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Ethernet networks for lighting systems

As described in the previous section on general networking, there is a current trend to move towards Ethernet networking in today's lighting control systems.

At present, there is no common industry standard in how the control data (currently DMX512) transmitted over an ethernet protocol network is encoded and sent. This, of course, means that each manufacturer has their own propritary methods for doing so (a move away from the universiality of DMX). There is a trend for manufacturers to use the ArtNet ethernet protocol, developed by Artistic Licence and released into the public domain.

The advantages and disadvantages of Ethernet control systems when implemented in a lighting system are explored below, together with more specific information about the ADB Ethernet network.

General Information about Ethernet

The term 'Ethernet' refers specifically to a set of standards for connecting computers in order they can share information over a common wire or network. Strictly speaking, ethernet systems should comply to the International Standard ISO/IEC 8802-3 or IEEE 802.3.

As in all systems, there are reasons to use an ethernet network, but also difficulties that must be overcome. The main advantages of ethernet are:

  • The ability to carry several hundred times more information on a single cable than would be carried on a typical serial cable. Whereas DMX512 operates at 250kb/s, Ethernet operates at 100 Mb/s - 400 times faster;
  • The ability to connect multiple devices in a single network, regardless of the information interchange relationship between the devices. Ethernet allows all devices in the network to communicate;
  • A reduction in the amount of cable required. Economic factors will drive the demand for this technology;
  • The ability to add devices to the network at any time, giving a more flexible installation;
  • Required components are readily available and have a relative low cost.

Despite these factors, there are also disadvantages associated with ethernet systems:

  • Maximum cable length between two devices is limited to 100metres, compared with 250metres for DMX512 systems. In larger installations, where very long cable runs are required, it is necessary to utilise fibre-optic cabling;
  • RJ45 connectors used for ethernet networks are not suitable for heavy-duty use in industrial situations;
  • Data collisions can occur on the network, which slows the data transfer between devices: a collision occurs when two devices on the network attempt to send data at the same time. Any device that recognises a collision has occurred stops sending and waits a random time before attempting to resend the data. As more devices are added to the network, network traffic increases and eventually a point is reached where collisions always occur: the time taken for a single message to be transmitted then becomes infinite.

ADB Ethernet in lighting control systems

A lighting system structured around an ethernet network allows different parts of the control system to communicate. This interconnection provides a number of advantages to the user, and benefits to the lighting system as a whole:

  • Real-time bi-directional synchronisation between an infinite number of control desks (1-Master and n-Slaves) provides an integral backup system;
  • Centralised file server stores all shows and rehearsal data of the theatre;
  • Data can be loaded from any control desk on the network;
  • Each desk can be operated individually on the network if set to Independent Mode;
  • Show data can be locked on each desk;
  • A standard PC on the network can provide up to four remote monitor displays;
  • Hard patching of DMX universes is replaced by soft patching at the DMX-Ethernet Gateways. ADB provides two families of gateway units: Netgate & Netport.

ADB Networking

The ADB Ethernet network does not suffer from data collisions due to the use of a full duplex system, based on TCP/IP running at 100Mb/s. The ethernet cards used must be PCI and 10BaseT/100BaseT compatible. Wiring between devices should use Unshielded Twisted Pair (UTP) Cat5 cable, using RJ45 connections and limited to 100metres maximum.

It is important that the network used to interconnect all lighting equipment is kept independent from other systems, isolated from all other office workstations and equipment. It is possible to connect a PC to both an office network and the lighting network, however the PC will require two ethernet network cards. There will be no automatic data exchange (packet routing) between the two networks.

The ADB Network is divided into two parts: Synchro Ethernet and Full Ethernet. Synchro Ethernet is standard in ADB's ISIS lighting control software, whereas Full Ethernet is an option. A software key is required to enable the Full Ethernet functions.

ADB Synchro Ethernet

Communication in Synchro Ethernet replaces the old serial synchro link, which ran at 62.5kb/s and was restricted to two control desks. Control changeover between the Master & Slave desks is now automatic: DMX data is issued by the Master only, until the Slave detects that the Master is not responding. At this point, the DMX is calculated and output by the Slave.

The Master and the Slave desks synchronise via the Ethernet network cards and authorise a fast communication running at 100Mb/s. The desks can be connected by two standard ethernet cables and a Hub, or via a single Ethernet crossover cable.

ADB Full Ethernet

Full Ethernet offers communication between an infinite number of control desks, file servers and other office computers on the network, allowing bi-directional file-exchange. One desk on the network can be set as the Master, synchronised to any number of Slaves. There is the option to copy all show data and configuration information automatically to the Slaves each time the Master system is started.

A total of 16 DMX universes (ports) are supported through the Ethernet Network, allowing control of up to 8192 DMX addresses from the Master. Translation of lighting data from Ethernet to DMX512 format is achieved via the use of a Gateway. ADB offers two families of gateways: Netgate & Netport, both of which can be configured locally, or remotely via the network.

From the Master desk, ISIS computes up to four Virtual Screens which are sent through the ADB Full Ethernet lighting network, the content of each being user configurable. This allows information to be viewed remotely away from any control desk: for example on a laptop, standard computer, or via a Netgate/XT. The remote monitor can display each of the four virtual screens via the function keys, if access to these screens has been granted.

See also:

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