Routing Protocol Analysis for Wireless Mesh Networks

The Wireless Mesh Network is a multi-point-to-Multi-Point Wireless Network developed from the Ad Hoc network. Currently, the routing protocols of the wireless mesh network refer to Ad Hocl to a large extent ~ The typical routing protocol directly applies the Ad Hoc routing protocol to the wireless mesh network environment. This section describes typical wireless mesh network protocols and analyzes representative protocols.

I. Routing Protocol for Wireless Mesh Networks

Traditional routing protocols are designed for wired networks and are not suitable for wireless mesh networks. Because the traditional routing protocols cannot handle the rapid changes of common topology and link quality in the wireless mesh network environment. Wireless Mesh networks have some notable features, such as high dynamic performance, intelligence, Optimal Path Selection for end-to-end, multi-hop performance, limited bandwidth and insufficient computing capability. There are two reasons for the high dynamic nature of the Wireless Mesh Network: first, the vro itself may move and the network topology may change rapidly. Second, even if the router itself does not move, the quality of the radio link may change rapidly due to interference, geography, environment, and other factors.

From these features, we can know that a complete wireless mesh network protocol must have the following features: ① distributed operations; ② rapid convergence (to adapt to faster mobility); ③ Scalability: ④ suitable for a large number of small devices; ⑤ proactive operations (reducing the initial latency) with limited bandwidth and computing power: ⑥ The quality and capacity of the radio link should be considered when selecting a route; 7. Loop avoidance: token security.

The Wireless Mesh Network is a wireless network developed from the Ad Hoc network. Ad Hoc networks and wireless mesh networks have some similarities. Therefore, the existing mainstream wireless mesh networks are developed from AdHoc Network Routing Protocols, there are three main types of routing protocols: one is a prior routing protocol: one is a reactive routing protocol, and the other is a hybrid routing protocol.

Ii. Prior Routing Protocol

(1) Introduction 

A prior routing protocol is a table-based routing protocol. In this Protocol, each node maintains one or more tables that contain routing information to all other nodes in the network. When the network topology changes, the node sends route update information in the network. The node that receives the update information updates its table to maintain consistent, timely, and accurate routing information. The difference between different prior routing protocols is that the topology update information is transmitted over the network and the type of the table to be stored. The prior routing protocol constantly detects changes in network topology and link quality, and updates the route table based on changes. Therefore, the route table can accurately reflect the network topology. Once the source node needs to send a message, it can immediately obtain the route to the target node.

(2) DSDV protocol

The basic principle of DSDV is that each node maintains a route table to other nodes, and the table content is the "Next Hop" node of the route. The innovation of DSDV is to set a serial number for each route. A route with a large serial number is the preferred route. A route with the same serial number and a few hops is the preferred route. Under normal circumstances, the serial numbers of node broadcasts are monotonically increasing even numbers. When Node B finds that the route to node D (route serial number is s) is interrupted, Node B broadcasts a route information, inform the route that the serial number is changed to s + l, and set the number of hops to infinity. In this way, any route table of node A that sends information through B contains an infinite distance, this process ends until A receives A valid route (route serial number s + 1-1) that reaches D.

In this solution, all mobile terminals in the network create a route table, including the number of hops (or path matrix that identifies the distance vector) of all target nodes to each target node ). Each route record has a serial number set by the target node. The serial number allows the mobile terminal to distinguish the current valid route path from the obsolete route path. The route table is periodically updated across the network to maintain the communication effectiveness across the network. Generally, two route update methods can be used to reduce the amount of route information transmitted due to route table updates and reduce network route overhead. The first is the full clearing mode, that is, the route update information is transmitted throughout the network through multiple network protocol data units. If the terminal in the network moves, the new packet information is occasionally transmitted to all terminals in the network. The second is the partial update mode, or the incremental update mode. After the last full clear transmission, only the changed route information is transmitted, this information is usually stored in a standard NPDU to reduce the amount of route information transmitted. In the incremental update mode, the mobile terminal can add an additional table to store route update information.

The broadcast information of the new route information includes the address of the target node, the number of hops to each target node, the serial number of the received information, and the unique broadcast serial number. The new route entry applies to the latest serial number. If the two updates have the same serial number, the routes with a small distance from the Vector Array have priority. Because it represents the shortest path (or the least number of hops ). Under normal circumstances, there may be multiple paths from the source node to the target node. During the determination of the Optimal Route path, mobile terminals track the time of different route paths, the Optimal Route path is the shortest path. Before finding the optimal path, the time is subject to convergence fluctuations. Once the path is determined, the information is stored in the routing table of each terminal until the node receives the new routing information. Iii. Reactive licensing Protocol

The reactive routing protocol is a route selection method that finds a route when data is sent from the source node to the target node. Nodes do not store timely and accurate routing information for the entire network. When the source node sends a message to the target node, the source node initiates a route Query Process in the network and finds the corresponding route before sending the message. To improve efficiency, the node can save the routes in the cache for later sending. The characteristics of on-demand routing of reactive routing protocols can better adapt to the wireless network environment where nodes move more frequently. After a node moves, you only need to update the routing information of the relevant paths that need to send data.

4. Hybrid Routing Protocol

Hybrid Routing is a combination of the preceding two routing methods. It uses a prior routing protocol in a local range to maintain accurate routing information and narrow the range of routing Control Message propagation. When the target node is far away, the reactive routing protocol is used to find the route. The ZRP protocol represents the Hybrid Routing Protocol. ZRP is a tile routing protocol designed for changing communication environments (such as reconfigurable wireless networks and RwN. Each node defines an area, which contains nodes. The distance (that is, the number of hops) between these nodes is within a limited range. This distance becomes the region radius rzone. Each node only needs to know the topology of its routing region, and its routing information is updated with the topology updates in the region. In this way, although the network is large, updates are only performed in some regions. Because the distance is greater than 1, a large number of overlapping areas exist.

If s wants to communicate with D, s sends the query message and broadcasts it to the level 1 until it reaches D. D responds to this request, indicating that the Lushan is S-H-B-D.

B knows the routing path mechanism as route accumulation. The accumulation process is as follows: when a query message passes through a node, the node information is added to the query message. In order to limit the information size and reflect the way out from the discovery process, the number of hops is limited in the query message, and each time a node passes through, the number of hops is reduced by l. If the number of skip fields is 0, the message is discarded. The region adopts a prior routing protocol.

We can see that ZRP only requires a relatively small amount of query information, which is only sent to the surrounding nodes. Because the region radius is always relatively small compared to the entire network, it is known that the overhead of the region topology is only a small part of the entire network. In addition, the saving information for each node is greatly reduced. In addition, the ZRP protocol is faster than the full-network reactive routing discovery mechanism.

V. Conclusion

As a solution that can solve the bottleneck of "last mile" network access, the wireless mesh network works with smart antennas, Ad Hoc networks, and ultra-broadband technology, it is becoming an overwhelming Technology in the wireless communication field. Therefore, it is of practical significance to analyze the routing technology of the wireless mesh network on the premise that the protocol standards of the wireless mesh network are uniform.