ANSI SCTE 142:2017 pdf free download – Recommended Practice for Transport Stream Verification
5.0 INTRODUCTION
The SCTE and ATSC standards define the contents and characteristics of the emission Transport Stream. There may be a large number of interactions and interrelationships amongst various components. Successful tuning and display of programs can be enabled if this Transport Stream adheres to the SCTE standards. The connection between the emission remultiplexer and the QAM modulator is the reference analysis point assumed in this document, as shown in Figure 1. Please note that this diagram shows only a conceptual, functional block view of a DTV system. In practice, actual implementations will only share MPEG data with other devices using the MPEG-2 Transport Stream (TS), as Elementary Streams (ES) or Packetized Elementary Streams (PES) cannot tolerate the introduction of any transmission errors and once synchronization is lost the system crashes. Furthermore, real systems may group the functions in different ways and will likely appear different on an electrical or physical block diagram. This Standard uses terms and acronyms defined in ISO 13818-1 [14], A/53-3 [5] and A/65 [6], and assumes a fair degree of familiarity with MPEG-2 systems as implemented per the SCTE standards. Readers that do not recognize the terms should read A/54A [17], A/69 [10], SCTE 54 [2], and SCTE 65 [3].
6.1 Regarding
“Technically Non-Conformant” error handling Considering these classes of errors, particular attention needs to be paid to the “TNC” or “Technically Non-Conformant” class. In Standards as complex as MPEG-2 and those from the SCTE, situations arise where two “shall” statements collide. At such junctures, the Transport Stream (TS) may be momentarily non-conformant. An example of this might be “PAT repetition error” (see Section 7.1). If the multiplexer is faced with a choice of outputting a packet carrying a PTS on a video PID on the schedule required by Section 11.2 or a repetition of the PAT within the requirements of Section 7.1, an implementer may choose to output the PTS sample rather than the PAT. Either way, the TS is for a moment non-conformant. Neither choice of non-conformance will affect any real-world receivers. Neither will result in disruption of service. Either will be non-conformant. There is no avoiding these conflicts, and they arise periodically in real-world equipment. Should a manufacturer of MPEG analysis equipment choose to make either of these errors the cause of an operator alarm, after multiple false alarms the operator may ignore all alarms. That is not desirable. A number of the possible errors within this Section fall into these categories. While a continuous occurrence of any should constitute an operator alarm, a single occurrence of any should (as indicated by the table) be treated merely as a minor problem, which, unless re-occurring, is not significant.
7.0 PSI ERRORS
An SCTE transport stream is also required to be MPEG-2 conformant (see Section 5 in reference [15]). Therefore, an SCTE transport stream must include the two mandatory Program Specific Information (PSI) tables. These two tables are known as the Program Association Table (PAT) and the Program Map Table (PMT). The syntax is defined within ISO/IEC 13818-1 [14]. The maximum interval for the PAT is specified in the SCTE standards as 100 ms. The maximum interval for the PMT is specified in the SCTE standards as 400 ms. Exceeding the interval on each of these tables by a small amount should not have a major impact on a receiver, especially since each SCTE conformant receiver should be able to fully tune to any SCTE channel through the use of the SCTE SI tables.