Program Streams, Channel numbers, and Setup
In 1957 WFSB began broadcasting in Hartford CT as the local CBS affiliate on Channel 3. Over the next 50 years it built a brand name around "Channel 3", painting its logo on the side of its news trucks and repeating the name in commercials and newscasts. When the FCC began the transition to digital TV, it assigned WFSB a second frequency of channel 33 for its digital signals, and the primary (HD) transmission was assigned Program ID 3 (making it 33-3 in most notations). At the end of the transition, Channel 3 stopped broadcasting on the frequency for channel 3.
To make things worse, on Comcast cable in New Haven WFSB is transmitted on physical cable channel frequency 134 under Program ID 18 (134-18). However, in all the program listings and documentation, it is associated with a cable set top box channel number of 233.
Despite all this technical reality, three things are true.
- Having built up the brand name for 50 years, WFSB does not want to change its "Channel 3" name, or its logo, or repaint its trucks. Even if it no longer has anything to do with the physical broadcast frequency associated with channel 3, it would like to pretend nothing has changed.
- In Connecticut, the millions of people who have been watching Channel 3 all their lives do not want to learn anything new.
- Everyone from the FCC to Sony wants the consumer to still be able to buy a TV set at Costco, take it home, hook it up to the same antenna or TV cable, and have it just work today the same as TV sets have always worked in the past.
The trick that makes this possible is that digital TV, whether broadcast over the air or on a cable, is just a digital sequence of data packets. Most of those packets contain picture or sound, but there is an ability to send control data and to have the TV set or cable set top box respond to the data. The protocol is called PSIP (Program and System Information Protocol). Every so often the TV channel or cable system sends a PSIP packet to any TV set or cable box listening.
After you buy a new TV set (or move to a new area) you hook the TV up to the antenna or cable and tell it to do a channel scan. It runs once through all the possible channel frequencies looking for usable signals and PSIP data. If you connect to an antenna, then when the TV gets to channel frequency 33 it will find a good signal and within a second read a PSIP message saying that when it displays the program stream from this frequency with program ID 3 that it should display to the user that this is channel "3.1". Generally speaking, the TV will rearrange the order of channels to correspond to the number being displayed (3) instead of the real frequency (33) when the user presses the Next Channel and Previous Channel (or Channel Up/Down) on the remote control. As a result, after the channel scan the TV, thanks to the PSIP data, pretends to the user that all the new digital channels have the same old numbers they had 30 years ago instead of the actual frequencies they are currently broadcasting on.
Things get a bit more complicated with you connect a digital TV set that is "Clear QAM" capable directly to Comcast Cable without a set top box and ask it to do a channel scan. Comcast combines two or more broadcast program streams on the same channel cable frequency, and they may translate the program ID that the broadcaster uses to a different program ID number. So Comcast cannot simply copy the broadcast PSIP data but instead has to generate its own version of PSIP on each cable channel. However, it can still play the same game of pretend. So when the TV set tunes to the frequency for cable channel 134 it gets a PSIP message saying that program ID 18 is to be displayed as "3.1".
There was a bit of uncertainty about how PSIP was going to be used on cable channels, and some providers may not have gotten it right. However, the emerging convention is for the cable channels to produce the same result as antenna broadcasts, so after a cable ready Clear QAM TV complete scanning all the cable channels, it will appear to the end user to have exactly the same channels (and maybe a few extra) with exactly the same numbers at least for the channels that have a broadcast ID. Of course, Comcast wants to earn a few extra dollars in profit so it will always add the QVC shopping channels and any other content it gets paid to broadcast, or the community origination that it is obligated by government regulation to distribute, and since this stuff doesn't have a broadcast channel number it gets some other identification that doesn't collide with the real broadcast channels.
If you have a set top box, or a device with a CableCard plugged in, then the same program stream will be identified by the three digit made up "cable channel number", which in the case of Comcast in Connecticut is channel 233 for WFSB "Channel 3" in HD.
Your Cable Company may Blindside You
Once you finally get your channel scan working, you are set until your cable company decides to move things around. It may move programs from one frequency to another to consolidate or improve its management. Sometimes it just changes things to change things. The last time Comcast in New Haven changed the channel scan layout was three or four years ago, but then one day after this page was updated with Fall 2011 information they did it again unannounced. Suddenly the WFSB CBS programming simply disappeared from the cable.
It turned out that Comcast had changed the program ID but not the frequency on the program streams on cable channel 134. WFSB had previously been 134-18 and suddenly changed to be 134-2. This is not a problem for anything that uses a CableCard because they update automatically. However, TV sets connected directly to the cable and any digital TV tuners connected to PCs have to be reprogrammed, generally by repeating the channel scan and then repeating all the manual fixups. Fortunately, this doesn't happen often.
The EPG (Electronic Programming Guide)
With a modern Digital Video Recorder, whether it is built into the cable set top box, or purchased as a Tivo, or provided by Windows 7 Media Center, you get an internet delivered TV Guide for the next 10 to 14 days. Using the computer or the TV remote control you can browse through the program listings and select which shows and series you want to record.
If you use an antenna then you will want to see a program guide for over the air (OTA) broadcast. You will probably see channels listed by their virtual number rather than their physical frequency, so WFSB will be listed as 3.1 even through it is physically 33-3. Similarly, if you connect to a cable system, then you will probably want the EPG based on your cable company virtual channel numbers where WFSB is listed as 233.
The EPG has a lot of information about the shows themselves. Each series has a title, description, and the regular cast. Then each episode of a series has a title, description, and guest stars. If it is a repeat, there will be the date the episode first aired. Movies have the year they were released. Sports shows have the teams and location of the game. All this stuff is the same no matter how you receive the data (OTA, cable, or satellite) and no matter where you are or which cable company you use.
So the EPG data transmitted over the internet to your computer or device is broken up into sections. One part describes the programming that is broadcast in a time period that is pretty much the same for everyone. This will contain an entry saying that a particular episode of "NCIS" is broadcast at 8:00 PM Eastern Time on Tuesday on CBS. Then there will be a customized channel lineup for your area and cable company. It would say that your CBS station is WFSB and that it is virtual channel "3.1" (OTA) or virtual channel 233 (Comcast Cable). That is as far as the EPG can go. The last piece, where virtual channel 3.1 is associated with physical 33-3 or virtual channel 233 is associated with physical 134-18 has to be programming into your Tivo or Windows Media Center by the Channel Scan and setup because the central EPG data doesn't know about your personal equipment setup.
If you have an OTA antenna setup, the EPG will list all the channels it thinks you might be able to find. Sometimes it is wrong, typically by listing a bunch of channels that are too far away for you to really receive. So you many manually delete them so your EPG reflects reality.
If you use a CableCard device like a Tivo, SiliconDust Prime, or Hauppauge 2650 then the CableCard gets programmed by the cable company so it exactly knows the channel lineup just like a set top box. You will see CBS on 233 and never be exposed to physical channel frequencies.
However, if you connect to cable TV with a Clear QAM device that picks up unencrypted network broadcast HD channels on cable, then you may have to do all the configuration yourself. The problem here is that the PSIP data may be incomplete, contradictory, or misleading. In fact, the PSIP data may be different for different channels. PSIP has historically been used to configure the TV set to display some information about a particular channel/datastream. When cable systems program their own set top boxes and CableCards, they may use a different data stream than the one your SiliconDust device finds during a channel scan.
Therefore, the CBS data signal may be labelled as "WFSB", "WFSBDT", "WFSB-DT", or even "WFSB HD" in the PSIP stream, and the computer may have trouble associating this lable with a particular entry in the EPG. Furthermore, even though this is a cable system, the PSIP data your device receives may declare that the virtual channel number is "3.1" like it was an over the air broadcast.
Tivo has to be a consumer device that works automatically no matter what. So part of what you are paying for is that the central Tivo system you connect to knows ever cable company in the country and configures your device automatically without any intervention. If you decide to save the montly subscription cost (or the lifetime subscript which can amount to $600) and use Windows Media Center yourself, you may have to manually go back after the automatic scan and fix the labels and virtual channel numbers yourself.
Digital Channel Change Delay
When each TV frequency was an analog TV station, a TV set could begin to display the new channel immediately. However, when a digital tuner switches channels, it must select the right frequency and then wait a few seconds for the master packet to appear. Then you get the program data and start receiving packets of video data.
Unfortunately, since the video data is compressed you simply can't start in the middle of a compression sequence. Once every 3 seconds or so the compression resets and you can start viewing at that reset point. So changing channels on a digital system involves a few second delay to get the program data stream info, and then a few more seconds to get to a video reset point.
So the couch potato who used to flip through channels as fast as possible may be annoyed by the switch to digital technology. He has been annoying the rest of us for years, so I suppose this is OK.
The Google Wild Card
In 2011 Google purchased the part of the Motorola business that builds set top boxes. They also purchased SageTV, one of the best PC TV recording and viewing software products. So far, no resulting hardware or software has been announced.
Google is in the business of indexing, integrating, and delivering information that is already out there somewhere on the internet or in the public domain. TV is not in the public domain, but it is data that is probably already delivered to every household. Google has the resources to clean up a lot of these loose ends and simplify the configuration and use of modern TV technology. We look forward to announcements in this area.