Vaisala VaiNet AP10, User Manual

Page: 12 / 48

VaiNet wireless devices are not limited to using a single access point. If multiple access points
are available, VaiNet devices can switch access points to maintain their connection to the
viewLinc Monitoring System. The strength of the wireless signal is used to determine the
optimum network data path.
Wireless transmissions between VaiNet devices are encrypted to protect against
eavesdropping, data tampering, and transfer errors.
2.3.2 Delays in a VaiNet Network
VaiNet protocol and VaiNet devices are designed for power-efficient operation. Some of the
design choices that enable long battery life also create significant delays that the users should
be aware of.
Intermittent Radio Connections
Radio connections between VaiNet access points and data loggers are not continuous. Access
points take turns communicating in a two-minute cycle, and connected data loggers send their
measurement data to their connected access point every four minutes. This introduces various
delays:
• Data loggers that are not currently connected (new devices or ones that have fallen out of
radio contact) have to scan for available access points for a complete cycle before they
can decide what is the optimal access point for them. This means that connection
attempts typically take at least a couple of minutes. Additionally, some joining scenarios
may take multiple attempts. For example, when filling a single access point up to its full
capacity of 32 data loggers, it may take an hour for the last data logger to successfully
connect to the access point.
• Access points request missing data and issue management commands to data loggers
within their communication window. Transferring a full month's worth of measurement
data from 32 data loggers using one access point takes several hours.
Data Logger Scanning Interval
Scanning for available access points consumes power. To prevent repeated scanning from
draining their batteries, RFL100 Data Loggers shut down their radio temporarily if they can
find no access points to join. They will resume scanning after a waiting interval that gets
progressively longer if they keep failing to find an access point. The maximum interval is 8
hours and 30 minutes.
This means that when access points become available after an outage, it may take several
hours for data loggers to discover them. This is why you should always keep your access points
powered up, and why you should start your network installation by installing the viewLinc
Enterprise Server and access points first.
You can manually wake up the radio of an RFL100 Data Logger by pressing its
Refresh button. The button is located next to the service port under the silicone
plug.
AP10 User Guide M211860EN-A
10