set up anytime, anywhere, offer flexible deployment, and are cost-effective, they have been widely used in large-area wireless sensing scenarios, disaster relief, and military operations.

[0003] In centralized wireless networks, mobile nodes connect to a fixed network through a fixed wireless access point. From a network layer perspective, these centralized networks are single-hop networks, and research focuses primarily on channel access control. However, in ad hoc networks, communication between non-adjacent nodes must be relayed through other nodes. Therefore, fast and accurate routing technology is a core issue currently facing ad hoc networks.

[0004] OLSR (Optimized Link State Routing) is an active routing protocol widely used in wireless ad hoc networks. The Internet Engineering Task Force (IETF) has developed and maintains its RFC documentation. OLSR has the following characteristics:

[0005] 1. In the OLSR protocol, each node periodically performs topology discovery, enabling it to grasp the network topology in real time;

[0006] 2. Because nodes have global routing tables, the status of end-to-end connections can be known immediately using OLSR;

[0007] Based on these characteristics, OLSR is particularly suitable for network application scenarios that require short transmission latency (such as most UAV combat reconnaissance information reporting applications).

[0008] However, due to the mobility of nodes and the instability of the channel environment (wireless links are affected by distance, interference, and many environmental factors), topology changes in wireless ad hoc networks are quite frequent. This undoubtedly poses a challenge to end-to-end routing. Even if the OLSR performs active topology detection and maintenance, there will still be situations where the topology information held by nodes is inconsistent with the actual topology information. When end-to-end data transmission encounters a sudden link interruption, the OLSR has difficulty responding in time, which will cause misrouting and packet loss, resulting in end-to-end transmission interruption, reduced end-to-end packet delivery rate, and thus affecting the overall network performance. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a wireless ad hoc network link interruption recovery method based on OLSR, which can automatically detect and quickly recover link interruptions, improve the operating performance of OLSR routing protocol in networks with dynamically changing topologies, and increase end-to-end packet delivery rate.

[0010] The objective of this invention can be achieved through the following technical solution: a method for recovering from a link interruption in a wireless ad hoc network based on OLSR, comprising the following steps:

[0011] S1. Run the OLSR routing protocol on each node in the network;

[0012] S2. Perform link interruption detection. During data transmission, the node determines whether the link is interrupted based on feedback information from the MAC layer.

[0013] S3. Perform link state update. If the node detects a link interruption, it updates the corresponding link information in the local link set and the corresponding neighbor information in the neighbor set, and updates the routing table.

[0014] S4. After the node completes the link status update, it sends a HELLO message and broadcasts a link interruption message.

[0015] S5. Global Disconnect Synchronization: When other nodes in the network receive a link interruption message, they update the corresponding interrupted link information in the topology information database.

[0016] S6, Local Topology Refresh, triggers nodes within a specified range to send HELLO messages via link interruption messages.

[0017] Furthermore, the specific process of the node running the OLSR routing protocol in step S1 is as follows: the node sends a HELLO message once at a first preset time interval to discover neighbors, and sends a TC message once at a second preset time interval to share topology information with the entire network. The node maintains a global topology information database, including link sets, neighbor sets, 2-hop neighbor sets, and remote topology sets. At the same time, the node also maintains an MPR node set and an MPR selector set to realize the MPR mechanism of OLSR.

[0018] Furthermore, the feedback information of the MAC layer in step S2 is as follows: the MAC layer will send back an ACK control frame for each transmission of each unicast packet. If no ACK is received within the set reception time, the current data packet will be retransmitted. When the retransmission reaches the preset maximum number of times, the MAC layer will discard the current packet and send back the transmission failure and a complete copy of the current data packet to the upper layer before the packet is lost.

[0019] Furthermore, in step S2, if a node receives feedback information indicating a transmission failure from the MAC layer, it is determined that the link has been interrupted.

[0020] Furthermore, step S3 specifically includes the following steps:

[0021] S31. When a node receives feedback on transmission failure and information about the current transmission failure data packet from the MAC layer, it extracts the IP addresses at both ends of the interrupted link from the IP layer header in the data packet and searches for the corresponding link information in the link set in the OLSR.

[0022] S32. If the corresponding link information cannot be found or the link information shows an asymmetric status, it indicates that the current link has been marked as unavailable, and the current process ends.

[0023] Otherwise, proceed to step S33;

[0024] S33. Update the corresponding link information in the local link set and the corresponding neighbor information in the neighbor set, and update the routing table.

[0025] Further, the specific process of step S33 is as follows: change the current link information status to asymmetric, change the status of the corresponding neighbor information in the neighbor set to asymmetric neighbor, delete the corresponding 2-hop neighbor information, update the MPR node set, and update the routing table.

[0026] Further, the link breakage message in step S4 specifically refers to: defining a new message type—Link Breakage (LB) message—on the original OLSR message, with a type value of 5. The LB message header adopts the same format as other OLSR messages, including an 8-bit message type field, an 8-bit validity time (Vtime) field, a 16-bit message size field, a 32-bit originator address field, an 8-bit remaining hops (TTL) field, an 8-bit hop count field, and a 16-bit message sequence number field.

[0027] The LB message modifies the Vtime field to the TU_HOP field to indicate the scope of the local topology refresh. The LB message content includes a 16-bit ANSN field, a 32-bit IP address field FROM, and a 32-bit IP address field TO. FROM and TO form a directed edge, indicating interrupted link information. The LB message uses the same ANSN field as the TC message to compare which of two LB messages or TC messages sent from the same node represents the latest node state. The ANSN is incremented when the node's MPR selector set changes.

[0028] Further, the specific process of step S5 is as follows: after receiving the LB message, the node extracts the interrupted link information, i.e. (FROM, TO), finds the entry with neighbor address FROM and 2-hop neighbor address TO from the 2-hop neighbor set, deletes it, recalculates MPR, and updates the MPR node set; finds the entry corresponding to (FROM, TO) from the remote topology set and deletes it directly; and updates the routing table.

[0029] Further, the specific process of step S6 is as follows: after receiving the LB message and completing step S5, the node determines whether to send a HELLO message by comparing the value of the Hop Count field with the size of the TU_HOP field.

[0030] Furthermore, in step S6, if the value of the Hop Count field is less than or equal to the TU_HOP field, a HELLO message is sent.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] I. This invention enables link interruption detection and rapid recovery by running the OLSR routing protocol on each node in the network and utilizing MAC layer feedback information during data transmission. When a link interruption is detected, the corresponding link information in the local link set and the corresponding neighbor information in the neighbor set are updated, the routing table is updated, and after the node completes the link state update, a HELLO message is sent and a link interruption message is broadcast. This achieves link interruption detection and rapid recovery. Utilizing MAC layer feedback for link interruption detection improves the responsiveness of the OLSR protocol, allowing for faster responses to link interruptions and updates to the routing table. Global circuit breaker synchronization via link interruption messages prompts all nodes in the network to update routes for interrupted links, quickly restoring transmission and effectively suppressing loops.

[0033] Second, this invention designs the MAC layer to send an ACK control frame for each unicast packet transmission. If no ACK is received within a specified time, the current data packet will be retransmitted. When the retransmission reaches the preset maximum number of times, the MAC layer will discard the current packet. Before packet loss, it will send a transmission failure report and a complete copy of the current data packet to the upper layer. Based on the feedback information from the MAC layer, nodes can perform link interruption detection in a timely and accurate manner, which helps improve the timely response performance of the OLSR, avoids end-to-end transmission interruptions caused by misrouting and packet loss, and improves the end-to-end packet delivery rate.

[0034] Third, this invention employs a custom link interruption message (i.e., LB message) for global short-circuit synchronization. This link interruption message is a new message type defined on top of the original OLSR message. The LB message header uses the same format as other OLSR messages, and the Vtime field is modified to a TU_HOP field to indicate the scope of local topology refresh. The LB message content includes a 16-bit ANSN field, a 32-bit IP address field FROM, and a 32-bit IP address field TO. FROM and TO form a directed edge representing the interrupted link information. In addition, the LB message uses the same ANSN field as the TC message to compare which of two LB messages or TC messages sent from the same node represents the latest node state. The ANSN is incremented when the node's MPR selector set changes. Based on the above custom link interruption message, global short-circuit synchronization can prompt all nodes in the network to update routes for interrupted links, quickly restore transmission, and effectively suppress loops.

[0035] Fourth, the present invention is designed to perform local topology refresh after global disconnection synchronization update. Through local refresh of link interruption, local topology awareness and reconstruction can be further enhanced, which is conducive to improving the overall network performance. Attached Figure Description

[0036] Figure 1 This is a flowchart of the method of the present invention;

[0037] Figure 2 This is a flowchart of the link state update process in this invention;

[0038] Figure 3 This is a schematic diagram of the link interruption message structure in the embodiment;

[0039] Figure 4 This is a schematic diagram of a link interruption simulation scenario in the embodiment. Detailed Implementation

[0040] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0041] Example

[0042] like Figure 1 As shown, a method for recovering from a link interruption in a wireless ad hoc network based on OLSR includes the following steps:

[0043] (1) Each node runs the OLSR routing protocol. In this embodiment, the node sends a HELLO message every 2 seconds to discover neighbors and a TC message every 5 seconds to share topology information with the entire network. The node maintains a global topology information database, including a link set, a neighbor set, a 2-hop neighbor set, and a remote topology set. At the same time, the node also maintains an MPR node set and an MPR selector set, thereby realizing the MPR mechanism of OLSR.

[0044] (2) Link interruption detection: During data transmission, the node determines whether the link is interrupted based on the feedback information from the MAC layer. The feedback information from the MAC layer is based on the following process: The MAC layer sends back an ACK control frame for each transmission of each unicast packet. If no ACK is received within a specified time, the current data packet will be retransmitted. When the retransmission reaches the preset maximum number of times, the MAC layer will discard the current packet. Before the packet is lost, the MAC layer will send back the transmission failure and a complete copy of the current data packet to the upper layer. When the node receives the transmission failure information from the MAC layer, it determines that a link interruption has occurred.

[0045] (3) Link state update: When a node detects a link interruption, it updates the corresponding link information in the local link set and the corresponding neighbor information in the neighbor set, and updates the routing table. The process is as follows: Figure 2 As shown:

[0046] When a node receives feedback of transmission failure and information about the current failed data packet from the MAC layer, it extracts the IP addresses at both ends of the interrupted link from the IP layer header of the data packet. Then, it searches for the corresponding link information in the link set in the OLSR. If the corresponding link information is not found or the link information shows an asymmetric status, it means that the current link has been marked as unavailable, and no further steps are needed. Otherwise, it changes the current link information status to asymmetric, changes the status of the corresponding neighbor information in the neighbor set to asymmetric neighbor, and if the neighbor is the current node's MPR selector, it needs to add the current node's ANSN. Then, it deletes the corresponding 2-hop neighbor information, updates the MPR node set, and updates the routing table.

[0047] (4) After the node completes the link state update, it sends a HELLO message and broadcasts a link interruption message. The structure of the link interruption message is as follows: Figure 3 As shown, a new message type—LinkBreakage (LB) message—is defined on top of the original OLSR message, with a type value of 5. The LB message header uses the same format as other OLSR messages, including an 8-bit message type field, an 8-bit validity time (Vtime) field, a 16-bit message size field, a 32-bit originator address field, an 8-bit time-to-live (TTL) field, an 8-bit hop count (HopCount) field, and a 16-bit message sequence number field. The LB message modifies the Vtime field to a TU_HOP field to indicate the scope of the local topology refresh. The LB message content includes a 16-bit ANSN field, a 32-bit IP address field FROM, and a 32-bit IP address field TO. FROM and TO form a directed edge representing the broken link information. The LB message uses the same ANSN field as the TC message to compare which of two LB messages or TC messages sent from the same node represents the latest node state. The ANSN is incremented when the node's MPR selector set changes.

[0048] In this embodiment, the message type field of the LB message is set to 5, the TU_HOP field is set to 2, the message size field is set to the total number of bytes of the message, the TTL field is set to 255, the Hop Count field is set to the initial value of 0, the message sequence number field is set to the current message sequence number value of the OLSR protocol, the ANSN field is set to the current ANSN value of the OLSR protocol, and the FROM and TO fields are set to the IP addresses of both ends of the currently interrupted link.

[0049] (5) Global Disconnect Synchronization: When other nodes in the network receive a link interruption message, they update the corresponding interrupted link information in the topology information database. Specifically, after receiving the LB message, a node first compares the ANSN in the message with the ANSNs of all entries from the LB message sending node in the remote topology set. If the ANSN of the current message is greater than the ANSNs of all remote topology entries corresponding to the same sending node, it indicates that the message corresponds to the latest node status; otherwise, processing of the message will stop. Next, the interrupted link information (FROM, TO) in the LB message is extracted. Entries with neighbor addresses of FROM and 2-hop neighbor addresses of TO are found in the 2-hop neighbor set, deleted, and MPR recalculated to update the MPR node set. Entries corresponding to (FROM, TO) are found in the remote topology set and deleted directly. The routing table is then updated.

[0050] (6) Local topology refresh, triggering nodes within a specified range to send HELLO messages through link interruption messages: After completing step (5), the nodes compare the value of the Hop Count field with the size of the TU_HOP field. If the former is less than or equal to the latter, a HELLO message is sent.

[0051] To verify the effectiveness of this solution, this embodiment is designed as follows: Figure 4 The scenario shown was simulated, in which 100 nodes move within a 6000m*6000m area. The direction of the nodes' movement speed changes randomly, and the speed ranges from 0-50m / s. Additionally, 20% of the nodes are randomly damaged. Figure 4 (Red node in the middle), source node and destination node ( Figure 4 Communication between the blue nodes in the middle is carried out using a constant rate service flow. NS3 is used for simulation and end-to-end packet delivery rate performance is tested. The packet delivery rate is defined as the ratio of the number of data packets received by the application layer at the receiving end of the service flow to the number of data packets sent by the application layer at the sending end of the service flow. The simulation parameters are shown in Table 1.

[0052] Table 1

[0053] parameter numerical values Simulation duration 60 seconds Number of experiments 10 MAC layer protocol 802.11b, CSMA / CA Physical layer rate 11Mbps Maximum communication distance between nodes 1 (km) HELLO message interval 2 seconds TC message interval 5 seconds Application layer packet size 512 bytes Application layer data rate 500kbps Application startup time 10 (seconds) Node failure time 10-60 random (seconds) Total number of nodes 100 Node movement range 6000m*6000m Node movement speed (average) 25 (m / s) Node failure rate 20％

[0054] The test results show that when using OLSR for routing alone, the end-to-end packet delivery rate is 43.75%. After adopting the link interruption recovery method designed in this scheme, the end-to-end packet delivery rate is increased to 63.29%.

[0055] Experimental results show that the present invention can effectively improve the end-to-end packet delivery rate performance of the OLSR routing protocol in networks with dynamically changing topologies.

Claims

1. A method for recovering a wireless ad hoc network link interruption based on OLSR, characterized in that, Includes the following steps: S1. Run the OLSR routing protocol on each node in the network; S2. Perform link interruption detection. During data transmission, the node determines whether the link is interrupted based on feedback information from the MAC layer. S3. Perform link state update. If the node detects a link interruption, it updates the corresponding link information in the local link set and the corresponding neighbor information in the neighbor set, and updates the routing table. S4. After the node completes the link status update, it sends a HELLO message and broadcasts a link interruption message. S5. Global Disconnect Synchronization: When other nodes in the network receive a link interruption message, they update the corresponding interrupted link information in the topology information database. S6, Local Topology Refresh, triggers nodes within a specified range to send HELLO messages via link interruption messages; The feedback information of the MAC layer in S2 is as follows: the MAC layer will send back an ACK control frame for each transmission of each unicast packet. If no ACK is received within the set reception time, the current data packet will be retransmitted. When the retransmission reaches the preset maximum number of times, the MAC layer will discard the current packet and send back the transmission failure and a complete copy of the current data packet to the upper layer before the packet is lost. The link interruption message in S4 is specifically defined as follows: a new message type is defined on the original OLSR message - link interruption message, i.e. LB message, with a type value of 5. The LB message header adopts the same format as other OLSR messages, including an 8-bit message type field, an 8-bit validity time field, a 16-bit message size field, a 32-bit node master address field, an 8-bit remaining hop number field, an 8-bit hop count field, and a 16-bit message sequence number field. The LB message modifies the Vtime field to the TU_HOP field to indicate the scope of the local topology refresh. The LB message content includes a 16-bit ANSN field, a 32-bit IP address field FROM, and a 32-bit IP address field TO. FROM and TO form a directed edge, indicating interrupted link information. The LB message uses the same ANSN field as the TC message to compare which of two LB messages or TC messages sent from the same node represents the latest node state. The ANSN is incremented when the node's MPR selector set changes.

2. The method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 1, characterized in that, The specific process of the node running the OLSR routing protocol in step S1 is as follows: the node sends a HELLO message once at a first preset time interval to discover neighbors, and sends a TC message once at a second preset time interval to share topology information with the whole network. The node maintains a global topology information database, including link set, neighbor set, 2-hop neighbor set and remote topology set. At the same time, the node also maintains MPR node set and MPR selector set to realize the MPR mechanism of OLSR.

3. The method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 1, characterized in that, In step S2, if a node receives feedback information indicating a transmission failure from the MAC layer, it is determined that the link has been interrupted.

4. The method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 3, characterized in that, Step S3 specifically includes the following steps: S31. When a node receives feedback on transmission failure and information about the current transmission failure data packet from the MAC layer, it extracts the IP addresses at both ends of the interrupted link from the IP layer header in the data packet and searches for the corresponding link information in the link set in the OLSR. S32. If the corresponding link information cannot be found or the link information shows an asymmetric status, it indicates that the current link has been marked as unavailable, and the current process ends. Otherwise, proceed to step S33; S33. Update the corresponding link information in the local link set and the corresponding neighbor information in the neighbor set, and update the routing table.

5. A method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 4, characterized in that, The specific process of step S33 is as follows: change the current link information status to asymmetric, change the status of the corresponding neighbor information in the neighbor set to asymmetric neighbor, delete the corresponding 2-hop neighbor information, update the MPR node set, and update the routing table.

6. The method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 1, characterized in that, The specific process of step S5 is as follows: After receiving the LB message, the node extracts the interrupted link information, i.e. (FROM, TO), finds the entry with neighbor address FROM and 2-hop neighbor address TO from the 2-hop neighbor set, deletes it, recalculates MPR, and updates the MPR node set; finds the entry corresponding to (FROM, TO) from the remote topology set and deletes it directly; and updates the routing table.

7. A method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 6, characterized in that, The specific process of step S6 is as follows: After receiving the LB message and completing step S5, the node compares the value of the Hop Count field with the size of the TU_HOP field to determine whether to send a HELLO message.

8. A method for recovering a wireless ad hoc network link interruption based on OLSR according to claim 7, characterized in that, In step S6, if the value of the Hop Count field is less than or equal to the TU_HOP field, a HELLO message is sent.

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