Genuine P25 Interoperability: Tips and Traps When Moving

to Digital Radio

www.taitradio.comScott Skibness

Tait Communications

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Learning Objectives

1. An update on the latest standards, interfaces and certification bodies and their implications for procurement decisions

2. Understand why the P25 Compliance Assessment Program matters to you

3. With all of this why don’t all P25 radios work on all P25 networks?

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Project 25: History

Designed for public safety by public safetyDeveloped in partnership between APCO and TIA

• Initial P25 standards were released in 1995- P25 is a suite of mobile radio standards and bulletins which

define interoperable communications for emergency services- They are continuing to evolve; Phase 2 trunking is in progress

The result? • True multi-source procurement and interoperability• Smooth migration from analog

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Project 25/TIA 102 Standards Suite

The standards suite allows forsome features that are:a) Mandatoryb) Standard options: where if

offered they must follow the standard

c) Manufacturer’s extensions to the standard: these can fit within the framework of the standard

Caveat: watch out for manufacturer extensions that are similar to standard options

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Inter RF Inter RF SubSystemSubSystem

Interface Interface (ISSI)(ISSI)

Telephone Telephone InterconnectInterconnect

(PSTN)(PSTN)

Data Data InterfaceInterface

e.g. Databasese.g. DatabasesGateway

NetworkManager

Consoles

P25Portables

P25 Repeaters

PSTNPSTN

Other P25Systems

Other P25Systems

Common Air Common Air Interface (CAI)Interface (CAI)FDMA & TDMAFDMA & TDMA

ConsoleConsoleSubSystemSubSystem

InterfaceInterface(CSSI)(CSSI)

Fixed StationFixed StationInterface Interface

(FSI)(FSI)

P25 RF SubSystem(RFSS)

Subscriber Subscriber Data Data

Peripheral Peripheral Interface Interface e.g. MDTe.g. MDT

MDT

P25 Mobiles

GatewayFunctionality*

*Not all manufacturers will require a separate gateway device.

Project 25: More Than An Air Interface

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Project 25 Standards: Roll-out Phases

Phase 1• P25 requirements and standards for a digital Common Air Interface

(CAI) using FDMA 12.5 kHz channels and for the supporting system

• Must be backwards compatible with FM analog

Phase 2• P25 requirements and standards for a digital CAI using

6.25 kHz channels or equivalent and for the supporting system • Must be backwards compatible with Phase 1 digital only

The primary improvement in Phase 2 is spectral efficiency

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Project 25 Standards Status: Phase 2

• Most vendors are offering P25 Phase 2 upgradable equipment today

• A number of test documents are still to be started• Uses half rate vocoder in 2-slot TDMA• Conventional Phase 2: work will commence on

conventional 2-slot TDMA

What does this mean for you?

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P25 Compliance Assessment Program (CAP)

Supplier’s Declaration of Compliance (SDoC)Summary Test Reports (STR)SDoCs/STRs on the Responder Knowledge Base (RKB)

CAP Test Bulletins

Lab Assessments

Multi-Vendor CAP Testing

Suppliers Declaration of Compliance

Responder Knowledge Base Posting

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Responder Knowledge Base (RKB) Website

www.rkb.us → Other Content → Certifications and Declarations → P25 SDoCs

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Why Do We Need The CAP?

Choice for buyers•Multiple users on a single network can use the P25 technology and various vendors’ P25 products on that network•Users can purchase the right fit for their needs with more optionsSecurity to buyers•The CAP offers a formal assurance program•Confidence in interoperabilityP25 equipment meeting the CAP standards

Federal grant money in the US is dependant on interoperable products … but the CAP is still of interest in other regions

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Who Defines The CAP?

• Approved by the CAP Governing Board- Comprised of representatives from US Government

agencies

• Generally follows the TIA recommendations for compliance assessment tests

• References standard tests

• Published in Compliance Assessment Bulletins (CAB)

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Four Vendors with P25 CAP Recognized Labs Worldwide

• Standard test process to become recognized• Vendor hosted CAP interoperability testing in

a recognized lab• Tait, Motorola, EF Johnson and Harris• Other CAP testing such as performance

testing is also completed• After testing, SDoCs and STRs are published

to the RKB website

Goal: cooperation between P25 vendors for interoperability

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Trade-offs

Interoperability ≠ Total Interoperability- Proprietary extensions

Performance ≠ Coverage Guarantees- Testing- Culpability

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Why don’t all P25 radios work on all P25 networks? • Different interpretation of the standards• Different implementation of the

standards• Usability of the radio• Requirement for non-standard

functionality

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Interpretation of the P25 standards

• Different interpretations of the standard• Features outlined in the standard that WILL work

- group calls- registration- affiliation- unit to unit calls

• However… on most networks there are other features required.- Patch Calls- Dynamic Regrouping- Failsoft

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Differences in Implementation

Not all standards are clearly defined

• Many of the items in the standards are open to interpretation- Control Channel Hunt – items like acquisition, retention, what is a

valid CC, and when to leave are detailed but how to find one and select which to use or keep are not.

• Or deployed with additional capabilities- Radio inhibit and uninhibit – The standard defines how this will

work but the data is unencrypted as defined so vendors add encryptions within the system for these which limits the functionality to others.

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Usability of the Radio

Differences in features and operation. • ‘Usability’ is one of the major obstacles for

having multiple vendors on a state-wide network.

• Acceptance or certification testing is based on an existing terminal and how it operates and not the P25 standard- Scan configuration- Programming Units- Alert sounds and configuration

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User Misunderstandings About the Standard

VendorProprietaryFeatures

StandardOptions

Core Features

P25 Feature Sets User P25 Experience

P25Air Interface& Signaling:ID, Alarms,Features,etc.

Defined by the P25 Feature Sets At the 3

levels

Largely defined by the individual vendors, or the user when programming. Therefore NOT uniform.

User ProgrammingInterface:channel lists, pull down menus, Etc..

User Programming:Tones, Channels,Features, etc.

User Interface:Tones, Display,Lights, Knobs, etc.

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Non-Standard Functionality

Adding functionality that is not available to other suppliers• Network suppliers add services that help make its terminals function

more efficiently.- Dynamic Power Control

• Providing functionality that limit interoperability with other vendors radios on the network. - Non-standard Encryption – insist on AES or DES- OTAP

• Limit what is granted in a license to a few features

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Lesson Learned

Examples from past systems

- Non-standard frequency splits- Failsoft function with unique code words where

in some cases it included a specific manufactures ID

- Unused bits that change states from system to system.

- Lack of testing on the system means some conditions are not found out until the units are deployed

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Lessons Learned

• Limit testing of “proprietary” features• Vendors need more than the minimum information to work

effectively• Willingness of the network owners to work with the other vendors• Not all users will need or want the same functionality so make sure

you are not limiting their choices with the certification process

SAVINGS – customers have seen a 30% to 40% savings or more in the cost of subscriber units when multiple vendors radios are offered on a system.

Test failures are not just a failure for a vendorThey are a failure for the P25 standard and interoperability.

Genuine P25 Interoperability: Tips and Traps When Moving

to Digital Radio

www.taitradio.comScott Skibness

Tait Communications