Compact TETRA
Section 1
Introduction and System Overview
Contents
1.
Introduction 1-1
1.1. What is TETRA? 1-1
1.2. Compact TETRA Design Concept 1-1
1.3. System Elements 1-2
2.
System Overview
2-1
2.1. System Elements 2-1 2.2. Interfaces 2-2 2.3. Actors 2-33.
System Components
3-1
3.1. Base Station CTS100/200/300 3-13.1.1. Base station details 3-2
3.2. System Equipment 3-6
4.
Call Features
4-1
4.1. Speech Services 4-1
4.2. Data Services 4-1
4.3. Short Data Service (Type 1 - Status) 4-1
4.4. Short Data Service (Type 4 – Text Messages) 4-1
4.5. Packet Data Service 4-2
4.6. Voice Call Capabilities 4-2
5.
System Configurations
5-1
5.1. Basic configurations 5-1 5.2. Stand-alone System 5-1 5.3. Single-Site System 5-2 5.4. Multi-Site System 5-46.
Resilience 6-1
7.
The System Signalling Path
7-1
7.1. Overview 7-1
7.2. Radio Air Interface 7-1
7.3. Software Applications 7-2
7.3.1. OSI Layers 7-2
7.3.2. The system Voice Path 7-3
7.3.3. MS/BS Air Interface Protocol (DLL – Layer 2) 7-4
7.3.4. Overview of the CSCIs on the Base Station. 7-5
7.4. Transceiver 7-5
7.5. Base Station Controller 7-6
7.6.1. The Structure of the Gateway PC 7-6
7.6.2. Functions of the Gateway PC. 7-7
7.6.3. Gateway Computer Software Configuration Items (CSCIs) 7-7
7.7. Dispatcher Work Station 7-8
7.7.1. The following diagram shows the structure of the Gateway PC 7-8
7.7.2. The CSCIs on the Dispatcher Workstation 7-9
7.8. Tetra Air Interface Layer 2 – Overview 7-9
7.9. Tetra Air Interface Layer 3 – Overview 7-10
7.9.1. Base Site Link Entity (BLE) 7-10
7.9.2. Circuit Mode Control Entity (CMCE-L) 7-10
7.9.3. Air-Interface Resource Manager (AIRM) 7-11
7.9.4. Mobility Management (MM-L) 7-12
7.9.5. Packet Data (SNDCP-L) 7-12
7.9.6. U-Plane Switching (USWITCH) 7-12
7.9.7. Distributed Application – Overview 7-12
7.9.8. Circuit-Mode Control Entity (CMCE-U) 7-14
7.9.9. Mobility Management (MM-U) 7-14
7.9.10. Dynamic Data Distribution (DD) 7-15
7.9.11. Packet Data Handling (SNDCP-U) 7-15
7.9.12. Subscriber Profile and Configuration Data Distribution (SPCDD ) 7-15
7.10. Tetra Codecs 7-16
7.11. PABX/PSTN Gateway (ISDNGW) 7-16
7.12. Packet Data Gateway (PDG) 7-16
7.13. Registration of a Mobile/Dispatcher 7-17
7.14. Deregistration of a Mobile/Dispatcher 7-17
7.15. Call Set-up Procedure 7-17
7.16. Inter-Site Call Set-up 7-18
7.16.1. Calls Originating at the PABX/PSTN Gateway 7-18
7.16.2. Calls Terminating at the PABX/PSTN Gateway 7-19
7.16.3. Calls Originating at a Dispatcher 7-19
7.16.4. Calls Terminating at a Dispatcher 7-19
7.16.5. Call Restoration Multi Site 7-19
7.16.6. Call Restoration – Group Call 7-20
7.17. Pre-emptive Priority Call 7-21
7.18. CLIP and TPI 7-21
7.19. Subscriber Data Management 7-21
7.20. Short Data Service (SDS) 7-21
7.21. Packet Data 7-22
7.22. Logging and Tracing 7-22
7.23. System Start-up 7-22
7.24. GPS Interface 7-23
7.25. BSC-Transceiver Interface 7-23
7.25.1. The Clock Interface. 7-23
7.25.2. The PCM Highway. 7-23 7.25.3. The HDLC bus. 7-23 7.26. Inter-Site Interface 7-24 7.27. U-plane Communication 7-24 7.28. Signalling Communication 7-24 7.29. Management Communication 7-25
7.31. BSC Ethernet Interface 7-25
7.32. BSC RS232 Interface 7-25
8.
Accessing the BSC Locally
8-1
8.1. Frequency Configuration 8-1
9.
Dispatcher Workstation CTD-1
9-1
9.1. Dispatcher operation 9-1
10.
Gateway Server CTG-1
10-1
10.1. The NMS.cfg Configuration File 10-2
10.1.1. The NMS.cfg File 10-3
10.2. Network Management Configuration (NMA) 10-4
11.
Packet Data Gateway
11-1
12.
Connecting a Server to the Packet Data Gateway
12-1
12.1. Gateway LAN (Server) Port 12-1
12.2. At the Server: 12-1
13.
Connecting a PC to a Radio
13-1
13.1. PC Configuration 13-1
13.2. Dial-Up Connection Settings 13-6
13.3. Accessing a Server via a Radio/PC Connection 13-15
13.4. Setting Up The Packet Data Connection 13-15
14.
Account Management
14-1
14.1. Feature Description (Single and Multi-Site) 14-2
14.2. System configuration overview 14-3
14.3. System parameters and specification 14-4
14.4. Base Station Specification 14-5
15.
Radio (MS – Mobile Subscriber) Registration
15-1
15.1. Mobile De-registering 15-1
16.
Call Release
16-1
17.
Reasons for Call failure
17-1
18.
Group Attachment / Detachment
18-1
20.
Call Restoration
20-1
21.
Pre-emptive Priority Call
21-1
22.
CLIP and TPI
22-1
23.
Failure of a Traffic Transceiver
23-1
24.
Failure of the MCCH Transceiver
24-1
25.
Failure of Base Station Controller (BSC)
25-1
26.
The Tetra Air Interface
26-1
27.
Time Division Multiplexed Radio Carriers
27-1
27.1. Slot Structure 27-1
27.2. Control Channel 27-3
27.3. Traffic Channel 27-3
27.4. Unallocated Channel 27-3
27.5. Single Slot Full Duplex Operation 27-4
27.6. Multi Slot Full Duplex Operation 27-4
27.7. Single Slot Semi Duplex 27-4
28.
Uplink Time Slot Structure
28-1
28.1. The Control Uplink Burst 28-1
28.2. The Linearisation Up link Burst 28-2
28.3. Normal Uplink Burst 28-2
29.
Downlink Time Slot Structure
29-1
29.1. The Normal Continuous Downlink Burst 29-1
29.2. The Synchronisation Continuous Downlink Burst 29-2
29.3. Burst Mode Power Ramping 29-2
29.4. The Normal Discontinuous Downlink Burst 29-3
29.5. The Synchronisation Discontinuous Downlink Burst 29-4
29.6. The Linearisation Downlink Burst 29-4
29.7. The Normal Training Sequence 29-4
29.8. Phase Adjustment Bits 29-5
29.9. Synchronisation Training Sequence 29-5
29.10. The Broadcast Block 29-5
30.
Transmission Power Levels
30-1
30.2. Base station Output Power Levels 30-2
31.
Communication Channels
31-1
31.1. Traffic Channel Assignment 31-1
31.2. The Broadcast Control Channel 31-2
31.3. The Linearisation Channel 31-2
31.4. The Signalling Channel 31-2
31.5. The Access Assignment Channel 31-2
31.6. The Stealing Channel 31-2
32.
Control Channel Assignment
32-1
32.1. Control Channels 32-1
32.2. The Common Control Channel 32-1
32.3. The Dedicated Control Channel 32-2
33.
Traffic Control
33-1
34.
Mobility Management
34-1
34.1. Cell Acquisition at Power Up 34-1
34.2. Channel Selection 34-1
34.2.1. RSSI - RxLev_Access_Min = > 0 34-2
34.2.2. Radio Improvable 34-2
34.2.3. Radio Relinquishable. 34-2
34.3. Cell Optimisation 34-3
34.4. Acquiring an Adjacent Cell 34-3
34.4.1. C2 – Radio Improvable 34-4
34.4.2. C2 – Radio Relinquishable 34-5
34.4.3. C2 - Radio Usable 34-5
34.4.4. *Typical System Settings for Cell Coverage 34-5
34.5. MS Actions at Cell Reselection 34-6
34.5.1. Announced 34-6
34.5.2. Unannounced 34-7
34.5.3. Undeclared 34-7
35.
Miscellaneous 35-1
35.1. Ethernet 10/100Base-T Straight Through Cable. 35-1
36.
Interoperability Test for Compact TETRA
36-1
37.
Motorola Terminals used for Compact TETRA
37-1
1. Introduction
This system overview explains the Motorola solution for a compact trunked radio system conforming to the European ETSI - TETRA standard.
Compact TETRA provides speech and data communication and suits a wide range of users.
1.1.
What is TETRA?
Terrestrial Trunked Radio (TETRA) is the modern digital Private Mobile Radio (PMR) and Public Access Mobile Radio (PAMR) technology for police, security services, military, public access, fleet management, transport services, closed user groups, business and industry services etc.
TETRA offers fast call set-up time, addressing the critical needs of many user segments, excellent group communication support, direct mode operation between radios, sophisticated data services, full duplex communication,
frequency economy and excellent security features. TETRA uses Time Division Multiple Access (TDMA) technology with 4 user channels on one radio carrier and 25kHz spacing between carriers. This makes it inherently efficient in the way that it uses the frequency spectrum.
1.2.
Compact TETRA Design Concept
Compact TETRA is a new design using distributed intelligence and latest state-of-the-art technology.
The system provides a high degree of resilience through inherently distributed architecture. It can tolerate the failure of individual components and links without employing expensive centralized redundancy concepts. Equipment failures have only a limited effect on system operation; should a transceiver fail, another one will take over the operation. The switching intelligence is distributed across the sites without the need of a central controller. Should one site fail or be interrupted the system will continue to operate with the remaining sites. This system behavior is called graceful degradation.
The system uses digital voice coding throughout the network. This results in the best possible end-to-end voice quality and the fastest possible call set up times. The system also operates in multi-site configurations.
In the maximum network configuration, the system provides 128 simultaneous channels and supports up to 8 sites.
Compact TETRA is easy to set up and to configure. Extensive monitoring and control facilities ease initial system set-up and reduce cost of ownership. Online monitoring functions and extensive logging and tracking facilities are also offered. Applications Specific Interfaces (API’s) such as the Packet Data and Short Data Service Gateway and the Peripheral Equipment Interface allow a wide range of customer specific applications.
1.3. System
Elements
Transceiver - this handles one Tetra AI carrier and is composed of one frequency pair, the Uplink and Downlink.
Base Station – this is a single Tetra cell and it can have up to 8 transceivers, 1 Base Station Controller (or 2 to meet redundancy requirements), an antenna subsystem with associated supporting infrastructure including racks, PSUs etc. Gateway PC - this is the interface between the tetra network, dispatchers and external networks such as PABX/PSTN and other external data networks. It is responsible for voice transcoding and the inter working at upper network layers and also fulfil the rolls for both system and subscriber management, allowing: • The viewing and the updating of the static and dynamic system data. • The monitoring and maintenance of the system
Dispatcher Workstation - this is a specially equipped multi functional PC that primarily enables the dispatcher to co-ordinate mobile users and also has the capability to:
• Monitor and participate in multiple group activities. • Have both voice and SDS access to the network.
The workstation can also fulfil the rolls for both system and subscriber management, allowing:
• The viewing and the updating of the static and dynamic system data. • The monitoring and maintenance of the system.
2. System
Overview
The following figure (Fig. 2-1) shows the system components and their interfaces. The circle indicates the system boundary. Objects within the circle are part of the distributed system (some of them are optional). The objects outside the circle are not part of the system and are referred to as ACTORS (see paragraph 2.3). Double-ended arrows denote logical interfaces whereas physical interfaces are indicated by straight connections between the objects. Interfaces that cross the system boundaries are open and committed to the customer or approved application partner.
Fig. 2-1: Real World Object Model and System Interfaces
2.1. System
Elements
● Base Station (BS): Handles a single TETRA cell and all layers of the TETRA AI. The BS consists of up to 8 transceivers, one BS Controller, an antenna subsystem, and supporting
infrastructure (racks, power supply, etc.)
● Transceiver: Handles one TETRA AI carrier consisting of a frequency pair (uplink / downlink).
● Gateway Server: (Not part of the stand-alone system) is the interface between the TETRA network, external networks (PABX/PSTN and data networks), and Dispatchers. It is responsible for the voice transcoding and interworking at upper network layers.
From the internal network point of view, the gateway server is just an additional node in the E1 ring.
● Dispatcher Workstation:
(Not part of the stand-alone system) Is a specially equipped workstation that primarily serves the dispatcher user in co-coordinating mobile users. It provides extended capabilities to: ● Monitor and participate in up to 5 group activities
● Support voice and SDS access to the TETRA network
● Provide access to the system management and subscriber management application
● Allow viewing and updating of system static data
● Provide system monitoring and maintenance applications
● Stand-alone Configuration PC:
This is any standard PC using MS Netmeeting that provides access to the stand-alone system management and subscriber management interfaces.
2.2. Interfaces
● Air Interface: TETRA standard air interface
● E1 link: (Not part of the stand-alone system) Each BS can be
connected to 1 or 2 other BS or the Gateway Server via 2Mbits E1 links. The topology used is either ring or a daisy chain. The structure within the E1 links is proprietary to the system.
● Dispatcher Workstation Interface:
(Not part of the stand-alone system) The Dispatchers are connected to the Gateway Server via 100Mbps Ethernet links. There must be a Switch in case more than one workstations are connected.
● Configuration Interface:
Is a logical interface that provides the ability to change the system parameters and static subscriber data.
● Monitoring Interface:
(Not fully supported by the stand-alone system) Is a logical interface that provides monitoring of the system status and its sub-elements.
● Logging and Tracing Interface:
Is a logical interface on the Gateway Server which provides log files with the following information about the system usage: ● Call logs, listing calling and called party with timestamp and call duration ● Mobility logs, listing the movements of mobiles
● SDS (Short Data Service) logs, listing a sender and a receiver with the timestamp for user defined messages
● Dispatcher User Interface:
(Not part of the stand-alone system) Is the HMI (Human Machine Interface), with which the dispatcher interacts. It displays the actual status of selected ongoing calls, the messages addressed to the dispatcher, etc. It allows the dispatcher to communicate with the system.
● Packet Data Interface:
This interface provides IP (Internet Protocol) connectivity between the mobiles and an external IP network with access to several external applications.
● SDS Transport Service Interface:
(Not part of the stand-alone system) This interface provides SDS transport to/from mobiles from/to an external server via a TCP connection.
● PSTN/PABX Interface:
(Not part of the stand-alone system) This interface links the TETRA network to a public (PSTN) or private (PABX)
telephone network. It allows for individual voice calls between the TETRA network subscribers and external subscribers.
2.3. Actors
● Terminal: Ordinary TETRA mobile radio or portable radio, which connects to the system over an air interface (AI). It can be used for voice communications, sending status or text SDS messages, or connecting a data application to the system.
● Dispatcher: A person using the dispatcher workstation. The dispatcher primarily co-ordinates the mobile users.
● External subscriber:
Anybody who connects to the system via the Gateway PSTN/PABX interface.
● Maintenance staff:
Configures the system parameters, maintains the hardware elements, installs new hardware and software, and performs the second level trouble-shooting.
● Operator: A person who collects information about the system status/performance and usage, and performs the first level trouble shooting.
● Packet Data Application:
This application uses the system as an IP sub-network to route IP traffic to/from a mobile application.
3. System
Components
3.1.
Base Station CTS100/200/300
The Compact TETRA base station comprises all necessary hardware and software to control the entire site. The base station includes:
• Base station controller including switching SW • Interface to the E1 network
• Receiver/Transmitter including amplifier and combiner • Power supply
The base station sites are linked together through 2Mbps E1 connections in a ring or ‘open ring’ topology.
The Base Station Controller (BSC) handles all functions related to the operation of the base station and the switching. The BSC also provides internal clocks for time and frequency synchronization. The BSC is equipped with its own crystal oscillator and with a GPS receiver. The synchronization priority will be set in the order: GPS, E1 reference, internal clock. Accurate time base is needed for synchronization in Multisite Systems only.
The BSC is driven by a Pentium Processor, which controls the TETRA protocol, the subscriber database, the network management and all multi-site switching functionality.
The base stations provide the following features: • TX output power 25W TETRA (10W after combiner)
• Freq. bands 380-400, 410-430, 450-470 MHz, 806-870MHz • Dual Receiver Diversity
• Optional Redundant Base Station Controller (BSC) • Advanced remote diagnostics down to module level • Tower Mounted Amplifier (TMA) to save feeder costs • Redundant Power Supplies 110/230VAC and –48VDC. • Antenna Combiners and filters
Alarm functions for all Base Stations
Alarm circuits will supervise all major Base Station circuits.
8 ext. alarm inputs are available from which one is dedicated to the door alarm. All alarms will be forwarded to Dispatcher PC.
Antennas for the Base Stations
Each base station requires one TX antenna plus one or two RX antennas. The Intelligent Dual Receiver Diversity increases the coverage of the system.
Duplexers are not recommended when using several transceivers due to the risk of generating intermodulation. One GPS Antenna per Base Station Controller is required for the synchronization of the Base Stations in Multi-site systems.
3.1.1. Base
station
details
Three generic base station configurations are available for Compact TETRA. The selection should be made depending on the traffic prediction and the
requirements for future channel upgrades.
CTS100 - Compact base station with up to 8 channels
CTS 100
• 1 or 2 TETRA-Carriers/Transceivers • 8 HU version
• AC/DC power supply including Battery charge • Optional built-in backup battery, 48V/7Ah • Optional redundant AC/DC power supply • Hybrid Combiner
• Base Station Controller BSC • Optional redundant BSC
• Tower Mounted Amplifier (TMA), external • GPS receiver built-in for synchronization • Measures (HxWxD): 476,6x542x520 • Weight: 47 kg (fully equipped)
• Power Consumption: 280 Watts (fully equipped) Hybrid Combiner
Tower Mounted Amplifier (TMA) Same Frequency band As Transmitter Filter
Power Supply
Battery Unit
Transmitter Filter N Type Tx Antenna Connector 2 GPS Antenna Connectors
Remove Cover to access Junction Box
Cooling Fan Tray & LED Indicators
AI411 Dual Receiver Multi Coupler
2 Transceivers Base Station Controller
CTS200 - Compact base station with up to 16 channels.
CTS200
• 1-4 TETRA-Carriers/Transceivers • 22 HU version
• AC/DC power supply including external battery charge • Terminal for external backup battery
• Optional redundant AC/DC power supply • 1 Cavity Combiner (Hybrid Combiner optional) • Base Station Controller BSC
• Optional redundant BSC
• Tower Mounted Amplifier (TMA), external • GPS receiver built-in for synchronization • Measures (HxWxD): 1054x542x520 • Weight: 97 kg (fully equipped)
• Power Consumption: 512 Watts (fully equipped)
Base Station Controller
4 Transceivers Power Supplies Dual Receiver Multi Coupler RF Test Loop Combiner Transmitter Filter TF413 behind rear panel
Antenna Connector Types Tx - ‘7/16 Din’ Tx Rx - ‘N’ Type GPS - BNC
Junction Box behind Door
Cooling Fan Tray With LED Indicators
CTS300 - Compact base station with up to 32 channels
CTS300
• 1-8 TETRA-Carriers/Transceivers • 37 HU version
• AC/DC power supply
• Terminal for external backup battery • Optional redundant AC/DC power supply • 1 or 2 Cavity Combiners (1 for 4 carriers each) • 1 Base Station Controller BSC
• Optional redundant BSC
Power Supplies Dual Receiver Multi Coupler
8 Transceivers
Transmitter Filter Behind rear panel
Antenna Connector Types Tx - ‘7/16 Din’ Tx Rx - ‘N’ Type GPS - BNC
RF Test Loop Combiner Junction Box behind Door
Note: TMA is mounted by the antennas.
Cooling Fan Tray with LED Indicators
• GPS receiver built in for synchronization • Measures (HxWxD): 1720x542x520 • Weight: 147 kg (fully equipped)
3.2. System
Equipment
Equipment TS100 CTS200 CTS300
Transceiver 4 8 8
Base Station Controller 1 1 1
Base Station Controller (redundant) 1 1 1
Power Supply with Rectifier 1 1+ 1+
External Battery Kit 1 1 1
TR Cassette for BS 1 1 1
PS Cassette for BS 1 1 1
Ant. Interface 1 1 1
Tower Mounted Amp. 1 1 1
Hybrid Combiner 1 1 (Optional)
Tx Filter 1
Dual 4/8-way divider 1 1
RFTL Combiner
Tower Mounted Amp. 1 1 1
4 or 4-8 way TX Combiner 1 1
TX Combiner kit 4 or 4-8 ch 1 1
TF411 TX Filter 25dB 1 1
Connection Box for 1-2 x BSC 1 1 1
Gateway PC 1 1 1
Gateway PC + Switch (Redundant) 1 1 1 Central Recording Equipment 1 1 1 Dispatcher Console 1 to 8 1 to 8 1 to 8 Antenna Connectors
Tx ‘N’ Type’ ‘7/16 Din’ Tx ‘7/16 Din’ Tx Rx ‘N’ Type ‘N’ Type ‘N’ Type
Note: A configuration may have from 1 to 8 carriers per site, 1 or 2 BSCs, and 1 to 5 PSUs and dependant on the type of CTS, the number of carriers and whether or not redundancy is ordered.
4. Call
Features
Compact TETRA provides a wide range of call features, which enables a large number of user groups intelligent and efficient ways to communicate.
The call features can be subdivided into speech calls (individual calls, group calls, telephone) and data calls (status, short data, packet data).
4.1. Speech
Services
The users have a fast and efficient way of communicating with each other while maintaining full privacy.
Individual Call
● Half-duplex call for short precise messages
● Full-duplex call for high quality and comfortable telephony-type calls Group Call
● Allows the users to communicate with team members spread among the coverage area with fast call set up and late entry facility
Pre-emptive Emergency Group Call
● Initiated by the subscriber – a pre-emptive function clears a channel with lower priority in case all traffic channels are too busy to operate an emergency call
4.2. Data
Services
This provides the users with a means to get “operational” applications into the field as well as a means to send precise messages between users. The feature allows fast and efficient communication when there is little time to talk. Typical applications are: Text Messaging, Automatic Vehicle Location (AVL), Automatic Vehicle Monitoring (AVM), Short Dispatch Messages, Database enquiries, Telemetry, Fleet Management.
4.3.
Short Data Service (Type 1 - Status)
● Allows the user to transmit pre-defined individual status messages, even if subscribers are engaged in a speech call
● Provides for up to 250 status messages (also depends on subscribers)
4.4.
Short Data Service (Type 4 – Text Messages)
● Allows the user to transmit and receive text messages, even if subscribers are engaged in a speech call
● Up to 140 characters can be transferred in one message (also depends on subscribers)
4.5.
Packet Data Service
● With IP-based Packet Data a mobile user can be permanently connected to a central database or the Internet
4.6. Voice
Call
Capabilities
Terminal-to-Terminal call:
• Full duplex individual call • Half duplex individual call
• Group Call including Late Entry feature
• Short Data Service (Status and Text up to 140 Characters) • Packet Data Calls
Terminal to Dispatcher call:
• Full duplex individual call • Half duplex individual call
• Group Call including Late Entry feature
• Short Data Service (Status and Text up to 140 Characters) Dispatcher to Terminal call:
• Full duplex individual call • Half duplex individual call
• Group Call including Late Entry feature
• Short Data Service (Status and Text up to 140 Characters) Dispatcher-to-Dispatcher call:
• Full duplex individual call • Half duplex individual call
• Group Call including Late Entry feature
• Short Data Service (Status and Text up to 140 Characters) Dispatcher to Telephone call:
• Full duplex individual call
Terminal to Telephone call (PABX or PSTN): • Full duplex individual call
Telephone to Terminal call
• Full duplex individual call with Direct-Dialing-In feature Telephone to Dispatcher call
• Full duplex individual call
All calls directed to terminals will be queued in case of busy resources
(transceivers). Calls from terminals to telephone subscribers will be blocked if all telephone lines are busy.
5. System
Configurations
5.1. Basic
configurations
The system is flexible and extendible and supports the following basic configurations:
• Stand-alone system
(without telephone interconnect, without external Packet Data and Short Data interconnect and without dispatcher)
• Single site system
with up to 32 channels, 8 or 30 ISDN channels and a maximum of 8 Dispatchers supporting up to 2.500 subscribers
• Multi site network
with up to 8 sites, up to 128 channels, 8 or 30 ISDN lines and a max. of 8 Dispatchers supporting up to 10.000 subscribers
5.2. Stand-alone
System
The Stand-alone system configuration is focused on customer groups needing local coverage without dispatch functionality and gateways. It supports Individual and Group Calls as well as Short Data and Packet Data Services among
subscribers.
The Stand-alone Compact TETRA can be configured by means of a standard PC connected to the Base Station Controller (BSC). For online monitoring of the system status and load conditions, the PC needs to be permanently attached to the system.
Because this system configuration requires no supporting infrastructure or networking other than power supply and the antenna, this configuration is most suitable for transportable and quick installable applications.
The stand alone system can be either of the 3 types of base station, CTS100,200 or 300, with:
• Up to 8 Transceivers giving 32 virtual channels • 2,500 Subscriber radios in 256 Groups
• A redundant BSC
• Redundant power supplies • Battery charging capabilities
It has no connectivity to the outside world (ISDN or Packet Data Gateway).
5.3. Single-Site
System
Besides the Basestation the single site system provides a Gateway Server with the following interfaces:
● Interface to PABX/PSTN following the Euro-ISDN standard for up to 8 full duplex individual speech calls (4xISDN)
● Interface to external customer IP network for Packet Data and Short Data Service.
● Interface to connect up to 8 Dispatcher Workstations
Dispatcher Workstations with On-line monitoring, control of system status and health and subscriber management user interface.
The single-site system is targeted primarily at customers who need local TETRA coverage and additionally dispatch functionality and/or gateways. The connection between the Site and the Gateway is a single fractional E1 link.
The connections to the Dispatcher Workstations or the IP-networks require 100Mbps Ethernet LAN infrastructure.
Single –site System
The single site system can be either of the 3 types of base station and it can have: • Up to 8 Transceivers giving 32 virtual channels
• 2,500 Subscriber radios in 256 Groups. • A redundant BSC
• Redundant power supplies • Battery charging capabilities
The system has a Gateway PC (GWPC) that provides connectivity to the outside world via an ISDN Gateway for Telephone links and a Packet Data Gateway for data linking.
The Gateway acts as the master node of the system for: All data base files, subscriber management etc.
All base stations check their files against the GWPC files on power up.
Up to 8 Dispatcher consoles may be connected to the Gateway PC via a switch with the equivalent (or better) specification to that of the HP Procurve Switch 2512
5.4.
Multi-Site System
The Multi-site system offers all of the features of the single-site system with, additionally, multi-site individual and group calls, including call restoration of all individual and group calls (seamless handover from one site to another one). An intelligent paging strategy conserves air interface resources yet ensures that subscribers may be reached for group communications at all sites. Subscribers are only attached to group calls at Basestations where at least one subscriber of the called group is registered.
The multi-site system supports up to 10,000 subscribers. The system tracks the location and group attachment status of the registered subscribers in a
distributed database that allows fast local access to the information on call set-up.
The multi-site system uses a chain of E1 links to interconnect the sites and the Gateway Server. When the chain is closed (ring configuration) a break of a single link would not cause any communication error.
For reduced cost of ownership, smaller system configurations can use fractional E1 using multiplexers. The system can be configured to limit the E1 time-slots used for communication to a certain range.
This has the features of the single site system and can have up to a further 7 base stations giving a maximum total of 32 Transceivers that give 128 virtual channels, supporting 10,000 Subscriber radios in 256 Groups.
6. Resilience
Distributed intelligence
Because of the de-centralized structure of the entire system and the distributed intelligence, the basic TETRA features can be performed on each site
independently. This allows local site fallback in the case of failures in the infrastructure. All sites can work in local trunking mode without gateway and dispatchers.
Redundant power supplies and Base Station Controller
The site can be equipped with redundant power supplies and a redundant Base Station Controller (BSC). In the case of a failure of the operational BSC all ongoing calls will be lost but the stand-by controller will take over and start operating without the need of reconfiguration.
Inter site links
The chain of base stations can be either open, or closed with one additional E1 link. This additional link affords system fault-tolerance against single link failures; if one of the links fails, all system services will continue unimpaired.
Even in the open-chain configuration, the multi-site system performs graceful degradation in the case of link failures. If the network is partitioned, each of the sub-networks will continue to function and allow unhindered communication between all subscribers in the sub-network. The speech transmission will be interrupted for a maximum of 1 second during switchover.
E1-Ring-Configuration:System capabilities, parameters and specifications
7.
The System Signalling Path
This section explains the following:
● The OSI protocol layer structure of the system.
● The interaction of the different layers.
● The sub divisions, where appropriate, of each layer.
● The functionality of the different protocols running on each layer.
● Where, on the system hardware, these layers/protocols sit.
7.1. Overview
The hardware construction is based on the transceiver and Base Station Controller.
The Cells and Gateway are linked through 2Mbit E1 connections in a ring or linear topology with drop and insert functionality. Sub-rated (fractional) E1 can be used to scale the number of E1 channels required for the size of the system. The ring topology can offer a high grade of redundancy if routing is provided in both directions.
The gateway is used for system connection to PABX/PSTN/IP network(s) and for dispatcher console connectivity to the system and supports the following
functions:
● Network Management
● Subscriber Management
A dispatcher console may support the following functions:
● Dispatcher
● Network Management
● Subscriber Management
7.2. Radio
Air
Interface
This consists of the transceivers and the antenna combining system.
The transceivers have an output power of up to 25W Tetra, giving approximately 10W Tetra after combining.
The antenna branching system contains the following:
● Tx filter.
● Antenna interface.
● Rx filtering.
● Tower Mounted Amplifier (TMA).
The Hybrid combiner is only used for combining 2 transceivers (Carriers), if more carriers are used, then a cavity combiner is used.
Note: Only the system designed combiners can be used, no other combiner has the capability to work with the system and give the same functionality.
7.3. Software
Applications
The OSI layers are software applications running on the system that inter re-act. The receive information from one application (a lower layer), is passed to a higher layer application.
The application may action the information and pass it back to the previous layer, or it can pass the information on to the layer ‘above’ and/or to its peer at another node.
7.3.1. OSI
Layers
The OSI model showing its 7 functional layers, is now accepted for description and specification of layered communication architectures.
The bottom 3 layers of the protocol stack are associated with the network services and have to be implemented in every node of the network, both infrastructure and MS. End User Functions Network Functions Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer
Physical Layer Higher Level Protocols Network Services End User A Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer End User B 6 2 5 4 3 1 7 Physical Medium Layer Number
The upper 4 layers of the protocol stack provide services to the end users and are thus associated with end users, not the network.
The philosophy of layered architecture is based on each layer being
independently specified in terms of the services it provides to its immediately higher level and the services it relies on from its immediately lower level. The Layer architecture provides ‘Peer to Peer’ exchanges, in which each layer exchanges information with its peer entity at the remote end.
Note: The Tetra Standard defines the network protocol only up to layer 3.
7.3.2.
The system Voice Path
8Kbits/s Tetra Coded in E1 Time Slots
MAC MAC MAC
E1 E1 E1
Transceiver Transceiver Transceiver
A1 A1 A1 8KbitsTetra Coded Mic Loud Speaker Gateway PC E1 Card ISDN Card DSP Tetra Codec Pentium Pentium VoIP Ethernet Card Ethernet Card VoIP Packetised G711 Over PCI Packetised G711 H.100 Dispatcher PC G711 Analogue I/O Head Set
7.3.3.
MS/BS Air Interface Protocol (DLL – Layer 2)
C-Plane Traffic:
MM Mobility Management – Controls roaming, migration and handover. CMCE Circuit Mode Control Entity – CC – call control,
– SS – supplementary services & short data service (SDS).
PD Packet Data - CONS – connection oriented network service CLNS – connectionless network service
Note: MM, CMCE & PD are collectively called Sub-network access functions (SNAFS) U-Plane Traffic:
Responsible for:
Clear/encrypted speech, Circuit mode unprotected data,
Circuit mode protected data (low), Circuit mode protected data (high), End to end user specific data.
MM CMCE PD
MLE – Mobile/Base Link Control Entity
LLC – Logic Link Control
MAC – Medium Access Control
Physical Layer
C-Plane (Control Plane)
Layer 3
Layer 2
Layer 1
U-Plane (User Plane)
7.3.4.
Overview of the CSCIs on the Base Station.
7.4. Transceiver
The transceiver handles one Tetra air interface carrier, i.e., one uplink and one downlink frequency.
It handles all layers of the Tetra air interface up to and including the upper MAC. It is responsible for:
Routing of Tetra U-plane traffic between the Air Interface and the PCM Highway leading to the BSC.
Routing of Tetra C-plane traffic between the Air Interface and the HDLC bus leading to the BSC.
Handling of modulation and synchronisation for receiving and transmitting over the radio interface
Distributed Application (Site)
CMCE-U AI L2 MAC LLC CMCE- L SNDCP- L A I R M Message Router D B SPCDD U SWITCH SNDCP -U MM-U AI L3 MM-L BLE To other sites and GWPC
7.5.
Base Station Controller
The functions of the BSC are:● Control the transceivers of the Base Station
● Handle all layers of the Tetra air interface from LLC upwards
● Switches the PCM sub-timeslots between the internal communication paths to/from the transceivers and the external E1 links.
● Alarm reporting
● Operations and Maintenance
Communicate with other base station controllers and the Gateway PC for the following purposes:
● Inter-site call control
● Distribution of global status information about the status of the nodes in the distributed application
● Distribution of subscriber-related static data (subscriber profiles)
● Distribution of subscriber-related dynamic data (current registration status and location of subscribers).
7.6.
The Gateway PC.
7.6.1.
The Structure of the Gateway PC
PDG Dispatcher LAN PSTN/PABX Gateway H.100 Bus Inter-Site Links E1 Card DSP Card ISDN Card Ethernet Card Ethernet Card
7.6.2.
Functions of the Gateway PC.
It contains commercial off-the-shelf (COTS) components and is the:
● Speech gateway for the inter working between TETRA speech calls and an external telephone network. Two types of gateway are available:
● A 4-fold ISDN-BR gateway offering 8 simultaneous speech calls over four Euro Isdn basic rate links.
● An ISDN Primary Rate gateway offering 30 simultaneous speech calls over a G.703 2048kbit/s link.
● Packet data gateway for the inter working between TETRA SNDCP packet data and an external IP-based network.
● Dispatcher Gateway for the connection of Dispatcher Workstations.
● Tetra Codecs for PABX/PSTN and Dispatchers
● Operations and Maintenance Server
● Subscriber Management Server
7.6.3.
Gateway Computer Software Configuration Items (CSCIs)
Distributed Application (Gateway PC)
Message Router DISPS SPCDD ISDNGW OMSA SMSA Switch PDG E1 To Sites D B MM-U SNDCP- U CMCE-U DA-IF U-SWITCH Codecs canceller To PSTN or PABX To External IP Network To Dispatcher Work Stations
7.7. Dispatcher
Work
Station
The Dispatcher Workstation HWCI is a standard PC containing commercial off-the-shelf (COTS) components and provides the human interface to the Tetra system. The following applications are accessed at this PC:
● The dispatcher client application that allows dispatchers to set up and receive calls, and send and receive SDS.
● The Operations & Maintenance client application that allows users to monitor and control the operation of the system.
● The Subscriber Management client application that allows users to manage the subscriber data base of the system.
The Dispatcher Workstation uses a standard headset connected at the sound card (PC SoundBlaster compatible).
7.7.1.
The following diagram shows the structure of the Gateway PC
PCI BUS Dispatcher LAN MIC Sound Card Ethernet Card Pentium Motherboard Windows NT Headset Loudspeaker CD ROM Hard Disk
7.7.2.
The CSCIs on the Dispatcher Workstation
7.8.
Tetra Air Interface Layer 2 – Overview
The Tetra Air Interface Layer 2 consists of the MAC CSCI and the LLC CSU.
MAC
● The MAC SW is running on the transceiver cards and handles the lower layers of the Tetra Air Interface Layer 2.
LLC
● The LLC is running on the BSC HWCI as part of the AI CSCI.
● The LLC handles the upper layer of the Tetra Air Interface Layer 2.
● It provides basic the link for CMCE, MM, and SNDCP signalling and the advanced link for SNDCP data transmission.
Dispatcher WS DISPC OMCA SMCA HMI To Dispatcher Work Stations
7.9.
Tetra Air Interface Layer 3 – Overview
The Tetra Air Interface Layer 3 consist of the BLE, the CMCE-L, the AIRM, the MM-L and the SNDCP-L CSUs. Together with the LLC CSU, they make up the AI CSCI.
Structure of Tetra Air Interface Layer 3
7.9.1.
Base Site Link Entity (BLE)
● The BLE is running on the BSC HWCI and is the SwMI-side counterpart of the MLE in the MS.
● It routes messages between the LLC and the other Layer 3 entities, and it handles the MLE protocol.
7.9.2.
Circuit Mode Control Entity (CMCE-L)
The CMCE-L CSU is running on the BSC HWCI as part of the AI CSCI and is the SwMI-side counterpart of the CMCE in the MS. It handles the protocol for circuit-mode calls and SDS transmissions. Its main responsibilities are:
● PDU encoding and decoding
● Protocol timer handling
● Interaction with the AIRM for air interface resource management
● Mediation between the air interface and the CMCE-U.
AI Layer 3 BLE MM-L CMCE-L SNDCP -L AIRM Distributed Application LLC
It cooperates with the Air Interface Resource Manager (AIRM) to allocate and de-allocate air interface channels and queues calls when these resources are not immediately available.
It passes all uplink call signalling to the higher layers and is not concerned with:
● The routing of calls or the decisions as to whether or not a call may proceed.
● Call log generation.
For downlink call signalling, all call setup requests are received from CMCE-U and there is no “shortcut” for single-site calls.
For SDS transmissions, it converts the uplink PDUs to internal primitives and passes them on to CMCE-U and it converts the downlink primitives to downlink PDUs.
7.9.3.
Air-Interface Resource Manager (AIRM)
The AIRM CSU is running on the BSC HWCI as part of the AI CSCI.
It handles the allocation and de-allocation of both Traffic Channels (TCH) and Packet Data Channels (PDCH) and is responsible for the:
● Air Interface Stack start up and shutdown.
● Allocation and de-allocation of TCH on behalf of CMCE-L.
● Allocation and de-allocation of PDCH on behalf of SNDCP-L.
● Queue management for as-of-yet unfulfilled requests for resources by CMCE.
● Management of transceiver failures.
For single-site semi-duplex individual calls, it is responsible for merging the allocation requests of the independent CMCE-L entities into a single channel allocation and for this purpose, the AIRM keeps a reference count for each allocated TCH and de-allocates the TCH only when the last reference goes away.
7.9.4.
Mobility Management (MM-L)
The MM-L CSU is running on the BSC HWCI as part of the AI CSCI and is the SwMI counterpart of the MM in the MS.
It handles the protocol for registrations, de-registrations, and group management and its main responsibilities are:
● PDU encoding and decoding
● Mediation between the air interface and the MM-U
It is a stateless protocol converter that sends and receives all uplink/downlink signalling to/from the MM-U.
7.9.5.
Packet Data (SNDCP-L)
The SNDCP-L CSU is running on the BSC HWCI.
It handles the Tetra SNDCP protocol and passes context activation and deactivation commands to the SNDCP-U.
It routes datagrams between BLE and SNDCP-U and manages AI resources for Packet Data channels.
7.9.6.
U-Plane Switching (USWITCH)
The U-Plane switch runs on the Base Sites and Gateway PC.
On the inter-site links, Tetra speech is transmitted in 8kbit/s channels.
On the LAN, to the Dispatchers, speech is transmitted via IP and on the speech gateway, speech is transmitted in G.711 format
The channels on the inter-site links are always present on all nodes of the system.
The U-Plane switch is a software layer that can locally switch speech channels and has the following functionality:
It hides the details of the physical implementation of the switch, which is different on the sites and the Gateway PC.
It handles re-switching of speech connections when a system component fails.
7.9.7.
Distributed Application – Overview
The distributed application consists of a number of CSUs, each of which is responsible for one group of functions.
There is one instance of the distributed application running on each site and Gateway PC.
The peer instances communicate with each other using the inter-site communication protocol.
● The global static subscriber data base (GSDB) holds the static subscriber profile.
● Each node holds one copy.
● The GSDB is only updated by subscriber management actions.
● The global dynamic subscriber data base (GDDB) holds the dynamic subscriber information, i.e., location information and group attachment status.
● It is updated dynamically by user actions (roaming, registration, deregistration, and group management actions).
Structure of Distributed Application
Distributed Control, Management &
AI Layer 3 / PSTN/PABX GW / Dispatcher Server Inter-site Communication
GSDB
CMCE-U
MM-U
GDDB
r
w
r
w
SNDCP-U
SPCDD
7.9.8. Circuit-Mode
Control Entity (CMCE-U)
The CMCE-U runs on the Sites and on the Gateway PC and it handles the protocol-independent aspects of the Tetra CMCE functionality.
On the sites, it cooperates with the Air Interface Layer 3, and on the Gateway PC, it cooperates with the PABX/PSTN Gateway and the Dispatcher Server application.
It communicates with its peer entities in other nodes via the Inter-site communication layer.
For calls originating on the local node, it is responsible for:
● Call validation.
● Location lookup.
● Routing of the call setup signalling to one or several remote nodes, and/or to one or several local protocol stacks (CMCE-L, DISP-GW, PABX/PSTN-GW).
● Handling of call duration timers and call inactivity timers (for semi-duplex calls).
For calls terminating at the local node, it is responsible for:
● routing the call setup signalling to one or more local protocol stacks. In either case, the CMCE-U is responsible for:
● Mediation between the local protocol stacks and the peer entities for call maintenance procedures.
● Generation of call logs.
● Failure management.
If a network node fails or becomes unreachable, each CMCE-U instance is responsible for locally disconnecting all ongoing individual calls with that node.
7.9.9.
Mobility Management (MM-U)
The MM-U runs on the Sites and on the Gateway PC and is responsible for the protocol-independent aspects of the Tetra MM functionality. It acts as a server for the local protocol stacks.
During mobility management requests on the local site, MM-U is responsible for the following:
● Validating the request and rejecting it if the validation fails
● Triggering the transmission of the updated information to all peer entities for registration and deregistration requests.
7.9.10.
Dynamic Data Distribution (DD)
The DD is responsible for maintaining a global up-to-date and consistent view about the location of the subscribers in the face of user actions and system component failures. The peer entities of the DD communicate with each other via Inter-site communication layer.
If a node becomes connected again after being disconnected, or after a reboot, the DD is responsible for synchronising the state of the dynamic subscriber data with the global state.
For requests coming in from a local stack, the DD is responsible for distributing the information to its peers.
For requests coming in from a peer entity, the DD is responsible for updating the local copy of the dynamic subscriber data.
7.9.11.
Packet Data Handling (SNDCP-U)
The SNDCP-U CSU is running on the Sites and on the Gateway PC and is responsible for the transmission of Tetra packet data among sites, and between the sites and the packet data gateway.
It sits on top of SNDCP-L on the sites, and on top of the packet data gateway in the Gateway PC.
On reception of a datagram from the lower protocol (SNDCP-L in the case of the site, the Packet Data Gateway in the case of the Gateway PC), the SNDCP-U CSU looks at the destination IP address.
If the net mask indicates that the datagram is for a Tetra subscriber, SNDCP-U looks up the SSI of the destination subscriber, otherwise, it uses the Packet Data Gateway SSI.
On reception of a datagram from another node, it checks whether the subscriber is reachable on the node.
● If not, it sends back an ICMP “Host unreachable message”.
● If yes, it passes the datagram to the lower protocol stack.
Tetra packet data is transferred through the system as signalling data, not as standard IP traffic.
7.9.12.
Subscriber Profile and Configuration Data Distribution (SPCDD )
This is running on the Sites and on the Gateway PC and it consists of a server application running on the Gateway PC and of client applications running as part of the distributed application. It handles the distribution of the following:● Subscriber profiles.
● Software updates.
All static configuration data is kept in files containing a timestamp and version number and all master copies are kept on the Gateway PC.
The distribution server keeps a record of the file version that should be on each of the sites and if the version of a file changes on the Gateway PC, it is
distributed to the clients. On reception of an updated configuration file (e.g. for subscriber profiles), the clients DD reads the new version of the file into internal data structures and switches over to the new version of the configuration data. If a site becomes connected again after being disconnected and after a reboot, the local SPCDD instance will send a message to the distribution server to notify it of its local current versions of all configuration files. The server will then inform the site of any new versions of configuration files that have been created in the meanwhile.
7.10.
Tetra Codecs
The Tetra Codecs are implemented on DSPs in the Gateway PC
The Tetra Codecs convert speech between the 8kbit/s Tetra encoded format and 64kbit/s G.711 (A-law) encoded format.
7.11.
PABX/PSTN Gateway (ISDNGW)
The ISDN Gateway is a feature of the Gateway PC and it enables the inter working of individual full-duplex speech calls between the Tetra System and either a PABX or the ISDN. It has the following main responsibilities:
● Inter working of Basic Call signalling between the ISDN and the Tetra system
● Control of U-Plane transcoding and switching
● Employment of echo cancellation to attenuate the reflected echo from the PABX/ISDN. This is needed as a result of the speech delay introduced in the Tetra system imposing more stringent requirements for attenuation of echoes.
7.12.
Packet Data Gateway (PDG)
The PDG is a feature of the Gateway PC and it enables the inter working of IPv4 between the Tetra System and an external IP network. The Tetra network
appears as one Class B subnet to the IP network.
Within the system the packets are routed using the mobility information of the mobiles. The packets are transported via the signalling interface between the sites.
All packets with external IP addresses are routed to the Gateway. The translation between internal packet representation and IP is done at the Gateway.
7.13. Registration
of
a Mobile/Dispatcher
Registration of a mobile at a site is handled locally by the site and triggers an update of the distributed dynamic subscriber databases.
For the registration of a mobile to the local site, the main operational steps map to the CSCIs as follows:
● The MM-L receives a U-LOCATION UPDATE DEMAND PDU from the BLE and signals the registration to MM-U.
● The MM-U consults the local copy of the static subscriber data base to check the permission of the subscriber to register.
● The MM-U updates the local copy of the dynamic subscriber database, sends an update request to all peer entities and creates a log entry.
● The MM-U acknowledges the registration to MM-L.
● The MM-L then sends a D-LOCATION UPDATE ACCEPT PDU to the BLE. If the permission check is unsuccessful, U rejects the registration to the MM-L, which sends out a D-LOCATION UPDATE REJECT.
The MM-U also creates a log entry.
On reception of an update request from a peer:
● The MM-U will update the local copy of the dynamic subscriber database.
● If the peer was previously registered at the local site, the MM-U will inform the MM-L of the deregistration.
7.14.
Deregistration of a Mobile/Dispatcher
Deregistration of a mobile at a site is handled locally by the site and triggers an update of the distributed dynamic subscriber databases.
For the deregistration of a mobile from the local site, the main operational steps map to the CSCIs as follows:
● The MM-L receives a U-ITSI DETACH from the BLE, clears all AI L3 context for the mobile and signals the deregistration to the MM-U.
● The MM-U then updates the local copy of the dynamic subscriber database, sends an update request to all peer entities and creates a log entry.
On reception of an update request from a peer:
● MM-U updates the local copy of the dynamic subscriber database.
7.15.
Call Set-up Procedure
The main operational steps are as follows:
● The CMCE-L receives a U-SETUP via the BLE and signals the call to the CMCE-U.
● The CMCE-U consults the GDDB, detects that the call is local, and signals the call back to CMCE-L.
● The CMCE-L then sends a D-SETUP to the BLE for the outgoing half-call. Further call-related signalling is routed along the same path.
The CMCE-L consults the AIRM, for allocation of air interface resources, at through connect and for half-duplex calls
The AIRM will re-use the allocated channel for both the outgoing and incoming half-call.
7.16.
Inter-Site Call Set-up
Individual calls between two mobiles registered at different sites are handled by the two sites without intervention of external central equipment.
The main operational steps are as follows:
● The CMCE-L at the originating site receives a U-SETUP from its BLE and signals the call to its local CMCE-U.
● The CMCE-U consults the GDDB, detects that the call is an inter-site call and signals the call, via the inter-site communication platform, to its peer on the destination site.
● The CMCE-U at the destination site signals the call to its local CMCE-L.
● The CMCE-L then sends a D-SETUP to its BLE.
Further call-related signalling is routed along the same path between the CMCE-Ls.
The CMCE-Ls consult their AIRMs, for allocation of air interface resources, at through-connect.
7.16.1.
Calls Originating at the PABX/PSTN Gateway
The PABX-GW receives a SETUP request from either the PABX or PSTN and signals the call to its local CMCE-U, which handles the distribution of the call as per the call set-up procedure.
PABX-GW is responsible for the inter working of the signalling between the ISDN and the internal signalling protocol.
On through-connect the switching layer at the Gateway PC allocates a Tetra codec to transcode the voice.
If a mobile modifies a call to be half-duplex, the PABX-GW will clear down the call in both directions.
7.16.2.
Calls Terminating at the PABX/PSTN Gateway
When the PABX-GW receives a call from its local CMCE-U, it signals the call to the ISDN.
The PABX-GW is responsible for the inter working of signalling between the ISDN and the internal signalling protocol.
At through connect, the switching layer at the Gateway PC allocates a Tetra Codec to transcode the voice and connects the inputs/outputs of the Codec to the appropriate channels on the ISDN.
If a mobile modifies a call to be half-duplex, the PABX-GW will reject the call attempt .
7.16.3.
Calls Originating at a Dispatcher
When the DISPSERV CSCI receives a call from a dispatcher, it signals the call to its local CMCE-U, which then handles the call set up.
The DISPSERV CSCI is responsible for the inter working of the signalling between the Dispatcher access protocol and the internal signalling protocol. On through connect, the switching layer at the Gateway PC allocates a Tetra Codec to transcode the voice and sets up a VoIP connection between the dispatcher and the Gateway.
7.16.4.
Calls Terminating at a Dispatcher
The DISPSERV CSCI receives a call from its local CMCE-U and signals the call to the Dispatcher.
The DISPSERV CSCI is responsible for the inter working of the signalling between the Dispatcher access protocol and the internal signalling protocol. On through-connect the switching layer at the Gateway PC allocates a Tetra Codec to transcode the voice and sets up a VoIP connection between the dispatcher and the Gateway.
Also the system allocates only one Tetra Decoder for all dispatchers monitoring a group call.
7.16.5.
Call Restoration Multi Site
Call restoration is handled by the CMCE-U application at each sites. Up to three sites may be involved:
● The old site where the moving subscriber previously held the call.
● The new site where the call will be restored.
● The peer site which hosts the other party in an individual call.
The main operational steps for restoration of an individual call are as follows:- At the new site:
The CMCE-L receives a U-CALL RESTORE indication from LLC and signals this to CMCE-U. To reduce the length of the speech break, the AI resource allocation may proceed in parallel with inter-site signalling.
The CMCE-U uses the call identifier to locate the “old” site and signals the call restoration request to the old site.
At the old site:
The CMCE-U looks up the context related to the call and sends the call
parameters, which includes information about the used E1 sub-channels and the peer site, back to the “new” site.
It then checks to see if the call still has local participants, if not, it clears the call locally.
At the new site:
The CMCE-U signals the call restoration to the “peer” site, including information about the new E1 sub-channel bearing the speech of the moved subscriber. If the restored call is queuing for resources at this point, then this signalling will be delayed until resources become available.
At the peer site:
The CMCE-U updates the information and switches the downlink speech channel to the new E1 sub-channel.
In the above, the “old” and “peer” may be the same site, as may the “new” and “peer”.
7.16.6.
Call Restoration – Group Call
The restoration of a group call is as follows:
The CMCE-L receives a U-CALL RESTORE indication from LLC and signals this to CMCE-U. To reduce the length of the speech break, the AI resource allocation may proceed in parallel with inter-site signalling.
The CMCE-U uses the call identifier to locate and signal the call restoration request to the old site.
At the old site:
The CMCE-U looks up the context related to the call and sends the call
parameters, which includes information about the used E1 sub-channels and the peer site used by the talking party back to the new site.
At the new site:
If the moving party is currently transmitting, the CMCE-U signals the information about the new E1 sub-channel bearing the speech of the moved subscriber to all peer entities participating in the group call.
If the restored call is queuing for resources at this point, then this signal will be delayed until resources are available. Otherwise, if another party is currently transmitting, it switches the downlink speech channel to read the E1 sub-channel of the talking party.
7.17.
Pre-emptive Priority Call
Pre-emption Does Not place a call at the top of a queue. If someone with pre-emption wishes to talk to person ‘A’ who is already in a call, pre-pre-emption will override this call and set the call up with person ‘A’.
If a call is made with pre-emptive priority, the AIRM may clear down a call to free resources for the pre-emptive priority call. This applies to initial call set up, as well as to call restoration.
There is no announcement of the imminent pre-emption to the pre-empted parties.
At the dispatcher, a call with pre-emptive priority is indicated as an incoming call with dedicated signalling.
If the incoming call queue at the dispatcher is full, one call is immediately pre-empted and the priority call is displayed.
7.18.
CLIP and TPI
All signalling interfaces in the system carry Calling Line Identification Presentation (CLIP) and Talking Party Identification (TPI) information for presentation to the user. No other provisions exist for CLIP and TPI.
If a call is to an external number, the PSTN/PABX Gateway builds the calling party information element, into the outgoing SET UP, from a decimal
representation of the calling party’s SSI and an optionally configured prefix string.
7.19. Subscriber
Data
Management
Subscriber Management is used to define both the Short Subscriber Identity (SSI) and the user rights for each MS.
The subscriber data is distributed through out the system as text files. The synchronisation of the subscriber data is controlled by the Gateway. The user interface for changing the subscriber data is implemented at the Gateway & Dispatcher PCs.
The Base Stations are updated via the Subscriber Profile and Configuration Data Distribution.
