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As described in the previous section on communication protocols, there are several ways in which control data can be sent from one device to another. There is currently a move towards using the Ethernet network infrastructure to transmit DMX lighting control data, although other network systems exist to allow, for example, dimmers to communicate and report errors.

This page aims to explore networking in general, and Ethernet structure in particular.
The advantages and disadvantages of an Ethernet network when implemented in a lighting system are explored in the next section, together with more information on specific manufacturer's Ethernet network systems.

What is a network?

A network has two main characteristics:

  • Interconnectivity
    Interconnectivity describes anything that is tied together through many intersection points (such as a grid). Computer networks work like a freeway system where roads intersect, but instead of relying on a patchwork of roads, computer networks depend upon a patchwork of wires.
  • The capability to facilitate communication
    In networks, machines 'talk' to one another by packaging data into small units and by sending these units across the network.

In essence, a network is a series of computers that can communicate with one another by virtue of their interconnectivity.
There are several reasons to have a network:

  • Resource sharing
    Users at different workstations can share the same printers, backup devices, dimmers, moving lights, etc. These could be accessed through the network by several users simultaneously, taking into account priorites defined by the network manager.
  • Organisation and centralisation
    Networks allow you to centralise databases (shows, user preferences, files, ...) so that users in different locations can access the same data and use the same storage space.
  • Communication and convenience
    Networks provide easy communication solutions such as messaging and on-line collaboration.

Local Area Networks (LANs)

Local area networks are normally confined to a single building (hence the term "local"). Essential components of a LAN are:

  • Servers
    Servers are the machines that centralise data, management, and security, amongst other things.
  • Workstations
    Workstations are the machines upon which network users do their work.
  • Network operating system (NOS)
    These are operating systems specifically designed for transmitting data over a network. Linux is the perfect example of such an NOS.
  • Communication links
    Software and hardware designed to facilitate data transport.

However, LANs are not limited to these four components but support many other devices including printers, modems, nodes, etc.

Types of Networks

The most common network types in use today are peer-to-peer networks, and client/server networks. These are examined below.

Peer to peer networks

Peer to peer networks are typically small (ten workstations). THey have no centralised server and, therfore, no centralised control but the ability to share files, peripherals and other resources. Each workstation has roughly the same capabilities as its peers. All machines can share their files and directories and all workstations can share the same printer.

The advantages of this type of network are simplicity and economy. The disadvantages are limited resource potential and a lack of centralised control.

Client/server networks

In client/server networks, workstations (clients) rely on data and services from one or more centralised servers. Advantages in this case are twofold: firstly an easier and more efficient management is possible through centralisation. By enforcing centralised file storage, it is possible to protect the system against even the most disorganised operator. Secondly, increased security is possible, as client/server environments allow for discretionary access control, allowing you to incisively grant or deny access to files, directories, and resources based on the user, time, date, etc.

A disadvantage is that clients rely on the server for data. If the server dies, the clients die with it. It is also more difficult to configue and administer this type of network, and it is inherently more expensive.

Network topology

Once a network type is chosen, you must next choose a topology. Topology refers to the manner in which your network is wired - some types are examined below. The choice of network topology will be influenced by some considerations including:

  • centralisation
  • cost
  • maintenance and troubleshooting
  • scalability
  • security
  • speed
  • stability
  • distances
  • single point failure:
    This is a physical or logical location (a server, hub, wire, etc) where one or more network devices are connected. When this connection fails, one or more workstations will be unable to transmit data. For critical tasks like transmitting DMX, the trick is to minimise the damage that occurs when that single point fails.

Bus Topology

The network is supported by a long, uninterrupted cable called a backbone. This backbone is the root of all connectivity. Network devices (workstations, perpipherals, ...) draw their network feed from the backbone. The backbone must be terminated at both ends.

Bus topology is simple, cheap and popular but difficult to troubleshoot. It lacks central administration and is subject to speed and performance constraints. Moreover, if the backbone fails, the entire network is knocked out.

Star topology

Star topology is significantly more structured than bus topology and focuses on centralisation. In a typical star network, each computer or peripheral is connected to a central point (usually a hub). Thus, failure of one connection will not usually affect the others.

A hub is a hardware device that centralises network activity. Network cables run from workstations to the hub. The hub then repeats hte signals it receives, and these are routed out again to other network devices.
Star networks offer centralisation, are usually faster, more stable and more easily managerd. This topology allows you to break the network into segments.

The main disadvantage of a star network is that it has a single point failure at the hub level. If the hub fails, all workstations will lose connectivity. Moreover, the star topology is more expensive due to the price of the hubs.

Daisy chain topology

This topology is also sometimes called a star-bus. Hubs (which could contain star network segments) are linked in series.

Daisy chain topology is used to inexpensively transform small LANs into medium-sized ones. However, daisy chaining many hubs can significantly reduce the network performance.

Mesh topology

Mesh topology is highly advanced. Its purpose is to interconnect two or more sizeable LANs. Isolated networks are given multiple paths to their counterparts through routers. This way, total system failure is unlikely.

The main advantages are stability and safety, but it is expensive and requires a high level of knowledge.

Switched topology

Switched networks closely resemble star networks but work differently. Network devices are attached to a central switcher (smart hub). Bandwidth is used on a device-by-device basis: each device is allocated the full bandwidth, rather than sharing the available bandwidth between all devices.

Switched networks are far superior in this respect, but are also quite expensive.


Ethernet is a LAN technology (originally developed by Xerox) that connects computers and transmits data between them. Data is packaged into small units called frames or packets and sent over wires. Strictly speaking, Ethernet complies to the international standards ISO/IEC 8802-3 or IEEE 802.3

To describe an Ethernet LAN, we can use the analogy of a large pipe with outlets spaced along its length, used as a speaking tube by a number of people. Each person listens at an outlet for any message shouted down the tube that might be meant for him or her. If you have something to say, you listen until no-one else is speaking, and then you shout your message. The pipe can carry a lot of messages, because it's a big, fast pipe (Ethernet most commonly runs at 10 Mbits per second, 40 times faster than DMX). Furthermore, information can go back and forth between any two listeners (or nodes in network jargon) without having to go through some central authority.

Collisions occur on an Ethernet network because all computers broadcast without waiting for a turn, sometimes running messages into each other. Ethernet is designed to correct this, but if there are too many computers on the network, collisions can slow down the network performance.

Network hardware

There are several hardware areas that need to be covered in a network.

Cabling and connectors

Popular types of cable are:

The table below indicates the evolution of twisted-pair cabling catagories and classes.
Category/ClassFrequencyTypical Bit-rateYear Introduced
1 / A100 kHZ'voice grade'n/a
2 / B1 MHz1 MBit/sn/a
3 / C16 MHz10 MBit/s1985
420 MHz16 MBit/s1991
5 / D100 MHz100 MBit/s1992
5 / D100 MHz1000 MBit/s1995
6 / E200 MHz1000 MBit/s +1998
7 / F600 MHz1000 MBit/s ++1998

Further information on structured data cabling is available in the data cable guide. See also the definition of bits, Bytes & data rates.

Ethernet connection standards

A variety of standards define the types of cable and connectors to be used, which in turn define the distances between computers that can be supported. ESTA's 'Recommended Practice for Ethernet Cabling Systems in Entertainment Lighting Applications' specifies 10Base2, 10Base-T and 10Base-FL (fibreoptic cable).

  • Ethernet 10Base2 uses thinnet and coaxial cables.
    A daisy chain can be created by using a T-connector on each computers Network Interface Card (NIC) and a BNC 50-ohm terminator at both ends of the chain. Each segment (from one end to the other of the chain or the point to point connection) can be up to 185 metres (600 feet). Up to 30 connections can be supported.
  • Ethernet 10Base-T relies on twisted pair wiring (shielded or unshielded) to connect computers.
    The typical bit-rate of this system is 10Mbit/s.
    Most often, wires are plugged into the NIC on one end and a hub on the other. The distance from the hub to the NIC should not be more than 100 metres (328 feet).
  • Ethernet 100Base-T also uses twisted-pair wiring.
    The typical bit-rate of this system is 100Mbit/s.

Hubs & Switches

Hubs & Switches are used to connect multiple Ethernet segments. These segments can be of different media types (thinnet, twisted pair, and so on). The hub acts as a repeater by taking incoming signals and repeating them through all the ports. Hubs also amplify the signals that may have weakened from travelling long distances.


A gateway routes messages from one type of network to a completely different type of network. For example, they route messages between a 10Base-T Ethernet LAN and a DMX network.
A gateway may add additional features, such as the output of video information, additional switching and control facilities, or MIDI.

The advantages and disadvantages of an Ethernet network when implemented in a lighting system are explored in the next section, together with more information onspecific manufacturer's Ethernet network systems.

See also:

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