Category Archives: Know How

Ethernet – The Basics

Just Enough to Break Something

Ethernet has been around for a very long time (for technology that is) and has evolved to the monster it is today. There are millions of pages of information on the subject and hundreds of classes, certifications and degrees you can get. For our use of ethernet, however, we will just need to start with a very limited view. So first a little bit of history, you know for that bar wager with your friends, then we will get into it.

Back in the 1970’s Xerox started developing ethernet based on a government system in use at the time. It was introduced commercially in 1980 and then standardized in 1983 by the IEEE or Institute of Electrical and Electronics Engineers as IEEE 802.3. This first version was called 10BASE5 using a coax cable ring to connect computers in a building, later in 1990 the standard was updated to IEEE 802.3i which is how we see it today as 10BASE-T using twisted pair cabling. Since then several enhancements have been made both is speed and usability including, the addition of power over ethernet or POE (IEEE 802.3at-2009, my personal favorite).

That is the uber abridged history, now let’s see how we can use it to take over the world.

Equipment

When we look at creating a production network, one of the first things to look at is the equipment needed to carry the data. For our needs, in the entertainment industry, there are three basic pieces of gear (one of them is hardly ever seen anymore), hubs, switches, and routers. They do basically the same job, connect ethernet devices together, but with varying levels of sophistication

Network Devices

Hubs

nearly obsolete at this point with the price of better Ethernet equipment going down. Hubs usually have low port count (four or five generally) and function basically as data splitters, so data comes in on one port and is sent to all the other ports at the same time, with very little processing. This is ok for slow speed, noncritical applications but not for today’s much higher speeds and complex networks.

Switches

Ethernet switches are very “in” these days, a large amount of company’s make these, you can almost pick one up at 7eleven. There are a couple of manufacturers that provide specialized products for us in entertainment (yeah) Switches come in multiple port configurations from 4 to 32 ports or more and could be desktop or rackmount. For the most part, switches are also data splitters but they do this in a smarter way, data comes in on one port and is sent out to only the port that needs it. This allows for faster data rates and greater data integrity. It is capable of a bunch of other things and can even do some of the functions of a router too, but for now…

Routers

These are the big brains on the network, and do a lot of processing of data. These come in all sorts of configuration from a four port desktop model to 900-pound refrigerator-sized units. At the lowest level, routers move data between multiple networks or “route” data. This is why you have one in your house (probably), it is moving traffic between your internal network, your computers and iPads, and the external network of the ISP. Consumer routers, these days, combine other network processes together in the same unit like a firewall, a DHCP server, a modem a switch and WIFI access points, kind of the Swiss Army knife of networking.

Cabling

Since the 1990’s we have been using twisted pair cable to transport ethernet short distances within buildings (100m or 328 ft). Today this cable has become a commodity, for the most part, because the specifications of it are an industry standard, category 5 cable or CAT5 defined in EIA-568-A. With a few exceptions, rugged construction being almost the only one, any brand of CAT5 will do the job. Depending on the situation, CAT5 cable is fairly cheap and available almost anywhere. There are several enhancements to twisted pair like CAT5E, CAT6, and CAT7, these are mainly for increased speeds.

Color-Chart

CAT5 uses a standard RJ45 8 pin modular connector or 8P8C (8 pins 8 contacts). The 4 pairs of the cable or 8 individual wires connect to the 8 pins of the connector then they are crimped on with special tools. There are two specs for the order of the wires in the connector, 568A, and 568B, below there is a visual of the differences. To make a standard cable just pick one of the specs then make sure you use it on both ends of the cable. Building a network cable is a fairly easy and straightforward process, the tools and connectors are easily found and pretty cheap (you see why we like ethernet so much, cheap and easy to use).

Ethernet Tool

The IP Address

Every piece of equipment on the network needs to have an address, like our post office example in other posts, if the mailman does not know where to send our letter, the letter will end up in the dead letter office. The address for the mailman on a network is called the IP address. In use most often today is IPv4 which looks like this 192.168.2.122, but since the world is running out of those addresses a new standard is being deployed, IPv6 which looks something like this 2001:cdba:0000:0000:0000:0000:3257:9652, a load more confusing so we will just focus only on IPv4.

The IP address can be assigned in two ways, statically and dynamically. Dynamic addressing is used most often, at your house when you connect your phone to your WIFI, the router will give it an IP address because it has joined the neighborhood and the mailman has a letter. You never have to set up your phone with and address, this job is handled by a DHCP (Dynamic Host Configuration Protocol) server, usually build into your router. This is great for everyday use but since we need to access things directly by their IP address this method is not ideal because the address could change. Static addresses are the solution, this is where we manually set up the device with an address, it will never change so we can depend on it (like an old friend).

There are several different scenarios for setting up IP addresses in various environments which we will discuss in other articles

Couple of Examples

Here are two examples of common, simple configurations of a network.

1) Computer, Switch, and Interface – Static address

Example-1
2) Computer, Router, Switch, Printer and multiple interfaces – static and dynamic

Example-2

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DMX 512 – What is it Really

DMX512 - What is it Really

Basically, DMX512 or just DMX is a way to control things from a central control device. Officially, this is now an ANSI standard developed in 1986 by the United States Institute for Theatre Technology or USITT to replace analog control of dimmer systems. It has gone through many revisions to become an industry standard, it is now “ANSI E1.11 – 2008 (R2013)” maintained by Professional Lighting and Sound Association or more commonly know as PLASA. DMX stands for “Digital Multiplex with 512 individual pieces of information” unless you are on Jeopardy or need to win a bet you can forget this right now, but the question comes up a lot. It was initially based on an existing standard of the time EIA–485 so, much of the electrical parts of DMX are the same.

With that out of the way, the important stuff, how to use it successfully.

Today DMX can control a bunch of devices like dimmers, LED lighting fixtures, moving lights, fog machines and other environmental effects and special use tools. We now can even run DMX over an Ethernet network, more on this in future posts. Because it has no error correction (the information is not guaranteed to arrive exactly right) it can not be used for critical environments where safety is a factor such as pyro, motorized sets, etc. There are four main areas to focus on when setting up a DMX control system.

Addressing

We hinted to the fact that DMX has “512 individual pieces of information”, each one of the 512 pieces of information is known as a channel and a group of 512 channels is called a universe. Within each channel there are 256 steps of control, in most cases this relates to intensity but could be movement or some sort of internal selection within the device. Each device has a start address, imagine the street where you live as the DMX universe and the houses are devices. Each house has an address so the mailman knows where to deliver the packages, in the same way, devices need an address so the controller knows where to deliver the commands.

Most modern devices use more that one DMX channel, so the start address would be the first channel the device will use. So in the below example we have four devices:

DMX-Setup

To set the address some devices have a number display (the easy way), some units have binary dip switches (the hard way). Usually, the user manual will have a chart to tell you what to set the dip switches to, or there are a couple of apps that will help with this:

Cabling

Traditionally DMX cabling uses a 2 conductor shielded 120-ohm cable with a 5 pin connector. However many brands on the market are now using 3 pin XLR connectors, this opens the door for microphone cable to be used. There is a great debate about this and its implications, but we will not get into it for now (maybe in later posts). For now here is a good set of recommendations

  • Use only DMX cable (CAT5 and CAT6 network cable are also an option now)
  • 5 pin or 3 pin connectors – need to work within the manufacturers design
  • Limit the number of units on a single run to 32 units (EIA-485 Spec)
  • Limit the total length of cable to 3200 feet in a single run (EIA-485 Spec)
  • Use a 120-ohm terminator on the last device (these are readily available)

All DMX devices have an input connector (Male) and an output or thru connector (Female) and are connected together by “daisy chaining” them. This means you connect the controller to the input of the first device, then connect the second device from the output connector of first and so on till you get to the last unit. On the last unit, we will plug in your terminator to the output connector.

Controller

The controller can be a lighting console, a computer running software or a computerized console. Either way, this is the unit that will send the commands out to the devices and where you will interface with your system to make changes. The controller will be set up to know what DMX channel the devices are listening to so it can send the commands to the right place. With older controllers each fader will be a channel, this gets a little cumbersome when you start using LED’s and moving lights with all the different parameters that can be controlled. Software based controllers will take all this into consideration and present different controls tailored for each parameter type (color, movement, etc). No matter what controller you are using they all act as the Post Office, from our earlier example, sending packages to specific addresses.

Device to be controlled

These are the units that will receive the commands from the controller and make changes based on them. For example, if it’s a dimmer, it will change its intensity; if it’s an LED fixture it could change its color. DMX uses 256 steps for making these changes so, a value of 0 is 0% intensity or Off and a value of 255 is 100%. This value is like the volume on your TV, click the up button and the volume is increased by one click, it went from a value of two to a value of three (or if you are like me with an old TV, from two bars to three bars). Some devices will also have a selection of options that can be controlled with DMX, for example, the range to set an LED fixture to strobe could be between 20 and 30, so we would set that channel to a value of 25 (the fixture should be strobing now).

Here are a couple of resources you may find useful

Now you can amaze and astound your friends with you new found knowledge of DMX. Go out in the world and spread good things and make the place you live better.

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