Thoughts on the ATSC Standard and Program Numbers
By Trip Ericson on Monday, September 12 2011, 01:46 - Opinion - Permalink
On a thread on Radio-Info, friend W9WI brought up a point during a discussion on KCFG in Flagstaff, AZ:
"[A]lthough since they'd already be in violation of the ATSC standard, one couldn't rule out the use of program_number 1 instead of 3 as the standard calls for..."
I knew there was a rule something like this floating around but didn't have a citation for it. My impression had been that the PIDs were important and not the program number. To answer my own question in response to this, I did some digging. The rule is in ATSC standard A/53C, Part 3. In Section 6.9, the text reads:
"In order to avoid collisions with fixed PID values and ranges already established in this and other international standards, PID values used to identify Transport Stream packets carrying TS_program_map_section() or program elements shall not be set below 0x0030."
I might have missed it elsewhere in the document, but I can't find anything in the standard that requires the program number to be 3, only that the PIDs be no lower than 0x0030. I did find ATSC document A/58 (which is no longer valid) which states:
"DVB SI is carried in the MPEG-2 Transport Stream in PIDs 0x0010 through 0x0014. Therefore, it is recommended that when the program paradigm is used, Program Number 1 is not used. The lowest PID value that should be used to carry services is 0x0020, corresponding to Program Number 2.
It is noted that re-multiplexing equipment is capable of PID re-assignment, which necessarily involves rebuilding the Program Association Table (PAT) and Program Map Table (PMT) for each service in the multiplex. Such equipment can re-map PIDs to avoid 0x0010 through 0x0014, as long as no intrinsic meaning is carried in the Program Number value itself." [Emphasis mine.]
I read that to mean that program number 1 is a valid value so long as the PIDs in the range 0x0010-0x001F are not tied to it. For example, WCBS in New York has its program number set to 1, but uses 0x0030 for its PMT PID, 0x0031 for its VPID, and 0x0034/0x0035 for its APIDs. My interpretation is that this is a valid configuration under the cited ATSC rules.
Thoughts?
Comments
I obviously stand corrected about 3 as a minimum program number being part of the ATSC standard...
indeed, a scan of Trip's listings for Chicago shows only seven of the eighteen stations (including LPTVs) for which there are TSReader captures start with program 3. (the rest start with program 1, except WMAQ which starts with program 5.....) The figure is five out of twelve for full-power stations.
The numbers are very different here in Nashville, where eleven of the thirteen stations -- including all but one of the full-power stations -- start with program 3.
I think I confused a common practice with a standard.