First introduced in 1994 by the European Telecommunications Standardization Institute (ETSI), terrestrial trunked radio - better known as TETRA - has become a prominent standard for private digital wireless communications, with networks spanning 70 countries. TETRA defines a common mobile radio network for both voice and data services that meets the needs of professional mobile radio (PMR) applications, such as police, public safety and emergency rescue services, and private access mobile radio (PAMR) applications, including maintenance and repair teams, courier and delivery services, construction, and public transportation. Technology and TopologyTETRA networks use technology and a hierarchical topology similar to cellular networks, in which an individual radio terminal's transmission is picked up by the local enhanced base transceiver station (EBTS) or the tactical receive equipment (TRE). The EBTS/TRE sites are then connected to a central mobile switching office (MSO). From the MSO the radio call can be connected to remote dispatcher sites or control rooms, directly to other radio terminals within the network or linked externally to other networks or the public switched telephone network (PSTN). Similar to cellular networks, the connection or backhaul of the TETRA radio traffic from the EBTS sites to the MSO, as well from the MSO to the remote dispatcher sites, is generally dependent on conventional terrestrial or wireless data communications lines, typically with X.21 or E1 network interfaces. Leading ApplicationsPMR and PAMR networks have similar network topologies but the difference in the nature of their applications has an impact on the access and backhaul network. Police and emergency rescue services, for example, require ubiquitous coverage in both highly populated and rural areas. In many instances, they must also have radio communications where ordinary network coverage is not possible, such as in tunnels and other out-of-the way places. Utilities rely heavily on voice communications for keeping critical power and water services in operation, but future applications such as transmission of schematics or digital maps to distant repair teams will require increased bandwidth. Public transportation is dependent on TETRA for reporting locations and conveying "next bus/train" information to platform displays. In addition, TETRA may also be used for more bandwidth intensive data such as video surveillance images for real-time security measures. Other applications with special needs include courier and delivery services, temporary construction sites, residential and commercial security operations, taxi dispatchers, and even the military. Regardless of the actual application, TETRA backhaul networks share the following basic transmission and transport characteristics: · Traffic is packetized (similar to IP or Frame Relay) · Very sensitive to delay - end-to-end delay cannot exceed 10 milliseconds (msec) · Star or ring topology in the transport and backhaul network · Low bandwidth usage - usually 128 to 256 kbps per EBTS · Requires a resilient network design with reliable backup for fail-safe communications · Backup capability over external networks Backhaul Network Topologies and Product Solutions • E1 Ring, Star and Daisy Chain Solutions - Megaplex Multiservice Multiplexers RAD's Megaplex-2100 and Megaplex-2104 Modular Integrated Access Multiplexers are ideal for supporting TETRA applications in ring, star and daisy chain environments. These versatile devices offer multiple user ports with a variety of low-speed and high-speed data user interface modules, including Ethernet, as well as digital and analog voice modules. The Megaplex systems also have a wide range of main link interface modules, allowing for backhaul over a variety of public and private networks. Because each EBTS connection typically requires only a small amount of bandwidth - about 128 to 256 kbps - the Megaplex multiplexers can be used to efficiently aggregate and groom traffic from a large number of connections and transport the voice and data over a few high-speed main links. • Reliability, Redundancy, Robustness The Megaplex incorporates several features that make it an ideal product solution for TETRA backhaul. Multiple main links on the trunk, along with automatic link switching triggered by network events, an automatic database flip mechanism, and automatic E1 ring protection with self-healing, can support E1 network topologies effectively for vital mission-critical public safety and emergency service applications. Moreover, the Megaplex can also offer pre-planned backup through ISDN and other networks. Combined with redundant hardware options for trunk and tributary interfaces, common logic modules and power supply, the Megaplex offers robust reliability and fail-safe operation. • Cost-effective Connection of Small and Medium Sites to the E1 Ring - FCD-IP RAD's FCD-IP access unit provides up to four fractional E1 links with automatic by-pass in case of link failure. This compact and cost-effective access unit can be deployed in TETRA E1 ring networks together with the Megaplex multiplexers, to affordably connect small to medium-sized sites to the E1 ring, while at the same time offering the same self-healing link protection capabilities as the larger devices deployed at the central or large sites. • ISDN Access - FCD-E1A The low bandwidth requirements of TETRA make ISDN a good alternative to leased lines or radio, either as a main transport solution or for backup. RAD's compact FCD-E1A E1 or fractional E1 access unit, available with ISDN S0 interface, is optimized for applications requiring ISDN network access. 
Megaplex and FCD units providing EBTS to MSO connectivity over an E1 ring network
with backup over ISDN
Remote Dispatcher Room to MSO BackhaulMany organizations using TETRA networks control their mobile calls from a dispatcher room or control site that receives all the traffic via a connection to the MSO. Although the MSO performs the technical routing of the mobile call through the network, the dispatcher room is where the mobile call is answered and the appropriate action taken, including the determination of whether the call will be connected to other mobile users, to a specific service or to another network. The dispatcher/control room is usually located at the user's facilities (e.g. at the police or taxi station) while the MSO is located at the user's central site or the TETRA network operator's facility, which may be great distances apart. As with EBTS to MSO backhaul, the TETRA traffic between the MSO and the dispatcher/control room is transported over traditional network lines. Here again, RAD's Megaplex modular integrated access multiplexers and FCD access units provide a winning combination of multiple interfaces, efficient bandwidth usage, reliability, and convenient remote management from a central location. These features benefit both users and operators by streamlining network performance and minimizing transport bandwidth requirements and costs for TETRA applications, even supporting applications that require connectivity between MSO sites and multiple remote dispatcher/control rooms. 
Backhaul from MSO site to remote dispatcher/control rooms over E1 lines
TETRA over Ethernet, IP, MPLS The growing availability and economic attractiveness of packet-switched networks (PSNs) is causing many public safety organizations, utilities and transportation companies to consider migrating their TETRA applications to cost-effective Ethernet-based radio systems instead of traditional PDH-based radio networks. Despite the potential cost-savings and benefits of using PSNs, these networks normally lack the high level of redundancy and reliability demanded by TETRA applications and which are inherent in SDH/SONET or E1 ring topologies and equipment. • TDMoIP Technology - IPmux TDMoIP Gateways RAD Data Communications offers a field-proven, commercially available product solution for overcoming the deficiencies of the PSN for transporting voice and data over Ethernet, IP and MPLS networks. The solution is based on RAD's patented TDMoIP® technology, which takes TDM circuits, mainly voice connections, and provides a transport tunnel across the packet network without distortion and transparent to the underlying protocol. The original traffic is reconstructed at the other end. By using advanced clock recovery algorithms, the TDM timing is propagated accurately across the PSN, overcoming packet delay, delay variation and packet loss. RAD's TDMoIP products for TETRA include the company's line of IPmux-8 and IPmux-16 TDMoIP gateways. These devices transport from 8 to 16 full or fractional E1 and T1 circuits across the PSN. Quality of service is ensured through support of ToS and DiffServe on the IP layer and VLAN tagging and priority labeling per 802.1 p&Q. In addition, the IPmux features Ethernet link module redundancy with configurable automatic switchover should the active link fail. 
Transport of TETRA traffic between EBTS and MSO sites across the PSN with Ethernet link redundancy
• Ethernet Ring Topology - Megaplex with TDMoIP Main Links Also incorporating TDMoIP technology on the main link are RAD's Megaplex multiservice access multiplexers. Equipped with Fast Ethernet main links, Megaplex units can be deployed to build Ethernet ring networks supporting up to 100 Mbps data rates. Resiliency is ensured through RAD's Resilient Fast Ethernet Ring technology, which guarantees automatic link switching between redundant Ethernet links in less than 50 msec. The modular Megaplex systems, supporting both TDM and IP link modules, provide a built-in future-proof migration path for organizations currently desiring to retain their TDM-based infrastructure yet considering a PSN solution down the road. |
