Hessischer Rundfunk (HR)

IT has begun to revolutionize the way the broadcast community goes about business: PCs have replaced tape recorders, IT networks are the new »audio cables«, while transmitting audio is now called »file transfer«. Needless to say, this has major consequences for all aspects of the entire campus-routing system. In its new radio building, the German radio station »Hessischer Rundfunk« (HR) has decided to move off the beaten track using a new system with NEXUS as the core component. 

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Background Routing

Eight radio programs, computerized editing and broadcasting departments in multiple buildings, central services such as Astra satellite feeds for other TV broadcasters – this is what we call a challenge. Hessischer Rundfunk (HR) have moved their entire radio-broadcasting complex from analog to digital – in one go, undeterred by the number of simultaneous steps it has had to take. After all, the new technology is not a simple digital replica of existing structures but rather a whole raft of new possibilities and techniques combined with the time-tested approaches of yore. The result of HR's bold move is an innovative state-of-the-art system!

While every larger radio station today features one or more digital programs, the fact that an entire broadcasting complex has been computerized is a novelty. Of course, in the planning stage, this required thorough analyses of how signals are distributed inside the complex. Quite a number of classic signal-distribution tasks are rendered obsolete by a computerized network: audio, for example, is moved around a radio station, sometimes also between stations, as data files. Some audio lines are no longer necessary. On the other hand, several new routing methods need to be catered for. Therefore, BFE Studio- und Mediensysteme GmbH, acting as contractor, carefully analyzed the exact routing requirements and designed a mesh network built around 19 NEXUS base devices.

Inside the Control Rooms

At HR, two very different routing service requirements were identified early on: the local routing around the on-air area and the wider distribution all over the campus.

Most of the local audio feeds are delivered from a total of 17 on-air servers with four stereo outputs each. These are located in the machine room and connected to a dedicated NEXUS base device. Capable of routing the 68 signal outputs to the five broadcast control rooms and six production control rooms, the NEXUS also takes care of feeding the outgoing signals to the live-recording computers in the central machine room.

Conveniently located in a compact area, the control rooms share four base devices that perform several functions: this is where the aforementioned audio feeds arrive and where signals are transmitted to the rest of the campus, whilst the base devices also take care of local control-room routing and monitoring lines. Based on the MADI system, the links to the digital mixing consoles are unusual in that a maximum number of monitoring channels had been requested. This prompted Stage Tec to program a special, unidirectional MADI card. Unlike conventional cards that also receive signals, this card only handles transmissions, thus occupying a significantly lower number of time slots and routing lines. A small detail perhaps, but nonetheless it epitomizes Stage Tec's response to the client's requirements.

Ultimate Routing

So much for the local connections in the actual broadcasting domain. However, a broadcasting complex also requires many cross-links, such as from the O.B. van to the transmitter or from the broadcasting control room to a production studio. That is why nine additional NEXUS units were installed in various places across the campus. The requirement for this network was that it must be capable of distributing any signal to any location inside the HR facilities. Back in the analog days, this would have implied the use of huge audio patchbays at the routing center, with the ability to patch any of the 1,300 signal sources to any of the 2,300 destinations. Nowadays, the NEXUS approach is far more elegant and compact: a TDM bus performs all tasks that used to require real signal-line nodes. Thanks to a bus technology that »wraps« the audio data to time slots, all signal sources are available for all receivers.

While each NEXUS base device provides 256 time slots, a clever cascading and cross-link system enables the system to be expanded to the required capacity.


The NEXUS network is controlled by a BFE patching unit. The NEXUS units at the router center – and at other crucial points as well – are controlled by dedicated PCs that, in addition, establish all required links and monitor existing connections. Thanks to this BFE patching controller, it is also possible to configure broadcasting and production consoles directly in the control rooms at the press of a button.

And this is only half the story, for in a digital broadcasting complex, there are also other users who need to establish their desired connections: a reporter may need to book a line for exchanging program material and route it to his location. There used to be a time when such links had to be requested centrally; nowadays, the users can achieve this themselves using HR's computerized D'Accord broadcasting system by Management Data. The NEXUS units can therefore also be controlled by the D'Accord system. The clever thing is: while reporters and producers can establish their links, the vital ones – such as the broadcasting feeds – remain off-limits.

The exchange of program material and the related transfers make up the bulk of the tasks to be performed in the routing center. For some time now, HR has been using specialized routing software by Veith. Now, this software also controls the NEXUS devices. The combination of the Veith software with NEXUS provides excellent crash protection because one can switch the entire broadcasting functions from one control room to another by the press of a button. The Veith system even carries all audio signals by post-controlling the NEXUS.

Small and Smart

This network (actually – in terms of links per hour – one of the biggest NEXUS networks ever) does its job behind the scenes. Though physically small and quiet, this NEXUS network takes care of all routing tasks at Hessischer Rundfunk, acts as interface for the various signals, and even processes the signals for the desired broadcast format. This is true background routing!

What is a Central Router?

In larger NEXUS networks, signals are distributed among several base devices that interconnect all parts of a building or campus. In fact, each base device is an independent router, capable of transmitting signals to any connected output. It is understood that most applications also require data exchange between base devices. Therefore, the NEXUS base devices are networked, which is accomplished via optical cables. For maximum routing flexibility, a type of routing node is inserted at the center of the NEXUS network. A simple example of this would be a single NEXUS unit receiving signals from all base devices and distributing them as necessary. Since this distributor unit is necessarily located at the logical heart of the network, it is called the »central router«. One NEXUS base device can handle 256 different signals and route them to as many outputs as necessary.

As the NEXUS network grows, one centralized routing system is no longer capable of handling all signal transfers. Therefore, multiple cross-connected NEXUS units are sometimes used as the central router. The number of base devices and their connections depend on the required signal flow. Hessischer Rundfunk uses five base devices for signal distribution, three of which act as input modules while the two remaining ones function as outputs. This provides for routing any of the 768 signal sources originating from anywhere on the premises to any of the remaining 16 base devices scattered across the campus. Each base device takes care of local routing of signals that are not needed elsewhere, so that the total routing capacity of the entire NEXUS network is actually much better than what the central router cluster is able to handle on its own.

The user hardly ever notices the formidable complexity of the network, as he merely needs to select the desired destination for a signal. NEXUS then finds the optimal signal path, either on a local level or via other base devices and the central router.

TV and Radio Broadcast


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