The goal of mission-critical communication systems is to minimize the response time of first responders in emergency situations across several agencies. A dedicated push-to-talk button offers an efficient mechanism that simplifies the speaker-to-listener process to a minimum. This feature is useful when coordinating large group activities and to enable the instant flow of tactical status and commands with minimal overhead and latency. Wireless radio push-to-talk represents the foundation of mission-critical communications, enabling the exchange of voice information with a group of listeners in a quick, reliable and effective way.

From PTToC to Mission Critical PTT

Push-to-talk over cellular (PTToC) technology has come far since its early days. The evolution and technology refinements of LTE reduced round-trip latency and boosted data capacity. Just as important, mobile network operators have aggressively expanded LTE coverage across large geographic regions, delivering nearly ubiquitous coverage. This combination of high performance and ubiquity offers a solid solution fit for the stringent requirements of the critical communications user community.

The demand from first responders for bandwidth-rich critical applications is driving governments to establish dedicated LTE/5G mobile data networks to serve public safety and other agencies' mission-critical requirements. Selecting the appropriate implementation of the PTToC protocol is a fundamental step in the design of the national critical networks of the future.

Nowadays, the PTToC market is dominated by generalized proprietary solutions. However, there is an emerging range of new PTToC options. Long-standing PTToC approaches based on over-the-top (OTT) protocols now coexist with new 3GPP-based offers embedded in the LTE network architecture to support mission-critical-grade optimization and a feature-rich suite of services. This 3GPP-based group, known as Mission Critical PTT (MC-PTT), has caught the attention of the public safety community due to its higher level of reliability and performance guarantees.

To achieve the required performance, network-integrated MC-PTT servers are hosted within the mobile network operator (MNO) architecture or with a standalone private core network. Data traffic over the network is marked with standardized QoS Class Identifier (QCI) values that provide preferential transmission during congestion in the core or radio access network on mission-critical LTE networks. The combination of network-integrated MC-PTT with MC-LTE forms the basis for most government PTToC deployments. Following the steps of FirstNet in the US and Safe-Net in South Korea and their MC-PTT solutions, multiple new government programs to establish mission-critical public safety broadband networks are progressing across Europe, Canada, Australia and New Zealand. These programs will reshape the PTToC market and thus reduce the dominance of simple OTT protocols.

Network-integrated standard MC-PTT deployments have focused on government public safety deployments. But several commercially oriented services are now available to enable critical communications in industry verticals (e.g., manufacturing, mining, utilities, transport, etc.). MC-PTT network integration is, however, complex, and the procurement processes are challenging. To reflect this issue, Omdia forecasts the most dramatic increase of MC-PTT users in the 2026–30 timeframe.

Standards-based MC-PTT and Interworking Function

These new MC-PTT systems will not operate as isolated islands but in heterogeneous hybrid environments. Mission-critical users need to be able to reliably communicate regardless of technology or solution type. Public safety agencies need to blend MC-PTT devices with land mobile devices, and enterprises will seek migration strategies that accommodate LTE and land mobile radio (LMR).

Consequently, one of the most significant factors facing any MC-PTT deployment is interoperability. Technology interworking is fundamental to guarantee the effectiveness of the MC-PTT solution. Interconnection between existing LMR devices and across other MC-PTT or PTToC devices, along with the control room console applications, is a vital problem that the ecosystem must address with an Interworking Function (IWF).

Additionally, one of the main drivers of MC-PTT market growth can be attributed to the 3GPP standardization efforts. Governments gain several important benefits by making standards the basis for PTToC deployments. In particular, standards-based approaches facilitate roaming and interoperability and benefit from economy-of-scale advantages.

Other benefits of 3GPP standardization include the following:

3GPP Release 16 introduced an IWF to bridge communications between legacy systems and MC-PTT. This Interworking Function brings well-defined and open protocols that help avoid silo and vendor lock-in challenges. More work is needed across the industry, but already today, a limited number of vendors provide carrier-grade IWF that can host group calls across smartphones and LMR radios.

The evolution of PTToC will be shaped by technology, competition and customer preferences. It is undeniable that critical communication users will benefit from mission-critical service beyond voice-centric features. The rich communications suite underpinning MC-PTT provides a foundation for other mission-critical services, including data transport and video. Indeed, push-to-video is now specified in 3GPP specifications, and mission-critical service architectures have started to refer to push-to-X functionality instead of the more limited push-to-talk.

This blog is sponsored by Samsung Networks.

— Ildefonso De La Cruz Morales, Principal Analyst – Critical Communications, Omdia