GB2393070A

GB2393070A - Monitoring service description tables of a compressed transport stream

Info

Publication number: GB2393070A
Application number: GB0221074A
Authority: GB
Inventors: Matthew Towler
Original assignee: Tektronix International Sales GmbH
Current assignee: Tektronix International Sales GmbH
Priority date: 2002-09-11
Filing date: 2002-09-11
Publication date: 2004-03-17
Also published as: GB0221074D0

Abstract

A compressed transport stream 20, comprising programs, is analysed to determine whether there are program identifiers in Service Description Tables (SDT) 10,11,12 of the transport stream for all of the programs in the transport stream. The transport stream is received to identify, in the transport stream, a program association table (PAT) containing a transport stream identifier and a plurality of program numbers, each of the plurality being associated with one of the programs respectively in the transport stream. A checklist 44 is generated from the PAT of the plurality of program numbers. The transport stream is analysed to detect a SDT containing a transport stream identifier and a second plurality of program numbers and associated program descriptions to determine whether for each member of the checklist for the transport identifier corresponding to the detected SDT there is a program number and program description in the SDT.

Description

Monitoring Service Description Tables of a compressed transport stream.

This invention relates to a method of monitoring Service Description Tables of a

compressed transport stream, and in particular of, but not restricted to, MPEG-2 based 5 streams.

A compressed transport stream, for example a MPEG-2 transport stream, typically carries multiple programs or channels. It is known for such transport streams to carry up to 150 programs. The transport stream comprises program elements in packets, each packet being identified by a Packet Identifier (PID). Program 10 Association Tables (PATs) are included as packets in the transport stream, which list, for each program, PIDs that identify Program Map Tables (PMTs) which describe the program and provide PIDs of constituents of a given program. Also included in the transport stream there are repeated instances of a Service Description Table (SDT)

describing each of the services or programs being transmitted by that transport stream, 15 including, for example, a program name for each service, which may be displayed at a receiver when a user receives a service. This is referred to as the actual SDT. For example, where the service is a broadcast television channel, the name of the channel may be displayed on a television receiver. There may also be included in the transport stream other SDTs giving details of services being transmitted in other transport 20 streams, for example at other radio frequencies, which are also receivable by the receiver. This provides the user the ability transparently to receive details of all receivable services without needing to be aware that they are transmitted in different transport streams, or in which transport streams they are transmitted.

The standard ETR 211 "Digital Video Broadcasting (DVB); DVB guidelines for 25 implementation and usage of Service Information (SI)", available from ETSI, 650 Route des Lucioles, F-06921 Sophia Sntipolis Cedex - France, makes the inclusion of an actual SDT mandatory and requires that the SDT of an actual transport stream shall list at least all the services or programs of that transport stream. In addition, any SDT for another transport stream than the actual transport stream in which the SDT is 30 transmitted shall list all the services or programs of that other transport stream.

Each of the programs transmitted in the transport stream is assigned a program number in the PAT and the respective program number also appears in the SDT, the program number, or service identity, being unique within each transport stream. These tables are repeated approximately every two seconds in the transport stream so that an 5 SDT is received within approximately 2 seconds of a user seeking details of programs being transmitted in the transport stream.

Monitoring and analysis of such compressed transport streams for the presence of such SDTs is known. For example, European Telecommunications Standards Institute standard TR 101 290 "Digital Video Broadcasting (DVB); Measurement 10 guidelines for DVB systems", available from ETSI, 650 Route des Lucioles, F-06921 Sophia Antipolis Cedex - France stipulates that an actual SDT should appear in the transport stream every two seconds. However, even although a transport stream may pass this basic test, this does not test whether the SDTs contain details of all the services being transmitted in the transport stream, as required by the standard. This 15 may result in a failure to name a program being received by failing to display the program identifier.

It is an object of the present invention to at least ameliorate the aforesaid disadvantage in the prior art.

According to a first aspect of the invention there is provided a method of testing 20 a compressed transport stream comprising programs, the method comprising the steps of: receiving the transport stream; identifying, in the transport stream, a program association table (PAT) containing a transport stream identifier and a plurality of program numbers, each of the plurality being associated with one of the programs respectively in the transport stream; generating from the PAT a checklist of the 25 plurality of program numbers; and analysing the transport stream to detect a Service Description Table (SDT) containing a transport stream identifier and a second

plurality of program numbers and associated program descriptions and determining

whether for each member of the checklist for the transport identifier corresponding to the detected SDT there is a program number and program description in the SDT.

30 Advantageously, the step of identifying a PAT includes detecting any version change in the PAT from a previously detected PAT and suspending analysis of the

transport stream for a first predetermined period of stream time around the PAT in which a version change is detected.

Conveniently, the step of analysing the transport stream includes detecting a version change in a SDT from a previously detected SDT and suspending analysis of 5 the transport stream for a second predetermined period of stream time around the SDT in which a version change is detected.

Alternatively, the step of analysing the transport stream to detect Service Description Tables comprises detecting a Virtual Channel Table (VCT) and

determining whether for each member of the checklist for the transport stream 10 identifier TSID of the VCT there is a program number and program description in the

VCT. According to a second aspect of the invention, there is provided a test apparatus for a compressed transport stream including programs, the apparatus comprising: a receiver for receiving the transport stream; identifying means for identifying, in the 15 transport stream, a program association table (PAT) containing a transport stream identifier and a plurality of program numbers, each of the plurality being associated with one of the programs respectively in the transport stream; list generating means for generating from the PAT a checklist of the plurality of program numbers; and analysing means for analysing the transport stream to detect a Service Description

20 Table (SDT) containing a transport stream identifier and a second plurality of program numbers and associated program descriptions and for determining whether

for each member of the checklist for the transport identifier corresponding to the detected SDT there is a program number and program description in the SDT.

The invention will now be described, by way of example, with reference to the 25 accompanying drawings, in which: Figure 1 is a conceptual diagram of actual and other Service Description Tables

of a transport stream suitable for analysis by the invention; Figure 2 is a conceptual diagram of packet identifiers in the transport stream of Figure 1;

Figure 3 is a flowchart of steps of the present invention; and Figure 4 is a conceptual diagram of the apparatus of the invention.

Referring to Figures 1 and 2, a transport stream contains an actual Service Description Table 10, identified as such by Table Identifier = 42, containing a

5 transport stream identifier 101 and details of services or programs carried by the transport stream, including program identifiers 102 for each program number. There may also be other SDTs 11, 12 in the transport stream relating to programs in other transport streams. Because program numbers are only unique to a transport stream, there may be identical program numbers with different program identifiers in different 10 SDTs.

As illustrated in Figure 2, since the actual SDTs 20 with Table Identifier equal to 42 are dispersed and repeated throughout the transport stream, within a given time period, say every two seconds, a packet containing an SDT section should be received, and this is all that is tested in the prior art.

15 Therefore, although in the prior art it is checked that service description tables

are regularly received, it is not ascertained that they are the correct tables or that all the required program identifiers are present. If incorrect tables are received, or some tables are not received at all, a receiver will be unable to display, either temporarily or permanently, one or more program identifiers.

20 As shown in Figures 3 and 4, in the test of the invention, additional steps are carried out to determine that all required program identifiers are present in the transport stream.

A transport stream is received, step 31, by a receiver 41 and the Program Association Tables are identified, step 32, for example by their inclusion in the 25 transport stream in packets with a PID of zero and table identifiers being equal to zero. The Transport Identifier and Program numbers are extracted, step 33, from the Program Association Tables by a list generator 43 to form a list 44 of Program numbers for the Transport Identifier.

Service Description Tables in the transport stream are analysed, step 34, against

the Program Numbers list 44 by an analyser 45 to ascertain whether for each of the Program Numbers in the list there is a corresponding Program Number and Program Identifier entry in the Service Description Tables for the subject Transport Identifier.

5 By listing with their corresponding Transport Identifiers the Program numbers for all receivable transport stream it is apparent that completeness of both the actual and other SDTs may be analysed.

If a Program Descriptor is found to be missing, an alert or other warning is provided on a user interface 46. Reparative action may then be initiated.

10 A special situation arises where programs are added, removed or adjusted within the transport stream. Such changes must be reflected in a version change in the Program Association Tables and Service Description Tables, but the changes cannot

be made simultaneously in both types of table. This is particularly so because the SDT can be large and take a considerable time to be received or to be updated. Partly 15 because the order of packets may change during transmission, it cannot be predicted whether an updated Program Association Table or an updated Service Description

Table will be received first by a receiver. Therefore a false error may be detected because an updated Program Association Table may be incompatible with a Service Description Table which has not been updated, and vice versa.

20 The versions of the tables are reflected in version numbers carried within the tables, which are updated for each version change. In an embodiment of the invention, when a version change is detected in a table, the test is suspended and not applied to the transport stream for a predetermined period of stream time both before and after the version change. The test is conveniently suspended for a user-adjustable period of 25 1 second of the transport stream both before and after the version change.

It will be apparent that the invention has applicability not only to Digital Video

Broadcasting (DVB) systems but also at least to other transport streams having MPEG-2 based compression. For example, according to ATSC Standard A/65 "Program and System Information Protocol (PSIP) for Terrestrial Broadcast and 30 Cable" there are required to be PS1P tables in a transport stream complying with the standard which describe all the digital channels multiplexed in the transport stream.

The tables may optionally include information about analogue channels as well as other digital channels available in different transport streams. In this case the consistency test of the invention is passed if for all programs listed in the PAT there is an entry in a Virtual Channel Table (VCT) whose program number matches that in the 5 PAT and whose channel Transport Stream Identifier (TSID) matches the PAT. That is, the test checks that the VCT does contain a description for all the programs in the

multiplexed transport stream.

Claims

-7 CLAT1\iS 1. A method of testing a compressed transport stream

comprising programs, the method comprising the steps of: a. receiving the transport stream; b. identifying, in the transport stream, a program association table (PAT) containing a transport stream identifier and a plurality of program numbers, each of the plurality being associated with one of the programs respectively in the transport stream; c. generating from the PAT a checklist of members, each member representative of a respective one of the plurality of program numbers; and d. analysing the transport stream to detect a Service Description Table (SDT)

containing a transport stream identifier and a second plurality of program numbers and associated program descriptions and determining whether for

each member of the checklist for the transport stream identifier corresponding to the detected SDT there is a program number and program description in the SDT.
2. A method as claimed in claim I, wherein the step of identifying a PAT includes detecting any version change in the PAT from a previously detected PAT and suspending analysis of the transport stream for a first predetermined period of stream time around the PAT in which a version change is detected.
3. A method as claimed in claim 2, wherein the step of analysing the transport stream includes detecting a version change in a SDT from a previously detected SDT and suspending analysis of the transport stream for a second predetermined period of stream time around the SDT in which a version change is detected.
4. A method as claimed in claim I, wherein the step of analysing the transport stream to detect Service Description Tables comprises detecting a Virtual Channel

Table (VCT) and determining whether for each member of the checklist for the transport stream identifier TSID of the VCT there is a program number and program description in the VCT.

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5. A test apparatus for a compressed transport stream including programs, the apparatus comprising: a receiver for receiving the transport stream; identifying means for identifying, in the transport stream, a program association table (PAT) containing a transport stream identifier and a plurality of program numbers, each of the plurality being associated with one of the programs respectively in the transport stream; list generating means for generating from the PAT a checklist comprising members each representative of a respective one of the plurality of program numbers; and analysing means for analysing the transport stream to detect a Service Description Table (SDT)

containing a transport stream identifier and a second plurality of program numbers and associated program descriptions and for determining whether for each member of

the checklist for the transport identifier corresponding to the detected SDT there is a program number and program description in the SDT.
6. A test apparatus as claimed in claim 5, wherein the identifying means is adapted for detecting any version change in the PAT from a previously detected PAT and the analysing means is adapted for suspending analysis of the transport stream for a first predetermined period of stream time around the PAT in which a version change is detected.
7. A test apparatus as claimed in claim 6, wherein the analysing means is adapted for detecting a version change in a SDT from a previously detected SDT and suspending analysis of the transport stream for a second predetermined period of stream time around the SDT in which a version change is detected.
8. A test apparatus as claimed in claim 5, wherein the analysing means is adapted for detecting a Virtual Channel Table (VCT) and determining whether for each member of the checklist for the transport stream identifier (TSID) of the VCT there is a program number and program description in the VCT.
9. A method substantially as herein described with reference to and as shown in Figures 3 and 4 of the accompanying drawings.
10. A test apparatus substantially as herein described with reference to and as shown in Figures 3 and 4 of the accompanying drawings.