Project 25 Technology Information Group

Monday, November 18, 2019

Project 25 Technology Information Group

P25 System of the Month

Central Indiana Counties

City of Indianapolis, Marion County, Hamilton County, Madison County

Central Indiana Counties Partner to leverage

cost savings and form a regional interoperable

communications network


The Full Whitepaper including system demographics for the 3 Central Indiana P25 Systems can be down loaded using the link below:

P25 System of the Month: Central Indiana Counties

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The three-county system has realized many great benefits from sharing common infrastructure utilizing the P25 architecture.  Previously all three counties were required to maintain radios in their respective Public Safety Answering Points (PSAPs) and create patches to the respective jurisdictions.  Patching proved problematic and unreliable at best.  A great many of the field units did not have direct communications with the neighboring jurisdictions, especially during large or critical events.  This created a First Responder safety issue, which the counties realized needed to be addressed as soon as practical.

Since the counties have upgraded to P25, the three counties now share talkgroups including public works talkgroups to allow for greater efficiency.  The counties have created several mutual aid (MA) talkgroups that can roam across all systems in the event of a disaster or large-scale event like the Super Bowl.

An additional benefit of the three counties upgrading to P25 is the ability to have interoperable communications with the State of Indiana’s P25 system.  This system is utilized by hundreds of agencies throughout Indiana as well as Federal Public Safety partners.  No longer do officers need to have multiple radios available to communicate to these important partners.

Project 25 Technology Interest Group Releases New Whitepaper:

Project 25 Radio Authentication

The paper was authored by:

Jim Holthaus, Vice President, Chief Technical Officer, BK Technologies

Project 25 radio standards now provide a method of authenticating subscriber radios for operation on P25 trunked radio systems.  This paper explores the need for and functionality of P25 Link Layer Authentication services on trunked radio systems.

For decades, public safety communications system operators were protected from unauthorized access through the restrictions that equipment manufacturers placed on radio programming equipment.  So even if an unauthorized individual had radio equipment and programming software, without the so called ‘system key’, programming a radio for an individual radio system was not possible.  In general, this level of protection works quite well for many public safety agencies.  However, the use of the system key is only as reliable as the methods used to protect unauthorized access to such a key. 

As the technological abilities of those wishing to steal service or disrupt public safety communications systems expand, additional measures to protect unauthorized access to public safety communications systems are required.

Public Safety and government radio users, through the Project 25 Standards process have requested inclusion of additional measures to prohibit unauthorized access to P25 systems.  The Project 25 standard provides this protection through the use of authentication technology.  The Project 25 standard defines a challenge/response system that allows the radio system and/or subscriber radio to authenticate itself before service is granted. 

The full whitepaper on P25 Link Layer Authentication can be found using the link below:


Project 25 Radio Authentication

P25 Standards Update from the TIA TR-8 Meetings San Diego Oct 18-19

Andy Davis, Chairman TIA TR-8

This document highlights TR-8 accomplishments and work in progress for 2017.  The document will be updated after every TR-8 face to face meeting occurring in 2017.  After the first 2017 version, each update will use blue font to indicate the updates.



The full report can be accessed using the link below

Updates from the October Meeting:

Completed in 2017:

Air Interfaces

  • An addendum to the Trunking Control Channel Messages standard was approved for publication.

     This addendum introduces a “Vehicle Sensed Emergency” flag to the Emergency Alarm message.

  • An addendum to the Trunking Control Channel Messages standard was approved for ballot.

This addendum introduces an “Accessory Sensed Emergency” flag to the Emergency Alarm message.

Wireline Interfaces

  • An addendum to the ISSI Messages and Procedures for Supplementary Data was approved for ballot.

This addendum introduces the messages and procedures for Individual Regrouping control across an ISSI/CSSI.



  • A revision of the Location Services Overview bulletin was approved for publication.

This revision aligns the content of the Overview document with the content of the Tier 1 and Tier 2 Location Service Specifications.


Work in Progress:

Air Interfaces

  • A revision to the Conventional Interoperability Test standard is in progress

This revision corrects editorial errors and makes clarifications on various test procedures but does not add, remove or technically alter tests. 



Project 25 Technology Interest Group Releases New Whitepaper:

Project 25 Trunking Control Channels

The paper was authored by:

Dominick Arcuri: DVA Consulting

Andy Davis: Chairman TIA TR-8, Senior Resource Manager-Motorola Solutions

The New Project 25 Technology Interest Group Whitepaper defines the use and benefits of the current P25 Frequency Division Multiple Access (FDMA) Trunking Control Channel used in most P25 Trunking Systems today as well as application and benefits of the new, recently released, P25 Time Division Multiple Access (TDMA) Trunking Control Channel.  Planning and User Interoperability considerations required for transition from FDMA to TDMA P25 Trunking Control Channels are also covered.  These include a thorough inventory of the subscriber base and roaming requirements for all agencies supported by the system, including visiting radios from interoperability and roaming partners. 

The P25 suite of standards is evolving and continuing to grow as technology and user requirements evolve.  The standardization of the TDMA control channel will enable multiple manufacturers to support this capability with interoperable equipment.  Additionally, the TDMA control channel will provide another option for system managers and user agencies to effectively support their users and to improve the spectrum efficiency of their network both low density and high density situations. 

A copy of the Full whitepaper can be found on the Project 25 Technology Interest Group Website using the following link:


Whitepaper: P25 Trunking Control Channels



A P25 trunked system can be deployed with either FDMA or TDMA traffic channels or a mixture of FDMA and TDMA traffic channels.  The FDMA Common Air Interface (CAI) is designed to provide 12.5 kHz spectral efficiency and meet FCC (Federal Communications Commission) narrow-banding requirements, while the TDMA CAI is designed to provide 6.25 kHz “equivalent” spectral efficiency by providing two virtual channels within a 12.5 kHz channel.  For TDMA, the two virtual channels are commonly referred to as “TDMA slots”.  When a 12.5 kHz channel is operating in TDMA mode, the infrastructure is using both slots for outbound signaling.  Depending on how the TDMA channel is being used, radios are instructed to use one or the other slot for inbound signaling (radio to infrastructure) and radios will listen to one or both slots for outbound signaling (infrastructure to radio).

Prior to the development of the TDMA control channel, both FDMA and TDMA trunking traffic channels utilized an FDMA 12.5 kHz control channel.  A new addition to the P25 suite of standards defines a TDMA control channel for P25 trunking operation.  Similar to the FDMA trunking control channel, the TDMA control channel includes an inbound (radio to infrastructure) channel which is used for individual or group service requests for voice, data or supplementary service.  It also includes an outbound (infrastructure to radio) channel which broadcasts system information, control signaling, and provides call assignments.

The Project 25 Technology Interest Group is pleased to welcome ACD Telecom as our newest PTIG member.

Founded in March of 1998, ACD Telecom, an engineering and management communications consulting firm specializing in Public Safety Communications.  ACD Telecom’s headquarters are in Lake Mary, Florida with two other offices located in Pennsylvania and California. 

ACD Telecom has been involved and active in P25 since its inception in 1989.  Ali Shahnami was a former APCO Headquarters' Director of the Frequency Coordination Department where he was involved and active within P25/TIA committees such as: Encryption Selection, Compatibility and Interoperability between various manufacturers (lockdown committee) and TSB88 documents development. 

As a natural progression from working with public safety agencies nationwide it made sense to retain those core ideals and capabilities in Public Safety Communications.  ACD Telecom has strong background, knowledge and experience in P25 system technology, FCC/FAA rules & regulations, spectrum management and licensing, project management, in-building/on-street coverage testing, RFP development and negotiation, and needs assessment.

ACD Telecom Business Development Contact 

Name: Ali Shahnami  

Title: Vice President

E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.This email address is being protected from spambots. You need JavaScript enabled to view it.

Phone: 407-333-2300

Company WEB site:

Mailing Address: 103 Commerce Street, Suite 180 Lake Mary, FL 32746





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