Purchasing P25 equipment that has been assessed and approved under the P25 Compliance Assessment Program (CAP) is the best way to ensure P25 equipment is interoperable. A list of approved grant-eligible P25 equipment is available on the Department of Homeland Security (DHS) website.
However, interoperable communications extend beyond P25 equipment. The SAFECOM Interoperability Continuum is designed to assist emergency response agencies and policy makers to plan and implement interoperability solutions for data and voice communications. This tool identifies five critical success elements that must be addressed to achieve a sophisticated interoperability solution: governance, standard operating procedures (SOPs)/standard operating guidelines (SOGs) and field operations guides (FOGs), technology, training and exercises, and usage of interoperable communications. Jurisdictions can use the Interoperability Continuum to track progress in strengthening interoperable communications.
More details on each of five elements is available in the SAFECOM Interoperability Continuum brochure: https://www.cisa.gov/resources-tools/resources/interoperability-continuum

Interoperability Best Practices:
Define your needs. Familiarize yourself with standard offerings that serve your needs. Specify your desired capabilities and user interface. Engage vendors and validate interoperability via testing, then purchase.

Note: Sometimes vendors’ implementations of a feature are P25 compliant but not identical for the User. The look and feel of a P25 implementation i.e., the ergonomics of a device and user experience is not defined by the standard. Thus, while P25 features/functions may work the same, the User interface and experience of a device will vary between manufacturers. There are some common elements that are often implemented (for example the usage of a channel selector knob or PTT button in a SU) but these are not strictly required by the standard.

A variety of manufacturers offer multi-band, multi-mode subscriber units capable of P25 Phase 1, P25 Phase 2, and analog channels. In addition, there are numerous interoperability products and consoles that provide hard and soft patches between conventional and P25 trunking. Other network vendors also support mapping from conventional to trunking user groups without patching. The full range of solutions can be found through links on the PTIG P25 Products and Services Matrix. A link to the matrix is below.
https://www.project25.org/index.php/products/p25-supplier-matrix

The systems operator of your regional P25 network is the key to access for new users. Most have standard policies and procedures to accomplish this. Call them to understand the things that can affect your ability to get access: Radio programming policy, frequency band used by the system, if the system is a P25 Phase 1 or P25 Phase 2 system, and what the rev level is for the system’s trunking software. Many systems have already tested and approved specific P25 subscriber units for operation on their system from multiple vendors. This list should be available. Some systems permit some, but not all makes/models of P25 radios. Most P25 System operators require testing on their system to receive approval to operate.

Your organization should start by capturing user needs and defining options that are both operationally and commercially in your organization’s best interests. A variety of consultants with extensive Project 25 experience are available if your organization requires assistance with this process. A variety of manufacturers offer interoperability products, network bridges and patches.
Other network vendors also support mapping from conventional to trunking user groups without patching.
The full range of solutions can be found through links on the PTIG P25 Products and Services Matrix. A link to the matrix is below:
https://www.project25.org/index.php/products/p25-supplier-matrix

Contact the PTIG director who will query the involved vendors for possible solutions. mailto:[email protected].
Each State in the USA has a designated “State-wide Interoperability Coordinator” (SWIC). They can offer potential resolution to interoperability issues in your state. A list is available using the link below.
https://www.cisa.gov/safecom/ncswic-membership A variety of consultants with extensive Project 25 experience are available to assist you.

From the perspective of the user, “automatic roaming” refers to the radio’s ability to move from the coverage of one RF site or system to another without user intervention (or often even user knowledge). The user’s radio automatically knows when coverage is degrading, it automatically searches for better coverage, and then automatically switches and registers with the new RF site’s control channel.
Alternatively, “manual roaming” from the user’s perspective requires the user to physically select the new site, or system using radio control methods (i.e. menu, selector, etc.). The radio then tunes to the newly selected site frequency and attempts to register on the new RF site’s control channel.
Identity management programming for the roaming radios and infrastructure is key to successful reliable roaming. A Whitepaper on P25 Roaming and Identity Management is available at
https://www.project25.org/index.php/documents/p25-whitepapers?view=frontlist&catid[0]=10016

Prior to known events and on an ongoing basis, collaborate with neighboring agencies to compare system set up and programming parameters. Conduct tests for various scenarios to ensure interoperability. Changes in standards, testing, hardware, firmware, features and services may affect your interoperability.

The CAP documents will tell which new features and software releases have been tested for interoperability between manufacturers. Good communication with your neighboring jurisdictions and the manufacturers is strongly recommended. Check with your consultant or P25 Equipment manufacturer for the latest documentation and ensure your equipment has been updated to the latest software and about how they ensure new products are compliant and their programs to keep legacy equipment up to date.

Check that the features or interfaces that you are interested in are covered by the published standards. Check that the manufacturers that you are interested in have implemented these features or interfaces to the published standards. Check to see if the manufacturers of interest have tested the features and interfaces that you require.