Project 25

Project 25 is a public safety communications standard dedicated to ensuring interoperability in communications. It's designed to ensure fast & secure communications between local, state and federal agencies when protecting the public's welfare.

The Project 25 standard organization is comprised of the Association of Public Safety Communications Officials (APCO), the National Association of State Telecommunications Directors (NASTD) and the U.S. Federal Government. The Telecommunications Industry Association (TIA) offers representation in the standard's creation and modification.

VIAVIis a multi-faceted high-technology company that designs, develops, manufactures and markets a diverse range of microelectronic & test and measurement products. Cobham AvComm is the manufacturer of the 8800, 3550 & 3920 P25 Radio Test Sets.

Project 25 Purpose

The Project 25 standard enables interoperability among multiple manufacturers’ P25 products designed to the P25 standard. The P25 Common Air Interface (CAI) is the most widely deployed P25 interface enabling interoperability between P25 radios and between P25 radios and P25 infrastructure regardless of manufacturer. Public safety users can now obtain documented proof of interoperability between P25 Phase 1 CAI Trunked Subscribers and P25 Phase 1 CAI Trunked Infrastructure in manufacturer issued SDoCs (Supplier’s Declarations of Compliance) and STRs (Summary Test Reports) as part of the DHS Compliance Assessment Program.

In addition to the FDMA Common Air Interface, the Project 25 standard suite also enables interoperability for a TDMA Common Air Interface. The Project 25 suite of standards enables interoperability for several wireline interfaces including but not limited to the Inter-RF Subsystem Interface (ISSI) for connecting disparate P25 networks together which allows users to roam from one network to another network, have encrypted communications across the networks, and permits roamers to talk back with their home users. ISSI gateways are now commercially available in the marketplace today and recently in March 2010 interoperability testing was conducted by several manufacturers successfully demonstrating this capability.

The Project 25 suite of standards enables interoperability for several Data and Secure Services including but not limited to OTAR which provides for key management of encrypted voice and data communications regardless of radio or Key Management Facility manufacturer. Today there are multiple P25 Manufacturers offering commercially available OTAR solutions. Additionally many of these manufacturers have conducted preliminary interoperability testing for OTAR capabilities.

Developing a Test Solution - A Historical Perspective

In the examination of their current and future needs, public safety communications agencies identified several factors that pointed to the need to develop advanced digital two-way communications to replace aging and spectrally inefficient analog systems.

  • The growing scarcity of available radio spectrum
  • Better voice quality over greater areas
  • The growing demand for the integration of new, bandwidth intensive, data functions
  • Security concerns

The Project 25 initiative, has brought together a wide array of local, state, and government agencies with support from the U.S. Telecommunications Industry Association (TIA) to evaluate and develop a new standard for digital two-way radio.

Co-chaired by APCO International and the National Association of State Telecommunications Directors (NASTD), a steering committee was given the job of evaluating the plethora of technologies. Several sub-committees, in-turn, provide the technical expertise to research a number of specialized areas. Aeroflex, through its association with the Telecommunications Industrial Association, has been a key contributor to researching and defining testing parameters for the new standard.

The principle guiding the work of the steering committee was to establish an open narrowband digital radio standard so that multiple vendors could compete for contracts to supply compliant networks with interoperable products. Secondary principles include achieving maximum radio spectrum efficiency and simplifying P25 equipment.

The final documents establishing the Project 25 Standard were signed in Aug. 1995. The basic characteristics of Project 25 radios are these:

  • Phase I—Emission designator 8K10F1E (C4FM, compatible four-level frequency modulation) in a 12.5 kHz channel.
  • Phase II—Emission designator of 5K76G1E (CQPSK, compatible quadrature phase shift keying) in a 6.25 kHz channel.
  • Common receiver for both C4FM and CQPSK to ensure full interoperability.
  • Encryption—As defined in the U.S. Data Encryption Standard (DES) algorithms.
  • Improved Multiband Excitation vocoder—Providing 4400 bits/s of digitized voice, 2800 bits/s of voice error correction on the voice, and 2400 bits/s of signaling overhead, for an aggregate bit rate of 9600 bits/s.

VIAVI Leverages P25 Standard Expertise To Develop a Project 25 Test Solution

A long-time provider of test solutions serving the SMR marketplace, we had a great deal of interest and expertise to contribute toward developing a new SMR digital standard. Beginning in 1995, Aeroflex employees, through their membership in TIA’s TR8 Standards Committee, have been actively lending their expertise to several sub-committees working to develop the P25 standard.

Product Concept

It was through the exposure in the Project 25 development sub-committee that the platform that would later become the 2975 was born. Designed as a brand new platform, the core concept was to build a platform that could easily handle the phased implementation of the standard, as well as other testing requirements.

Technology & Its Practical Impact On Testing - White Paper

As deployment of Project 25 systems gathers momentum, operators, and maintenance personnel are beginning to focus considerable attention toward determining the implications of the migration from analog to a combination analog/digital test paradigm for their support and maintenance programs.

Part I and Part II of this paper detail the technical background of the Project 25 standard, while Part III and IV highlight the particular impact of the standard on testing professionals.