transport_stream_identifier [MPEG-2 Semantics]
To distinguish each transport stream within a single network (terrestrial, cable or satellite) from another, MPEG-2 established the use of a 16-bit (ranging from 0 to 65535) transport_stream_identifier, which is also called a tsid. MPEG-2 left the assignment of tsids to MPEG-2 users, like DVB, ATSC, SCTE and ARIB.
The ATSC decided not to assign individual tsids, and left that up to others. Initially, tsids for U.S. ATSC stations were issued by the Association of Maximum Service Television (MST), but in recent years tsid granting authority was transferred to the Federal Communications Commission (FCC) for stations operating within the United States. Within Canada, that authority would seem to be the responsibility of the Canadian Radio and Television Commission (CRC), and within Mexico, the respective authority was vested in COFETEL, a unit of the Mexican Secretariat of Communications and Transportation.
In the United States, a simple scheme was established. Analog television stations were each given a unique tsid (technically called a television station identifier) that was even divisible by two. Where the analog station temporarily had a digital companion channel, that was an odd number which was one greater than the analog tsid.
However, tsid 0 and 1 were not assigned and are used for "default" situations.
Technically, the only cases where tsids need to be coordinated with other countries are when there is a possibility that a television station or digital transport could be received terrestrially across a border, such as along the common U.S. borders with Canada on the North and Mexico on the South.
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