A new dimension in routing technology

The new audio router reference — 8k on a single card

NEXUS XRT is a new router board for the NEXUS digital audio network and STAGETEC's spring 2014 introduction — a quantum leap in the inexorable decentralisation of the NEXUS approach to routing in large networks

StageTec-NEXUS 02-14 079 A4NEXUS is considered to be the originator of distributed audio systems. From the very first, Base Devices formed a complete network that enabled inputs and outputs to be interconnected irrespective of their position in the network. The fibre-optic cables between the individual Base Devices enabled these networks to cover long distances, making links between rooms, buildings and later even cities. NEXUS STAR was developed as an answer to the ever increasing number of audio channels in networks. A large scale router that connects many NEXUS Base Devices in a star shaped network without loss of capacity.

Times change, and the star topology is obsolete as a basic requirement, because the new NEXUS XRT router board now shifts the high capacity networking to the Base Devices, opening up a plethora of possible topologies.

A variety of connections

The routing capacity of this new board is simply enormous with over 8 000 inputs and the same number of outputs. Until now, a single NEXUS Base Device could handle up to 256 signals — the XRT capacity is more than an order of magnitude higher. This increases the packing density of the already very compact NEXUS. The XRT is equipped with 12 fibre-optic ports to route the many I/Os to and from the device. Its power has increased considerably in comparison with the previous NEXUS FOC network but the new board is still backwards compatible with existing fibre-optic connections.

Six of the ports handle 512 channels each, more than double that of the previous FOC connections, while the remaining six high-speed ports can carry an impressive 2 048 channels each. In a nutshell, this single board services more than 15 000 fibre-optic channels. A true giant that fits into any 3 U sized NEXUS Base Device.
With this functionality, the XRT superimposes another layer of massive interconnectivity onto an existing NEXUS network without compromising existing capacity in any way. At the same time it opens up an entire realm of new architectural possibilities for distributed networks in the future.

Local and global simultaneously

Diagramm XRT 1At the time of its introduction some 20 years ago NEXUS represented a profound technological innovation in terms of performance. The Base Device's TDM bus then supported 256 time slots — an enormous number back then — which the plug-in boards could access. This principle hasn't changed until today, and remains an important factor in the longevity and backwards compatibility of NEXUS systems. The new XRT router board also remains faithful to this principle, even though it provides much greater performance.

In essence, a Base Device can manipulate up to 256 signals. These will be routed out of the XRT and fed to the TDM bus, where any I/O board or other module can pick them up and use them. The other XRT signals do not use Base Device time slots. They can be routed within the XRT and distributed to other Base Devices without diminishing the local routing capacity of the Base Device. The NEXUS Base Device manages both local audio routing to the I/O boards installed and high-performance networking and signal distribution between Base Devices.

The principle is also ideally suited to achieving cable redundancy when connecting Base Devices, and does not consume time slots or router switching capacity.

A ring of islands

Diagramm XRT 2 englischXRT surpasses even the routing capacity and connectivity of the NEXUS STAR with its enormous power. As a comparison, a single XRT board provides well over 70 million theoretical crosspoints, more than four times the routing capacity of a NEXUS STAR. This magnitude can be leveraged in comprehensive campus-wide networks in particular, where many individual NEXUS Base Devices are combined into a unified network.

In addition, the XRT marks a departure from the purely star-shaped topologies of large systems. A mesh network offers increased circuit redundancy, since signals can reach their destinations via multiple pathways. Ring structures and — a special feature of XRT networking — the annular connection of multiple routing islands via XRT connections, demonstrate interesting network topologies. The router board also supports the entirely unstructured system architectures characteristic of dynamic, continually changing networks.

Built-in tunnel

Some of the SFP ports can be used for Gbit Ethernet tunnelling if required. In plain English: Ethernet is fed into the system at one Base Device and can be tapped transparently by another Base Device. This works with copper and fibre-optic cables which connect a network switch’s high-speed fibre-optic port to the NEXUS tunnel.

The tunnel benefits from the NEXUS redundancy concept, since with redundant connections between the Base Devices the Ethernet signal is transmitted redundantly. Were a fibre-optic cable to fail, the connected Ethernet switches wouldn't notice.

Especially in outside broadcasts this method avoids additional cabling that would otherwise be required to supply Internet connections to external work environments. The Gbit Ethernet also supports other services such as connecting a DELEC oratis intercom and commentary system.

Long-standing technology innovator

NEXUS has been in service as an audio router for 20 years. During this time the system has been further developed continuously and today is capable of more than was even conceivable at its launch — all the while retaining the backward compatibility that makes it a safe investment.

Technical innovations to the digital NEXUS audio router have usually been subtle and this one is no exception. The XRT, which looks like just another new board at first glance, proves on closer inspection to be revolutionary. An innovation that opens up enormous development potential to new and existing systems alike.

daniel 6948About the author
Daniel Plagemann, a hardware designer at STAGETEC Entwicklungsgesellschaft and instrumental in the creation of the NEXUS XRT router board, has summarised the key facts about the new product for STAGES.

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