Glossary

This section provides a quick reference for terms likely to be encountered in the lighting industry.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

ACN

A standard managed by PLASA North America which provides a suite of network protocols for entertainment technology.

Originally ‘Advanced Control Network’, the standard was renamed ‘Architecture for Control Networks’.

Official designation: ANSI E1.17 – Entertainment Technology – Architecture for Control Networks (ACN).

ADC

Analogue to Digital converter. A component designed to convert analogue information into digital form. Examples include translating audio into a form that can be recorded on CD.

Analogue

A continuously varying signal. Contrast to Digital. (US spelling Analog).

ANSI

American National Standards Institute.

Art-Net

Open, royalty-free Ethernet protocol for the transmission of real time Entertainment Technology data over Ethernet. Invented by Artistic Licence. See the Technology Brief for more details.

ASC

Alternative Start Code. A DMX512 term used to describe any packet that uses a start code other than zero. ASC packets are used for the RDM (Remote Device Management) protocol. This is sometimes incorrectly written as Alternate Start Code.

ASCII

American Standard Code for Information Interchange. A coding system that allows alphanumeric characters and punctuation to be represented as a 7 bit code. The predecessor to ASCII was EBCDIC.

Asynchronous Transmission

A form of data transmission whereby the transmitter and receiver are not intrinsically synchronised. The data is enclosed in markers called start and stop bits, so that it can be decoded by the receiver.

DMX512 uses Asynchronous Transmission.

Attenuation

The reduction in the amplitude (or voltage) of a signal caused by the impedance of the cable.

Attenuation Coefficient

A measure of the attenuation of a cable per unit distance. The number is usually given in dB/m or decibels per metre. A lower number equates to a ‘better’ cable.

Attenuation Imbalance

A measure of the difference in attenuation between two pairs of a multiple pair cable. In good quality cable, this number should be almost zero.

AWG

American Wire Gauge. An American system for defining the size of a non-ferrous wire. See also SWG.

Backplane

The bus in the back of a hub chassis that connects interface modules.

Balanced Pair

An electrical transmission line that uses two identical conductors that are symmetrical with respect to a common reference point. The technique is designed to minimise signal interference.

Bandwidth

The data-carrying capacity of a transmission medium measured in bits per second (bps).

Baud

Number of physical transitions per second of a communication link. Expressed in ‘Baud’. 1 Baud = 1 transition per second. The Baud rate is not the same as the data rate which is measured in bits per second.

Bend Radius

The minimum radius to which a cable can be curved without sustaining damage.

BER

Bit Error Rate. The percentage of bits received that contain errors compared to those received that do not contain errors. A perfect transmission system will have a BER of zero.

Binary

A number system, also called Base-2, using only two digits, 0 and 1. This compares to decimal or Base-10 which uses the ten digits 0 to 9.

Bit

Bit is an abbreviation for BInary DigiT. A bit is the smallest element of computer storage and data transmission.

Bit/s

Also written as Bits per second or BitS^-1. This is the measurement of the speed of transmission of digital data.

Bluetooth

A short range radio protocol for connection between devices such as mobile phones and computers. Operates in the same radio frequency band as WiFi.

BNC

A bayonet-locking connector used for 10Base-2 (Ethernet) or video coaxial cabling. BNC is an acronym for British Naval Connector. Two types exist, 50 ohm and 75 ohm. The former is used for Ethernet and the latter for video.

Bonding

A permanent electrical connection. Commonly used in conjunction with Earth wiring.

Break

A Break is a logic zero state used in DMX512 to signal the start of a packet. In DMX512 (all versions) a break is 88uS (microseconds) or greater. RDM tightens this specification for transmitters to the range 176uS – 352uS. The increased minimum required by RDM is designed to allow multiple cascaded splitters to shorten the break whilst remaining within the DMX512 specification.

Broadcast Full

In RDM, a Full Broadcast packet is sent to the special UID address called ‘BROADCAST_ALL_DEVICES_ID’ of value 0xffff:ffffffff (where 0x denotes hexadecimal). All RDM responders will accept messages directed to this UID.

Broadcast Manufacturer

In RDM, a Broadcast Manufacturer (now also known as Vendorcast) packet is sent to the special UID address called ‘ALL_DEVICES_ID’ of value 0xzzyy:ffffffff (where 0x denotes hexadecimal). All RDM responders of Manufacturer ID 0xzzyy will accept messages directed to this UID.

BSI

British Standards Institute

BSR

An ANSI abbreviation for Board of Standards Review. It means a standard that is in development. For example, prior to ANSI E1.31-2009 becoming a standard, it was BSR E1.31.

Bus Topology

A network architecture in which all the nodes are connected to a single cable which is terminated at each end.

Byte

A group of 8 bits that allow representation of 256 different numbers.

Cable Tray

Metal or plastic trays used to support and secure cable installation.

CAN

CAN or Controller Area Network was originally developed by Bosch for the automotive industry. The CAN protocol is now an international standard, ISO 11898.

Capacitance

A measure of the ability of two conductors to store electric charge. Unit of measurement is the Farad. Prescalars are pF (pico, 10^-12), nF (nano, 10^-9) and uF (micro, 10^-6).

Checksum

A simple method of identifying errors in data transmission. The transmitter adds together all of the data bytes to be transmitted and sends this along with the data.

The receiver performs the same calculation and compares the result to that sent by the transmitter.

If the calculations do not match, an error has occurred. If they do match, there is a high probability that the data is intact. It does not guarantee that the data is intact as there are many different data sequences that result in identical checksums.

Both 8 and 16 bit checksums are used in different communication protocols. The 16 bit version provides a higher probability that matching checksums equate to good data.

The CRC provides a higher level solution to the same problem.

Coax

Coax is an abbreviation for Coaxial Cable. It is characterised by a central conductor, with a concentric insulating or dielectric material and an outer conducting screen.

The outer conducting screen is intended to contain the inner conductor in a Faraday Cage.

Collision

The term used when two or more RDM devices attempt to communicate at the same time. This occurs during the discovery phase of RDM.

Common Mode Conversion Ratio

A measure of the balance between the two conductors of a twisted pair, with respect to Earth-Ground.

Common Mode Voltage

A term used in the characterisation of balanced wiring systems. It is the part of the input voltages, for which the amplitude and either the phase or the polarity are the same, which exists between each of the input terminals and a reference point.

Compatible

A product that operates correctly with a standard but does not necessarily fulfil all the obligations mandated by a standard.

Compliant

A product that completely adheres to the requirements of a standard.

Conductance

The reciprocal of resistance.

Conducted Interference

Electrical interference that is propagated via electrical connection with the equipment causing the interference. Contrast with Radiated Interference.

CPWG

Control Protocols Working Group. A committee operated by ESTA and tasked with the management of standards such as DMX512-A, RDM and ACN.

CRC

Cyclical Redundancy Check. This is a mathematical calculation used to check the integrity of transmitted messages.

The transmitter performs the calculation on the data to be transmitted. The result is then sent with the transmitted data.

The receiver performs the same calculation and compares its result with the transmitter’s result.

If they match, the data is intact. If they do not match, a transmission error has occurred. The receiver then requests the transmitter to resend.

A CRC requires more processing power than the simpler Checksum, but is capable of detecting more errors.

Crimper

Tool used for terminating wires into a connector without using solder.

Crossed Pair

A colloquial term meaning a pair of wires within a twisted pair cable that are accidentally cross-wired. This fault is likely to cause significant signal degradation as the balanced transmission will not be able to operate.

Crosstalk

Crosstalk is a type of interference generated by running multiple twisted pairs within a single cable. The individual twisted pairs behave like the windings of a transformer, coupling a small amount of signal from one pair into the next.

Cut-Off Frequency

The frequency above which no significant energy is transferred into the cable.

DAC

Digital to Analogue converter. A component designed to convert digital information into analogue information. Examples include converting digital audio back into sound.

Data Compression

A generic term meaning a technique used to reduce the bandwidth required when transmitting data.

Data Slot

This is a term used in DMX512 and DMX over Ethernet protocols. Data Slots are numbered from 1 to 512 and identify the channel information. This contrasts with the term Slot.

DCE

Data Communication Equipment. A term used to define the pin wiring in RS232 equipment.

DeciBel

A logarithmic unit that expresses the ratio between two numbers. Abbreviation dB.

Demultiplex

Often abbreviated to DEMUX. This is the opposite of Multiplex and involves translating one signal into many. It may also include digital to analogue conversion and decompression.

Dielectric

The electrical insulator used in the fabrication of capacitors and coaxial cables.

Dielectric Loss

The attenuation of a signal caused by the extent to which the cable dielectric conducts.

Digital

A generic term meaning that a circuit or system uses binary information as opposed to continuously varying analogue information.

Distortion

Any unwanted affect of circuitry or transmission system that causes the output to differ from the input.

DMX over Ethernet

A generic term used to describe protocols such as Art-Net and ShowNet that are geared to transmitting DMX512 frames over Ethernet. This is as distinct from protocols such as ACN.

DMX512

The USITT standard for transmission of lighting control data over a balanced RS485 data link.

The term DMX512 is used to generically describe all variants of the protocol.

DMX512 (1990)

The second issue of the standard was released in 1990. The only significant change was the relaxation of the Mark After Break timing from 4uS to 8uS. The difference is significant to product designers as the 4uS requirement was a significant technical burden when using microprocessors to receive the protocol.

Very little pre DMX512 (1990) equipment remains in the market. This is largely due to the significant support or the standard starting in the early 1990s.

DMX512 2000

DMX512 2000 is a colloquial name for DMX512-A. It is no longer in common use.

DMX512-A

DMX512-A is the third issue of the DMX512 standard. It was approved by the ESTA Control Protocols Working Group on 18^th March 2004. DMX512-A is backwards compatible with DMX512 (1990). The new standard provides a range of increased functionality, much of it aimed at simpler integration with Ethernet based networks.

In 2004 the protocol was made an ANSI standard: DMX512-A (ANSI E1.11 – 2004, Entertainment Technology – USITT DMX512-A – Asynchronous Serial Digital Data Transmission Standard for Controlling Lighting Equipment and Accessories.

In 2009 a further revision to DMX512-A was released, full name: ANSI E1.11 – 2009, Entertainment Technology – USITT DMX512-A – Asynchronous Serial Digital Data Transmission Standard for Controlling Lighting Equipment and Accessories.

See the Technology Brief for more information.

DTE

Data Terminal Equipment. A term used to define the pin wiring in RS232 equipment.

Duplex

A system that allows signals to travel simultaneously in two directions. The word is a compression of ‘Dual Multiplex’. Contrast with Half Duplex.

Earth

UK use: Electrical connection to equipment chassis and therefore the third conductor of the electricity supply.

See also: Signal-Common, Ground & Earth-Ground.

Earth Loop (Ground Loop)

The flow of current through Signal-Common conductor caused by voltage differences between local Earth-Ground points.

Earth-Ground

ESTA sponsored international term meaning: Electrical connection to equipment chassis and therefore the third conductor of the electricity supply.

See also: Signal-Common, Earth & Ground.

Echo

See Reflection.

EEPROM

Electrically Erasable Programmable Read Only Memory. It differs from EPROM by using an electronic control rather than ultraviolet light for erasure. Largely superseded by Flash memory.

EIA-485

An upgrade to the earlier RS485 standard. Full name: ANSI/TIA/EIA-485-A-1998, Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems.EIA-485-A is the electrical specification for DMX512.

EIA/TIA 568

The wiring standard for telecommunication cable plant, including termination detail for the RJ45.

EIA/TIA

Electronic Industry Association/Telecommunications Industry Association. A body involved in the setting of various industry standards including those applicable to cabling.

Electrical Screen

An Earth-Grounded metal or conductive shield placed around electronics to isolate the circuitry from external electromagnetic fields. See Faraday Cage.

EMC

Electromagnetic Compatibility. The ability of differing electronic and electrical systems to coexist without being disrupted by electromagnet interference, or disrupting other equipment by causing interference. EMC is a major component of the CE (European) and FCC (US) regulatory standards.

EMI

Electromagnetic Interference – unwanted “noise” created by current-producing devices such as electric motors and fluorescent lights. EMI affects the quality of the signal passing through data transmission medium.

Encoding

The conversion of data into a particular format suited to a particular purpose.

Encryption

A method of encoding data that includes a security system for security purposes.

EPROM

Erasable programmable read only memory. A type of memory that can be erased using ultra-violet light. EPROM was widely used for firmware before the invention of Flash memory.

Error Detection

A generic term used to describe various methods for detecting and or repairing transmission errors.

ESTA

Entertainment Services and Technology Association

ETC NetII

A TCP/IP proprietary protocol used by Electronic Theatre Controls.

Ethercon

A connector developed by Neutrik. It provides an RJ45 mounted inside a latching XLR housing.

Far Field

The electromagnetic field that exists at a distance of several wavelengths from the equipment generating the field. Contrast to Near Field.

Faraday Cage

A metal enclosure designed to stop electromagnetic radiation.

Filter

A device used to remove certain frequencies from a signal. This may be to reduce bandwidth in a transmission system or for aesthetic reasons such as audio filtering.

Firestop

The filler used to restore the burn time rating of a firewall that has been penetrated by cable or other services.

Firewall

A building partition that has a specific rating of burn time, allowing occupants of the building to escape in an emergency.

Firmware

The operating software of a product. Firmware is invariably held in a chip as opposed to software, which is usually stored by magnetic media.

Flash

A form of non-volatile memory. It is frequently used to hold the operating software of a product. It has the benefit that it can be updated for product improvements.

Frame

A well-defined block of data ready for transmission.

Frequency

The number of times that a signal repeats within one second. The unit is Hertz (Hz). The usual SI (Standard International) multipliers apply: 10⁹Hz = 1GHz, 10⁶Hz = 1MHz, 10³Hz = 1KHz.

Frequency Response

The relationship between the frequency of a signal and the attenuation of the transmission medium at that frequency.

FTP

File Transfer Protocol. A communication protocol that forms part of TCP/IP. It is used to transfer files over a network.

Ground

UK use: Common voltage in a circuit

US use: Electrical connection to equipment chassis and therefore the third conductor of the electricity supply.

See also: Signal-Common, Earth & Earth-Ground.

Ground Loop

See Earth Loop

Half Duplex

A system that allows a signal to travel in one direction at any given time. Contrast with Duplex.

Harmonic

A waveform that is an integral wavelength multiple of the original. See Overtone.

Harmonic Distortion

A type of distortion caused by the interaction between a signal and harmonics of that signal.

Inner Diameter. The internal diameter of a tube.

IEEE

Institute of Electrical and Electronics Engineers – a professional organisation that formulates computer and communications standards in the US and works with other standards-setting bodies including the International Standards Organization (ISO).

Inductance

The property of a conductor whereby a current is induced as a result of the voltage changing. The unit is the Henry, symbol H.

Insertion Delay

The signal delay caused by the insertion of a component in a transmission system. Insertion delay is usually expressed in time, e.g. nS.

Insertion Loss

The reduction in amplitude of a signal caused by the insertion of a component into a transmission network. The insertion loss is usually expressed as a percentage of output voltage to input voltage such that no insertion loss is represented as zero percent.

Inter-slot Time

The time between the end of the second stop bit of slot x and the beginning of the start bit of slot x+1. In RDM the average Inter-slot Time must not exceed 76uS and any specific Inter-slot time must not exceed 2.0mS (subject to the overall packet length being less than 1S).

ISO

International Standards Organization – an internationally recognized standards body.

Jabber

An error condition whereby RDM devices transmit on the DMX cable without being requested to do so.

Jacket

The outer plastic or rubber protective cover of a cable.

Krone

UK manufacturer of Ethernet termination connectors. Often used as a generic term. See Punch Down (US term).

LAN

Local Area Network

LED

Light Emitting Diode – a semiconductor device that produces light via electrically induced emission. See also the Technology Brief.

MaB (Mark after Break)

This is the time period between the end of a DMX512 Break and the beginning of the start bit of the Start Code (see Slot). In DMX512 this value must be 8uS or greater. RDM tightens this parameter to 12uS or greater.

MbB (Mark before Break)

This is the time period between the end of the second stop bit of the last Slot and the beginning of the next DMX512 Break.

May

In ‘standards speak’, the word ‘may’ means that an item is optional, i.e. you are at liberty to decide whether you consider the item to be important. ‘May’ sits below ‘should’ and ‘shall‘ in priority.

MIDI

Music Industry Digital Interface. A serial communication protocol developed to allow interconnection of musical equipment. It is also commonly used for remote control between lighting equipment. See also the Technology Brief.

Midspan Power Inserter

A product which adds PoE (Power over Ethernet) to an Ethernet cable. Also known as a PoE Inserter or PoE Injector.

Mismatch Loss

Loss of power developed into a load caused by connection to transmission medium with non-matching impedance.

Multiplex

Often abbreviated to MUX. Multiplex is a technique for converting many signals into one, usually for transmission by cable. Multiplex systems may include both analogue to digital conversion and compression.

Near Field

The electromagnetic radiation field that exists within one wavelength of the source.

NEC

National Electrical Code. US standard for electrical safety in building installation.

Nibble

Nibble is one half of a byte or four bits. A byte has an upper and a lower nibble. See US spelling Nybble.

Non-volatile RAM

Random Access Memory which holds its information even when main power is turned off. Usually, non-volatile RAM is backed up via a battery.

NVP

Nominal Velocity of Propagation. The speed of a signal in cable expressed as a percentage of the speed of light.

The NVP for Cat5 (Category 5) cable is approximately 75%. That means that the signal travels at around 2.3 x 10⁸ ms^-1, or passes 1m every 4.3nS.

Nybble

See Nibble.

Outer Diameter. The external diameter of a cable.

Overtone

A waveform that is an integral wavelength multiple of the original. See Harmonic.

Patch Bay

A cable termination area where DMX cables connect between equipment.

PLASA

Professional Light & Sound Association. International trade organisation for the entertainment technology industry.

Plenum

The air-carrying portion of a heating or air conditioning system that can be used for carrying communication cable.

Plenum Cable

A cable conforming to local wiring regulations for installation into a Plenum Area.

Plenum Rated

See Plenum Cable.

PoE

Power over Ethernet. A method for supplying operating power as well as data over the ethernet cable. Defined in the IEEE802.3af-2003 standard. Each powered device receives 48V at a current up to 15.4W. See the Technology Brief for more information.

PoE+

A method for supplying operating power as well as data over the ethernet cable. Defined in the IEEE802.3at-2009 standard. Each powered device receives 48V at a current up to 25.5W.

PoE Injector

See Midspan Power Inserter.

Port Mirror

Port Mirror is a configuration option available in some Ethernet Switches. It allows a specific port to be configured as a duplicate or mirror of another. This is very useful when monitoring the network, particularly when searching for unicast packets.

PROM

Programmable Read Only Memory.

Propagation Delay

The time taken for a signal to pass along a transmission line.

Propagation Velocity

The speed at which a signal travels within a specific media.

Protocol

A standardised set of rules specifying the packet format, timing, sequencing and/or error checking for data transmission.

Punch Down

A method of making electrical connection by ‘punching’ the wire into a conductive slot which displaces the wire’s insulation.

Q-switching

In the context of lasers, a method to generate a short, intense pulse.

Radiated Interference

Electrical interference that is propagated by electromagnetic radiation from the equipment causing the interference. Contrast with Conducted Interference.

RAM

Random Access Memory.

RDM

Remote Device Management. The colloquial name for ANSI E1.20 -2006, Entertainment Technology – RDM – Remote Device Management Over DMX512 Networks. RDM provides bi-directional data transmission over the primary DMX512 data pair. See the Technology Brief and http://www.rdmprotocol.org for more information.

RDMnet

RDMnet (previously known as sRDM) is the colloquial name for streaming RDM in an ACN friendly form. sRDM (BSR E1.33) data is formatted in such a way that a full ACN (ANSI E1.17-2010) device will also be able to interpret the data.

The standard is in development and was in public review as of January 2012.

Reflection

A wave that has been reflected from one or more points in a transmission system. Reflections are typically caused by an impedance mismatch at the cable end. If reflected waves are of significant amplitude, partial or complete loss of data can occur. This is caused by the destructive superposition of the transmitted and reflected waves causing zero amplitude.

RFC

Request For Comment (a document describing an Internet protocol).

RFI

Radio Frequency Interference – unwanted ‘noise’ created by current-producing devices such as electric motors and fluorescent lights. RFI affects the quality of the signal passing through some data transmission media.

RJ Lynx

A robust and waterproof version of the RJ45.

RJ45

An 8 pin connector primarily used for Ethernet connections, although increasingly used for DMX512.

RLE

Run Length Encoding. A simple method of compressing data.

ROM

Read Only Memory.

Recommended Practice. A document that generally augments a standard. It usually contains real world examples of how the standard writers felt the standard should be implemented.

RS232

An EIA standard definition for the 25-pin interface linking data terminal equipment (DTEs) and data communication equipment (DCEs). RS232-C is suitable for both synchronous and asynchronous communications.

RS422

An EIA recommended standard definition for extending an RS232-C interface beyond the 50 foot limit.

RS485

An earlier standard upon which the ANSI/TIA/EIA-485-A-1998 standard was based. Similar to RS422 but is used in multi-point application where up to 64 network devices may be interconnected. EIA-485-A is the electrical specification for DMX512.

sACN

sACN is the colloquial name for the streaming version of ACN. sACN (ANSI E1.31-2016) data is formatted in such a way that a full ACN (ANSI E1.17-2010) device will also be able to interpret the data.

Screen

Identical to Shield

SFP

Small Form factor Pluggable transceiver. This is a small module that plugs into an ethernet switch or router to allow the connectivity of the port to be customised, for example between copper and fibre.

Shall

In ‘standards speak’, the word ‘shall’ means that an item is not optional, i.e. you are not compliant with the standard if you do not implement this item. ‘Shall’ sits above ‘may’ and ‘should’ in priority.

Shield

Outer metallic conductor in a cable. Intended to produce a Faraday Cage.

Should

In ‘standards speak’, the word ‘should’ means that an item is theoretically optional, but the standards writers feel you would need a very good reason to ignore the item. ‘Should’ sits between ‘may’ and ‘shall’ in priority.

ShowNet

A DMX over Ethernet protocol developed by Strand Lighting. The protocol is based on broadcast UDP packets and uses a simple form of Run Length Encoding (RLE).

Signal-Common

The common voltage in a circuit.

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