So Far And Yet So Near
German radio stations have entered a new stage in the digital revolution. After the introduction of small digital production islands and their subsequent interconnection, an all-embracing network of the separate sites is now overdue. The result is a State-wide NEXUS network
HR Regionet Relies on Teaming NEXUS with IT
For many years, Germany’s State broadcasting corporations have exchanged signals extensively between their main broadcasting centres and the associated regional studios. This has been driven even further forward by the increased use of digital technology. In the past, dedicated individual technical solutions had been utilized for single audio or video signals, for telephone, network and control data. Over the years this has grown into to a confusing and inefficient hotchpotch of physical and logical interconnections. Changing this situation is now essential. To make full use of emerging technologies, all these services should be bundled together and implemented by just one service provider with a single consistent technology.
The first German broadcaster to institute such a service bundle is Hessischer Rundfunk (HR). Their Regionet project connects five external sites to the main broadcasting complex located in Frankfurt. HR developed its own creative interpretation on the bundling theme and finally settled on using Dark Fibre1together with a CWDM2 system. One of the spectral colours of this optical multiplex technique has been reserved for transmitting SDI, intercom signals, and Gigabit Ethernet for file transfer. Two other colours will be used for mass storage networking at a later stage of the project. Finally, the fourth colour serves exclusively for interconnecting all the sites’ NEXUS audio routers.
Quantity and Quality
HR radio is already well acquainted with NEXUS since they had replaced their analogue audio system at the central control room with a NEXUS router in 1999. All production studios and several regional sites already use NEXUS. The new Regionet combines these separate NEXUS islands into a total network for HR, covering all main sites and satellite locations. This is unprecedented in the world of radio broadcasting! Consider this: Normally, audio connections between different locations are made either using expensive 2-wire or 4-wire leased lines or nowadays more frequently via low-cost but data reduced audio codec lines. However, with this second approach, quality suffers which is in glaring contrast to the ever higher quality standards in radio production.
If all the local NEXUS audio routers at the various sites are networked, then these imperfections in programme exchange disappear. In fact, HR’s Regionet now offers four linear AES/EBU lines at each site compared with the previous data reduced single codec line. Thus, the NEXUS network not only offers more choice and greater flexibility to the users of HR’s Regionet but also enhanced audio quality.
Shrinking the Distances
One of the keys to the Regionet project’s success is the fast optical lines between Base Devices installed great distances apart. Using NEXUS and Dark Fibre, an audio signal can be transferred within just 3.5 ms from the Frankfurt broadcasting complex to the most distant site at Kassel and back. When compared with the 13 ms required for the same transmission using audio codecs, this represents a considerable improvement! The latency on this signal run, with an overall length of about 400 kilometres (250 miles), is so small that it is now possible to produce problem free live interviews or even live music performances involving multiple sites. So the low latency Regionet solution featuring NEXUS and Dark Fibre is also opening up entirely new applications. A welcome side effect at no extra cost!
HR has introduced a further innovation by utilizing the option of distributing the digital clock through the NEXUS to all the locations. This results in all NEXUS Base Devices operating in sync to the same digital clock. In each regional studio installation, NEXUS now acts as word clock master. With this strategy, HR’s entire digital audio system at all locations and regional studios run in sync. There is no requirement for sample rate converters at the source and destination points.
Metering for All
Since the Regionet project encompasses a total of six sites each with four AES/EBU lines, many incoming and outgoing lines require monitoring. NEXUS has long supported this function with its multimeter display which might have been applicable to the Regionet. However, HR requires one significant restriction on their set-up: While multiple users must be able to view the multimeters, by no means all Regionet users are allowed access to change settings and crosspoints using the NEXUS Matrix software.
This access rights dilemma is remedied by a new multimeter application running separately from the NEXUS Matrix programme. Up to 48 channels can be monitored simultaneously with the new MultiMet.exe software which enables metered sources and destinations to be freely selected by each user. The display colours are configurable, and the window is scalable up to full-screen view. Thus the metering can be adapted to suit the individual requirements of the local studios. Unlike the classic Matrix 5 metering signal parameters such as the input gain cannot be altered.
The Word is Mightier Than The Code
In a large audio network, system monitoring has an even more important role than in a small installation. Therefore, the NEXUS internal monitoring of all modules is a real benefit. When a module such as a NEXUS Base Device power supply unit fails, a message containing precise error information will be sent. But there is more to it than that. The user often also wishes to monitor external equipment. For example, with HR Regionet, the AES/EBU emergency fall-back switches are constantly monitored. In case of failure, the watchdogs used for this purpose close a relay contact at the input of a NEXUS XRI board, triggering the NEXUS Logic Control sub programme to generate an error message.
Normally this message contains an automatically generated numerical error code. However, a different sub-routine can now be employed to convert this cryptic code into easily understandable text. In the HR Regionet system, for example, the error code, “Error No. 4711” is translated into the message “Fulda LTG1 path: No signal”. This function can also be used with ideograms and foreign characters from almost any language in the world.
Clockwise or Widdershins
NEXUS Logic Control is also used for other security functions on the Regionet. This particularly applies to monitoring optical lines. Due to the length of the leased Dark Fibre lines the possibility always exists that a fibre linking two cities could fail. In order to minimize the effects of a line failure, Regionet is based on a figure-of-eight shaped topology between the cities, with the Frankfurt broadcasting centre at the intersection of the eight. Thanks to this topology, there are always at least two network paths available from any one site to any other – clockwise or anticlockwise.
If a section of the Dark Fibre path were to fail, this would be recognized immediately by NEXUS Logic Control. The software at HR’s Regionet is configured in such a way that a failure triggers a remote controlled and fully automated reconfiguration of all NEXUS crosspoints - in brief, a status reload will be performed. By doing this NEXUS automatically chooses the alternative route around the loop that is not affected by the failure.
At the present stage in the project, the audio line assignments are static, i.e. like permanent lines leased from an external provider. Currently, the main benefit of using the new NEXUS rather than the old strategy is the increased number of high quality audio connections. In principle, a dynamic mode for Regionet is also possible where the connectivity is used differently as required. For example, there are plans for allocating a pool of sources to the editorial sites which users can freely select from. This can be the stock exchange news or the weather forecast for instance.
The conceptual details of this visionary deployment are still being worked out in cooperation with the editorial departments since they will be the actual users. This is a great environment for a technology offering total creative freedom for producing programmes in the future - thanks to Regionet and NEXUS.
CWDM on the NEXUS
CWDM2 connectivity on a NEXUS network is no novelty. Experience had already been gained in cooperation with tv productioncenter zurich during the preparations for the Ski World-Cup 2002 in St. Moritz. Whilst at that time, external transponders were required, the current
generation of NEXUS fibre-optic boards support CWDM technology directly. This means that the NEXUS fibre optic interfaces work with a selection of the frequency bands used for CWDM transmissions to enable a single fibre optic line to be shared with other services. This elegant solution would have saved the cost of an external converter for HR’s Regionet. However, this was not part of the initial project because HR, as a long term NEXUS user, consequently already owned numerous legacy fibre optic modules which are now incorporated into the Regionet. These older NEXUS modules, in the common broadband version, are good for the budget since they were purchased several years ago.
1 Dark Fibre: An optical fibre, or a CWDM band on an external provider’s fibre, where the customers themselves must take care of the light on the line.
2 CWDM (Coarse Wavelength Division Multiplex)
An optical frequency-division multiplex technique used for transferring data via optical lines. It uses light signals composed of various spectral colours for transmission over a single optical-fibre cable.