ECP####AECP3078A

P25 Trunked System Overview for Radio User Train-the-Trainer

Training Session Notes

ECP3078A page 3

Contents

What is P25?

M/A-COM P25 Terminal Equipment

Call Types

Unit ID’s

Call Processing

Emergency Calls

Group Scanning

ProScan

Terminology

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What is P25?

Interoperable digital radio system standard

Intended for all public safety LMR bands (VHF, UHF, and 800 MHz)

Developed Jointly by:

– TIA

– Association of Public-Safety Communications Officials (APCO)

– National Association of State Telecommunications Directors (NASTD)

– Various agencies of the Federal government (FED) in the early 90’s

to improve spectral efficiencies.

TIA/EIA Standard in 1999. Under TIA/EIA-102

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Project 25 Benefits

Key benefits sought by the user community:

– Competitive procurement of equipment

– Interoperability of equipment

– Spectrum efficiency

– User-friendly operation equivalent to today's public safety

equipment and common across all bands, system configurations,

services, and manufacturers.

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Project 25 Features

Key voice features

– IMBE vocoder

– Group and Individual calls

– Telephone interconnect

– Emergency

– Encryption (DES, AES)

– Console dispatch

– Preempt

– OTAR (Over-the-Air-Rekeying) Packet switched IP backbone

– Full control of the system and radios

– Interoperability - network level and radio level

– Group, individual, emergency calling

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Some P25 System Basics

Each Radio:

– Unique Unit ID

– One or More Systems (sites)

– One or More Talk Groups (Group ID)

Talk Group:

– A ”Logical” Collection of Units

– Unique Group ID

Capacities:

– 16,777,216 Unit IDs

– 65,536 Group IDsTRAININGTRNG 1

TRAININGTRNG 1

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P25 Portable Radios

P7150(Scan

Model)

P7170(SystemModel)

P7130(SelectModel)

P5130(SelectModel)

P5150(Scan

Model)

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M7100 Mobile Radio

System Control Head

ScanControl Head

Hand-held

Controller

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P25 Terminal Features

P25 Group call transmission/reception

Talk group identification

Group call alert

P25 Individual call transmission/reception

Individual identification (PTT ID)

Emergency and Emergency Indication

Priority Scan

Carrier control timer (CCT)

Transmit lockout

Up to 256 conventional channel capacity

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Call Types

Voice Calls

– Group Calls

• Normal

• Emergency

• Announcement Groups

– Individual Call

• Unit to Unit

– System All Call

Radio displays Group and Caller ID for each call

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Unit Identification

Unit ID

– Uniquely identifies radio to system

– 24 Bits – 16,777,216 Possibilities (0 - 16,777,215)

– Only allow 1 – 9,999,999

– Must be programmed into radio

– Allows Individual Calling

– Allows Call TrackingTRAININGTRNG 1

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Conventional vs. Trunked

Computerized Assignment of Channels

Service Employee

Customer

Conventional Trunked

Service CounterService Counter Service CounterService Counter

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Call Processing

Mobiles / Portables continuously monitor Control Channel

Operator makes selection, depresses PTT, and transmits a Channel

Request message

Channel Request received by Control Channel

System validates request against the Group and Unit databases

Control Channel responds with Working Channel assignment

Units switch to the assigned Working Channel

– Calling Unit is now ready to talk, caller can be advised by a grant

tone “beep” to start talking

– Working Channel adds messages to voice signal that provides for

extracting units from calls

– Control Channel continues to send update messages to provide late

entry for other units

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Call Processing (cont.)

Calling unit releases PTT and sends Channel Release message

Working Channel sends Channel Drop message out to all units

All units return to Control Channel

Channel Access

– If Channel Request is valid, Control channel will assign the call to a

Working Channel

– If Group or Individual ID is not properly programmed into system,

Call is denied

– Network Switching Server (VNIC) will route the call to other systems

as necessary

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Call Processing Exceptions

Call Queued

– All channels are assigned to other calls

– Automatically placed in queue for next available Working Channel

– Queuing priority determines order of channel assignment

Call Denied

– System programming does not allow request

– Out of range of Control Channel

– Retry in different location

System Busy

– System programming can not complete call at present time

– Individual call to busy radio

– Retry later

??

??

?

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Emergency Call Processing

Emergency button on mobiles and portables initiates emergency call or

emergency alert

Elevates talkgroup to emergency status

Dispatcher notification through console

Other radios listening to talkgroup are notified with an audible alert

Group call

– Requests access for a high priority Emergency call

– Flags Consoles and other units in group with *RX EMER*

– Identifies caller

Clearing an Emergency

– Return group to normal status

– Radio must be programmed for Clear Emergency

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Group Call Scanning

Radio is able to monitor multiple groups

Radio can only receive one group at a time

Responding to a call (programmable)

– Selected group

– Scanned group (within timer period)

Scan groups on Scan List

– Fixed list in programming

– Programmable by user

Scan Control

– Fixed in programming

– Controlled by user

Priority 1 Group

Priority 2 Group

Group 1

Group 2

?

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???

How Far Does it Cover?

Many factors affect coverage:

Site Location

Urban clutter (+ & -)

Reflections / Multipath (+ & -)

Ducting over water (+)

Wet pine needles (-)

Weather (+ & -)

Frequency (+ & -)

Earth curvature

Many others… (+ & -)

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ProScan

Enhanced System Scanning Feature (compared to WASS):

– Algorithm Based on Received Signal Strength Indicator and CC Verification

– Scans after Signal RSSI Drops below a User Defined Threshold

– Searches for new System Based on Defined Adjacent System Scan List

– Switches to new System, if User Defined Criteria is Met

– Provides Better Audio Quality

Site 1 Site 2Network

SwitchingCenter

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Programming CablesTQ 3392 – P7100, P5100TQ 3409 – M7100 (Shop)TQ 3410 – M7100 (Field)

TQ 3419 – P7100, P5100 (without TQ 3370 interface)

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Radio Programming

Every M/A-COM P25 radio is programmed with a personality.

A Data file:

– Directs the operating characteristics of the radio

– Interfaces the radio to a system

This personality is what makes a radio unique to the user of the radio.

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C3 MaestroIP Dispatch Consoles

Purpose:

Monitors & controls multiple Groups at a single physical position

A single Microphone/PTT and Selected & Unselected Speakers

Adds Patch & Simulselect capability to the P25 System

Provides EMERGENCY control

Physically:

Can be programmed with 112 Groups

Simultaneous audio based on Talk path licenses

– Standard – 4 talk paths

– Maximum – 20 talk paths

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Terminology

AES Advanced Encryption Standard (256 bit encryption)

CAI Common Air Interface

CNM Centralized Network Manager

CTCSS Continuous tone coded squelch system

DES Digital Encryption Standard (56 bit encryption) – Type III or

DES-OFB

DVU Digital Voice Unit

FDMA Frequency Division Multiple Access

GWB Gateway Board; OpenSky term for the Interoperability

Gateway DVU board

IMBE Improved Multiband Excitation – 3rd generation voice

encoder developed by Digital Voice Systems, Inc.

IP Internet protocol

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Terminology

KMF Key Management Facility

LMR Land Mobile Radio

MDIS Mobile Data Intermediate System; software on the NSS

MES Mobile End System. Mobile or portable.

MME Miniature Mobility Exchange

NAS Network Administration System

NMC Network Management Console. Previous name for RNM

NOC Network Operations Center

NSC Network Switching Center

NSS Network Switching Server

P25 APCO Project 25; a standard Common Air Interface protocol

for radio operation and system interface specifications

developed by TIA to provide for interoperability of different

manufacturer’s equipment

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Terminology

PSTN Public Switched (or Service) Telephone Network

PTT Push-To-Talk (depressing the radio transmit key)

RF Radio Frequency

RNM Regional Network Manager

RX Receive or Receiver

SitePro SitePro Controller (controller for each repeater station)

SMI Site Management Interface; software installed on the Network

Sentry

TDMA Time Division Multiple Access

TX Transmit or Transmitter

UAS Unified Administration System

VES Voice End System. User.

VNIC Voice Network Interface Controller, software on the NSS

VoIP Voice over IP