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,
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