As the public-safety community migrates to Long Term Evolution (LTE) broadband technology for its communications, it is imperative that standards-compliant solutions are used by everyone to ensure emergency response is not compromised by lack of interoperability between agencies.

Interoperability needs to be enabled at a number of different levels, including among networks, agencies, multivendor devices, applications and software. Interoperability at all these levels ensures a fast and efficient collaboration at the scene of an incident. Lack of interoperability can severely hinder effective collaborative emergency response management and potentially pose a risk to life.

By selecting standards-compliant solutions, customers avoid being locked into a proprietary product from a single supplier. This ensures they have second source security and are not dependent on a supplier that might cease to support a particular product after it reaches its end-of-life date or does not wish to fulfil the requirements of small user organizations.

A multivendor environment creates competition, which helps keep prices low, encourages innovation and spurs a faster development cycle for new products. A standardized testing and certification process ensures compliance with the standard and interoperability between vendors’ equipment.

Transition to LTE
As public safety begins its migration to 4G LTE broadband technology, it is vitally important that this kind of multivendor, open standards approach is continued because this will ensure interoperability among networks, equipment and public-safety agencies is maintained at all levels.

The biggest interoperability challenge facing the public-safety community is enabling the successful integration of push-to-talk (PTT) and mission-critical push-to-talk (MCPTT) services across multiple LTE networks and with existing professional mobile radio (PMR) networks. MCPTT refers to the standard specification drawn up by the Third Generation Partnership Project (3GPP).

To achieve interoperability, it is necessary for network operators, MCPTT client application providers, device manufacturers and app developers to adopt open standards, namely 3GPP’s MCPTT, mission-critical data (MCData) and mission-critical video (MCVideo) specifications. However, some threats to interoperability are emerging.

MCPTT’s Future
In the United States, AT&T, the mobile operator building the U.S. First Responder Network Authority (FirstNet) nationwide public-safety broadband network, plans to introduce a 3GPP standards-compliant MCPTT service in 2019. AT&T also offers its Enhanced PTT (EPTT) service using technology from Kodiak, a Motorola Solutions company. That technology is based on the Open Mobile Alliance Push-to-Talk over Cellular (OMA-PoC) standard. AT&T also supports over-the-top (OTT) PoC providers that are certified on the FirstNet network.

Rival U.S. carrier Verizon also offers carrier-integrated PTT services, again based on Kodiak technology, and also supports OTT PoC providers. Sprint launched its Direct Connect Plus solution, again using Kodiak PTT technology, earlier in 2018. No testing has been conducted to ensure AT&T’s PTT customers can talk to other carriers’ PTT users.

Over-the-top (OTT) PTT solutions operate independently of carriers’ wireless networks. There are two types: basic OTT PoC provides a PTT service using the carrier’s wireless network as the data transportation provider, and advanced OTT PoC offers PTT plus enhanced quality of service (QoS) solutions provided by the carrier. Some PTT platform providers offer both of these types of services.

Maintaining Interoperability
The risk is public-safety agencies may choose various “MCPTT-like” services or proprietary PTT products that may not be interoperable, or carriers may not allow PTT products to be interconnected even if they are compatible. This lack of seamless MCPTT communications between carriers is a political rather than technical issue, but it must be resolved if the goal of true interagency interoperability is to be achieved. However, the issue is not confined to interoperability between carriers but also between users of different PTT solutions on the same carrier.

For example, a carrier-integrated MCPTT solution based on 3GPP standards will provide users with access to the full suite of mission-critical services. But those using a non-MCPTT carrier-integrated PoC service or one or more different OTT PTT products will not be able to access full carrier solutions.

This could create interoperability issues between carrier-integrated MCPTT users and OTT PTT users at both transport and application levels, as well as between users of different MCPTT/PTT products if they are not compliant to 3GPP standards.

There is also a range of other delivery models in between full carrier integration and an OTT application, such as the mobile virtual network operator (MVNO) approach the United Kingdom is adopting for its Emergency Services Network (ESN). Here, mobile operator EE is providing the network, while Motorola Solutions is providing the MCPTT services, again using Kodiak technology.

Yet another complication is the possibility that a mission-critical services provider does offer an MCPTT-compliant solution but locks users into its way of applying MCPTT with proprietary “enhancements.” End users are therefore tied into using this specific MCPTT client application to enable their devices to access the mission-critical application server on the network. If the users do not like this particular client application or a later release of it, there is nothing they can do about it.

MCPTT Clients
However, if the host network and/or separate MCPTT platform provider allow users to deploy the MCPTT client application of their choice, provided it is compliant with the 3GPP standard, that would open the ecosystem to a multivendor environment and avoid locking customers into a single MCPTT solution in a way that would not compromise interoperability with other end users.

It is important, therefore, that end users understand the benefits of developing a true multivendor standards-compliant MCPTT LTE market rather than opting for myriad proprietary solutions. Public-safety stakeholders need to encourage the development of standards-compliant solutions by multiple suppliers to take advantage of the choice, lower prices and innovation a competitive multivendor environment provides. User can then select and purchase standards-compliant solutions that suit their particular requirements and change the client at any time to another MCPTT compliant client.

It is also helpful if MCPTT client and application developers work to a single standard, so their products can be used across different carriers and devices. To this end, TCCA is supporting the Mission Critical Open Platform (MCOP) research project, funded by the U.S. Department of Commerce’s (DOC) National Institute of Standards and Technology (NIST) Public Safety Communications Research (PSCR).

MCOP provides an open source implementation of an MCPTT client. The MCOP software development kit (SDK) and sample MCPTT app make the development of MCPTT services faster and easier by handling most of the complexity of application development. MCOP will therefore help ensure interoperability and provide a catalyst for more players to enter the MCPTT market by making the business case more attractive.

MCPTT will co-exist as a complementary technology with traditional PMR networks for some years. That means there must be a standardized way of interworking between the two technologies to ensure users of one technology can talk to the other.

3GPP, together with the European Telecommunications Standards Institute (ETSI) and Alliance for Telecommunications Industry Solutions (ATIS), are developing the interworking standards, but it remains to be seen whether vendors will implement the standards and, more urgently, whether carriers will do so and, if so, at what cost to users. The MC community also needs to devise an MCPTT testing and certification regime to ensure devices, solutions and apps are compliant with 3GPP MCPTT, MCData and MCVideo.

Interoperability will encourage a multivendor ecosystem, as well as boosting competition. It will also save a great deal of time and cost because device and app vendors can avoid having to submit their products to individual test and certification with every operator providing a mission-critical service.

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Tony Gray is chief executive for TCCA. Previously, he was regional business director for P3 Group, a global communications engineering and consulting services provider. He has worked in the mobile communications industry for more than 40 years. Before becoming TCCA’s chief executive, he served as a board member and director of TCCA and was founding chairman of TCCA’s Critical Communications Broadband Group (CCBG).