MOTOTRBO: ARS

A radio can be configured to automatically announce its presence to (usually) a computer-based application. The radio would typically be configured to send an Automatic Registration Service (ARS) message either when the user turns the radio on; when the user changes channel or the radio moves (roams) between repeater sites.

This allows, for example, a dispatch application to not only determine whether a radio user is "on the air" but also which channel or site that radio is on.
ARS also saves applications, like Radio Management and IMPRES Battery Fleet Management, from having to check whether radios are online before commencing with any tasks.

Also, users don’t necessarily have to “report in” when starting their working day - the radio informs the dispatcher automatically that they've turned their radio(s) on and are ready for work.

ARS results in a small increase in system loading. A computer-based application is always needed to receive and process these ARS messages.

Portable radios will consume a little bit more energy when ARS is enabled, so if you're designing a system, you might want to think about a higher capacity battery; account for additional battery discharge or limit the amount of ARSes sent.

A radio will send an ARS, even in the absence of location data (i.e. no GPS signal). Radios without GPS are also able to send ARS messages. This is a digital only feature and available on all MOTOTRBO radios.

Note that if ARS is enabled in the radios, there must be a control station or MNIS-based application to receive the messages otherwise, all radios will endlessly retry thereby flooding the channel/system with traffic (imagine: data storm).

Trunked Systems

In Capacity Plus, ARS messages can be sent either on the current rest channel or, if enhanced GPS is enabled, on a data revert channel (if one is available).

Capacity Max does not use or need ARS as there is a standardized DMR Tier 3 registration process which provides presence (i.e. on or off) and mobility (i.e. which site) information via the site and trunked controller.

Initialization Delay

When switching on, radios normally send an ARS message immediately. Some customers may experience congestion on their system when many radios switch on at the same time and try to send ARS.

To reduce the likelihood of this and to prevent collisions, you can set an ARS Initialization Delay value in the codeplug/configuration. This can be set anywhere between 0 minutes and 4 hours.

When set it to 0, the ARS message is sent 5-15 seconds from power on or site change. If you select 30 minutes, then the radio randomly chooses a time between 5 seconds and 30 minutes and sends the ARS then. The cumulative result is that ARSs are spread out over time and the number of collisions and retries drops greatly.

ARS and Roaming

When a radio, with ARS enabled roams, it can be setup to automatically send ARS messages to DDMS.

Interestingly, when a radio with ARS disabled, is executing a Passive Site Search, it will only roam when the RSSI of the repeater roamed to is greater than the RSSI of the current Home Channel by 0dB.
However, when ARS on roaming is enabled, the radio roams only when the RSSI of the repeater roamed to is greater than the RSSI of the current Home channel by 6dB. As a result, this reduces frequent ARSes when the radio moves between sites often.

During Active Site Search, when ARS on roaming is enabled, the radio automatically sends an ARS message to DDMS if it roams into a site successfully. This ARS on roaming capability can be used by the application to monitor which repeater site a radio is currently using.

System Requirements

In general, there needs to be a radio channel (i.e. frequency pair + slot) to carry the ARS message. The channel can be a rest channel on a Capacity Plus system; a channel on an IP Site Connect system or simply a simplex channel. In these systems (i.e. everything except Capacity Max), ARS messages are directed to the Motorola DDMS middleware hosted on a PC somewhere in the system. DDMS tells the application which radio is active and on which slot/site it is.

If DDMS is used with an application, there either needs to be a Control Station connected to the PC or the PC needs to be connected to a repeater and the repeater(s) on which ARS will be sent, need(s) to have the NAI Data licence activated.