I was fortunate enough to look in on the tech rehearsals for a major Broadway show recently. I was blown away by the technology on parade, not so much on stage as in the house. In what looked like a scene from a science fiction movie, almost every seat in the orchestra section was covered with sheets of plywood, each of which served as a table top for a couple of computer work stations.
Each workstation had two or three computer monitors and some type of computer, whether it was a console, controller, laptop, or some other silicon-filled box. Behind each of these workstations sat various programmers, assistants, producers, directors, techs and other unidentified personnel.
To witness the sea of glowing monitors in what was otherwise a complete blackout was more fun than any dark ride at Disney. It served as a stark reminder that this computer thing is not a fad. But that's not new, at least not in the last 25 years. What is new, however, is the proliferation of local area networks (LANs) and our increasing insistence on linking two or more computers, controllers or consoles. That will be happening more and more as computers become even more powerful, affordable, and as software continues to be more highly developed.
The savvy techs among us are already tuned in to networking; how to build them, how to configure them and how to troubleshoot them. The rest of us had better figure it out soon. I recently used a programming wing and a playback wing that had no other means of connection other than an RJ-45 connector. I had to use a network switch to connect them to a PC-based lighting controller. As more devices in our industry are being networked and require network configuration, we need to understand the basics of networking including IP addressing and subnet masking.
An internet protocol (IP) address is a way of telling every other device on a network exactly where a particular device can be reached over an IP network. In some ways, it's similar to the way your mail delivery person uses your house address to deliver your mail, except that computer data sent to you is never delivered to your neighbor's computer by mistake, and an IP network doesn't take the day off for holidays.
Like your street address, which has a street number and name and a postal code, an IP address has a couple of parts. There's a network part and a "host" part. Think of the network part of an IP address as the postal code. It routes data to the right general area but not straight to your door. Then there's the host part, which identifies the exact location of the host or the computer to which the data is intended.
Unlike a postal code, the network portion of an IP address is variable in length, depending on the size of the network. IP addresses are currently formatted in what's called "quad-dotted decimal notation." That's a geeky way of saying it has four segments, each of which are separated by a dot, and although a computer sees them as an eight-bit binary number, we notate it in decimal because it's much easier for humans to read. So IP addresses range from 0.0.0.0 to 256.256.256.256. If the network is to accommodate, say, 32 computers, then the host portion will need to be able to represent 32 unique numbers in binary. That takes five bits because 00000 in binary is 0 in decimal and 11111 in binary is 31 in decimal. Since the entire IP address is 32 bits long, that leaves 27 bits for the network portion of the IP address.
All of the computers or devices that are connected on the same data link have matching network prefixes, meaning that the first portions of their IP addresses are the same. That allows the network to filter data according to where it's going using a bridge or a switch. It's something like the way your letters and all other mail addressed to the same postal code go to the same post office before being delivered to the proper mailbox. Or, in the case of the U.S. mail, it might go somewhere in the vicinity of the proper mailbox.
To make it the last mile to your mailbox, the bridge or network switch is configured with what's called a subnet mask, which logically breaks the IP address into its two components – the network portion and the host portion. It does it by performing what's called a logical AND operation with the destination IP address. An AND operation is when two or more digital bits are compared and the result is a logical 1 if, and only if, all of the bits being compared are a logical 1. For example: 0 AND 1 is 0; 1 AND 0 is 0; 1 AND 1 is 1.
The subnet mask is in the same format as the IP address; it's a series of 0s and 1s in quad-dotted decimal notation. The prefix of the subnet mask is always a series of 1s and the suffix is a series of 0s. The number of 1s and 0s depends on how many hosts there are: for two hosts there is one 0; for four there are two; for eight there are three, etc. By performing an AND operation with the IP address, the result is the network portion and the remainder is the host portion.
Once the two portions of the IP address are determined, then the data can be routed to the proper destination. The subnet mask works like the key to your mailbox, except it uses digital tumblers instead of physical ones. The subnet mask is important because it helps reduce the traffic on a data link. If all the data in the world had to pass through the cable connected to your computer, then you would never be able to send or receive any data. The network would choke worse than the 1951 Brooklyn Dodgers. By filtering out data with mismatching IP addresses the network runs faster and better.
Faster computers, faster networks, and more savvy techs all add up to more and more dependence on computers and better shows. The next time you see a Broadway show, think of all the 0s and 1s they had to move around to make the show happen.
