On the contrary, a mesh wireless network is a system composed of receiving/transmitting nodes with multiple repeated links. Nodes help each other and transmit data along the network, which is especially suitable for harsh working conditions. You don't need to be too careful when installing the power grid. As long as you throw them anywhere, it will become a reliable and flexible system, which can be extended to thousands of devices in Qian Qian at will.
The topology developed by MIT for mesh network is a point-to-point or peer-to-peer system, that is, a network composed of nodes with repeated receiving/sending functions. Each node can receive/send data and send data to its neighboring points like a router. Through relay processing, the data packet passes through the intermediate node with reliable communication link and reaches the specified target.
Similar to the Internet and other peer-to-peer routing networks, mesh networks have multiple redundant communication paths. If one path is interrupted for any reason (including radio frequency interference interruption), the mesh network will automatically choose another path to maintain normal communication. Usually, the mesh network can automatically choose the shortest path, which improves the quality of the connection. According to practice, if the distance is reduced by two times, the signal strength at the receiving end will increase by four times, which makes the link more reliable without increasing the transmitting power of the node. In mesh networks, as long as the number of nodes is increased, the reachable range can be increased, or more reliability can be brought by adding redundant links.
Self-configuring and self-repairing renaturated mesh network has the characteristics of self-configuration and does not need human intervention. Adding new equipment or relocating old equipment is very simple. As long as the power supply is connected to the new site, the grid network will find this new node and automatically incorporate it into the existing system.
Mesh network is not only highly reliable, but also adaptable. If the sensor or data receiver is too far away from the fixed RF communication source, only a few relay nodes need to be arranged between them to fill the gap.
On the wired Internet, if a router stops working, packets will pass through other nodes and choose another link to transmit data. Similarly, if a node or link in the mesh network fails, the packet will automatically choose another path. First, the loss of two nodes will not have a fatal impact on the grid, and the mesh network has the ability of self-healing and does not need foreign manpower to rearrange the path.
Redundancy and Extensibility Redundancy in the real world means the degree of safety reserve of the system and the tense procedures carefully managed by users. A system without redundancy is an unreliable system; A system with too much redundancy will bring too much waste. In the wireless network of mesh network, redundancy is the basic function brought by node density. For the sake of reliability, a well-designed system is needed, which can be completed only by a few more nodes in the grid. Each node has multiple links, and the route is automatically selected according to the situation. In other wireless systems, there are few such methods to obtain redundancy.
Mesh networks also have excellent scalability, which can be extended to manage hundreds to thousands of nodes. Because there is no central control unit in this system, there is no trouble to add multiple link points or gateways.
Reliability, adaptability and expansibility are very important characteristics in wireless communication and industrial control. Point-to-point network is reliable, but it cannot be extended to make nodes have multiple links. Point-to-multipoint network can manage multiple endpoints, but its reliability is limited by the configuration of access points and endpoints. It is difficult to improve the reliability of one-to-many network under bad environmental conditions. On the contrary, under the restriction of environment or structure, grid has inherent reliability and adaptability, and can be extended to thousands of endpoints at will.
When the grid network is used in industrial control, it can also realize distributed control and diagnostic monitoring. At present, the WLAN in network format mainly uses the standard based on 802. 1 1a/b/g, but it can be extended by any radio frequency technology, such as ultra-wideband or 802. 15.4 Zigbee. Because network intelligence is installed on every node, there is no central exchange. The operation of grid only depends on each intelligent node with network processor, switching function and system software.
In order to realize the communication between nodes in the grid, each node has the ability of self-discovery. First of all, they must decide whether to act only as an access point in a wireless system, just like a network backbone transmits data to another node, or whether to play the role of a combined function. Secondly, these specific nodes use the query/response protocol to determine their neighbors. These operations should not occupy too many resources and should not exceed 1% to 2% of the available bandwidth of the link.
In the mutual identification of nodes, the main trade-off is path information, such as signal receiving strength, throughput, bit error rate, waiting time and so on. These data must interact at adjacent points without taking up too much bandwidth. Then, according to these data, the best path is decided. Therefore, the best quality at that time can be obtained at any time.
Link discovery and path selection are carried out in the background, so each node knows which neighboring points exist at present and frequently operates to find the best path. If a node stops working for any reason, such as maintenance, rescheduling or failure, the neighboring nodes will immediately re-record, recalculate and select the path. This ability of self-repair or fault transcendence is the main sign that mesh wireless networks are different from other wireless communications.
Each node is a self-managing node and an organic part of the network. The network can be managed and configured from a specified point to form an entity. Use the hypervisor SNMP to monitor a specific device, node, domain or the entire network. The discovery protocol simplifies the process of searching and locating the specified nodes and displays them on the manager's screen.
Grid network depends on all kinds of management, control and discovery messages, so it needs security measures, using in-band messages and encrypted tunnels to prevent eavesdropping and attacks. 802. 1x, advanced encryption standard encryption and other standardized security technologies ensure the security of nodes and devices. Industry heavyweights, such as Cisco and Intel, have confirmed that grid technology is the next logical extension of wireless communication. The use of grid can help enterprises quickly establish new wireless networks or expand existing wireless local area networks without wired connection to base stations. Base stations with mesh multi-links can easily achieve load balancing because they can choose the best path for data transmission. In addition, industrial users can also use embedded wireless grid to quickly establish sensor and controller networks for industrial management and transportation management.
The upstart of grid technology and traditional IT companies have sold wireless local area networks with grid function. Relevant institutions in charge of standard formulation are formulating supplementary rules to incorporate the grid into the 802. 1 1 (i.e. WiFi) and 802. 16 (i.e. WiMax) standards that have just met the public. In the embedded market, grid technology began to form standards, such as ZigBee.
In fact, the basic concept of grid is not a new invention, but extends the practice in the world of Internet connection to the wireless world. Sott Burke, vice president of PacketHop engineering, said: "Today's fixed Internet is a large fixed grid."
When each device on the grid receives/sends its own data, it also acts as a router for other devices. The inherent intelligence of each device enables it to automatically configure an effective network and readjust the link when the node is overloaded and fails. The advantage of grid network is not only easy to set up, but also can be extended from a central link to cover a large area in a wireless way, and it has strong survivability.
Maybe it's a military secret. Wireless grid is a research achievement launched by the Defense Advanced Research Projects Agency of the Pentagon. The early technology of PacketHop originated from the research conducted by Stanford Research Institute for the Pentagon, which equipped the soldiers in the field with a lightweight high-speed wireless data network. Florida emerging company MeshNetworks also originated from advanced national defense research institutions and developed grid technology.
Military departments and security departments are still the most direct markets for grid products. "There is a great demand in this market," Burke said. Nortel and several new companies engaged in grid development have confirmed that WLAN in grid format will bring more benefits to enterprises. In the first half of this year, Nortel introduced the Wi-Fi grid product-wireless 7200 series to the market. "In the traditional WLAN scheme, every node is connected to the backbone network, but we eliminate this need in the network format WLAN," said Peter Zwinkels, business development manager of wireless mesh network. "It enables us to realize wireless LAN in areas where wiring is difficult or expensive."
These areas include large indoor and outdoor spaces, such as warehouses and golf courses. Power supply is one of the problems. Maybe there are no traffic lights and street lights for traffic management here. However, Nortel promised to the public that as long as the traditional wired network can be generated, the nodes can be powered by Ethernet itself.
In the grid experiment of Dartmouth University in New Jersey, Intel connected every student to the school network in every part of campus space. The plan was implemented in the spring to provide students with broadband connection, and they need to pay the telephone company and cable TV company.
These studies show that the grid is mainly used for wide-area broadband wireless connection. Although market information shows that Wi-Fi hotspots are popping up in coffee shops, railway stations and airports in the United States, wireless ISPs and telecom companies believe that they can use the extended grid of Wi-Fi hotspots to attract users and use it as a gift to sell the Internet, standard mobile phones and 3G services. Grid technology can greatly accelerate the development trend of broadband services: there is no need for a large number of T 1 and ADSL lines, each wireless node is a hot spot, and only a high-bandwidth connection is needed to cover the whole area with wireless grid. Nortel classifies this as a "hot spot" and claims that this system is not only cheap, but also has better coverage performance than the hodgepodge of current hot spots.
Use "hot spots"
Some cities are preparing to launch similar services for employees. For example, Verge Wireless has launched hotspot grid services in baton rouge and New Orleans.
Some ISPs are still waiting for the final solution of wireless communication, using WiMax to provide broadband services to areas that are difficult to connect. However, Nortel believes that the grid technology based on Wi-Fi can better meet these fields. "In areas without DSL lines, WiFi grid can provide broadband service for 100~200 households in a small village," said Mr. Zwinkels. "MiMax requires users to install special equipment, but the Wi-Fi grid only requires users to plug in the computer with a standard PMCIA card."
After Radio Frequency Identification (RFID), embedded grid has been further developed. Sensors and controllers on the grid are not fixed scanning devices, but talk to each other and transmit information on the wireless network. Ember Company in Boston specializes in manufacturing RF chips, which are used to monitor the transported containers on large transport planes. Sensors are distributed all over each container, which not only records the detailed information of the items in the container, but also transmits the storage status of the container during transportation. For the purpose of anti-terrorism, American airports will quickly use this wireless monitoring system to replace the slow and expensive customs manpower inspection.
"A container is a network, and each container is a node in a larger network format," said Jim Schoenberg, commercial director of Ember. "Because the container itself is part of the network, there is no need to install an antenna at the port or airport. Grid is a communication system with almost no infrastructure. "
Embedded grid can also be used to collect readings of household water meters and meters, or installed in light switches to reduce unnecessary wires. Ember company is drafting ZigBee standard, which is an integral part of EmberNet technology. Many new companies such as BelAir Networks, Tropos, FireTide and Strix System are developing grid products. Although most products are extended under the standard of Wi-Fi, the methods of each family are different. These patented products lack interoperability, so they can't work together. Since the grid is going to enter the social infrastructure, the formulation of standards is an urgent and important thing.
According to the rules of IEEE, to formulate a standard, a unit must first put forward an initiative, then set up a research group, and finally set up a standard-setting working group.
At the end of 20031February, Intel and Cisco announced that they would put forward an initiative to formulate wireless network standards in network format at the IEEE conference in Vancouver.
"The current situation is obvious," said Eric Griffith, editor of the publication Wi-Fi Plant. "Nortel and many new companies are engaged in grid products. If these products are put together, it is impossible to talk to each other at all. Some companies use cellular technology, while others use 802.438+0438+0A. Honeycomb grids can be erected along telephone poles to reach a longer range. 802. 1 1a works well in short distance and is not interfered by 802. 1 1b or 802.11g. "
At the initiative of Intel, Cisco, MeshNetworks and other companies, IEEE set up a grid research group, hoping to finally add the grid to the WLAN standard. This year 1 month, the research group held its first meeting. Critics believe that the standard will be completed under the principle of "the lowest common denominator". By then, the Sharp effect of various patent agreements will be greatly limited. Therefore, MeshNetworks repackaged its patents as licensable products for wireless device manufacturers, and began licensing in the second quarter of 2004.
"It is very interesting that Intel is involved in this matter," Griffith said. "Intel is absolutely willing to provide standards for the grid at the chip level. In my impression, Intel is trying to make up for small mistakes in the past. They entered Wi-Fi too late, and now they must be at the forefront in WiMax and grid. "
Wireless LAN with network format is the inevitable trend of wireless communication development. It is in the best interests of most manufacturers and users to copy new functions from existing wireless standards. Although patent standards have temporary advantages, they cannot be recognized by the further development of technology. Only by grasping the mainstream of technological development and participating in international research is the safest way.
Case study: Garland, Texas, USA
Garland, northeast of Dallas 15 mile, with a population of 226,5438+00,000, replaced the communication system for social security personnel such as police, firefighters and hospital emergency room staff. Lockheed Martin won the contract last September, and chose the grid technology of MeshNetworks to replace the cellular communication system. The new system will cover 57 square miles and become the largest mobile communication network in the world. According to the plan, the project was completed in the second quarter of 2004, providing mobile data services first, and then providing image and voice services.
Grid technology has brought great benefits to Garland, which is 50 times higher than the bandwidth of the original infrastructure. Darrell McClanahan, communications manager, said: "We got rid of the headache problems such as communication tower, line rent and zoning required by the old system. The grid system maintains the normal throughput of 1Mbps, with a peak value of 6Mbps.
The new system only needs PC card, wireless repeater, gateway, geolocation software, improved Pocket PC PDA and command and control center server. Repeater and gateway are hung on buildings, street lamps or traffic control traffic lights to provide energy for the next repeater and equipment. PC card and PDA also play the role of relay and router, making the network very robust. Geographic location software provides latitude, longitude, altitude and other information without GPS. The system supports industrial standards TCP/IP, DHCP and SNMP.
Before choosing the grid communication system, Garland conducted an experiment in 2003 in an area of 5 square miles along the 190 highway. When two cars are driving in opposite directions at the speed of 60 miles per hour, real-time streaming images and VoIP calls are successfully completed, and the throughput is 1.5Mbps.
Tim Scannell, a mobile communication expert, talks about grid.
Q: According to the initiative of Zigbee International Alliance, an important operating concept of IEEE 802. 15.4 is to build a grid network. Each 802. 15.4 node can be used as a dynamic router, extending from a gateway to infinity, as long as the nodes are arranged in this area. This is not a new concept, but it is still a challenge for self-organization and self-healing.
Can IEEE 802. 15.4 be used to complete the network format, and is the technology of IEEE 802. 16 similar? That is, through internal cooperation, broadband internet access can be realized without restrictions?
A: When we lay more and more wireless networks and use various technologies, these networks will eventually connect to the grid environment and become the strongest, or at least be able to communicate with each other across different boundaries and standards. Cellular technology jumps from one cellular communication tower to the next, which enables users to roam seamlessly in the grid communication framework, seize the strongest available signal and form a wireless connection.
A new company like Cometa Networks, exploring the overlapping use of 802. 1 1(Wi-Fi) networks, provides a grid wireless access environment in a wide range, and its basic purpose is man's idea. The problem is that in order to achieve operability and reliability, every access point on the network cannot be interrupted. If a section is interrupted, it will become a weak link area and the service will be damaged, similar to the unlit light bulbs in the decoration of large light strings at Christmas.
Zigbee promises to inject wireless functions into a large number of devices and non-communication systems such as built-in environmental control, but it is not the best choice for grid. Zigbee is not suitable for continuous communication system, because the time exceeds the preset time, or the inactive nodes are sleeping. But it can maintain the long life of the battery, a battery can be used for 5 years, so the system can survive for a long time. Zigbee can transmit small packets, but it is not suitable for large-capacity information.
Radio frequency identification (RFID) systems are similar. They are used to transmit limited data information, and most systems are in a passive position until the reader activates them. Finally, we will use more active RFID systems in retail and logistics transportation.
Although there are problems in power grid management, control and charging, they can all be solved. We have been able to monitor and control the radio frequency, and we can manage the data flow from point A to point Z with layered technology and various algorithms. Zigbee and RFID grid can communicate and exchange data, but 802.6438+0 1 will be a more general technology.