Wireless DMX

[Nick S]

I am currently researching the use of wireless DMX, specifically using wi-fi and in large scale tours/productions involving many automated fixtures. Has anyone experienced problems with latency, or interference? I found a thread which touched upon such issues briefly, but it was a couple of years old. I'm assuming as the technology has become cheaper more people will have experimented with it and issues will have been improved upon. If there is a degree of latency in a wireless setup, at what point would it become unacceptable? (subjective, I know). I'm also interested if anyone has had problems with interference from other wi-fi devices and networks.

 

I'm not looking for advice on an install - this is all in aid of a research project looking at new ways to control fixtures and lighting...I'm of the opinion that there are methods of control that havn't really been investigated or approached simply because the current norm 'works', even if it doesn't work as we'd like it to all the time. As part of this I'm investigating the more recent innovations wi-fi has brought about.

 

Thanks (hopefully) for your help <_<

[Simon Lewis]

Nick,

 

There was a good article about wireless DMX in in L&SI recently, although from memory they couldn't find a suitable method for determining some issues such as latency. There were a few letters in the following month's issue concerning this.

 

We use a wireless DMX system, but have found it susceptible to crashing. we believe this is due to the close proximity of WiFi, (probably the laptops at FOH) but haven't determined this objectively.

 

Simon

[Tomo]

(This information is based on 802.11b, but most still applies to the g variant)

 

WiFi suffers from the problem of completely unknown latency.

 

If there is a burst of interference, then you'll get a burst of long latency while the link rearranges itself around the interference, often by dropping the bitrate/bandwidth (which introduces further latency)

 

When surfing the web, you barely notice that your link suddenly took half a second to respond, when it normally took a tenth or less - if nothing else, IE can't render the graphics that fast anyway.

 

When running your lighting rig, this uncertain latency may be a problem - sometimes the wireless portion of your rig will respond almost immediately, but sometimes it may take much longer.

 

The severity of this depends on the DMX-over-ethernet protocol chosen.

Broadcast packets may be lost entirely as the transmitter has no way of knowing if all hosts recieved it, multicast packets may be automatically re-sent over unicast if such error-correction exists in the protocol.

 

As with all wireless systems, what works will change from venue to venue, and from moment to moment.

 

WiFi is particularly difficult to predict because it uses frequency hopping - it will often find a way around interference, because the communication often still gets through by using the other frequencies in the spread-spectrum hopping.

 

There are also only really three bands within the WiFi spectrum - Channels 1, 6 and 11.

 

All other channels overlap to some degree - due to the aforementioned frequency-hopping this is usually not fatal, but it means that if you have one access point for internet, one for lighting, and the guy next door has the same then you will automatically have some overlap. This ignores the other users of the band, of which there are a great number - even microwave ovens can have a significant effect.

 

On top of this, WiFi is inherently insecure.

If the link is unencrypted, then any person with a WiFi device could browse into your lighting network and play merry hell with it.

If the link is encrypted, then you will have to accept some extra latency due to the encryption/decryption process - although to be fair this is usually fairly small and consistent.

Even with an encrypted link, there have been cases of poor firmware in the WiFi equipment that have allowed attackers to gain access - this will remain a risk, albeit a small one.

It's always possible to create a denial-of-service attack, even by accident!

 

In summary -

We recommend against DMX-over-Ethernet being sent over WiFi for the reasons given above - primarily the latency and security issues.

We do know that ETCNet 2 usually works when used this way, but we can't guarantee it.

 

For good DMX-over-air systems I would look to the dedicated solutions, if only because they will have been more thoroughly tested for latency.

 

(Edited for clarity.)

[dbuckley]

You could ask on the theatrewireless Yahoo group; it's run by a manufacturer of a wireless DMX512 system, and they should be able to provide you with some real life numbers.

[lightsource]

May be worth having a word with someone at Martin if possible. They have done projects using

their wireless DMX-512 units, including outdoor work (see the project in news archive article 19).

 

 

Their own coments (News archive article 30) Worlds longest Catwalk - Sony Playstation Event.

Martin WDMX system proves “stable” on high profile events by Germany’s

Lightcompany and Electric Fly Productions UK.

 

Hope this helps.

[Ken Coker]

Nick,

 

There was a good article about wireless DMX in in L&SI recently,

Simon

 

LSI - Technical Focus

 

KC

[gus_b]

Nick,

 

The Technical Focus Article in LSI is good, but it has some short comings – read letters to the editor in the latest issue of LSI.

 

The W-DMX (blackbox) system from Wireless Solution Sweden is very interesting.

 

W-DMX differs from all other wireless DMX systems on the market. The majority of systems send DMX512 data relying on a proprietary standard such as 802.11b (Wi-Fi, or W-LAN).

 

W-DMX Blackbox systems employs Frequency hopping techniques, in which the transmitter jumps from sub-channel to sub-channel at a rapid pace.

 

W-DMX takes the Frequency Hopping Technology one step further, by using employing adaptive features. This means that the W-DMX system automatically avoids interference on channels in use and changes frequency 1000 times per second, but never to a frequency in use by other equipment on the same frequency band. W-DMX also uses the TDMA technology to make the system the most reliable on the market and the safest for clients to use.

 

I'd be happy to send you some more information.

 

Gus

[back_ache]

"proprietary standard such as 802.11b".

 

err, I think you'll find the 802.11b standard is not under private ownership, but the one your recomending is!

 

It think the problem with any broadcast wireless technolgy is that it operates in a shared space (espically the overcrowded 2.4ghz range), we'll use it for rigging and designing but come showtime, wired everytime!

[Guest harry.xiong]

Hello, SIR,

 

I see 433MHz wireless DMX512 CAN can support this, You know it is legal in EU, and the price is just USD 120 For one transmitter and One Receiver, The RF distance is up to 150M , It is a new product.

 

To more detail: WWW.gigawit.com.

 

Or Please feel free to contact with us: Harry01gigawit@gmail.com

 

Harry

 

W-DMX differs from all other wireless DMX systems on the market. The majority of systems send DMX512 data relying on a proprietary standard such as 802.11b (Wi-Fi, or W-LAN).

 

Hello, 2.4GHz is short distance technology, and It is hard to support 100 meter with FCC oR CE certitification.

[paulears]

I'd have thought that having a low power radio system operating in the middle of an amateur radio band is bad news when integrity of data is critical. I've never bothered testing it, but the presence of high power transmissions just a few KHz away sound a little risky to me.

[Guest harry.xiong]

I'd have thought that having a low power radio system operating in the middle of an amateur radio band is bad news when integrity of data is critical. I've never bothered testing it, but the presence of high power transmissions just a few KHz away sound a little risky to me.

 

Hello.

 

2.4Ghz is short distance Wireless Technology, The RF range is very limited with CE and FCC certification, But the 900Mhz is illegal in the EU, So we choose the 433MHz And 915 MHz.. Just two channel.. 433 MHz FOR EU, AND The 915Mhz and 433Mhz for USA, The Cost is very well too, I know it is not suitable for National holiday lightting project, BUT It should be well in some filed, and The Market is very well in the USA, but It is blank in the UK..I'm looking for somebody to take care my business//

 

Harry

 

harry01gigawit@gmail.com

 

www.gigawit.com

[Alan Beattie]

I can recommend the City Theatrical WDS Wireless Data System -- Had absolutely no problems using large amounts of it over a number of years, and thats in central london! Has been very reliable..

 

http://www.citytheatrical.com/

[dbuckley]

On the "contact me" form on my personal website today I got this:

 

Have a good day!

 

New Product!! wireless DMX512 Transmitter and receiver--Light Port

 

our price is USD 120 UNIT for one transmitter and one receiver FOB shenzhen in china. and Wireless transmitter/Receiver: USD60/PCS.

 

Would you like to purchase a sample for evaluation?

 

Heres a link to their Website: http://www.gigawit.com - it's in products, page 2.

 

At this price I suspect we'll see a few of these about...

[gareth]

Hmm. So it seems that this chap has harvested your details from your Blue Room profile and is using them to send you unsolicited commercial e-mail (it seems far too much of a coincidence that he contacted you trying to sell you stuff just a few hours after he joined a forum of which you're a member). I was under the impression that the BR administration took a very dim view of members' details being harvested and used commercially by other members in this way?

[dbuckley]

It came in from the website contact form (note website addy in sig), not via email; BR doesn't display my email, but anyway, oddly enough, he did claim his name was Harry Xiong. Now that is a coincidence Harry's IP was 220.231.192.127.

 

I've filed the original note in a mail folder entitled "good spam". It does p*ss me off I get so much spam, but the folder has (now!) 79 items in it that I've thought worth saving...