Tips & Tricks – The interval: On request

by Christian Hansen

18. July 2024

The On Request interval is a special interval. It differs from the other intervals in terms of the processes involved in data transfer. How this interval works in detail and what needs to be considered when using it is described in this article.

Differences between intervals

As the name suggests, data transfer is only initiated with the On Request interval when the GPS tracker receives the appropriate command. The request is made via the app and is processed asynchronously. This means that the request is sent, but no direct response is awaited. This is because the request does not reach the GPS tracker immediately, but with a time delay. The reason for this is described in more detail in the following sections.

For the other intervals with reference to a fixed time unit (e.g. 10 seconds), the data transfer only takes place after the interval has expired.
You can read why the GPS tracker reacts this way at these intervals in our article on energy management: Tips & Tricks – Battery Management and Intervals

Process of communication

If you tap the “Request position” field/button in the app, our system will send an SMS to the GPS tracker. If the SMS is successfully received by the GPS tracker, the GPS tracker will attempt to determine a position. After a maximum of 15 minutes, the GPS tracker will send a response to the server, with or without position data.
In order for the GPS tracker to receive the SMS and for further communication to run smoothly, it must not be shielded.

Why an SMS?

In order to save energy, the GPS tracker reduces the possible communication paths to a minimum. This interrupts communication via the data network, but the path to receiving an SMS remains open.
Basically, at the other intervals – there are small differences depending on the interval – a connection to the network is established at a given time in order to transfer the data.

The 15-minute rule

The 15-minute rule applies to GPS trackers for two reasons:

Technical requirements
Energy management

The GPS tracker stores data that tells it where the GPS satellites will be within the next two hours or so. This allows for faster positioning. If the GPS tracker has been idle for a long time without communication, the stored data may have expired. This means that the GPS tracker must update the data after waking up before it can determine a position. This usually takes up to a maximum of 12 minutes. So, if it takes 15 minutes, the GPS tracker would then have three minutes left to calibrate the position better so that it becomes more accurate.

Determining a position is an energy-intensive task for the GPS tracker. Therefore, this should not be carried out for too long in order to avoid unnecessarily affecting the battery life. However, since a so-called cold start can take up to 12 minutes before the GPS module can determine a position, the GPS trackers are given a grace period of three minutes for calibration. In most cases, this time is sufficient to successfully determine a position.

If the GPS tracker finds a position within 15 minutes, it is transmitted. It then waits for the next command to find the position. However, depending on the environmental conditions, it is not always possible to determine a position.

Sending SMS

It can happen that an SMS does not reach the GPS tracker immediately. In this case, this is not necessarily due to the availability of the GPS tracker, but also to how SMS are processed by the network operators. If an SMS cannot be delivered on the first attempt, it is not lost. The SMS is usually tried to be delivered for a day before the process is aborted.

Communication status

To help you follow the process, when a position is determined by “On Request”, push notifications are generated that you will receive. A push notification is generated when:

The GPS tracker confirms that it has received an SMS
The GPS tracker was able to determine a position
The GPS tracker was unable to determine a position

Summarized

The On Request interval allows the GPS tracker to transmit data only when requested. Unlike the other intervals, communication is partly based on SMS. This type of communication can be subject to delays depending on environmental conditions. The Prothelis system informs about the current status of the communication process with the GPS tracker using push messages.

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