Is It Unicast...or Multicast?

In the latter part of the last century (just feels kind of neat to say that-I'm actually referring to the year 1999), my company was involved in fairly extensive testing of live streaming via multicast distribution. I remember seeing the same 1.5 Megabit MPEG-1 stream playing off of an SGI server to dozens of PC screens simultaneously. Given that the intranet was a 10 Mbit LAN...this was impressive to say the least. The possibilities were exciting. Why? Well, to understand that, you need a primer on the inherent difference between Unicast and Multicast distribution of streaming media.

Unicast is the most common distribution method even today. It is a "one to one" method. For each PC accessing the stream, the bandwidth is compounded. As an example, if I were serving a 1.5 Megabit stream...and 10 PC's in an office sharing a T1 line tuned in simultaneously...well, the experience would certainly not be "like TV". Since every connection would require it's own individual 1.5 Mbit stream...all viewers would fall victim to simple math. The network would be choked.

Enter Multicast distribution. Multicast is a "one to many" distribution method wherein the source stream is simply replicated by routers on the network. Instead of compounding bandwidth for each viewer, the viewers simply "tune in" to the same 1.5 Mbit stream. Think of it as a broadcast on television. The difference is, that your viewers need to all be members of a "multicast group". Sounds simple and obviously desirable. But...there are security issues that have precluded the method becoming common place on the Internet. I'm certainly not qualified to explain in granular detail what those issues are. Just Google "multicast security issues" and you'll find many expert opinions.

Here's an analogy that might help: Imagine Unicast video of a corporate presentation being streamed to 20 viewers, each of whom have their own private TV screen and headphones on. Now, picture them in the middle of a room surrounded by passers by. Even though everyone in the room is in close proximity...they can't really see or hear the message well. Now, picture a video message streaming to a big screen in front of those same 20 viewers. No headphones this time, just big fat Bose surround-sound speakers. This time, everyone in the room can see and hear the message. While the video and audio are of a better quality...the message gets to anyone who happens to be in the room.

So, how do you take advantage of the network conservation benefit of IP Multicast while overcoming the obvious security risks that I have certainly over-simplified above? Well...

Fast forward to this century! It is my belief that there will be explosive growth and adoption of IP Multicast technology, especially by enterprise customers. There are a handful of companies who are making it possible to "multicast enable" your network so it provides the network benefits while reducing or eliminating the security risks.

You will still need publishing software, head-end capture hardware and many of the pieces and parts already used for Unicast streaming. But instead of your streams navigating a "contention based collision domain" to get to viewers...they will travel an easier, less congested path. Consider IP Multicast as an HOV lane on the information superhighway!