Once upon a time, changing channels on the TV meant standing up, walking to the television, and turning the dial. Another channel appeared, usually the second of three available channels, maybe four.
Then came the wired remote. From the Barcalounger, you pushed a button on a brick-sized object hard-wired to the television, and another channel appeared - the second of maybe 12 channels.
Next: the cordless remote. Whether it came with the settop box, the TV or both (which spawned the age of “remote clutter”), you pointed the thing at the TV, pushed a button, and something else appeared on the screen. Maybe it was another channel, or a grid guide, or an on-demand menu.
Right now, at this very moment, the channel change is changing again (the plumbing of it, anyway).
No surprise: It’s yet another tangent in the ongoing story that is video-over-IP.
First is how the zapper zaps. Most set-tops and TVs right now use infrared to signal back and forth with the remote. What’s coming next: The use of Wi-Fi, Bluetooth and RF (radio frequency) to switch channels. This means you won’t have to point the remote (or the iPad, or the BlackBerry) at the TV. Note: This is weird at first, but great when the dog is standing between you and the TV.
Then, there’s the back-end plumbing. Let’s start off by noting this only affects channels moving through a video switch or a CMTS (cable-modem termination system, the shepherd of IP traffic in cable: it’s also a switch).
Here’s how it works on today’s switched digital-video systems. You change channels with the remote. Your click goes into your set-top box, which pops it upstream to the switch.
If anyone in your “service group,” or neighborhood node, is watching what you asked for, the switch responds by telling your set-top what frequency and “PID” (packet ID) to tune.
If not, the switch consults a thing called an “SRM,” for “session-resource manager.” It grabs the PIDs of the channel you want to watch, then says how that stream gets back to your house - over what frequencies, on which edge QAMs (quadrature amplitude modulators).
In the world of IP, the channel change is known as “joining a stream.” There is no broadcast in IP - only “multicast.” Instead of one to all, it’s one to many. “Joining a stream,” in the multicast world, sends you your stream using a protocol called “IGMP,” for Internet Group Multicast Protocol.
Note that IGMP isn’t all that widely deployed, mostly because there’s not so much multicast video moving over the Internet - it’s more on-demand and point-to-point. “Unicast,” in IP speak. In cable, the logical place for channel changing on the IP side of the network is within the work CableLabs is doing within the “PacketCable Multimedia” (PCMM) group. People tend to correlate PacketCable with voice, but “PCMM” grew since then. It supports both unicast and multicast delivery protocols - but isn’t “gear” yet.
In any case, you still won’t have to stand up to change the channel.