RDM/DMX Performance - E1.20 RDM (Remote Device Management) Protocol Forums

Schlais01 · February 25th, 2009

I have a customer who is very concerned about RDM traffic having an adverse effect on DMX traffic.

The concern is that if RDM is taking up to 50% of the bandwidth that there could be flicker or less than smooth DMX transitions on big lighting rigs.

We have done quite a bit of testing and with up to 93 RDM units we have not encountered any negative performance issues, flicker, or other kinds of DMX impacts.

I am wondering if anyone has any data, or if anyone has done specific RDM performance testing to quantify the effects of RDM on a large lighting rig, say 200+ fixtures and or accessories.

Thanks,
Lee

ericthegeek · February 26th, 2009

In most cases, RDM won't take up anywhere near 50% of the bandwidth. Most RDM packets are relatively short (under 80 bytes for the request plus response), so even if you're sending an RDM request between every NSC refresh it's still only a marginal impact on refresh rate. And most controllers don't send DMX at the maximum refresh rate anyway.

The few RDM packets that are longer than about 100 bytes aren't things you're likely to do during a show. They're primarily setup messages that you send one time when you're first patching the rig.

Some badly designed products will flicker when they see RDM traffic because they don't properly ignore non-zero startcodes. RDM discovery can also cause flicker under some conditions, so you may want avoid running discovery during shows.

February 25th, 2009	#1
Schlais01 Junior Member Join Date: Jan 2009 Posts: 1	RDM/DMX Performance I have a customer who is very concerned about RDM traffic having an adverse effect on DMX traffic. The concern is that if RDM is taking up to 50% of the bandwidth that there could be flicker or less than smooth DMX transitions on big lighting rigs. We have done quite a bit of testing and with up to 93 RDM units we have not encountered any negative performance issues, flicker, or other kinds of DMX impacts. I am wondering if anyone has any data, or if anyone has done specific RDM performance testing to quantify the effects of RDM on a large lighting rig, say 200+ fixtures and or accessories. Thanks, Lee

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February 26th, 2009	#2
ericthegeek Task Group Member Join Date: Aug 2008 Posts: 383	In most cases, RDM won't take up anywhere near 50% of the bandwidth. Most RDM packets are relatively short (under 80 bytes for the request plus response), so even if you're sending an RDM request between every NSC refresh it's still only a marginal impact on refresh rate. And most controllers don't send DMX at the maximum refresh rate anyway. The few RDM packets that are longer than about 100 bytes aren't things you're likely to do during a show. They're primarily setup messages that you send one time when you're first patching the rig. Some badly designed products will flicker when they see RDM traffic because they don't properly ignore non-zero startcodes. RDM discovery can also cause flicker under some conditions, so you may want avoid running discovery during shows.