Overview of the P25 Standard
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Introduction To P25 What is Project 25? •Project 25 (P25) is a set of standards produced through the joint efforts of APCO, NASTD, NCS and selected Federal Agencies, and standardized under the TIA. •P25 is an open architecture, user driven suite of system standards that define digital radio communications system architectures capable of serving the needs of Public Safety and Government organizations. •These standards define the interfaces, operation and capabilities of any P25 compliant radio system. •The P25 standard exists in the public domain, allowing any manufacturer to produce a P25 compatible radio product.
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P25 Objectives P25 has had four main objectives since its inception: •Ensure competition in system life cycle procurement through Open Systems Architecture. •Allow effective, efficient and reliable intra-agency and inter-agency communications. •Provide enhanced functionality and capabilities with a focus on public safety needs. •Improve radio spectrum efficiency.
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P25 Phases P25 is designed to be implemented in Phases •Phase 1 •12.5 KHz analog and digital (mixed mode) radio system allowing backwards compatibility with analog radios •C4FM non-linear modulation for digital transmissions •Phase 2 •FDMA and/or TDMA for 6.25 KHz per voice channel •Backwards compatible with Phase 1 •FDMA solution is CQPSK (linear) modulation •Phase 3 – •High speed data (video) •Project MESA Pages 2-3 www.danelec.com
How does P25 Work? •P25 radios operate in both P25 digital mode, as well as analog mode. •In analog mode, the P25 radio will operate exactly the same as conventional analog systems, with the capability for CTCSS, DCS, etc. •In P25 digital mode, analog audio is converted to digital information (and vice versa) by an IMBE™ vocoder (or de-vocoder). •CTCSS and DCS are replaced by digital NAC codes, TGID, Source and Destination ID, etc. •Digital modulation is achieved by C4FM, a modified 4 level FSK. •The Common Air Interface (CAI) specifies the type and content of signals transmitted by P25 compliant radios.
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P25 Operation
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P25 Architecture
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Digital Coding •The IMBE™ vocoder converts analog audio to a digital bit stream at a rate of 4400 bps. •IMBE™ is heavily optimized for human speech and doesn’t do very well in reproducing other types of sounds, including continuous tones and DTMF. •Signaling information such as NAC, TGID, Source, Frame Synchronization, etc. are added to the digital bit stream at a rate of 2400 bps. •Error correction coding (to overcome noise, fading and interference) such as Golay, Hamming and ReedSolomon codes are added at a rate of 2800 bps. •Adds up to a data rate of 9600 bps.
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Digital Modulation •9600 bps is converted to 4800 symbols/sec (each symbol is two bits). •C4FM is used to transmit digital information over a 12.5 KHz channel. •C4FM modulation shifts the deviation of the carrier only, the amplitude of the carrier is constant. Information Bits 01 00 10 11
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Symbol +3 +1 -1 -3
C4FM Deviation +1.8kHz +0.6kHz -0.6kHz -1.8kHz
Benefits of P25 •Interoperability - users from different agencies or areas can communicate directly with each other. •Multiple Vendors – competing products from multiple vendors will be interoperable. •Backwards Compatibility – backwards compatible with analog radios providing a graceful migration from analog systems through future digital technologies. •Encryption Capability – optional encryption capability for secure transmission. •Spectrum Efficiency – maximizes spectrum efficiency by narrowing bandwidths (Phase 2). •Improved Audio Quality – greatly improved voice quality over analog signals, especially at noisy RF carrier levels. •Enhanced Functionality – 2400 bps allows a wide array of additional functions and features in P25 systems Pages 8-11 www.danelec.com
Other Digital Standards •There are many different digital radio standards in use around the world. •Digital radio systems can operate using different channel access methods such as FDMA (Frequency Division), TDMA (Time Division), or other methods such as FHMA (Frequency Hopping). •FDMA Systems •Project 25 - USA, Phase 1 = 12.5 KHz, Phase 2 = 6.25 KHz •Tetrapol - France, 10 KHz. •EDACS® Aegis™ - Sweden (LM Ericsson), 25 or 12.5 KHz •TDMA Systems •TETRA - Europe, four slot 25 KHz •DIMRS - Canada (IDEN™), six slot 25 KHz •IDRA - Japan, six slot 25 KHz Pages 12-13 www.danelec.com
P25 Worldwide Systems
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P25 Standards •The Telecommunications Industry Association has developed more than thirty documents (TIA-102) as part of the Phase 1 set of P25 standards. •P25 defines 7 interfaces to an RF Subsystem (RFSS) and 1 peripheral interface. •RF Sub-System (RFSS) •Common Air Interface (Um) •Inter-System Interface (ISSIg) •Telephone Interconnect Interface (Et) •Network Management Interface (En) •Data Host or Network Interface (Ed) •Fixed Station Interface (Ef) •Console Sub-System Interface (Ec) •Data Peripheral Interface (A)
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Core Infrastructure Radio to radio protocol RFSS to all other system interconnections (In progress) PSTN to RFSS definition Network to RFSS definition (In progress) Computer aided dispatch to RFSS definition Base station to RFSS / Console Sub-System definition (In progress) Console to RFSS definition (In progress) Radio to Data Peripheral definition
General System Model
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P25 Standards •RF Sub-System •Any collection of equipment bounded by the P25 interfaces, whose only requirement is that the equipment supports the CAI. •Common Air Interface •A standard allowing communications between P25 radios to take place over the air. •Inter-System Interface •ISSI permits multiple RFSS to be connected together into wide area networks. Also provides a common meeting place for RFSS of different technologies (TDMA, FDMA, microcell). •Telephone Interconnect Interface •Open interface to telephone networks, supporting both analog and ISDN telephone interfaces. Pages 19-21 www.danelec.com
P25 Standards •Network Management Interface •A single selected network management scheme within the RFSS will allow all elements of network management to be supported. •Data Host or Network Interface •Four different types of data connectivity, including a native interface for connecting host computers, as well as existing computer network interfacing for TCP/IP, SNA and X.25. •Data Peripheral Interface •A port through which mobiles and portables can connect to laptops or terminals. Open interface protocols are passed transparently into TCP/IP, SNA or X.25 fixed computer networks.
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P25 Standards •Fixed Station Interface •A set of mandatory messages supporting digital voice, data, encryption and telephone interconnect. Analog configuration options for 2 or 4 wire, E&M and tone control. Digital configuration is an IP based interface with an Ethernet 100 Base-T or 10 Base-T with an RJ-45 connector. •Console Sub-System Interface •Defines basic messaging structures to interface a console subsystem to an RFSS. A console subsystem can connect directly to a fixed station.
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Analog->P25 Transition •P25 equipment can be used in any configuration that is typically found in existing analog systems. •Base stations, remote bases, repeaters, voting, and simulcast systems are all configurations of P25 conventional systems. •Transmitter RF power output levels and receiver sensitivity levels of P25 equipment are very similar to analog equipment. •Analog equipment can be replaced “one for one” by P25 radio systems.
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P25 Frequency Bands •VHF 136 - 174 MHz •UHF 403 - 512 MHz •UHF 806 - 870 MHz •P25 Phase 1 has been adopted as the digital interoperability standard for the 746 – 806 MHz public safety band. P25 radios must be used in P25 digital mode in this band. •12 analog eligible channel pairs set aside for “low power on-scene use”.
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Common Air Interface •P25 transmission in digital mode can be sent out as a voice message or a data packet. •P25 Voice Message Structure
•P25 Data Message Structure
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P25 Digital Codes •Frame Synchronization •A special sequence of 48 bits at the beginning of every Data Unit (HDU, LDU1, LDU2, TDU) marking the beginning of the Data Unit. •Network ID (NID) •The NID is the name for the DUID and NAC combined. Occurs right after the Frame Synchronization in every Data Unit. •Data Unit ID (DUID) •The DUID specifies the type of Data Unit such as Header Data Unit, Packet Data Unit, Logical Link 1 Data Unit, etc. •These digital codes are not accessible or programmable by the user.
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P25 Digital Codes •Network Access Code (NAC) •NAC codes are user programmable and are typically used to steer repeater functions. •NAC codes are used the same way as analog CTCSS tones. •The NAC code ranges from hexadecimal $000 to $FFF. •Reserved values for NAC codes: $293 Default NAC code $F7E Receiver unsquelch on any incoming NAC Mobile, Portable, Repeater or Base $F7F Repeater will pass the NAC transparently Repeater Only Page 27 www.danelec.com
P25 Digital Codes •CTCSS to NAC Conversion •Early TIA documents (obsolete now) specified a conversion from analog CTCSS tones and DCS codes to specific NAC codes. CTCSS 67.0 Hz 69.3 Hz 71.9 Hz 74.4 Hz 77.0 Hz 79.7 Hz 82.5 Hz 85.4 Hz 88.5 Hz 91.5 Hz 94.8 Hz 97.4 Hz 100.0 Hz 103.5 Hz 107.2 Hz 110.9 Hz
NAC Code $29E $2B5 $2CF $2E8 $302 $31D $339 $356 $375 $393 $3B4 $3CE $3E8 $40B $430 $455
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CTCSS 114.8 Hz 118.8 Hz 123.0 Hz 127.3 Hz 131.8 Hz 136.5 Hz 141.3 Hz 146.2 Hz 151.4 Hz 156.7 Hz 162.2 Hz 167.9 Hz 173.8 Hz 179.9 Hz 186.2 Hz 192.8 Hz
NAC Code $47C $4A4 $4CE $4F9 $526 $555 $585 $5B6 $5EA $61F $656 $68F $6CA $707 $746 $788
CTCSS 203.5 Hz 206.5 Hz 210.7 Hz 218.1 Hz 225.7 Hz 229.1 Hz 233.6 Hz 241.8 Hz 250.3 Hz
NAC Code $7F3 $811 $83B $885 $8D1 $8F3 $920 $972 $9C7
P25 Digital Codes •Status Symbols •Status Symbols are interleaved throughout all voice and data messages. •Status Symbol every 70 bits. Symbol 01 00 10 11
Meaning Inbound Channel is Busy Unknown, use for talk-around Unknown, use for inbound or outbound Inbound Channel is Idle
Usage Repeater Subscriber Repeater or Subscriber Repeater
•Subscribers in the 700 MHz band may lock their local oscillator to a fixed station using AFC for higher stability requirements. Page 29 www.danelec.com
P25 Digital Codes •Manufacturer’s ID (MFID) •When a manufacturer uses non-standard (data only) features on their P25 radio, their MFID is asserted. •When the CAI is used, the MFID is set to the standard values $00 or $01. •Other manufacturer’s equipment may not operate properly when the MFID is not a standard value. •Low Speed Data •Intended for custom user applications not defined by the CAI. •Total capacity of 88.89 bps.
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P25 Digital Codes •Algorithm ID (ALGID) •ALGID identifies the encryption algorithm used. •ALGID is entered with encryption keys. •$80 - unencrypted •$81 - DES-OFB encryption •$84 - AES encryption
•Key ID (KID) •KID identifies the key in a multiple key system (also used for single key systems). •KID is used as a pointer to the encryption key. •KID is entered by a KMF or Key Loader. •Message Indicator (MI) •MI is the synchronization for the key stream generator (not programmable). Pages 31-32 www.danelec.com
P25 Digital Codes •Talk-group ID (TGID) •The TGID is user programmable and allows logical groupings of radio users into distinct organizations. •Could also be used to minimize co-channel interference. •The TGID ranges from hexadecimal $0000 to $FFFF. •TGID’s with specific functions: •$0001 Default TGID; Used when no talk groups are used •$0000 Used when making an individual call •$FFFF Talk Group which includes everyone
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P25 Digital Codes •Unit ID •Unit ID is a user programmable field that should be unique in each radio. •The Unit ID is used as both a Source ID (from the sending unit) and a Destination ID (in the receiving unit in an individual call). •The Unit ID ranges from hexadecimal $000000 to $FFFFFF (over 16 million addresses). •Unit ID’s with specific functions: •$000000 no-one, this value is never used. •$000001 to $98967F general use. •$989680 to $FFFFFE talk group or special purpose. •$FFFFFF everyone, for TGID group call. Page 33 www.danelec.com
P25 Digital Codes •Emergency Indicator •Used in group voice messages to indicate an emergency. •Designed to be selectable by a switch or programming. •0 = routine, non-emergency condition. •1 = emergency condition. •Link Control Format (sometimes called Octet) •Used to specify the format of the Link Control Word. •Identifies group call, individual call, etc. •Not programmable. •Packet Data Unit Codes •Many other codes used for data only communication (SAP, FMF, etc.). Page 34 www.danelec.com
P25 Voice Messaging •There are 3 main ways to send a voice message, with several options and variations of each case. Each of these 3 main ways to send a voice message can operate in clear or secure mode. •The three main types of voice message calls are: •Routine Group Call - This is the most common type of call and is intended for a group of users within the radio system. This type of call is typically initiated by asserting the PTT switch. •Emergency Group Call - This type of call is similar to a Routine Group Call, but is used during an emergency condition. An emergency condition is defined by the radio system users This type of call is typically initiated by asserting the Emergency switch. •Individual Call - This type of call is addressed to a specific individual. The caller enters the subscribers Unit ID, that they wish to call, and this is used as the Destination ID by the radio making the call. This type of call is made after the Destination ID is entered into the radio.
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P25 Encryption •IMBE™ vocoder produces a digital bit stream that can be encrypted. •Encryption does not affect speech intelligibility or usable range of the system. •P25 also includes a standardized Over The Air Rekeying (OTAR) function. •P25 radios are capable of multiple key encryptions. •A Key Management Facility, or Key loader is required to load encryption keys. •The two most common encryption processes are DESOFB, with a 64 bit algorithm and AES with a 256 bit algorithm. •AES and DES-OFB are compliant with the security requirements of FIPS.
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RF Coverage •C4FM uses non-linear power amplifiers resulting in digital RF power levels equivalent to analog RF power levels. •This would result in equal analog and digital coverage. •Not necessarily true! •More of the covered area is usable when sending a P25 digital signal, because of the built in forward error protection of P25 standards. •Fringe areas that were not clearly audible in analog systems are typically loud and clear with P25 digital.
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Audio Quality Graph
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Multipath Reflections •Although it appears that the digital radio signal performs with greater coverage area than an analog radio signal, other factors must also be taken into consideration, such as multipath reflections. •Where analog reception can become noisy, digital signals could be lost altogether.
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Testing P25 Radios •Testing a P25 radio system is very similar to testing an analog system. •In many cases, the radio can be tuned in analog mode, then simply tested for P25 compliance in P25 digital mode. •Analog Receiver Reference Sensitivity •Same test as analog radios (SINAD measurement) •Digital Receiver Sensitivity (BER) •A Standard 1011 pattern is injected into the radio. •The radio is placed into a special test mode and software evaluates the decoded 1011 Bit Error Rate.
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Testing P25 Radios •Audio Levels and Distortion •Same measurement as analog radios. •Not necessary for digital mode operation. Perform measurements before and after vocoder / devocoder. •Audio Frequency Measurements •Analog measurements the same (frequency counter). •Digital measurements must be done when transmitting a “LOW DEVIATION PATTERN”. •RF Power Measurements •Same measurement as analog radios (RF peak detecting power meter). Pages 41-42 www.danelec.com
Testing P25 Radios •Modulation Accuracy •Analog measurements the same (deviation meter). •Digital modulation measurements are made using a Modulation Fidelity meter. •Specific test patterns may need to be generated from the transmitter. •Common Air Interface Protocol Testing •A P25 communications test set is required with the capability of decoding and encoding the P25 CAI data.
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P25 Delay Times •Delay times can be separated into two different categories. •Attack Time – the time for the receiver or transmitter to turn on. •Throughput Delay – the time it takes for the signal to pass from analog audio to RF (or vice versa) through a receiver or transmitter. •P25 Radio Systems may have an increase in the delays depending on the system infrastructure.
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Throughput Delays
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Anatomy of the Common Air Interface
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Common Air Interface •P25 transmission in digital mode can be sent out as a voice message or a data packet. •P25 Voice Message Structure
•P25 Data Message Structure
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FS and NID
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Header Data Unit
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Voice Code Words
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LDU1
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LDU2
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Simple TDU
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TDU with Link Control
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Packet Data Unit
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Daniels Electronics Ltd. And P25 Radio Systems www.danelec.com
Daniels P25 Radios • Available in VHF and UHF frequency bands. • Currently producing: •Repeaters, repeaters with links, crossband systems, etc. •P25 analog remote controlled base stations. • Low standby current – less than 150 mA for a single repeater system. • P25 radio systems are primarily software programmed. • Modular style makes Daniels new P25 transmitters, receivers and controllers compatible with MT-3 subracks, power amplifiers, and system monitors.
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P25 Secure Base Station
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Multiple Link Controller •Interconnects up to 4 transmitter and receiver modules. •Steering based on NAC, COR, CTCSS, or DTMF tones. •Software programmable with GUI screen driven menus using the front panel USB or RS-232 ports. •Capable of changing Transmitter channels. •Enabling and disabling transceivers. •Optional E&M interface. •Operational from -40ºC to +60ºC. •Low current drain < 20 mA. •Built in self test diagnostics.
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Interoperability using Digital Ethernet Based Protocols
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The P25 RoIP Interface â&#x20AC;˘ The RoIP connection between a console and a base station radio is the proposed fixed station (Ef) and console (Ec) interface in the P25 General System Model.
P25 RoIP Fixed Station Interface
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Universal Interface Card • Daniels Electronics Universal Interface Card (UIC) provides an RoIP digital Ethernet interface from the P25 Base Station to an IP network via an RJ45 Ethernet connector. • The UIC card uses the TIA Ef standard as currently defined as the basis for the protocol signaling format. Daniels shares that protocol with any manufacturer that may wish to interface digitally with our P25 base station. • The first release in August will be compatible with Telex/Vega, Catalyst and Twisted Pair consoles. The following features are supported: • Channel Control (Channel Select, Bank A/B Select) • PCM Audio In/Out UDP • Base Control ( Secure/Clear - Control & Indication) • Squelch Control (Squelch Override) • Repeater Control (LVDS DATA - Reading NAC only) • Power Monitoring (Battery voltages) • Programming through the front panel connection www.danelec.com
Daniels UIC •Sits in one slot of the existing DE subrack. •Communicates with the DE P25 Base Station RX and TX. •Ethernet connection to consoles and RF subsystems. •USB port for programming. •Provides access to all backplane and front panel signals (100+).
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Timeline •By November 2005 an initial Fixed Station (Ef) interface standard will be complete. •4 wire interface •The full Fixed Station (Ef) interface standard is scheduled for completion October 2006. •It is expected the interface definition will include: •IMBE vocoding •PTT and Squelch Control •TGID and NAC Display •Analog / Digital Selection •Emergency call indication •Daniels is following the Fixed Station Interface definition and the UIC RoIP interface will be compliant with the standard when available.
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Planned UIC Releases Release #
Release Date
Functionality
Complete April 2005
Demonstration system showing Audio and channel selection with Catalyst console for IWCE tradeshow.
Sept 2005
A commercial release of UIC supporting encryption over the air from the Base Station and providing PCM based audio. Basic MT-3 analog radio support.
2
January 2006
IMBE vocoding and Encryption support from the console.
3
August 2006
Radio Management using the RSS capabilities remotely programmed via the UIC.
January 2007
Trunking to conventional radio conversion as well as repeater and two transmitter/ receivers in a subrack support. Scanning will also be provided
5
October 2007
Digital P25 Voting using BER and RSSI
6
March 2008
TIA Ef standard compliant interface.
7
2008
Daniels developed web based Software applications
0
1
4
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Development Partners • Companies currently supported:
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•
Companies developing RoIP interface with Daniels: – – – – – – – – – – – – –
Arinc Cartel / TASC Cisco Icom EF Johnson JPS Smartlink IPC Orbacom Pantel Avtec Omnitronics Voiceboard Zetron
Development Partners
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RoIP Benefits •Removes high cost of leased phone lines by using standard Internet connections already located at sites. •P25 digital radio systems can “transparently” pass digital information through the RoIP interface, such as NAC’s, TGID’s as well as encrypted voice signals. •Multiple PC (dispatch) consoles can be operated without the high cost of installing fixed consoles. •Base Station control can be utilized anywhere there is access to the network (locally, nationally, internationally). •RoIP, has less line level loss than fixed lines. This eases the maintenance and tuning of a base station system. •Legacy systems can be interfaced into the IP network via tone remote adapters or E&M to IP converters.
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