Telemetry2U Technical Bulletins

Bulletin TB02

LoRaWAN Glossary of Terms

Target audience:
All users with a technical interest in LoRa and LoRaWAN
Applies to:
All products
Release date:
April 04, 2022

Summary

Glossary of technical terms used by LoRa and LoRaWAN networks. Most are industry-wide but some references are made to concepts specific to Telemetry2U.

Adaptive Data Rate (ADR)

When adpative data rate is enabled the data rate and transmit power are automatically adjusted until the optimal performance settings are found to reduce power consumption to the lowest level while maintaining link reliability. ADR is controlled by the end-device and for nodes located in a static position we normally recommend that it is enabled.

Application Key (AppKey)

The application key is a secret shared between the end-device and application server that is used to derive the session keys used by a device while activating on the network. This 128-bit key is typically randomly assigned by device manufacturers and shown as a 32 digit hexadecimal number that must be entered when registering a new node on the Telemetry2U network.

Application Server

The application server sits at the top level of the LoRaWAN stack and handles encryption / decryption of data from the end-devices along with formatting, queueing and forwarding of packets. The Telemetry2U application server sits between the network server that communicates with gateways and the customer facing web application.

Bandwidth

The span between the lower and upper frequencies over which transmission takes place. LoRa uses bandwidths of 125 kHz, 250 kHz and 500 kHz depending on the channel plan and data rate selection. A higher bandwidth allows data transmission at a higher rate but also lowers the signal to noise ratio and therefore range.

Channel Plan

The set of supported data rates and frequencies LoRaWAN uses within various regions to comply with local regulations. Telemetry2U supports the channel plans AS923-1, AS923-2, AS923-3, AS923-4, AU915, CN470, CN779, EU433, EU868, IN865, KR920, RU864 and US915. When setting up a new node the channel plan configured in the device must match the profile setting. See also Sub-Bands.

Class A

Operation mode that is used by most battery-powered devices because of its low power consumption. It supports bi-directional communication between the gateway and node but communication is initiated by the end-device only. In between transmissions the device enters a deep sleep mode which lowers power consumption but also means than a downlink message cannot be received until the next uplink message is sent.

Class B

Class B extends on Class A by opening more receive windows periodically using time synchronised beacons sent from the gateway. This means that there are more opportunities for downlink messages to get through to the node between uplink transmissions. Telemetry2U does not support this mode.

Class C

Mode where the receiver is operating continuously (apart from when transmitting) so that uplink transmissions may be received promptly. Commands will come through with low latency but power use is greatly increased so this mode is normally only used with nodes that have an external power source.

Data rate (DR)

The overall speed at which data is transferred over the radio which depends on bandwidth and spreading factor. The minimum and maximum rates depend on the channel plan but for example on AU915 and US915 DR 0 is the slowest at 980 bits per second while DR 13 is the fastest at 21,900 bits per second. If data rates for some nodes in distant / obscured locations are noticeable lower than other nodes it may be worth investigating better antenna / mounting arrangements or installing additional gateways.

Device EUI (DevEUI)

Device Extended Unique Identifier that uniquely identifies each node. This is set by the device manufacturer and needs to be entered when registering a new node.

Downlink

Messages sent from the server to the end-devices are known as downlink messages.

Frame counter (FCnt)

Sequential frame counters for each device are maintained for both uplink and downlink messages. These are expected to increment by one for each message and packets with lower than expected frame counter values are ignored. This mitigates replay attacks and also avoids duplication of data received by multiple gateways.

Gateway

Hardware device that contains a LoRa transceiver to send and receive data to/from local nodes. Communications from the gateway to the network server occurs over the Internet so the gateway must be connected to the Internet. This may either be over a wireless WiFi connection or wired Ethernet.

Gateway EUI

Gateway Extended Unique Identifier that uniquely identifies each gateway. This is set by the manufacturer and needs to be entered when registering a new gateway.

LoRa

Stands for Long Range and is the name given to the radio protocol itself. It operates on frequencies available for public use without licensing using Chirp Spread Spectrum (CSS) technology.

LoRaWAN

Extends the LoRa radio protocol for use over a WAN (wide-area network) by introducing extra layers such as the network server and application server.

Network Server

Software that manages all communications between gateways and the application server(s). It performs many duties such as authenticating, acknowledging and deduplicating messages, selecting the gateway to use for downlink message and sending adaptive data rate (ADR) commands to optimise node data rates. Telemetry2U manages our own network servers so you simply need to point your gateway at our network server.

Node

An end-device in the LoRaWAN network also often referred to as a sensor or simply device. Telemetry2U typically uses the term node as it helps disambiguate between a specific device on the network (node) versus a manufacturer's type of device.

Over-the-Air Activation (OTAA)

This is the most secure mode for nodes to connect to the network and is the only mode supported by Telemetry2U. In this mode the application server needs to know the Device EUI (DevEUI) and Application Key (AppKey) of the node.

Payload

A single "packet" of data to be transferred from/to a node. The maximum length of a packet (maximum payload size) depends on the data rate that is currently being used.

Port

One byte value that can be attached to a packet to provide further information on its contents. Many devices set this to fixed value for uplink packets and ignore it for downlink packets.

Profile

Specifies the channel plan and class to be used when registering a new node on Telemetry2U. For example EU868 represents EU868 Class A and EU868-C is EU868 Class C. Class B is not supported therefore no corresponding options are available.

Received Signal Strength Indicator (RSSI)

An indication of the received signal strength expressed in decibels (dB). For LoRa these values will always be negative and may typically range from around -50 (very high) down to -130 (very low). Nodes will normally continue to communicate reliably and at high data rates down to -110 dB. Below that it may be worth investigating better antenna / mounting arrangements or installing additional gateways.

Spreading factor (SF)

LoRa uses Chirp Spread Spectrum (CSS) to encode data and the spreading factor affects the length of the "chirp" sent for each bit of information. A longer chirp (higher SF) gives the gateway a greater chance of receiving data and therefore increases the range, but it also requires more time to transmit and therefore lowers battery life.

Sub-Bands

Each channel plan is broken down into multiple sub-bands. For example the AU915 plan spans 13 MHz from 915 - 928 MHz and is broken down into 8 sub-bands that each span approximately 1.4 MHz. While the Telemetry2U system does not need to know the sub-band in use it is important that the sub-band selected in your gateway matches that selected in the nodes.

Uplink

Messages sent from the end-devices to the server are known as uplink messages.