The following figure is an example of the connectivity and protocols used in a Metasys network using the Many-to-One Wireless Room Temperature Sensing (WRS) application. The WRS system is supported at Metasys Release 9.0 or earlier.
|
Interaction between Callouts |
Protocol |
Communication Direction |
|
|---|---|---|---|
|
1 |
2 |
Tunneling over Ethernet |
Bidirectional |
|
2 |
3 |
Wireless Many-to-One Sensing (802.15.4) |
Bidirectional (2.4 GHz Channelized, 2.4 GHz DSSS Wireless Protocol) |
|
4 |
2 |
HTTP |
Unidirectional |
The WRS Series sensors and WRS receivers operate on the 2.4 GHz Industrial, Scientific, Medical (ISM) band and use multi-frequency DSSS technology. The receiver meets the IEEE 802.15.4 standard for low power, low duty-cycle wireless transmitting systems.
The 802.15.4 standard radio is used for employing control networks within a building. This technology uses 16 different channels, allowing 802.15.4 devices, such as the WRS Series systems, to coexist with 802.11 devices.
The Many-to-One system use two-millisecond multi-frequency redundant data transmissions. The sensor transmits a rapid sequence of high-speed (two millisecond) redundant data bursts to an associated receiver approximately every 60 seconds. The sensor transmits up to five redundant data bursts in rapid sequence, and each burst is transmitted on a different ZigBee frequency. When a single data burst is successfully received and acknowledged (or if all five redundant data bursts fail), the sensor goes dormant for approximately 60 seconds and then repeats the rapid transmission burst sequence.
Multi-frequency, redundant data-transmission sequences greatly enhance the success of the wireless sensing system data transmissions. Transmitting short, high-speed data bursts at 60-second intervals also reduces wireless data transmission collisions and interference with other Wi-Fi transmissions. The DSSS technology virtually eliminates accidental and unauthorized wireless interference.