Wi-Fi Mesh Networking
In a wireless mesh network all nodes or WAPs are interconnected wirelessly
instead of using cable to connect wireless antennas. Typically these “hot spots”
are created using omnidirectional Wi-Fi IEEE 802.11b/g antennas. Directional
antennas using Wi-Fi IEEE 802.11a are then used to connect the hot spots or
nodes and create the mesh. The 802.11a standard is used in the mesh backbone
because of its performance (54 Mbps) as well as different and noninterfering
radio frequency (IEEE 802.11a uses 5 GHz, while 802.11b/g antennas use
2.4 GHz).
The nodes on the mesh network automatically learn about one another and
self-configure network traffic through numerous network path configurations.
The result is extended coverage of a Wi-Fi network with the ability to route
traffic around congestion and around obstacles and interference. Mesh
networks provide redundancy and “robustness” because of their capability to
balance network traffic.
Wireless mesh networks create latency that can affect applications such as
voice over IP. They can also be noisy, possibly creating transmission errors,
resulting in retransmissions and reductions of available bandwidth. While cur-
rent implementations are proprietary, a standard for Wi-Fi mesh networks,
called 802.11s was finalized and released in 2007.
Zigbee
Zigbee is a wireless technology standard (IEEE 802.15.4) that provides for low
data-rate networks. It uses unlicensed frequencies (900 MHz and 2.4 GHz),
which are also available for cordless phones, Wi-Fi, and other devices. The
standard is aimed at control devices in residential, commercial and industrial
buildings. It is particularly useful for sensors and control devices in building
automation systems in a smart building where very small amounts of informa-
tion or data are being transmitted. This includes on/off switches, open/closed
devices, thermostats, and motor controls (Fig. 2.7).
The maximum speed of Zigbee devices varies between 192 and 250 Kbps (a
measure of bandwidth, kilobits per second). The maximum distance varies
between 20 and 50 meters. Zigbee has several advantages:
n Low power usage as the devices require only two AAA batteries
n Wide support from more than 100 companies supporting the standard
(companies such as Motorola, Honeywell, Samsung, and Mitsubishi)
18 Smart Building Systems for Architects, Owners, and Builders