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FOCUS ON FUNDAmeNtALS
PROJECTION LIGHTS & STAGING NEWS
Streaming DMX
By RichardCadena
Taming the Cable Monster
“Oh no, it wasn’t the airplanes. It was beauty
killed the beast.” — Robert Armstrong as
Carl Denham in the original King Kong (1933).
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There’s a new movie in the making that
will soon be playing in theatres and
performing arts spaces everywhere. It’s
about a new protocol that goes up against a
monster bundle of cable. The winners in this
battle are the techies and end users of large
lighting systems.
The movie is actually a sequel. The original
version came out in 1986 when 0-10V analog
control was getting out of hand. Lighting
systems went from tens of dimmers to hundreds
of channels of control, not only for dimming,
but also for automated lighting. What
once was a very manageable bundle of cable
because a huge ugly beast that terrorized
roadies and techies everywhere. Along came
DMX and suddenly there was a new hero who
conquered the analog cable bundle beast. In
its place was a single twisted pair that could
control up to 512 channels — enough for
even the larger lighting systems of the day.
But as we all know, in the movies, even
when the evil villain dies that’s no guarantee
they’re gone forever. And that’s why
we have sequels.
Cable Monster — The Sequel
FOF
In this case, the monster cable bundle
started rearing its ugly head again in the
late 1990s when lighting systems reached
epic proportions. But the thing went positively
steroidal after 1998 when the monster’s
sidekicks, the DMX-controlled media
server and the RGB LED luminaire, entered
the stage. Suddenly we went from hundreds
of control channels to thousands
of control channels. The single twisted
pair was overthrown by a massive bundle
of DMX universes and the monster cable
bundle was back in power.
Fortunately
for us, the smart
people in the
Controls Protocol
Working
Group of ESTA
saw the proverbial
writing on the
LED wall. The cavalry
mounted and rode
to meet the monster
head on. Several years
into the battle, ACN was
born and the industry had
a standard by which many
DMX512 universes could be
transmitted over a single cable.
They had slain the cable monster
once again. Or had they?
In an unexpected plot twist,
manufacturers stayed on the sidelines
in droves while the ACN train pulled out of
the station. While it’s too early to say that
few of them are on board with ACN, it’s not
too early to say there’s not a lot of evidence
to the contrary (other than ETC’s Eos console,
which outputs ACN). Meanwhile, several third
parties built their own platforms to slay their
own cable monsters by streaming DMX over
Ethernet with a proprietary protocol. Some
of these solutions including Artistic Licence’s
ArtNet, Pathway Connectivity’s Pathport,
ETC’s Net2, Strand’s ShowNet and probably a
few more.
Streaming to the Rescue
FOF
So, while there are plenty of white knights
ready to slay cable monsters everywhere,
there is no single solution that plays well with
all systems. If you were on a big job with lots
of nodes, it would be much easier if you could
mix and match across manufacturers. With
proprietary protocols, that’s not an option.
But the folks at ESTA aren’t satisfied to sit
on the sidelines and watch the parade go by.
Instead, they re-mounted their trusty steeds
and they are now working on a standard to
stream DMX over ACN.
The draft version of BSR E1.31 — Lightweight
streaming protocol for transport of
DMX512 over ACN is out for public review, and
it promises to slay the monster cable bundle
once and for all (or at least until the next sequel
— Streaming DMX512 Versus ACN: The
Cable Monster’s Revenge). As the title says,
this protocol will allow the transmission of
DMX512 data over an Ethernet network using
part of the ACN suite of protocols. It can also
send and receive RDM data as well.
New Cables, Old Gear
FOF
The advantage of streaming DMX512
over Ethernet is that an Ethernet network is
a much bigger pipe than a DMX512 network.
Ethernet can handle dozens and dozens of
DMX512 universes across a single cable,
which is how the monster cable bundle is finally
put to rest. You’ve heard of Cat5 cable,
no doubt. A Cat5 cable can support data
rates of 100 megabits per second, which can
reliably run up to 200 DMX512 universes, or
1,000 megabits per second, which can run
up to 2,000 DMX512 universes. Cat5e cable
is a better choice for 1,000BASE-T, or “gigabit”
Ethernet, which is what we call Ethernet
running at 1,000 megabits per second.
The disadvantage is that Ethernet networks
can only be run a maximum of about
300 feet before they run out of gas. Ethernet
also has a star topology, meaning that a cable
has to be run to each device, negating the advantage
of slaying the monster cable bundle.
The best of both worlds is to use a combination
of DMX512 and Ethernet infrastructure.
We start by using an Ethernet network
over which we stream DMX512, but then we
change it back to DMX512 before we distribute
it to all the devices on the network. This
allows us to take advantage of off-the-shelf
hardware like routers, switches, hubs and Wi-
Fi, but we still get the advantages of DMX512,
the biggest of which is probably the fact
that there are millions and millions of dollars
worth of DMX512-compatible gear already in
use every day. We don’t have to trash our gear
to take advantage of the new technology,
as was largely the case in the original movie
when DMX512 supplanted analog control.
The Beast — R.I.P.
FOF
For these reasons, DMX512 will probably
be around for a long, long time while
the monster cable beast might rest in peace
for as far into the future as our crystal ball
will allow us to see. Is streaming DMX512
over Ethernet for everybody? Not necessarily.
But for applications where there are multiple
universes of DMX512, like the Opening
Ceremony of the Games of the XXIX
Olympiad in Beijing where over 2,300
DMX512-controlled devices used more than
45,000 parameters — the equivalent of 88
DMX512 universes — it’s a an Oscar-winning
technology.
What does a bundle of 88 DMX512 cables
look like? Thanks to Ethernet, we may never
know.
Stream an e-mail to the author — rcadena@
plsn.com.
64 PLSN September 2008