Open digital integrated technology for wide-area networks Increasing demands for larger, more complex wireless communication systems strain the capabilities of existing radio system architectures. Open digital integrated radio network technology gives com

Since the invention of trunked two-way radio in the mid-1970s, the size of radio communication systems has grown at a remarkable rate. An average system used to provide local coverage for 100 subscriber radios. Today, county-wide systems serving several hundreds of radios are routine. Vast state-wide and regional systems with thousands of subscribers are becoming the norm. In public safety, there’s a growing need for agencies with overlapping geographic areas to share resources. As communication managers plan larger systems, they’re looking for ways to maximize over-the-air resources, minimize the cost of networking those radio resources, allow for change, and migrate to future standards and technologies.

What works, what doesn’t Most of today’s trunked radio systems employ a common topology: a hub-and-spoke arrangement of repeater sites connected by dedicated links to a central site, as shown in Figure 1 below left. On our company’s current wide-area trunking system, the hub is called the radio network terminal (RNT). The RNT provides central control and switching between the sites, as well as support for dispatch consoles, telco interconnects and system management.

Trunked systems can be channel-efficient and link-efficient, but closed architecture has its limits. As our engineers and product managers began to design the company’s next generation of trunking systems, they realized that communication managers will need greater network flexibility. The hub-and-spoke network topology doesn’t fit every application, and often it isn’t the most efficient use of network resources. Tighter budgets, especially for public safety departments, have focused attention on the total cost of a radio system, including the network. That pointed our team toward designing modular radio network components, adaptable to many different network configurations. Uncertainties surrounding frequency allocations and upcoming radio technologies meant creating an open architecture that could accommodate just about any radio band and protocol.

The result is an open digital integrated network for radio communications. (Footnote: The open digital integrated network described in this article is a proprietary system developed by E.F. Johnson, which it has trademarked under the name ODIN.)

An adaptable network Our new radio network technology provides open architecture and flexible topology to build wide-area radio systems for just about any application. A system can be designed to meet specific performance levels, special requirements such as fault tolerance or economic restrictions.

The open architecture radio system is built from modular components that can work independently but share necessary information to allow wide-area subscriber roaming. The system can operate in analog and digital modes, handling voice and data traffic, and it is frequency- and protocol-independent. The system is backward-compatible to conventional and trunking system protocols and equipment. The system is also forward-compatible to emerging radio technologies and compliant with APCO Project 25 requirements. So, digital UHF APCO Project 25, analog 800MHz Multi-Net trunking and analog low-band conventional communications can be combined on the same radio network.

Instead of one hub-and-spoke system, any number of central and remote sites can be networked in any arrangement, as shown in Figure 1 at the left. System control can be centralized or distributed across the network. Links can be dedicated, or on-demand. Networking is also scaleable: start with a small system, then expand and re-arrange the system as communication needs change.

Architecture To build these radio systems, we’ve developed a collection of unique network components–both hardware and software–based on proven network technologies. Wherever possible, our team has incorporated familiar industry standards, such as TCP/IP network links between sites, and Microsoft Windows NT-based system management software.

The core of the wide-area system consists of some basic building blocks: the trunking controller interface (TCI), the trunking group controller (TGC) and (as needed) the system call router. The exact type, quantity and configuration of these components depends entirely on the individual system’s design. Through these hardware components, a suite of microcomputer-based system management programs direct the entire system, from setting user access to testing a microwave link. Once the core system is built, options include system applications, data gateways, telco interconnects and interconnects to other radio systems.

Network core The core components begin with the TCI. This logic card plugs inside each of the Johnson 2000 series modular repeaters at a site. The TCI controls the trunking process at the site and manages the high-speed data bus between the repeaters. It also serves as the common interface to the TGC, translating whatever radio protocols the repeaters are using into standard network messages.

The TGC is the interface and controller between repeater groups and call routers and other site link equipment. The unit consists of independent modules, each controlling as many as five repeaters. One TGC can control 30 channels, and multiple TGCs can be directly connected to manage very large systems. The TGC handles call processing tasks such as user and group validation, site authorization and wide-area group routing.

The system call router is only required as radio system design dictates. It provides wide-area call routing when trunking dedicated links, and it may control audio switching between sites for systems with more than 30 channels. The system call router is also the gateway to applications and interconnects to the outside world.

These core components communicate with each other via one or both of two open-architecture paths. The system control bus carries status and control information about users and network resources throughout the network. The system control bus uses TCP/IP protocols for communication. Within a site, the system bus is a 10Base-T Ethernet line running at 10Mbps. Between sites, the system bus uses frequency-shift keying (FSK) blank-and-burst or an Ethernet link running from 9.6kbps to 56.0 kbps.

The system audio bus carries all the system audio between TGCs, call routers, dispatch consoles, telephone interconnects and similar equipment. For intrasite control, the system audio bus is an E1 (time-division multiplex) bus. Between sites, the audio bus can be linked by various analog or digital methods, depending on the client’s link capacity.

Network management and applications Since the network can combine many radio systems and thousands of users, powerful management tools are a must. The network management software is a suite of three programs that can reside on one or different microcomputers. These managers communicate with the network at any location that has access to the system control bus, either through a dedicated TCP/IP connection (such as an Ethernet line to the TGC) or through a remote dialup.

The subscriber manager is the only required management component. This software package controls the radio system’s subscriber data bases. It manages user privileges and sets each user’s capability level for site roaming, telephone interconnect calls and call priority. The subscriber manager can provide over-the-air programming of radios to dynamically assign new capabilities to subscriber radios, and it can flash-program new features into the radios. The subscriber manager also controls emergency regrouping of radios and captures all user traffic data and accounting information.

The optional system manager controls and tracks the status of all major radio system components. It manages the configuration, fault-handling, performance, security and accounting of the ODIN radio network, as well as reporting alarms and running remote diagnostics. The system manager is based on Hewlett-Packard’s HP OpenView network management environment running on the Windows NT operating system.

The third component, the network manager, allows supervision of all aspects of the radio network. It employs the industry-standard SNMP protocol so that third-party components such as bridges, microwave links and UPS units can be managed along with the other network components.

The network can support a wide variety of applications. Its Windows-based dispatch console allows computer-aided dispatch and 911 interfaces across distributed positions. The telephone interconnect works with digital (T1, E1, DS0 or ISDN), or analog (2- or 4-wire) links. It also can provide voice mail, voice paging and call forwarding. For mobile data applications, data can be transported through TCP/IP, SNA, and X.25 gateways. Through the system interconnect, the network can interface with other Johnson radio systems and Project 25 systems from other vendors.

Migration Routes The radio network technology also allows migration. For example, let’s say you want to migrate from a 450MHz conventional radio system for public safety to a Project 25-compliant trunking system. You could begin by adding open digital system components to gain networking features. Then you would switch to repeaters that are 12.5 kHz-ready and digital-ready for Project 25. The third step would be replacement of subscriber radios with Project 25-compliant units as your needs and budget permit. With the network in place, your conventional and Project 25 radios would communicate to each other on one seamless system.

A carefully managed migration not only means minimum disruption to your system users, it can also minimize disruption of your budget. Open architecture is geared to the realities of system funding, especially for public agencies. Instead of spending a huge amount of money up front, you can time each phase of the migration to fit each funding period.

Conclusion An open digital integrated network offers choices to communication managers, system planners, consultants, or purchasing agents, including flexibility, compatibility, features and growth potential. It allows them to dictate the structure of a radio system instead of the system dictating to them.