Warsaw Command and Control System includes The Radio Communication Module which uses Motorola's Dimetra IP TETRA system solution for both voice and data communication between the KSP headquarters and police officers in the field. In addition, the Radio Communication Module provides conventional VHF repeater stations for voice communication.

What is Dimetra IP?

Dimetra IP - DIgital Motorola Enhanced Trunked RAdio

Dimetra IP is a multisite digital trunking system. It is very similar to GSM network and has TCP/IP capabilities.
System configuration consists of two types of sites:
-Master Site
-Subsystem and Remote Sites (EBTS)
The system design is based on modularity (sites are comprised of device, device are comprised of modules and cards, and so on)
The Master Site contains the ZC with a local Dabase Server, User Server, optional User Terminals and backbone network.

Dimetra IP Architecture.



The Zone Controller (ZC)
The Zone Controller forms the heart of the Dimetra system.
It controls call processing, mobility management
(tracking the location of mobile stations), channel allocation and diagnostics.
The call processing functions include:
- Radio site registrations and group attachments
- Receive call requests
- Check call access privileges
- Queue calls as required
- Select and assign available traffic channels
- Issue "call grants" to requesters
Monitor and control call sequence The resource management functions include:
- Control and set-up of Group Switch
- Backup of Tetra system configuration (GSC, UCS, User server, Database server)
- Control of the EBTS resources
- Control of Transcoder resources
- Control of telephone interface lines

Ambassador Electronics Bank (AEB)
The Group Switch is a Motorola Ambassador Electronics Bank (AEB) which is a digital PCM switch. The Group Switch is specifically designed for wide-area systems with multiple fixed radio consoles.
Primary functions of the Group Switch include:
- Route digitised audio or data packets
- Route private radio and telephone interconnect calls between radio sites, consoles and/or telephone gateway
- Provide one-to-many routing where multiple radio sites are involved in a group call

Transcoder (XCDR)
The transcoder performs the necessary digital signal processing to support TETRA speech encoding and decoding. The speech transcoder converts the 64 kbps PCM audio from dispatcher microphones and telephone lines to the ACELP vocoder format used on the TETRA air interface and vice versa.

Site Link Multiplexer (SLM)
The SLM multiplexes voice, data, call processing and network management information from the master site onto the remote site links. The SLM consists of a 19" rack mount chassis, a single CPU card, Frame Relay Server card, Wide Area Network (WAN) cards, Interface Card, dual port X.21 cards, an IP router card and a power supply. SLM is used in Dimetra IP 3.8/4.0 System Release (look below for Wan Switch).

WAN Switch
The Site Link Multiplexer (SLM) & Zone Link Multiplexer (ZLM) used in Dimetra IP S.R. 3.8/4.0 are no longer used in Dimetra IP 5.x. These two components are replaced by the WAN switch and the Zone Core Ethernet Switch / Lan Switch. The WAN switch is a new switch in Dimetra IP and is used at the MSO (Zone Core) site to provide all WAN links internal to the Dimetra IP system. For connection to the customer Enterprise, the appropriate routers will take care of the WAN connections. The WAN switch is a Frame Relay/ATM.

Packet Data Gateway (PDG)
The PDG interfaces and manages the connectionless packet data communication features of TETRA. The data traffic to and from the mobile data terminals is routed through the Packet Data Gateway. The PDG is normally mounted in a 19" rack with the other master site equipment. To support the IP packet data service two processor cards are added to the chassis: a one to run the Radio Network Gateway (RNG) application and a PowerPC processor with 128 MB RAM to run the Packet Data Router (PDR) application. The RNG handles the TETRA air-interface protocol (advanced link) processing and the PDR handles the TETRA address to IP address mapping and IP routing functions.

Short Data Router (SDR)
The Short Data Router (SDR) is computer designed specifically for telecommunication applications. It is normally mounted in a 19" rack. The Short Data Router (SDR) supports the Short Data Transport Service by enabling routing of short data packets within the system based on TETRA Individual Short Sub-scriber Identities (ISSIs). All short data packets to be delivered to MSs via the TETRA Short Data Service (SDS) are sent to the SDR. The SDR communicates with the ZC to determine at which site the MS is currently registered, then forwards the short data packet to the appropriate Enhanced Base Transceiver System (EBTS).

Gateway GPRS Support Node (GGSN)
The General Packet Radio Service (GPRS) is defined and standardized by the European Telecommunication Standards Institute (ETSI). GPRS is an IP packet-based data service developed for Global System for Mobile Communications (GSM) networks. The Gateway GPRS Support Node (GGSN allows mobile users to access the customer network or specified private IP networks. User sessions are connected from a mobile station to the RNG. From there, the RNG provides, via the PDR, access to the GGSN, which serves as the gateway to the data network. The connection between the PDR and the GGSN is enabled through a protocol called the GPRS Tunneling Protocol (GTP), thus the PDR will function as a SGSN. In order to assign mobile user sessions an IP address, the GGSN can use the Dynamic Host Configuration Protocol (DHCP). GGSN is used in Dimetra IP 5.x S.R.


User Server
The user server provides the processing power to drive the applications and functions of the System Manager that do not reside on the Group Switch Controller or Database Server. The functions supported by the user server include Basic Statistics, Air traffic Information Access (ATIA) process, display services to drive the Graphical User Interface (GUI), print services, and support of the Manager, System Watch and Radio Dispatch Management applications. The user server is two Unix Workstation manufactured by Hewlett Packard.

Database Server
The database server provides two major system functions. Firstly, it contains the system configuration database, including Subscriber Access Control (SAC) records, used by the Group Switch Controller during the processing of call requests. Secondly, it performs the processing of all fault information for the system.

User Configuration Subsystem (UCS)
The User Configuration Subsystem (UCS) is the management application used for entering and maintaining system level configuration information. Through the UCS the system manager can configure subscribers, talkgroups, critical sites, adjacent control channels and security information at a system level. The UCS consists of two Unix servers: a Database Server and a User Server. Both servers are Unix Workstation manufactured by Hewlett Packard.

User Terminal
The User Terminals provide the Network Management users with a Graphical User Interface (GUI) to the various Network Management applications.

Enhanced Base Transceiver Station (EBTS)





Transport Network

At the core of Dimetra IP system is a transport core designed to carry the system applications. This transport core uses several network technologies. The Dimetra IP systems includes an IP based infrastructure that provides IP multicast technology for dispatch services.
IP multicast is a routing technique that allows IP traffic to be sent from one source and delivered to multiple destinations. Instead of sending individual packets to each destination, a single packet is sent to a multicast group, which is identified by a single IP destination group address. This technology allows group calls to be set up, processed, and torn down easily in a packet environment, replacing circuit switched methods. The transport core provides the ability to transparently transport vocoded and encrypted audio. Once voice is vocoded and/or encrypted at a source, the digital information is simply passed all the way through the network with no conversions required. Conversion to the original audio format is required only at the destination receiver.

Protocols in Dimetra IP

Dimetra IP carries traffic on the transport network, by the following protocols:
For Unicast Traffic:

Open Shortest Path First (OSPF) is used within the core network for unicast traffic, due to its relatively fast convergence times on larger links.

Border Gateway Protocol (BGP) is used on Inter-Zone links because of its route aggregation ability and to address scalability limitations associated with OSPF.

Static Routing is used on site links, which eliminates any convergence time lags due to dynamic routing convergence protocols links.
For Multicast Traffic:

Protocol Independent Multicast - Sparse Mode (PIM-SM) is used in the core network as the multicast routing protocol.

IGMP v2 - Internet Group Management Protocol enables hosts to subscribe to a multicast group
To Maintain Quality of Service:

CRTP - Compressed Real Time Protocol to improve the bandwidth efficiency.

FRF. 12 - Frame Relay Fragmentation to control the end-to-end delay of voice traffic.