Tuesday 20 January 2026: Around the world, first responders rely heavily on paging and callout services to quickly alert emergency services personnel on call to incidents, provide them with short and precise information about the incident at hand, and to find out who is able to respond. Callout is a defined specification developed by TCCA for TETRA networks for critical two-way alerting, but to date there has been no parallel specification for 3GPP 4G and 5G broadband networks. Now, TCCA has published new Broadband Callout specifications for 3GPP-enabled mission critical networks using broadband MCX functionality – Mission Critical Push-to-Talk Voice (MCPTT), Mission Critical Video (MCVideo) and Mission Critical Data (MC Data).

TCCA's Critical Communications Broadband Group (CCBG) established a task force to create the Broadband Callout specifications. Where TETRA callout uses SDS (Short Data Service) and TETRA voice communication, Broadband Callout is compatible with 3GPP MCX standards and uses MCData SDS and MCPTT.

“Similar to TETRA callout, Broadband Callout is a lightweight service designed for efficient alerting and user responses, and with added features to take advantage of broadband capabilities,” said task force leader Hans Petter Naper from The Norwegian Communications Authority (Nkom). “Callout is a vital part of dispatch functionality, and a widely adopted and interoperable callout service should be part of broadband mission critical networks.”

“These are the first technical specifications created on top of 3GPP standards expanding and complementing the capabilities of the under lying MCX services,” said Tero Pesonen, CCBG chair.  “TCCA’s mission critical Broadband Callout specifications are freely available to encourage the formation of a common global interoperable multivendor market that meets the user needs. We look forward to continuing to serve the critical communication sector with further specifications and guidelines.”

There are two types of Broadband Callout specifications. Simple callout uses SDS messages solely, to alert users and collect user responses. Full callout additionally includes a callout information phase in which the dispatcher and users can talk in the MCPTT callout group and exchange text information about the incident during the callout. After a simple or full callout ends, the users resume normal operation with their devices and MCX services for the incident handling phase.

Broadband Callout alert messages can be longer than TETRA callout messages, which allows more accurate and richer descriptions of the incident and its handling. The dispatch system can also include the incident location to allow a broadband device with a high-resolution display to automatically show the incident in a map and navigate the user to the scene of the incident.

TCCA’s Broadband Callout specifications include functionality for the users to indicate their future availability status to the dispatch system. Availability status can be on duty, off duty, on holiday, etc., and this enables the dispatch system to build and maintain a calendar for each user. The dispatch system can additionally have access to each user's location and select available users based on their distance from and travel time to the incident, their skills and equipment.

User devices that are part of a callout are instructed to use a particular callout communication group for MCPTT and MCData SDS messages during the callout. When the callout ends, the devices can be directed to another group for communication in the incident phase.

With TCCA’s new Broadband Callout specifications, it is possible to call out users to respond to incidents no matter who makes and delivers MCX clients and dispatch systems, as long as the specifications are followed. These support callout of users belonging to different user groups or agencies, and even across country boundaries.

Mission critical grade products can only be ensured by interoperability and certification testing. The next steps are to invite vendors to test their callout implementations as part of the ETSI MCX Plugtests™ program, and to add Broadband Callout to the Global Certification Forum (GCF) mission critical services certification program.

The two documents created by TCCA’s task force, the Broadband Callout Service Overview with requirements and use cases, and the Broadband Callout Service Definition with the detailed specifications, are available here.