A LoRaWAN® based network is made up of end devices, gateways, a network server, and application servers. End devices send data to gateways (uplinks), and the gateways pass it on to the network server, which, in turn, passes it on to the application server as necessary.
Additionally, the network
server can send messages (either for network management, or on behalf of the
application server) through the gateways to the end devices (downlinks).
The LoRaWAN specification defines three device types: Class A, Class B, and Class C. All LoRaWAN devices must implement Class A, whereas Class B and Class C are extensions to the specification of Class A devices. All device classes support bi-directional communication (uplink and downlink). While end devices can always send uplinks at will, the device’s class determines when it can receive downlinks. The class also determines a device’s energy efficiency. The more energy-efficient a device, the longer the battery life.
Class A
All end
devices must support Class A (“Aloha”) communications. Class A end devices
spend most of their time in sleep mode. Because LoRaWAN is not a “slotted”
protocol, end devices can communicate with the network server any time there is
a change in a sensor reading or when a timer fires. Basically, they can wake up
and talk to the server at any moment. After the device sends an uplink, it
“listens” for a message from the network one and two seconds after the uplink (receive
windows) before going back to sleep. Class A is the most energy efficient
and results in the longest battery life.
Class A end devices have very low power
consumption. Therefore, they can operate with battery power. They spend most of
their time in sleep mode and usually have long intervals between uplinks.
Additionally, Class A devices have high downlink latency, as they require
sending an uplink to receive a downlink.
The following are some of the use cases for
Class A end devices:
·
Environmental
monitoring
·
Animal
tracking
·
Forest
fire detection
·
Water
leakage detection
·
Smart
parking
·
Asset
tracking
· Waste management
Class B
Class B devices extend Class A capabilities
by periodically opening receive windows called ping slots to
receive downlink messages. The network broadcasts a time-synchronized beacon
(unicast and multicast) periodically through the gateways, which is received by
the end devices. These beacons provide a timing reference for the end devices,
allowing them to align their internal clocks with the network. This allows the
network server to know when to send a downlink to a specific device or a group
of devices. The time between two beacons is known as the beacon period.
Class B end devices have low latency for
downlinks compared to Class A end devices because they periodically open ping
slots. However, they have much higher latency than the Class C end devices.
Class B devices are often battery powered. The battery life is shorter in Class
B compared to Class A because the devices spend more time in active mode due to
receiving beacons and having open ping slots. Because of the low latency for
downlinks, Class B mode can be used in devices that require medium-level critical
actuation, such as utility meters.
The following are some of the use cases for
Class B end devices:
·
Utility
meters (electrical meters, water meters, etc)
· Street lights
Class B devices can also operate in Class A mode.
Class C
Class
C devices extend Class A capabilities by keeping the receive windows open
unless transmitting an uplink. Therefore, Class C devices can receive downlink
messages at almost any time, thus having very low latency for downlinks. These
downlink messages can be used to activate certain functions of a device, such
as reducing the brightness of a street light or turning on the cut-off valve of
a water meter.
Finally,
Class C (“Continuous”) end devices never go to sleep. They constantly listen
for downlink messages from the network, except when transmitting data in
response to a sensor event. These devices are more energy-intensive, and
usually require a constant power source, rather than relying on a battery.
Class
C devices open two receive windows, RX1 and RX2, similar to Class A. However,
the RX2 receive window remains open until the next uplink transmission. After
the device sends an uplink, a short RX2 receive window opens, followed by a
short RX1 receive window, and then the continuous RX2 receive window opens.
This RX2 receive window remains open until the next uplink is scheduled.
Uplinks are sent when there is no downlink in progress.
Compared to Class A and Class B devices,
Class C devices have the lowest latency. However, they consume more power due
to the need for opening continuous receive slots. As a result, these devices
cannot be operated with batteries for long time therefore they are often mains
powered.
The following are some of the use cases for
Class C end devices:
·
Utility
meters (electrical meters, water meters, etc)
·
Street
lights
·
Beacon
lights
· Alarms
Class C devices can also operate in Class A mode
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