Editing Project 25 (section)

== Suite of standards overview ==

===History===
Public safety radios have been upgraded from [[Analog signal|analog]] [[Frequency modulation|FM]] to [[Digital data|digital]] since the 1990s because of an increased use of data on radio systems for such features as GPS location, [[Trunked radio system|trunking]], text messaging, metering, and encryption with different levels of security.

Various user protocols and different [[public security|public safety]] [[radio spectrum]] made it difficult for Public Safety agencies to achieve interoperability and widespread acceptance. However, lessons learned during disasters the United States faced in the past decades have forced agencies to assess their requirements during a disaster when basic infrastructure has failed. To meet the growing demands of public safety digital radio communication, the United States [[Federal Communications Commission]] (FCC) at the direction of the [[United States Congress]] initiated a 1988 inquiry for recommendations from users and manufacturers to improve existing communication systems.<ref name="project1">{{cite web |url=http://www.project25.org/modules.php?name=Content&file=viewarticle&id=2|archive-url=https://web.archive.org/web/20090210120900/http://www.project25.org/modules.php?name=Content&file=viewarticle&id=2 |archive-date=2009-02-10 |url-status=dead |title=Project 25 Technology Interest Group - Content - General - What is Project 25? |website=project25.org |publisher=Project 25 Technology Interest Group |access-date=2014-06-06}}</ref><ref name="project2">{{cite web |url=http://project25.org/component/content/article/29-content-articles/49-what-is-p25 |title=What is P25? |website=Project25.org |publisher=Project 25 Technology Interest Group |access-date=2014-06-06 |url-status=dead |archive-url=https://web.archive.org/web/20140607000408/http://project25.org/component/content/article/29-content-articles/49-what-is-p25 |archive-date=2014-06-07 }}</ref> Based on the recommendations, to find solutions that best serve the needs of public safety management, in October 1989 APCO Project 25 came into existence in a coalition with:<ref name="project1"/><ref name="apcointl1">{{cite web|url=http://www.apcointl.org/frequency/project25/information.html |title=Spectrum Management |publisher=Apcointl.org |date=2013-09-30 |access-date=2014-06-06 |url-status=dead |archive-url=https://web.archive.org/web/20120212013100/http://www.apcointl.org/frequency/project25/information.html |archive-date=February 12, 2012 }}</ref>
* [[Association of Public-Safety Communications Officials-International]] (APCO)
* [[National Association of State Telecommunications Directors]] (NASTD)<ref>{{Cite web|url=http://www.nastd.org/home|title=Home - National Association of State Technology Directors|website=www.nastd.org}}</ref>
* [[National Telecommunications and Information Administration]] (NTIA)
* [[National Communications System]] (NCS)
* [[National Security Agency]] (NSA)
* [[United States Department of Defense|Department of Defense]] (DoD)

A steering committee consisting of representatives from the above-mentioned agencies along with FPIC ([[Department of Homeland Security]] Federal Partnership for Interoperable Communication), [[United States Coast Guard|Coast Guard]] and the [[United States Department of Commerce|Department of Commerce]]'s [[National Institute of Standards and Technology]] (NIST), Office of Law Enforcement Standards was established to decide the priorities and scope of technical development of P25.<ref name="apcointl1"/>

===Introduction===
Interoperable emergency communication is integral to initial response, public health, community safety, national security and economic stability. Of all the problems experienced during disaster events, one of the most serious is poor communication due to lack of appropriate and efficient means to collect, process, and transmit important information in a timely fashion. In some cases, radio communication systems are incompatible and inoperable not just within a jurisdiction but within departments or agencies in the same community.<ref>{{cite web|url=http://www.safecomprogram.gov/NR/rdonlyres/3FFFBFBA-DC53-440E-B2EF-ABD391F13075/0/SAFECOM_Statement_of_Requirements_v1.pdf |title=SOR.book |access-date=2010-09-26}}</ref> Non-operability occurs due to use of outdated equipment, limited availability of radio frequencies, isolated or independent planning, lack of coordination, and cooperation, between agencies, community priorities competing for resources, funding and ownership, and control of communications systems.<ref>{{Cite web|url=http://www.ncjrs.gov/pdffiles1/nij/204348.pdf|title=Why Can't We Talk?<!-- Bot generated title -->}}</ref> Recognizing and understanding this need, Project 25 (P25) was initiated collaboratively by public safety agencies and manufacturers to address the issue with [[emergency communication system]]s. P25 is a collaborative project to ensure that [[two-way radio]]s are interoperable.  The goal of P25 is to enable public safety responders to communicate with each other and, thus, achieve enhanced coordination, timely response, and efficient and effective use of communications equipment.<ref>{{cite web|url=https://www.motorola.com/staticfiles/Business/Solutions/Business%20Solutions/Mission%20Critical%20Communications/ASTRO%2025%20Trunked%20Solutions/_Document/Project%2025%20Whitepaper.pdf?localeId=33 |title=A Google Company |publisher=Motorola |access-date=2014-06-06}}</ref>

P25 was established to address the need for common digital public safety radio communications standards for first-responders and homeland security/emergency response professionals.  The [[Telecommunications Industry Association]]'s [http://tiaonline.org/all-standards/committees/tr-8 TR-8] engineering committee facilitates such work through its role as an ANSI-accredited [[standards organization|standards development organization]] (SDO) and has published the P25 suite of standards as the TIA-102 series of documents, which now include 49 separate parts on Land Mobile Radio and TDMA implementations of the technology for public safety.<ref>[http://global.ihs.com/search_res.cfm?currency_code=USD&customer_id=2125402A4E0A&oshid=2125402A4C0A&shopping_cart_id=292558332D4B20484B5B3D5B220A&country_code=US&lang_code=ENGL Search Results | IHS Standards Store<!-- Bot generated title -->]</ref>

{{cquote|Project 25 (P25) is a set of standards produced through the joint efforts of the [[Association of Public Safety Communications Officials International]] (APCO), the National Association of State Telecommunications Directors (NASTD), selected federal agencies and the National Communications System (NCS), and standardized under the [[Telecommunications Industry Association]] (TIA)... The P25 suite of standards involves digital Land Mobile Radio ([[Land Mobile Radio System|LMR]]) services for local, state/provincial and national (federal) public safety organizations and agencies...

P25 is applicable to LMR equipment authorized or licensed, in the U.S., under NTIA or FCC rules and regulations.

Although developed primarily for North American public safety services, P25 technology and products are not limited to public safety alone and have also been selected and deployed in other private system application, worldwide.<ref>Codan LTD., [https://cdn.codancomms.com/general-downloads/Products/User-Guides/Codan_TG-001-4-0-0-P25-Training-Guide.pdf P25 Radio Systems] Training Guide</ref>}}

P25-compliant systems are being increasingly adopted and deployed throughout the United States, as well as other countries. Radios can communicate in [[analog signal|analog]] mode with legacy radios, and in either [[Digital signal (signal processing)|digital]] or analog mode with other P25 radios. Additionally, the deployment of P25-compliant systems will allow for a high degree of equipment interoperability and compatibility.

P25 standards use the proprietary [[Improved Multi-Band Excitation]] (IMBE) and [[Advanced Multi-Band Excitation]] (AMBE+2) voice codecs which were designed by Digital Voice Systems, Inc. to encode/decode the analog audio signals. It is rumored that the licensing cost for the voice-codecs that are used in P25 standard devices is the main reason that the cost of P25 compatible devices is so high.<ref>{{cite web|url=http://forums.radioreference.com/general-scanning-discussion/146947-why-digital-scanners-so-expensive.html |title=p25expence |date=31 May 2009 |access-date=5 October 2016}}</ref>

P25 may be used in "talk around" mode without any intervening equipment between two radios, in conventional mode where two radios communicate through a repeater or base station without trunking or in a [[Trunked Radio Systems|trunked]] mode where traffic is automatically assigned to one or more voice channels by a [[Repeater]] or Base Station.

The protocol supports the use of [[Data Encryption Standard]] (DES) encryption (56 bit), 2-key [[Triple-DES]] encryption, three-key [[Triple-DES]] encryption, [[Advanced Encryption Standard]] (AES) encryption at up to 256 bits keylength, [[RC4]] ([[40-bit encryption|40 bits]], sold by Motorola as ''Advanced Digital Privacy''), or no encryption. 
The RC4 Advanced Digital Privacy can withstand casual attackers. It is supposed to offer 40-bit security, where an attacker must test the 2 to the power of 40 possible keys to find the right one. This level of encryption offers no real protection and there is software that allows you to find the key.<ref>{{cite web|title=P25 ARC4 ADP key finder|url=https://archive.org/details/p25arc4keyfinder}}</ref>

The protocol also supports the ACCORDION 1.3, [[BATON]], [[Firefly (protocol)|Firefly]], MAYFLY and [[SAVILLE]] [[Type 1 encryption|Type 1]] ciphers.

=== Standards development process ===

The P25 User Needs Working Group (UNWG), which represents P25 users, identifies user needs for the P25 standards, which are communicated to the P25 Steering Committee. The P25 Steering Committee adds identified P25 user needs to the Statement of P25 User Needs (SPUN) document. The [[Telecommunications Industry Association|TIA]] TR-8 Engineering Committee and its subcommittees, which represents manufacturers in the P25 industry, is then expected to develop TIA-102 standards that satisfy identified P25 user needs.<ref>{{Cite web |date=December 2021 |title=Project 25 (P25) Steering Committee Representative Handbook |url=https://www.cisa.gov/sites/default/files/publications/22_0105_p25-steering-committee-member-handbook_public_508C.pdf |url-status=live |archive-url=https://web.archive.org/web/20250422131451/https://www.cisa.gov/sites/default/files/publications/22_0105_p25-steering-committee-member-handbook_public_508C.pdf |archive-date=22 April 2025 |archive-format=PDF |access-date=10 May 2025 |website=[[Cybersecurity and Infrastructure Security Agency]] |format=PDF |ref=P25SCRHandbook}}</ref>

Once developed, TIA-102 standards may also subsequently be adopted by the P25 Steering Committee as P25 standards, and adopted by [[ANSI]] as American National Standards; however, TIA-102 standards do not automatically become P25 standards, and some TIA-102 standards have never been adopted by ANSI.<ref>{{Cite web |date=13 September 2024 |title=Approved Project 25 Standards |url=https://www.project25.org/images/stories/ptig/P25_Standards_Documents/P25%20SC%2024-09-002%20P25%20TIA%20Standards_Approved%20Sep2024.pdf |url-status=live |archive-url=https://web.archive.org/web/20250304022714/https://www.project25.org/images/stories/ptig/P25_Standards_Documents/P25%20SC%2024-09-002%20P25%20TIA%20Standards_Approved%20Sep2024.pdf |archive-date=4 March 2025 |archive-format=PDF |access-date=10 May 2025 |website=Project 25 Technology Interest Group |format=PDF |publication-date=26 September 2024 |ref=ApprovedP25Standards}}</ref> The TIA-102 standards, P25 standards, and associated ANSI standards have not been adopted by [[International Organization for Standardization|ISO]] as de jure international standards; however, P25 systems have been deployed in 83 countries, so they nonetheless serve as one set of [[De facto standard|de facto international standards]] alongside other international [[Land Mobile Radio]] (LMR) standards such as [[TETRA]] and [[Digital mobile radio|DMR]].<ref>{{Cite web |last=Giggetts |first=Cheryl |date=October 2023 |title=P25 for the Future: New Standards, Interoperability and Security for 2023 and Beyond |url=https://melbourne.comms-connect.com.au/wp-content/uploads/2023/11/P25-for-the-Future-20231010.pdf |url-status=live |archive-url=https://web.archive.org/web/20250510022931/https://melbourne.comms-connect.com.au/wp-content/uploads/2023/11/P25-for-the-Future-20231010.pdf |archive-date=10 May 2025 |access-date=10 May 2025 |website=Comms Connect |publisher=Principal CTA Consultants |format=PDF |ref=P25ForTheFuture}}</ref>

=== P25 open interfaces ===
P25's Suite of Standards specify eight open interfaces between the various components of a land mobile radio system. These interfaces are:

* Common Air Interface (CAI) – standard specifies the type and content of signals transmitted by compliant radios. One radio using CAI should be able to communicate with any other CAI radio, regardless of manufacturer
* Subscriber Data Peripheral Interface – standard specifies the port through which mobiles and portables can connect to laptops or data networks
* Fixed Station Interface – standard specifies a set of mandatory messages supporting digital voice, data, encryption and telephone interconnect necessary for communication between a Fixed Station and P25 RF Subsystem
* Console Subsystem Interface – standard specifies the basic messaging to interface a console subsystem to a P25 RF Subsystem
* Network Management Interface – standard specifies a single network management scheme which will allow all network elements of the RF subsystem to be managed
* Data Network Interface – standard specifies the RF Subsystem's connections to computers, data networks, or external data sources
* Telephone Interconnect Interface – standard specifies the interface to Public Switched Telephone Network (PSTN) supporting both analog and ISDN telephone interfaces.
* Inter RF Subsystem Interface ([[P25 ISSI|ISSI]]) – standard specifies the interface between RF subsystems which will allow them to be connected into wide area networks
* Key Fill Interface (KFI) - standard messaging protocol for bidirectional update of encryption keys via transfer of unencrypted and encrypted key variables from a Key Fill Device (KFD) to the equipment containing the encryption service
* Inter-KMF-Interface (IKI) - interface for encrypted interoperability between radios managed by different Key Management Facilities (KMF)
* KFD-KMF Interface - interface between KFD and KMF for radios managed by different KMF (under development)<ref>{{Cite web |date=March 2025 |title=Statement of Project 25 (P25) User Needs |url=https://www.cisa.gov/sites/default/files/2025-03/25_0319_s-n_statement_of_p25_user_needs_508C.pdf |url-status=live |archive-url=https://web.archive.org/web/20250505141551/https://www.cisa.gov/sites/default/files/2025-03/25_0319_s-n_statement_of_p25_user_needs_508C.pdf |archive-date=5 May 2025 |archive-format=PDF |access-date=10 May 2025 |website=[[Cybersecurity and Infrastructure Security Agency]] |format=PDF}}</ref>

=== P25 phases ===
[[File:Motorola hand-held.jpg|right|thumb|200px|A hand-held Project 25 radio used in US systems]]
P25-compliant technology has been deployed over two main phases with future phases yet to be finalized.

====Phase 1====
Phase 1 radio systems operate in 12.5&nbsp;kHz digital mode using a single user per channel access method. Phase 1 radios use Continuous 4 level [[FM broadcasting|FM]] (C4FM) modulation—a special type of 4[[Frequency-shift keying|FSK]] modulation<ref>{{Cite web |url=http://www.aeroflex.com/ats/products/prodfiles/appnotes/Understanding%20P25%20Modulation%20Fidelityiss1.pdf |title=Aeroflex: Application Note - Understanding P25 Modulation Fidelity |access-date=2012-03-26 |archive-url=https://web.archive.org/web/20120320083432/http://www.aeroflex.com/ats/products/prodfiles/appnotes/Understanding%20P25%20Modulation%20Fidelityiss1.pdf |archive-date=2012-03-20 |url-status=dead }}</ref>—for digital transmissions at 4,800 [[baud]] and 2 [[bit]]s per symbol, yielding 9,600 bits per second total channel throughput. Of this 9,600, 4,400 is voice data generated by the [[Improved multi-band excitation|IMBE]] codec, 2,800 is forward error correction, and 2,400 is signalling and other control functions. Receivers designed for the C4FM standard can also demodulate the "Compatible quadrature [[phase shift keying]]" (CQPSK) standard, as the parameters of the CQPSK signal were chosen to yield the same signal [[Absolute deviation|deviation]] at symbol time as C4FM. Phase 1 uses the [[Improved multi-band excitation|IMBE]] voice codec.

These systems involve standardized service and facility specifications, ensuring that any manufacturers' compliant subscriber radio has access to the services described in such specifications. Abilities include [[backward compatibility]] and interoperability with other systems, across system boundaries, and regardless of system infrastructure. In addition, the P25 suite of standards provides an open interface to the radio frequency (RF) subsystem to facilitate interlinking of different vendors' systems.

====Phase 2====
To improve spectrum use, P25 Phase 2 was developed for trunking systems using a 2-slot [[Time-division multiple access|TDMA]] scheme and is now required for all new trunking systems in the 700&nbsp;MHz band.<ref>{{cite web|url=http://www.p25phase2.com/p25-phase-2|title=P25 Phase 2|access-date=9 December 2016}}</ref> Phase 2 uses the [[Advanced Multi-Band Excitation|AMBE+2]] voice codec to reduce the needed bitrate so that one voice channel will only require 6,000 bits per second (including error correction and signalling). Phase 2 is not backwards compatible with Phase 1 (due to the TDMA operation), although multi-mode TDMA radios and systems are capable of operating in Phase 1 mode when required, if enabled. A subscriber radio cannot use TDMA transmission without a synchronization source; therefore direct radio to radio communication resorts to conventional FDMA digital operation. Multi-band subscriber radios can also operate on narrow-band FM as a lowest common denominator between almost any two way radios. This makes analog narrow-band FM the de facto "interoperability" mode for some time.

Originally the implementation of Phase 2 was planned to split the 12.5&nbsp;kHz channel into two 6.25&nbsp;kHz slots, or Frequency-Division Multiple Access (FDMA). However it proved more advantageous to use existing 12.5&nbsp;kHz frequency allocations in Time Division Multiple Access (TDMA) mode for a number of reasons. It allowed subscriber radios to save battery life by only transmitting half the time which also yields the ability for the subscriber radio to listen and respond to system requests between transmissions.

Phase 2 is what is known as 6.25&nbsp;kHz "bandwidth equivalent" which satisfies an FCC requirement for voice transmissions to occupy less bandwidth. Voice traffic on a Phase 2 system transmits with the full 12.5&nbsp;kHz per frequency allocation, as a Phase 1 system does, however it does so at a faster data rate of 12&nbsp;kbit/s allowing two simultaneous voice transmissions. As such subscriber radios also transmit with the full&nbsp;12.5&nbsp;kHz, but in an on/off repeating fashion resulting in half the transmission and thus an equivalent of 6.25&nbsp;kHz per each radio. This is accomplished using the AMBE voice coder that uses half the rate of the Phase 1 IMBE voice coders.<ref>{{cite web|url=https://www.teleco.com.br/tutoriais/tutorialprojeto25/default.asp|title=P25 in Brazil|access-date=4 March 2020}}</ref>

====Beyond Phase 2====<!--[[Project MESA]] redirects here-->
From 2000 to 2009, the [[European Telecommunications Standards Institute]] (ETSI) and TIA were working collaboratively on the Public Safety Partnership Project or '''Project MESA''' (Mobility for Emergency and Safety Applications),<ref>{{cite web|url=http://www.projectmesa.org/ |title=Mobile Broadband for Public Safety - Home Page |publisher=Project MESA |access-date=2014-06-06|url-status=usurped|archiveurl=https://web.archive.org/web/20081020103132/http://www.projectmesa.org/|archive-date=2008-10-20}}</ref> which sought to define a unified set of requirements for a next-generation aeronautical and terrestrial digital wideband/broadband radio standard that could be used to transmit and receive voice, video, and high-speed data in wide-area, multiple-agency networks deployed by public safety agencies.<ref name=projectmesa_tia>[https://www.itu.int/dms_pub/itu-r/oth/0A/0E/R0A0E0000540001PDFE.pdf Advanced Mobile Broadband For Public Protection & Disaster Relief Professionals]. David Thompson. Telecommunications Industry Association</ref><ref name=projectmesa_itu-t>[https://www.itu.int/itudoc/itu-t/workshop/ets/s5p1.pdf Project MESA: Broadband Telecommunications for PPDR]. David Thompson. Telecommunications Industry Association</ref>

The final functional and technical requirements have been released by ETSI<ref>{{Cite web|url=http://www.projectmesa.org/ftp/Specifications/|archiveurl=https://web.archive.org/web/20100613000949/http://www.projectmesa.org/ftp/Specifications/|url-status=dead|title=www.projectmesa.org - /ftp/Specifications/|archivedate=June 13, 2010}}</ref> and were expected to shape the next phases of American Project 25 and European DMR, [[dPMR]], and TETRA, but no interest from the industry followed, since the requirements could not be met by available commercial off-the-shelf technology, and the project was closed in 2010.{{citation needed|date=May 2013}}

During the [[United States 2008 wireless spectrum auction]], the FCC allocated 20&nbsp;MHz of the 700&nbsp;MHz [[UHF]] radio band spectrum [[Digital television transition in the United States|freed in the digital TV transition]] to public safety networks.  The FCC expects providers to employ [[Long Term Evolution|LTE]] for high-speed data and video applications.<ref>{{Cite web|url=https://www.fcc.gov/700-mhz-public-safety-narrowband-spectrum|title=700 MHz Public Safety Spectrum|date=March 17, 2011|website=Federal Communications Commission}}</ref>