Detailed analysis on the development of wireless mesh networks by technical applications

Edit comments:With the development of computer and wireless communication technology in recent years, mobile wireless computer technology has become more and more popular and widely used. As it is no longer subject to cable laying restrictions, users with mobile computer devices can easily and freely move and communicate with others without fixed network facilities. In this case, they can form a mobile Adhoc Network or a mobile wireless mesh network. The Mobile Wireless Mesh Network is an autonomous system composed of wireless mobile routers (and connected hosts. The system can be moved randomly to automatically adapt to network topology updates without any backbone network or network infrastructure.

In addition to mobile wireless mesh networks, more and more commercial applications of fixed wireless mesh networks have emerged recently. A typical example is "community wireless network ". It is used to provide access for communities without broadband access. In these fixed "community wireless networks", each wireless router not only provides Internet access for its users, it is also part of the network infrastructure-routing data to its destination in a wireless mesh network.

A layer-3 wireless mesh network features high flexibility and inherent fault tolerance. This network simplifies line-of-sight transmission and expands the network scale and coverage with the minimal network infrastructure and interconnection costs. In real life, there are also hybrid Wireless Mesh Networks: Some mesh routers in the network are mobile, while other mesh routers are fixed.

In either case (mobile or fixed or hybrid), the wireless mesh network has some notable features, such as: high dynamic, intelligent, end-to-end Optimal Path Selection, multi-hop, generally, the bandwidth is limited and the computing capability is insufficient. There are two reasons for the high dynamic nature of the Wireless Mesh Network: first, the vro itself may move (such as in a mobile or hybrid Wireless Mesh Network) and cause rapid changes in the network topology. Second, even if the router itself does not move (for example, in a fixed wireless Mesh Network), the quality of the radio link may change rapidly due to interference, geography, environment, and other factors.

From the above features, we can know that a complete wireless mesh network protocol must have the following features:

• Distributed operations
• Fast Convergence (to ensure faster movement)
• Scalability
• Suitable for a large number of small devices
• Use only limited bandwidth and computing power
• Proactive operations (Reducing Initial latency)
• When selecting a route, consider the quality and capacity of the radio link.
• Loop avoidance
• Security

Note 1: the concept of community wireless network is very popular in developed countries such as the United States and is still in the development stage in China.

In addition to traditional routing protocols (such as OSPF and RIP) designed for wired networks, there are also a large number of routing protocols designed for mobile adhoc networks. These routing protocols are generally divided into two categories:

Reactive routing protocols (such as XSL, DSR, and TORA ). This type of protocol only discovers and maintains the route when necessary. To meet traffic needs, they can use power supplies and bandwidth resources more effectively, at the cost of increasing the latency of route discovery.

Active routing protocols (such as DSDV and OSLR ). This type of protocol always maintains the route to each possible destination-the Protocol assumes that these routes may be used. In some cases, the extra delay caused by the reactive routing protocol may be unacceptable. In these cases, if bandwidth and power resources permit, the active routing protocol is more popular.

Traditional routing protocols (such as OSPF and RIP) are designed for wired networks. They are not able to handle the rapid changes in the topology and link quality that are common in the wireless mesh environment. They can be divided into two categories, according to their design philosophy: (1) distancevector; (2) linkstate ). Distance Vector routing protocols (such as RIP) are used in early English networks, such as ARPANET. Its main advantage is the simple and efficient distance vector calculation method. However, this method is prone to slow convergence and routing loops. The connection status routing protocol (such as OSPF) features that all routers store the full network topology information and perform periodic update (link state periodic update ). In addition, changes in any stage lead to instant updates. Compared with the traditional distance vector routing protocol, the connection status routing protocol has full topology information, so the routing loop is easier and the convergence speed is faster. Unfortunately, the connection status Routing Protocol relies on the network-wide broadcast (flooding) to transmit the latest information. Therefore, especially when high mobility (or severe radio interference causes connection status fluctuations) occurs, to keep up with the rapidly changing topology, such protocols consume a large amount of network resources and vro processing capabilities and generate excessive control overhead, making them unfeasible.

Many existing adhoc routing protocols have made significant improvements in dealing with fast topology changes. For example, the put-in-line routing protocol is a reactive distance vector routing protocol. The basic idea is to discover and compute routes only when necessary, and discover the route of the destination using the query/response packet. However, the route must be found before the actual data packets are transmitted. Using the reactive routing protocol increases the initial latency (InitialDelay ). In addition, when the mobility and load are high, this reactive routing protocol can suffer a huge protocol load. Simulation results show that these protocols have intolerable packet loss and latency under high mobility and high load. In addition, the vast majority of existing protocols, whether traditional or similar to Ad hoc, have serious problems in terms of scalability and stability when adapting to the rapid changes in the quality of common radio links.

A new wireless routing protocol, adelia's adaptive wireless routing (AWR), solves the above problems and will be introduced in the next section.

 

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AdaptiveWirelessRouting Protocol (AWR) is an adaptive and Distributed Active routing Protocol designed for wireless mesh networking.

In AWR, each vro maintains a route table containing all necessary information to forward data to its destination. The entries in each route table are specially processed to identify the old or new routes to avoid routing loops.

In AWR, each node keeps track of its connection with its peripheral nodes, and sensitive detection of broken connections. In order to maintain the consistency of the route table in a dynamically changing network, each node regularly communicates with the surrounding nodes and exchanges information. In addition, important new information is also communicated immediately. In addition to the routing loop Avoidance Mechanism (which eliminates the routing loop problem that causes most distance vector routing protocols to be plagued), a special message mechanism is also introduced to further enhance the convergence speed, and reduce the routing overhead by making the route as localized as possible. To further improve the adaptability and Stability of the route, AWR maintains multiple routes to reach each destination for Fast Error Recovery and load balancing. At any time, all routes are guaranteed to have no loops.

AWR is outstanding in both mobile and fixed wireless mesh networks. It combines a variety of attractive features:

• A fully distributed structure that provides self-recovery after short-term abnormal operation performance of links and nodes to ensure that there is no system-level spof;
• Dynamic, adaptive, and active routing: Automatic networking and self-recovery reduce initial latency;
• Fast Convergence: ensures high mobility and greatly improves service capabilities;
• Flexible adaptation to changes in topology structure and link quality;
• Maximizing user throughput by considering link quality (extremely important for Wireless Mesh Networks)
• High scalability (low computing and communication overhead ). It is particularly important to lay a large-scale wireless mesh network;
• Easy to implement routing-free loops at any time
• Each destination has multiple non-loop routes for fast fault recovery and load balancing.
• Security (all route packages are encrypted and authenticated)
• Supports multi-station and multi-hop Wireless Mesh Networks
• Uniquely identifies temporary wireless signal attenuation and substantial loss of wireless links caused by mobility and router faults.

AWR has been used in many practical scenarios. Many simulation and test results also show that AWR performs well in both mobile and fixed wireless mesh networks, in addition, AWR has obvious advantages over other similar routing protocols in more customer applications.

It shows the simulation test results of AWR compared with the other four well-known routing protocols, such as Oscar, DSR, OLSR, and DSDV. The test was executed by CP2, a simulation software recommended by ITU. As shown in, AWR has outstanding performance advantages over other protocols:

AWR has the highest packet delivery rate;

AWR has the smallest average latency;

AWR has the best toughness in terms of increased mobility and traffic load;

AWR is particularly outstanding in complex environments (such as high mobility and large traffic), greatly surpassing other similar protocols;

The AWR normalized routing load is smaller than other active routing protocols, and is stable when the mobility, network specifications, and traffic load increase gradually (attributes that are very required for the scalability of the routing protocol ).

As a leader in wireless routing protocols, AWR is not limited to wireless mesh network applications. For more wireless networks, AWR routing protocols can be used as long as node faults, topology changes, or link quality changes in wireless networks are involved. Now, AWR has improved its efficiency.

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