DMX Over Ethernet and Fibre Optic

[goochr96]

Hi there all, ive done a search for this but not quite found the answers that I am after, so hopefully somebody out there will be able to answer my questions?

We are looking at possibly lighting up some of our buildings at work, now this is a university campus, so covers a fairly large area, actually most of Coventry City Centre! My idea is to light up certain parts of buildings using LED lights, probably Pixel par stuff. Anyhow, as I said the campus is fairly large, so obvioulsy the best way of getting DMX around the site will be over Ethernet and probably Fibre Optic (I say this as I want to run the whole lot from one location, probably of an Artistic Liscence Four-Play on a time code. So I was wondering if anybody has had any experiance with DMX over a) Ethernet and b) Fibre Optic.

 

I have quite a few questions, like if you run DMX over fibre, does it have to be a dedicated fibre, or can it be shared with the like of a local network of computers?

How much will DMX load up a network by?

Will the data rate be quick enough over such a large scale?

Is there a potential for dropped packets?

Would you be able to gain access to the Ethernet device controlling the show from a remote locations, Ie over the internet? (Although I think I may have the whole DMX over ethernet confused in my head with pc's on an ethernet!

 

 

Quite a few questions there, any help would be most appreciated.

[Tomo]

Once the DMX packets are on the network, they are exactly the same as any other packet, and the physical layer is irrelevant.

 

As to the rest of your questions - it depends.

[goochr96]

So then, solonging you had a computer running sutible software you could pick up the DMX going around the network on a PC?

 

Apologies for posting here, I thought it was going in to the lighting one!

[paulears]

topic moved to lighting

Paul

[goochr96]

thankyou paul, I tried to do it myself, but couldnt work out how, must be an admin jobby!

Ta Muchly!!!

[Ken Coker]

You may find

 

http://www.artisticlicence.com/item336.htm

 

of some use. It's written by the owner of AL and is a good basic primer.

 

The rest of the AL site may also be of help. Having said that, you might already have been there so apologies if I'm having a teaching/egg sucking interface.

 

Cheers

 

Ken

[goochr96]

Cheers for that ken, ive just ordered myself a copy!

[bruce]

AS tomo suggests, it's a common misconception that "ethernet" means "wires". I'm really trying hard not to mention the good-ol'-OSI-7-layer-model....

 

But the basic principles are that up at layer 7 you have your applications - things like email, web, or even lighting control :)

 

Down at layer 1 you have electrical signals, or pulses of light, or physical movement of a semaphore flag, or changes in pressure, or whatever. Even by carrier pigeon.

 

And in the middle we have things like IP (does anyone remember IPX, Appletalk, DECnet and a whole host of other obsolete stuff), the transport and transmission protocols (using the words loosely), which basically tell the signal how to get from point A to point B and how to behave when doing so. In general, only network engineers worry about this bit, the application doesn't care.

 

The important thing is that each layer only needs to interface to the layer above and the layer below.

 

So email and web, up at the top, don't really care whether they are running over wires, or fibre, or radio, or a bit of wet string. You don't have to fire up a different sort of web browser when you move from a local web site to a transatlantic one.

 

The same applies to any high level application. As long as the underlying transport has a suitable throughput and latency, the application shouldn't care what it is.

[dbuckley]

...Anyhow, as I said the campus is fairly large, so obvioulsy the best way of getting DMX around the site will be over Ethernet and probably Fibre Optic (I say this as I want to run the whole lot from one location, probably of an Artistic Liscence Four-Play on a time code.

The AL box is a replay machine, so instead of using one expensive replay machine why not use several cheaper replay machines such as the LanBox?

 

Added: Some models of LanBox have an Ethernet port, so you can just plug them stright into your LAN and have full control from anywhere on the LAN. By "full control" I meant you can program them using their LCEdit software, and I'm fairly certain that you can syncronise them, by having one acting as a master timer, which commands the others to do things. Or you could trigger them from something else, again across the ordinary network. As this is normal TCP/IP traffic, there will be no latcency issues, unless your LAN is already busted :) This is what I was intending to suggest in my rather-too-brief original answer.

[mac.calder]

I put my vote in for the LanBox too - it is a very nice piece of kit. You could also look into some of the DMX2Ethernet/Ethernet2DMX products - some also allow computer control.

 

After reading Back_ache's comments - I thought I would just add something that may help - The DMXEtherGate (Enttec) quotes on it's site that by using Run Length Encoding on the DMX data, they can happily run 256 universes of DMX over a 10baseT network. So what ever system you use, bandwidth wise, you will use jack all, even without RLE.

[back_ache]

Before I try and answer your questions I'm going to assume you can get a university network engineer on-side otherwise it could be tricky.

 

I have quite a few questions, like if you run DMX over fibre, does it have to be a dedicated fibre, or can it be shared with the like of a local network of computers?

most of the popular units out there for sending DMX any distance do so by converting to IP. With a few caveats sharing an existing network is not a problem.

How much will DMX load up a network by?

That will change from product to product and how you implement it but one thing is for sure, to be a good network citizen your traffic will have to traverse the network as either multicast or unicast, you would not want to (or probably be allowed or able to, do it as broadcast)

Will the data rate be quick enough over such a large scale?

Your campus will no doubt be configured as a MAN and be using LES circuits(or similar high bandwidth connections) to transport the data, DMX's needs will be tiny in comparison, however it would be nice if your network admin would set a guaranteed minimum bandwidth for you.

Is there a potential for dropped packets?

not at DMX presentation layer, that should all be handled and abstracted by IP and the devices

Would you be able to gain access to the Ethernet device controlling the show from a remote locations, Ie over the internet? (Although I think I may have the whole DMX over ethernet confused in my head with pc's on an ethernet!

the network doesn't care what things are (PC, printer, DMX gateway, toaster) it just sees them as devices, it would be perfectly possible to connect from a remote location to your device on the network but would require the help of a friendly network admin, but you are going to need one of those anyway!

[goochr96]

Thanks for all the postes so far guys, have had a look at the LAN Box and I agree, it does look like a very neat piece of kit, espically for the money.

The reason for having it run from one location is; although it is a large site, you can see several of the features of different buildings from one location. So that as you walk around the campus you see part of one building red, then your eye is takenn further up the road to a roof top with a dome on it that is red, then infront of you they change to blue simutainiosly, and this is the same through out the entire site. (If you follow me?)

bach ache, This is just an idea at the moment with many meeting ahead of it, but I am sure that if they do want to go ahead of it then we will talk to the people in computing services. I know that we (Estates) are going to be putting our BMS (Building Management Software) on to the network, only because we have a few fibre opticss that the people in computing woulud like to share so some bargening has been done!!

 

to be a good network citizen your traffic will have to traverse the network as either multicast or unicast

 

Does that mean that the DMX once converted to ethernet has a specified route to take along the network to the next "drop off point" ?

[back_ache]

to be a good network citizen your traffic will have to traverse the network as either multicast or unicast

 

Does that mean that the DMX once converted to ethernet has a specified route to take along the network to the next "drop off point" ?

 

Okay, there are three types of way you can distribute packets broadcast, unicast and multicast

 

Broadcasts are like a guy with a megaphone, everyone in the "local area" (virtually speaking) wether they like it or not get to hear what they are saying it's good for the guy because he knows he's going to reach the everyone who's interested and he only has to say it once, problem being he's disturbing everyone else who's not interested.

 

Unicasts are like a telephone call, you get to pass the message on to those that are interested but you have to know their number and you have to repeat the message for every single interested person, a bit of a wasted time for for the guy, but good in not disturbing people.

 

multicast is like a radio station, if you want to listen to the guy you dial in his frequency, the guy only has to pass his message on once and no one uninvolved gets disturbed.

 

basically you should to choose a device that is unicast or multicast (the network has to be configured for multicast) the network will not normally forward on broadcasts though if your network supported it you could have a "trunked vlan" (a virtual local area with just your devices in) where it wouldn't matter how obnoxious your devices where being!

 

I think I'm making this more confusing, I need some sleep!

[bruce]

Chris,

 

I see you work for the estates department at your University. Talk to your networking people in the computing services. I can tell you who to talk to if you're not sure - I am the network manager at another University. We work fairly closely with our estates people, as more and more of their services (BMS, CCTV, telephony etc) are now using the data network as the underlying transport. But the thing that causes the most problems is when one of the "partners" in this partnership goes out and specs something without letting the other side know about it, then just "assumes" that it will work...and grumbles when it doesn't...

 

Only the networking guys will know the details of how the locations are interconnected, and what firewalls etc sit between them. It's not a difficult problem - there will be loads of bandwidth available - but get the IT people involved as early as possible.

 

As I said, I know some of the networking people at your site - send me a PM if you need some contacts.

 

Bruce.

 

to be a good network citizen your traffic will have to traverse the network as either multicast or unicast

Does that mean that the DMX once converted to ethernet has a specified route to take along the network to the next "drop off point" ?

 

Don't worry about it. That's one for the networking people. The network knows how to get your data to its destination.....

 

It gets back to that 7 layer model I mentioned above. When you point your browser at (say) www.blue-room.org.uk, your browser doesn't know where that is, or how far away it is, or how to get there. All it knows is that if it were to ask the underlying network to send packets to that location, then the network should be able to do it, and to get the reply packets back to the right place.

 

It's the same with your application. Your devices don't have to know the explicit route to each other; all they need to know is that they are connected in some way.

 

Bruce.

[dbuckley]

...have had a look at the LAN Box and I agree, it does look like a very neat piece of kit, espically for the money. The reason for having it run from one location is; although it is a large site, you can see several of the features of different buildings from one location...

Yep, got that, and I'm fairly sure (but dont actually know, as I have no practical experience with the beasts) that several LanBoxen will be able to syncronise themselves together using the LAN. Go have an ask on their forum. The LAN will only carry (effectively) go messages, so the bandwidth requirements will be tiny, and wont need any fun like multicasting or reserved bandwidth.

 

Another way of doing this (which I'm going to call the Disney Way) is to syncronise the show to time. Since its architectural you dont need timecode, real time would do, and the LanBoxes can probably do that too. I call it the "Disney Way" as thats the way they syncronise the lighting on the (dozens of) floats on some of their parades. They transmit timecode over the air (using VHF FM) and every float has a receiver and an autonomous lighting and sound rig. Thus all the floats change from coloured flashing lights to whit flashing lights simultaneously over a distance of hundreds of yards. It is a "wow" effect. And sound - some floats have soundtracks onboard and they play along with the music, all held together with timecode.