DMX -vs- E1.31

[jerrymac]

Since E1.31 protocal converters have RJ45 connector ouput -vs- 3 or 5 pin DMX plugs, does E1.31 require a different controller than standard DMX? or do you still use only two wires on the cat5 cable like you would with DMX ?

What is the difference between multi cast and single cast?

[WilliamS]

1.31 uses Ethernet cable in its true intended form from a router or switch. You sent the info to it from your network not from a DMX device. Most 1.31 devices I have seen are in only not 1 in 1 out. Im sure they are out there but once again its not a pass through device as each 1.31 device needs an IP from your router or switch.

Multicast means it sees all universes worth of data, just just a single stream for itself. Where a Unicast, has its own specific IP address that info must be sent directly to it. Multicast is easier as it can be anywhere in the network, when it ready universe what ever number it is, it pulls that data.

[Guest wbottomley]

jerrymac wrote:

Since E1.31 protocal converters have RJ45 connector ouput -vs- 3 or 5 pin DMX plugs, does E1.31 require a different controller than standard DMX?  or do you still use only  two wires on the cat5 cable like you would with DMX ?

 What is the difference between multi cast and single cast?

I suggest you read the information located at the link here: http://auschristmaslighting.com/forums/index.php/topic,1889.0.html

[LOR Staff]

There is going to be a lot of confusion on this... I'm probably going to add some.

E 1.31 is a PROTOCOL, not a TRANSPORT. Many people confuse the transport (the way things are connected) with how those devices talk to each other (the protocol).

Let's forget about E 1.31 for a min, and talk about something all of us should be familiar with: straight up LOR controllers and computers.

In this case, the protocol is a proprietary one called the 'LOR Protocol'. The LOR Protocol specifies how we talk between the computer, controllers, etc. Think of the protocol as a LANGUAGE. Currently I am writing in English (or at least attempting to!)

The transport between regular LOR controllers and the computer is RS485. RS485 doesn't care WHAT you are sending between devices, only how they are connected. In this case, RS485 is transmitted on 2 wires, and the RS485 specification tells us how to interpret the voltage levels on those 2 wires (using something called Differential Signaling). It just so happens that 'Cat 5' cable is cheap, plentiful, and works GREAT with RS485. We just only use a single pair of wires to transmit data out of the 4.

Ok, so what about DMX? Why does DMX run on 2 wires? Once again we need to separate the PROTOCOL from the TRANSPORT.

DMX is nothing more than a protocol. It specifies how 2 devices talk to each other -- IE, they both must speak the DMX language to understand each other. What confuses people is that they don't realize that DMX also specifies a physical layer. That physical layer is built on RS485.

With some minor internal technical differences, DMX and the LOR protocol use the exact same transport. Think of it as being 2 people speaking on a telephone. In once case both people are speaking English (LOR). In another case they are speaking German (DMX). The wire (phone) doesn't care what language the people speak. It's only job is to move a voice (data) from one spot to another.

When DMX was born, the specification was to use XLR cable. Why would they do that? Remember that DMX was originally relegated to stage lighting. If there was one thing a theater or traveling group had, it was XLR cables since those were also used for audio transport (microphone cables anyone?). We on the other hand are computer people. XLR is more expensive in comparison to CAT-5. In fact phone line was the original cable used since it was cheaper still.

SO now we come to E 1.31... Again, we separate the PROTOCOL from the TRANSPORT.

E 1.31 specifies how 2 devices will speak to one another. It 'encapsulates' the DMX protocol - basically when E 1.31 data gets to the destination it's E 1.31 'shell' is removed and what remains is DMX PROTOCOL'.

E 1.31 uses UDP as the transport.

UDP however is not really a transport. It is again a PROTOCOL that specifies how the data travels between devices on an IP network. So we have to go a layer deeper.

IP is yet another PROTOCOL. It specifies how data get's from 1 place to another. But it too doesn't specify the physical connection.

...and this goes on and on. I'm going to skip the rest of the 'layers' since things from here can get muddy. Now you can see why E 1.31 can be used over other transports as well.



Now that I've completely confused you, let's look at it the EASY way.

If you are going to use E 1.31, you are going to use hardware that you normal use for your home network: A Network Interface Card for your computer, one or more hubs/switches, and various devices that can understand E 1.31. Those devices are going to take the E1.31 they receive, strip the shell and turn it into DMX. A device that changes 1 protocol to another is usually referred to as 'a bridge'.

Some devices you use will have their own bridge - that is, you'll simply hook up a network cable from a switch/hub directly to the device. It will then convert the E1.31 into DMX and use it.

Other times, you'll have a 'stand alone bridge'. These stand along devices will hook up to the Ethernet side, take the E1.31 commands, strip the shell, and then transmit them out the other side as DMX over RS485 (which may or may not use the same kind of cable).

[jerrymac]

O.K. Mike I think I follow you (?). As an instance take the EthConGateway (one input and 4 outputs RJ45 with one for each universe), Once LOR supports E1.31 the data would be output (transported) via your RJ45 network card and into the EthCon (or switch). Your cat 5 cable would connected to the computer or switch device and send the DMX data with the E1.31 transport (?) to the input on the gateway. The EthConGateway would strip the transport and output the dmx signal trough one or more of the 4 outputs (based on which universe the data was set to). The controller would be regular DMX and not care anything about E1.31. the DMX signal would be on two of the Cat5 wires as with normal DMX.



Yes, No, Maybe or none of the above?

[LOR Staff]

Computer -> Ethernet Card -> Cat 5 Cable -> Switch/Hub/Router/Other Network Hardware -> Cat5 Cable -> Ethcon Gateway

This path is going to ALL be IP - that is to say it will use NETWORK type hardware where the EthConGateway is 'the bridge'. This is where all the E1.31 will travel.

Ethcon Gateway -> (whatever type of cable - XLR or RJ 45 terminated twisted pair) -> DMX Lighting Device.

The Ethcon Gateway (Bridge) receives the E1.31, strips off ALL the crud that was NETWORK related (leaving only the DMX), and then sends that DMX out the correct physical port to the lighting device.

[jerrymac]

Think I got it. Wasn't so hard

Thanks Jerry

[LOR Staff]

E 1.31 is going to be one of those 'Simple but hard' kind of things. Since it's IP/Ethernet/etc it pretty much 'just works' with minimal setup - as long as everything matches on both ends, the network itself will find a way to get there.

HOWEVER, you can VERY quickly create complex systems that will have you pulling out your hair when they don't work right.

[jerrymac]

DevMike wrote:

.... HOWEVER, you can VERY quickly create complex systems that will have you pulling out your hair when they don't work right.

Oh Oh I may be in for trouble then, since nature took care of the last part years ago !:dude:

[WilliamS]

Its not all that bad as long as everything is setup from go. Where I was pulling my hair out was on setup. And the fact I didnt have Sequencer to play lights. Hours wasted troubleshooting when that stupid checkmark was all I was missing.