P25 Trunked System Overview for Radio User Train-the-Trainer Training Session Notes
Contents • What is P25? • M/A-COM P25 Terminal Equipment • Call Types • Unit ID’s • Call Processing • Emergency Calls • Group Scanning • ProScan • Terminology
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
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.
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
TRAINING TRNG 1 TRAINING TRNG 1 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 IDs
P25 Portable Radios P7170 (System Model) P7150 (Scan Model) P7130 (Select Model) P5150 (Scan Model) P5130 (Select Model)
M7100 Mobile Radio Hand-held Controller Scan Control Head System Control Head
TRAINING TRNG 1 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
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
TRAINING TRNG 1 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 Tracking
Service Counter Service Counter Trunked Conventional Service Employee Customer Conventional vs. Trunked • Computerized Assignment of Channels
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
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
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 ? ? ? ? ?
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
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
Many factors affect coverage: Site Location Urban clutter (+ & -) Reflections / Multipath (+ & -) Ducting over water (+) Wet pine needles (-) Weather (+ & -) Frequency (+ & -) Earth curvature Many others… (+ & -) How Far Does it Cover? ???
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 2 Site 1 Network Switching Center
TRAINING TRNG 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. Programming Cables TQ 3392 – P7100, P5100 TQ 3409 – M7100 (Shop) TQ 3410 – M7100 (Field) TQ 3419 – P7100, P5100 (without TQ 3370 interface)
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
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
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
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