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Wireless Redundancy
Maximize Highly Available and Reliable WLAN Networks with Moxa’s Wireless Redundant Technology
Radio interference has been and always will be a major concern for wireless applications. In a wireless environment, data transmission is over the air. This unique medium requires a very different type of technical knowledge to ensure a reliable wireless connection. Because interference normally occurs at a particular frequency, if two or more different frequencies are used to communicate at the same time, then data transmission can continue even if there is interference on one of the frequencies.
The standard architecture of wireless infrastructures includes access points (AP) that connect many clients to an Ethernet network. Since the APs and clients are connected by a single-RF connection, if the RF connection fails, the system and network behind the client will be disconnected.
With dual-RF wireless architecture, two independent RF modules are used to form independent wireless connections using different frequencies to avoid interruptions in transmission. To achieve network redundancy without requiring a change in existing wireless LAN architecture, choose APs and clients that support dual RF channels to simultaneously operate at 2.4 and 5 GHz.
Dual-RF Redundancy
Moxa’s AWK-5222 series products are single wireless LAN devices with two RF modules to allow for two independent wireless connections. In addition, they are also IEEE 802.11a/b/g -compliant for reliable wireless redundancy. For enhanced reliability beyond wireless redundancy, Ethernet redundancy is also incorporated; the AWK-5222 series’ Ethernet ports support both RSTP and Moxa's own proprietary ring protocol.
This means that the devices can implement two independent wireless connections between the redundant AP and redundant client devices. One path uses 2.4GHz while the other operates at 5GHz to prevent interference. If one of the two wireless connections fails, the other connection will continue providing service between the redundant AP and redundant client devices.
Configuration involves setting up a redundant AP on the AP side, and a redundant client on the client side, each RF path uses a different SSID. The following figure shows the web console UI of the AWK-5222, in which WLAN1 is set to SSID1 and WLAN2 is set to SSID2. In addition to connecting to its redundant clients, the redundant AP can also serve one or more traditional single RF clients using the standard single path service.
Wireless Bridge Mode
Moxa's design allows the dual RFs to provide a “wireless bridge mode”, in which WLAN1 is configured as the master AP and WLAN2 as the slave client. The mode will not only reduce the bandwidth consumption but will also extend the wireless communication range. Most importantly, this design optimizes the WDS (Wireless Distribution System) mode in light of its throughput performance. The WDS mode's normal throughput is 25 Mbps/(n-1), in which n is the number of WDS nodes. For example, if there are 4 mesh nodes, then the throughput is approximately 8 Mbps. The AWK’s hardware wireless bridge mode can upgrade the throughput from 10 to 15 Mbps. This way, the performance of each bridge connection will remain the same.
AP-Client Connection Mode
Most WLAN applications use infrastructure mode. In AP-client mode, a wireless AP is required to set up a basic infrastructure service set (BSS) for wireless connectivity. The AP can be used alone to set up a WLAN, or can be used to connect the WLAN to a wired network. The AWK-5222 supports AP-client connections, which can be used to provide Internet access in areas where cabling is too expensive or impractical to install.