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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
ECP3078A page 4
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
ECP3078A page 5
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.
ECP3078A page 6
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
ECP3078A page 7
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
ECP3078A page 8
P25 Portable Radios
P7150(Scan
Model)
P7170(SystemModel)
P7130(SelectModel)
P5130(SelectModel)
P5150(Scan
Model)
ECP3078A page 9
M7100 Mobile Radio
System Control Head
ScanControl Head
Hand-held
Controller
ECP3078A page 10
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
TRAININGTRNG 1
ECP3078A page 11
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
ECP3078A page 12
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
ECP3078A page 13
Conventional vs. Trunked
Computerized Assignment of Channels
Service Employee
Customer
Conventional Trunked
Service CounterService Counter Service CounterService Counter
ECP3078A page 14
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
ECP3078A page 15
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
ECP3078A page 16
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
??
??
?
ECP3078A page 17
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
ECP3078A page 18
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
?
ECP3078A page 19
???
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… (+ & -)
ECP3078A page 20
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
ECP3078A page 21
Programming CablesTQ 3392 – P7100, P5100TQ 3409 – M7100 (Shop)TQ 3410 – M7100 (Field)
TQ 3419 – P7100, P5100 (without TQ 3370 interface)
TRAININGTRNG 1
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.
ECP3078A page 22
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
ECP3078A page 23
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
ECP3078A page 24
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
ECP3078A page 25
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