1 Wireless Mesh networking technology
Wireless mesh network (Wireless Mesh Network, WMN) as a new networking technology, in the past two years, quickly attracted industry attention. Similar to the background of many new technologies, the emergence of WMN is the result of direct application demand.
First, the rapid development of wireless local area networks (WLANs) has brought great freedom of communication to businesses and the public. WiFi (Wireless fidelity) is the first widely promoted high-speed WLAN technology, including approved IEEE 802.11a, b, g, and n specifications, which are sought after for their ability to improve productivity and are widely deployed around the world. . However, the range that WiFi can support is very limited: users can only achieve high-speed connections within 300 feet of the wireless access point device (AP). Therefore, if you want to turn WiFi service mode into ubiquitous coverage, its cost will be terrible. Then, can you use the wireless devices on the Internet as routers to continuously forward the data until they are sent to the destination, thus extending the coverage of the access point to a few miles or more, which is to propose wireless Mesh networking. The basic idea of ​​the technology is to use multiple wireless hops for networking (WiFi uses only one hop), so that the coverage of wireless signals can be greatly extended without adding wired infrastructure. Therefore, the wireless Mesh network is a wireless area network solution that is very suitable for covering large open areas (including outdoor and indoor). It is characterized in that it consists of a group of wireless APs distributed in a network, and the APs are point-to-point. The method is interconnected by a wireless relay link to expand the wireless "hotspot" in the WiFi into a wireless "hot zone" that is truly covered by a large area. The benefits of this structure include:
Self-configuration: The AP has automatic configuration and centralized management capabilities in the WMN, which simplifies the management and maintenance of the network.
Self-healing: APs can automatically discover and dynamically route connections, eliminating the impact of a single point of failure on the service and providing redundant paths;
Compatibility: that is, if the standard IEEE802.11b/g standard is adopted, it can be widely compatible with wireless client terminals;
Connectivity: A system using Mesh structure, the signal can avoid the interference of obstacles, make the signal transmission unimpeded, and eliminate the blind zone.
Therefore, the most suitable environment for deploying wireless Mesh networks is: university campuses, stadiums, and temporary emergency communications (such as disaster relief sites for large-scale disasters).
2 WiFi-based wireless mesh network
The basic structure of a wireless local area network (WLAN) is point-to-point or point-to-multipoint communication between two wireless devices. In point-to-point mode, the wireless connection replaces the communication cable and provides reliable data transmission when the two terminals are close together. In point-to-multipoint mode, the system has a central management unit AP, and all signals are aggregated into the access point. Therefore, the reliability of the wireless network depends on the quality of the radio connection between the AP and the terminal. The communication mode of the wireless mesh network is completely different from the above-mentioned point-to-point or point-to-multipoint communication mode. As mentioned above, WMN is a high-speed, high-capacity new network structure based on technologies such as multi-hop routing and peer-to-peer networking. It can dynamically expand, self-organize, self-configure, auto-repair, and self. Balanced. In response to the above characteristics, the industry standardization organization has begun to develop new standards for it to meet the needs of various coverage and network services. Among them, IEEE 802.11, IEEE 802.15 and IEEE 802.16 have established working groups for developing new standards for WMNs. The following is a brief introduction to the support of the 802.11 standard for WMN architecture. The original IEEE 802.11 service was mainly limited to data transmission, and the rate was only up to 2 Mb/s. However, the peak speeds of IEEE802.11b and 802.11a/g could reach 11 Mb/s and 54 Mb/s, respectively, while IEEE802.11n It is expected to reach 100 Mb/s, which makes existing cable and DSL connections limit the connection speed of home and office networks. If you can skip these wired parts, you can overcome this problem while reducing the overhead of laying and maintaining Ethernet cables. At this point, the idea of ​​WMN was introduced. Although the 802.11 peer-to-peer mode can be used to construct a wireless mesh network, the scalability of the MAC protocol makes the network performance poor and is not suitable for multi-hop WMNs. In order to commercialize it, IEEE has established a sub-working group of IEEE802.11s to develop a standardized extended service set (ESS), that is, IEEE 802.11s specifically defines MAC and PHY layer protocols for WMN. In such a network, a WLAN access point can forward messages like a router.
In the IEEE 802.11s working group, the mesh network can be of two basic structures: the network structure of the infrastructure and the network structure of the terminal equipment. The IEEE 802.11s working group has developed new specifications to support these two structures. In the infrastructure network architecture, the IEEE 802.11s working group defines an IEEE 802.11 MAC layer-based architecture and protocol to establish an IEEE 802.11 wireless distributed system that simultaneously supports broadcast/multicast and unicast at the MAC layer ( WDS); In the network structure of the terminal device, all devices work on the same plane structure in the point-to-point mode, using an IP routing protocol. A wireless point-to-point network is formed between clients without any network infrastructure to support.
3 existing solutions
Most of the WMN solutions currently available on the market are small companies such as MeshNetworks, Tropos, BelAir, Proxim, CoWave, Networks, Ember, etc. Let's analyze the advantages and disadvantages of several solutions.
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