Group Call

Group Call is a two-way call made from a radio or dispatcher to multiple radios (or sometimes even dispatchers). Radios that are party to a Group Call can respon by simply pressing the PTT within the Call Hangtime (or reestablish the same call, if the call hangtime has expired). It is often also referred to as a Talkgoup Call.

Details

The digital group is a way of enabling groups to share a channel without distracting and disrupting one another. Because two-way radios are well suited for “one-to-many” types of calls, the Group Call is the most common call in a MOTOTRBO system. Hence, the majority of conversations takes place within a group.

Group Call numbering and structure is part of the fleetmapping process and defined according to the organizational structure of the end user. When planning for groups, one should think about:

• which members of the functional workgroups in their organization that need to talk with one another,
• how those workgroups interact with members of other workgroups, and
• how users will collectively share the channel resources.

Greater detail on the fleetmapping process is provided in System Design Considerations.

Configuration in Radios.

In order for a radio to receive a Group Call, it must have the Group Call number provisioned in its RX Group List or in its TX Contact. The Group Call ID must also therefore be provisioned in the Radio's Contact List. Since the RX Group List and TX Contact are channel dependent configurations, it's possible to change between/select Groups via the Channel selector on a radio.

In Simplex, Single Site and IP Site Connect Systems

In Simplex, Single Site and IP Site Connect Systems, all parties to a Talkgroup Call must be on the same channel (frequency; slot and colour code).

The repeater(s) in a Single Site or IP Site Connect system do not require any specific configuration for groups. Radios can be configured to enable the user to select among multiple groups using the radio channel selector knob or buttons, or using the radio menu contacts list. Which group a radio user hears on a given channel depends on a configurable parameter called the RX Group List. A call preceding tone can be provisioned to alert the target user of the incoming Group Call. This can be enabled or disabled per Group.

In Capacity Plus (Single/Multi-Site) and Capacity Max Systems

In Capacity Plus systems, there is no need to select the channel as the frequency and slot are automatically assigned by the system. In Multi-Site Capacity Plus systems, the Talkgroup may (depending on he system configuration) only be allowed on certain sites and a user may miss Talkgroup calls if their radio strays onto a site where that Talkgroup is not allowed.

In Capacity Max Systems, the selected Talkgroup must be allowed on the currently roamed/home site.

Capacity Plus Single Site and Capacity Plus Multi Site systems allow a radio user to leave a Group Call and start another voice or emergency or control call (for example, Call Alert, Radio Check, Radio Inhibit/Uninhibit, and others) while the radio is busy listening in to a Group Call. The radio moves to the current Rest Channel and starts a new call there. If a user starts a non-Emergency Call when all channels are busy, then the call fails, and the radio stays on the voice (traffic) channel.

Number Range

The number Range for Group Call IDs in all systems except Capacity Plus is 1 to 16776415. The range for Capacity Plus is 1 to 254.

This number is used to form the CAI ID of the group call.

Capacity Max Talkgroup Call

In a Capacity Max system, a talkgroup can be selected in any of the following ways:

• A Capacity Max radio supports multiple personalities that can be selected using knob position. A personality has a “contact name”. A radio user can make a call to the contact name by just pressing the PTT button. If the contact names of multiple personalities of a radio are talkgroups then the radio user can select a talkgroup using the knob.
• A Capacity Max radio supports an address book. A radio user can make a call to an entry in the address book using the radio’s menu. This can be done even when the radio is receiving a call.
• A personality has a “group list”. The group list can have up to 16 talkgroups. A radio user can receive a voice or data group call, only if it is for one of the 16 talkgroups and scan is enabled or it is for a All talkgroup, that is site-wide or multi-site or system-wide.

List of Valid Sites

A Capacity Max system allows a system owner to list the sites that are valid for a talkgroup.

For a talkgroup call (including multi-site all call talkgroup), a system owner can list the sites where a call for the talkgroup can be initiated. A call for the talkgroup cannot be initiated from a site that is not in the list. In addition, a call for the talkgroup is never transmitted over the air at a site that is not in the list. By default, the list of valid sites for a talkgroup contains all sites.

This list allows a system owner to bill its customers based on the coverage area of a talkgroup.

If a radio requests registration and affiliation of its Tx talkgroup (contact name) at a site that is not in the list of valid sites for the talkgroup, the system registers the radio, but with a warning. The radio displays the warning, which may prompt the radio user to either roam manually to another site or use the knob to select a different talkgroup (if configured). The radio is not able to make a call to its TX talkgroup (contact name), but it can do the following:

• Receive calls for its Rx talkgroups in the “group list” that are valid at the site.
• Make or receive individual voice or data calls.
• Make a call to a talkgroup (including an emergency talkgroup) that is valid at the site.

List of Static Sites

A Capacity Max system allows a system owner to list sites where a talkgroup call is always transmitted over the air.

A call for the talkgroup is always transmitted over the air at all the sites in the list of static sites even when no radios have affiliated at the site. By default, the list of static sites for a talkgroup contains no sites. All sites in the list of static sites must be in the list of valid sites for the talkgroup. In other words, the list of static sites is a subset of the list of valid sites for a talkgroup.

Affiliation of a talkgroup by a radio is an optional DMR Tier III feature, and some non-Motorola Solutions radios may not affiliate their talkgroup. In that case, the system owner can statically associate their talkgroup to the required sites.

Normally, emergency talkgroups are exclusively used for emergency purposes. If no radios affiliate for the emergency talkgroup at a site then, and the emergency call cannot be transmitted at a site where recipient radios are not present. In that case, the system owner can either statically associate their talkgroup to the required sites or configure the emergency talkgroup into the radio's RX Group List as an affiliation talkgroup..

Static site associations should be used judiciously because transmitting a talkgroup call at a site where no listeners are present is a waste of channel resources.

Sites with Successful Affiliation

A talkgroup call is transmitted at all sites where at least one radio has successfully affiliated to the talkgroup.

A radio affiliates to zero to seven talkgroups at a time. The radio affiliates its Tx member (contact name) only if it is a talkgroup (excluding site-wide or multi-site All talkgroups). It affiliates to priority talkgroups when they are configured/selected. The configured/selected affiliation talkgroups must belong to the RX Group List.The system rejects affiliation of any talkgroup that is not valid at the site.

Talkgroup Call Affiliation

A talkgroup call can be initiated from any valid site for the talkgroup. Affiliation is required for receiving a call, but not for initiating a call. Thus, a radio can initiate a call from a site even when no radio has affiliated to the talkgroup at that site.

A talkgroup call is transmitted at all the valid sites for any of the following conditions:

• The site is statically associated with the talkgroup.
• At least one radio has affiliated to this talkgroup.
• The site is the source site.

Broadcast Talkgroup Call Configuration

A Capacity Max system allows a talkgroup to be configured as a Broadcast Talkgroup Call.

“Broadcast” is an attribute of a talkgroup call. A Capacity Max system sets this attribute to a usage (for example, a transmit member (contact name) of a personality, an entry in the address book) of a talkgroup. An address book can have two entries for a talkgroup – one with broadcast and other without broadcast.

In a broadcast talkgroup call, only the initiating radio transmits. The call has hangtime (same as a talkgroup call) but during hangtime only the call initiating radio can transmit. Other participating radios cannot interrupt a broadcast call.

Normally, a large number of radios are members of a broadcast talkgroup. By not allowing other radios to transmit during hangtime of a broadcast call, over the air collisions of responses of the other radios can be eliminated.

Radio Joining an Active Talkgroup Call

There are certain scenarios where a radio affiliates to a talkgroup at a site and the in-progress talkgroup call is not active at the site. Such scenarios include roaming to the site and changing the selected personality of the radio. When a radio affiliates to an active talkgroup at a site and the talkgroup call is not active at the site, the talkgroup call is routed to that site( if a traffic channel is available).

If the radio affiliates to a list of talkgroups, the system attempts to join only the highest priority affiliated talkgroup call

If a traffic channel is available, the control channel transmits channel grants and the radio joins the inprogress call. If this addition of a site equals the threshold to use the voice replicator, the call switches to use the voice replicator.