Radio technologies
P25 technology (Project 25): the digital radio standard of North American public safety.
P25, or Project 25, is the open digital radio standard created for public safety in North America. In Europe and Italy, the reference standard remains TETRA: here P25 matters mainly for interoperability, military and government contexts, and networks already in the field that need to be integrated or monitored. We explain what it is, the difference between Phase 1 and Phase 2, and what Teleproject offers as a multi-protocol integrator: dispatching with Respondr, carrier monitoring, and integration with your existing networks.
What P25 is
P25, short for Project 25 (or APCO-25), is a suite of digital radio standards defined by the TIA-102 specifications. It was created in the United States to give public safety an open, interoperable standard: radios from different manufacturers working on the same network, with no lock-in to a single vendor.
P25 originated and spread mainly in North America. In Europe and Italy, the reference standard for public safety is TETRA, not P25. For an Italian organization, P25 comes into play in specific cases: interoperability with the P25 networks of foreign partners, military and government contexts, international operations, and already-installed P25 networks that need to be integrated or kept under control.
Teleproject approaches P25 as a multi-protocol integrator: we integrate P25 into mission-critical radio networks and into dispatching systems for public safety, alongside TETRA, DMR, and VHF/UHF.
P25 Phase 1 and Phase 2
The standard is defined in two phases, with two different ways of using the 12.5 kHz channel. The difference is capacity.
Phase 1: FDMA, one 12.5 kHz channel
In Phase 1, each channel occupies 12.5 kHz in FDMA and carries one communication, with C4FM modulation. It is the foundation of P25 and is compatible with conventional analog FM: the same radios can work in digital and analog during migration.
Phase 2: TDMA, two communications on the same channel
In Phase 2, the 12.5 kHz channel is divided into 2 TDMA slots that alternate in time: two independent communications on the same frequency, with capacity equivalent to 6.25 kHz per voice channel. For the same spectrum, the network doubles its capacity. In both phases, voice is encoded with the AMBE+2 vocoder.
How it works and interoperability
Conventional or trunked network, the interfaces that make P25 interoperable, and the bridge to other radio networks: this is where the value of P25 lies for Teleproject.
Conventional or trunked
Like other professional radio networks, P25 works in conventional mode, channel by channel, or trunked, with dynamic channel assignment across a multi-site network. Trunked is the configuration used by large public-safety networks and large-scale government operations.
CAI and ISSI: the interfaces of interoperability
Two open interfaces are at the heart of P25. The CAI (Common Air Interface) defines the common radio interface, so terminals from different manufacturers work on the same network. The ISSI (Inter-RF Subsystem Interface) connects P25 subsystems and networks from different areas or agencies. Traffic can be encrypted with AES-256.
The bridge to TETRA, DMR, and other networks
P25 does not communicate at the radio level with TETRA or DMR, which are different standards. What connects them is the dispatch platform: Respondr bridges P25 with TETRA, DMR, VHF/UHF, and push-to-talk over cellular networks, putting radios of different standards into the same talkgroups, on a single console. This is the concrete value of P25 for an Italian organization: interoperability.
- CAI and ISSI (P25)
- The Common Air Interface makes P25 terminals from different manufacturers interoperable; the Inter-RF Subsystem Interface connects P25 subsystems and networks to one another.
- Gateway and dispatching
- Respondr bridges P25 with TETRA, DMR, VHF/UHF, and PoC networks: radio gateway and unified console on a single interface.
- Unified talkgroups
- An operator on a TETRA or DMR network and a team on a P25 network hear each other as if they were on the same network, with each one’s encryption preserved.
P25 or TETRA
Two digital standards for public safety, born in two different markets.
TETRA is the European standard for public safety; P25 is the North American standard. They are not interchangeable at the radio level and serve different markets: in Europe and Italy, civil public-safety networks run on TETRA, and in part on DMR, while P25 is found where it is already in the field, in military and government contexts or in exports.
It is not a matter of principle: Teleproject designs and integrates both, and makes them talk to each other. The comparison table between the digital standards is in the guide to TETRA technology, and the comparison between the network profiles is in the TETRA or DMR section.
Where P25 is used
For an Italian organization, P25 matters in specific contexts: interoperability, defense, international operations. It is not the standard of national civil public-safety networks.
Public safety
Interoperability with existing P25 networks and joint operations across agencies, where national civil networks remain on TETRA and DMR.
Defense and military
Encrypted communications for defense and national-security applications, with multi-protocol linking to TETRA and DMR networks.
Multi-agency interoperability
Radios from different standards and agencies in the same talkgroups, through gateways and dispatch consoles.
International operations and export
Projects where P25 is already the standard in the field, outside European borders or in multinational contexts.
In Italy, civil public-safety networks run on TETRA and DMR: P25 comes into play mainly in interoperability and in defense and national security contexts.
What Teleproject offers for P25
As a multi-protocol integrator, we place P25 inside systems that integrate multiple radio standards: dispatching, monitoring, and integration.
Integration and dispatching with Respondr
Respondr unifies P25 with TETRA, DMR, VHF/UHF, and push-to-talk over cellular networks in a single operator console, with shared talkgroups and TLS 1.3 and AES-256 encryption. This is interoperability between P25 and other radio networks.
P25 carrier monitoring
TP-RFX monitors the presence of P25 carriers in tunnels 24 hours a day and alerts technicians at the first missing signal; Track-TP supervises network devices and sites via SNMP, with real-time alarms.
Multi-protocol design and integration
We design and integrate systems in which P25, TETRA, DMR, VHF/UHF, and PoC coexist: existing investments are preserved, and new and already-installed technologies work side by side on the same platform.
Frequently asked questions about P25
Use in Italy, Phase 1 and Phase 2, compatibility, and licensing: the essential answers.
Is P25 used in Italy?
Not as the national public-safety standard: in Italy and Europe, civil public-safety networks use TETRA, and in part DMR. P25 is found in interoperability with foreign networks, in military and government contexts, and in already-installed P25 networks that need to be integrated or monitored.
In Italy. P25 is not the national public-safety standard; the reference for civil networks remains TETRA.
What is the difference between P25 Phase 1 and Phase 2?
Phase 1 uses FDMA access: a 12.5 kHz channel carries one communication, with C4FM modulation. Phase 2 uses TDMA access: the same channel is divided into 2 slots and carries two communications, with capacity equivalent to 6.25 kHz per voice channel. Phase 2 doubles capacity for the same spectrum.
Is P25 compatible with TETRA and DMR?
Not at the radio level: they are different standards and the radios do not communicate directly. Yes, through a dispatch platform: gateways and a unified console put P25, TETRA, and DMR networks into the same talkgroups. That is what Respondr does.
What frequencies does P25 use?
P25 has no band of its own: it works in VHF (136–174 MHz), UHF (380–470 MHz) and, in North America, also at 700 and 800 MHz. The actual bands depend on national assignments for professional mobile radio and public safety.
In Italy. Frequencies follow the national frequency allocation plan (D.M. 31 agosto 2022) and the assignments for professional mobile radio.
Is P25 compatible with analog FM radios?
Yes. P25 is backward-compatible with conventional analog FM: P25 radios can also work in analog and switch between the two modes, which is useful during migration from an existing FM network.
Do you need a license to use P25?
Yes. Like any radio network that uses its own frequencies, P25 requires authorization from the national regulator with the corresponding frequency usage rights. The only exception is those who operate on the already-authorized networks of third parties.
In Italy. A general authorization with frequency usage rights is required under D.Lgs. 259/2003; the application is submitted through the MIMIT portal. Teleproject handles the paperwork on the customer’s behalf.
Let’s talk about your P25 project.
Interoperability with P25 networks, supply of Motorola APX terminals, or carrier monitoring: we handle integration and technical support, with a single point of contact.