System and method for multiplexing a plurality of digital program services for transmission to remote locations

• US 5,319,707 A
• Filed: 11/02/1992
• Issued: 06/07/1994
• Est. Priority Date: 11/02/1992
• Status: Expired due to Fees

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta (Cisco Systems, Inc.)
• Inventors: Wasilewski, Anthony J., Bagley, Julius B.
• Primary Examiner(s): Cain, David C.
• Application Number:
  US07/970,918
• Time in Patent Office: 582 Days
• Field of Search: 380/10, 380/14, 380/13, 380/15, 380/19
• US Class Current: 380/212
• CPC Class Codes: H04N 21/2221 being a cable television head-end CATV in broadcast systems H04H20/78
• CPC Class Codes: H04N 21/2347 involving video stream encryption
• CPC Class Codes: H04N 21/23608 Remultiplexing multiplex streams, e.g. involving modifying time stamps or remapping the packet identifiers
• CPC Class Codes: H04N 21/23614 Multiplexing of additional data and video streams arrangements for simultaneous broadcast of plural pieces of information H04H20/28
• CPC Class Codes: H04N 21/2362 Generation or processing of Service Information [SI]
• CPC Class Codes: H04N 21/2365 Multiplexing of several video streams
• CPC Class Codes: H04N 21/4345 Extraction or processing of SI, e.g. extracting service information from an MPEG stream
• CPC Class Codes: H04N 21/4347 Demultiplexing of several video streams
• CPC Class Codes: H04N 21/4405 involving video stream decryption
• CPC Class Codes: H04N 21/6332 directed to client
• CPC Class Codes: H04N 7/1675 Providing digital key or authorisation information for generation or regeneration of the scrambling sequence pseudo-random number generators in general G06F7/58

Abstract

A system and method for multiplexing a plurality of digital programs for transmission to a plurality of remote locations is claimed. An encoder is provided that first generates a plurality of subframe data streams each comprising a continuous sequence of subframes. Each subframe in each subframe data stream comprises at least a transport layer region and a program data region. For each subframe data stream, portions of the program data region of each of the subframes in that subframe data stream are allocated to selected ones of the plurality of programs. Mapping information is provided in the transport layer region of each subframe for use by a decoder in extracting a selected program from each subframe. A multiplex data stream is then generated at the encoder that comprises a continuous sequence of superframes. Each superframe comprises a superframe transport layer region and a subframe data region. A portion of the subframe data region of each superframe is allocated to at least one subframe from each of the plurality of subframe data streams. A superframe map is then generated and transmitted with each superframe that specifies at least the location of each subframe within the superframe. The multiplex data stream is then transmitted to the plurality of remote locations. According to one embodiment, at an intermediate location, subframe data streams may be extracted from one multiplex data stream for re-routing within other multiplex data streams.

Claims

1. A method of combining a plurality of digital programs into a multiplex data stream for transmitting said programs from an origination point to at least one remote location, wherein each program comprises a single bit stream containing a combination of related digital services, said method comprising the steps of:

a) multiplexing selected ones of the digital programs to generate a subframe data stream having a format comprising a continuous sequence of subframes different portions of each subframe being allocated to different ones of said digital programs;

b) generating for each subframe a subframe multiplex map that at least indirectly specifies which portions of that subframe are allocated to which of said selected digital programs, and inserting the subframe multiplex map in the subframe;

c) repeating step (a) and (b) a selected number of times, each time for different selected ones of said digital programs, thereby generating a plurality of subframe data streams each containing different ones of said digital programs and each comprising a continuous sequence of subframes;

d) multiplexing selected ones of the subframe data streams to generate said multiplex data stream, said multiplex data stream having a format comprising a continuous sequence of superframes, each superframe containing at least one subframe from at least one of said selected subframe data streams; and

e) generating, for each superframe in the multiplex data stream, a superframe map that specifies the location of each subframe within that superframe, and inserting the superframe map in that superframe.

2. A method according to claim 1 wherein each subframe has a format comprising a plurality of lines, a first group of lines in each subframe defining a subframe transport layer region and a second group of lines defining a program data region, and wherein step (a) comprises performing the following steps for each subframe:

(i) partitioning the program data region of the subframe into a plurality of program data packets;

(ii) allocating different portions of each program data packet in the subframe to different ones of said programs;

(iii) generating a program multiplex control packet that specifies which portions of each program data packet in the subframe are allocated to which programs; and

(iv) inserting the program multiplex control packet in the transport layer region of the subframe, the subframe multiplex map generated in step (b) for that subframe specifying the location of the program multiplex control packet within the transport layer region.

3. A method according to claim 2 wherein each of said programs has a respective data rate, and wherein step (a)(ii) comprises allocating different portions of each program data packet to different ones of said programs in proportion to the respective data rates of said programs.

4. A method according to claim 3 further comprising the step of adjusting, on a per subframe basis, the size of the portions allocated to each program as the respective data rates of the programs change.

5. A method according to claim 2 further comprising the step of:

(a'"'"') generating a plurality of system related data packets including system data packets (SDP'"'"'s), system teletext packets (STT'"'"'s), addressable data packets (ADP'"'"'s), service seed packets (SSP'"'"'s) and program virtual channel map packets (PVCMP'"'"'s); and

(b'"'"') inserting selected ones of said system related data packets in the transport layer region of each subframe, the subframe multiplex map generated in step (b) for each subframe specifying the location of each system related data packet inserted within the transport layer region of that subframe.

6. A method according to claim 1 wherein each superframe has a format comprising an adjustable number of successive blocks, a first portion of each block comprising a block synchronization byte (BSYNC), a second portion of each block comprising a data portion, and a last portion of each block comprising a block error code generated in accordance with a block error coding scheme.

7. A method according to claim 6 wherein a first group of blocks in each superframe define a superframe transport layer region of that superframe, and a second group of blocks define a subframe data region, the superframe map generated for each superframe being inserted in the superframe transport layer region of that superframe.

8. A method according to claim 7 wherein each subframe has a format comprising a plurality of lines, and wherein the data portion of each block in the subframe data region of each superframe contains a single line of one of the subframes in that superframe.

9. A method according to claim 6 further comprising the step of inserting, in a first block of each superframe, a superframe synchronization word (FSYNC), and wherein the superframe map for each superframe is inserted in the superframe immediately following the superframe synchronization word.

10. A method according to claim 1 wherein each superframe has a format comprising an adjustable number of successive blocks, a first group of blocks in each superframe defining a superframe transport layer region of that superframe, and a second group of blocks defining a subframe data region, said method further comprising the steps of:

(i) generating a subframe virtual channel map packet that contains information that specifies, for each program, which subframe data stream contains that program; and

(ii) periodically inserting the subframe virtual channel map packet in the transport layer region of one of the successive superframes, the superframe map for each superframe into which the subframe virtual channel map is inserted further specifying the location of the subframe virtual channel map packet within the transport layer region of that superframe.

11. A method according to claim 1 further comprising the step of transmitting successive superframes of said multiplex data stream at a constant rate.

12. A method according to claim 6 wherein each block comprises a predetermined number of bits, and wherein said method further comprises the step of transmitting successive superframes of said multiplex data stream at a constant rate such that the multiplex data stream is transmitted at a bit rage equal to F_SF (n)(B) bits per second, where F_SF is the rate at which successive superframes are transmitted, n is the number of blocks in each superframe, and b is the number of bits in each block.

13. A method of decoding a multiplex data stream of the type recited in claim 1, said method comprising the steps of:

a) receiving the multiplex data stream and selecting one of said programs;

b) determining which subframe data stream contains the selected program;

c) for each successive superframe of the received multiplex data stream, performing the following steps;

(i) extracting the superframe map from the superframe and determining from the extracted superframe map the location of each subframe within that superframe; and

(ii) extracting from the superframe the subframe in that superframe that is one of the subframes of the subframe data stream that contains the selected program;

d) for each subframe extracted in step (c)(ii), performing the following steps;

(i) extracting the subframe multiplex map from the subframe and identifying, based at least in-part upon information contained within that multiplex map, which portion of the subframe is allocated to the selected program; and

(ii) extracting the identified portion from the subframe; and

e) combining the portions extracted from each subframe in step (d)(ii) to reconstruct the selected program.

14. A method according to claim 13 wherein the multiplex data stream contains mapping information that specifies, for each program, which subframe data stream contains that program, and wherein step (b) comprises:

(i) extracting the mapping information from the received multiplex data stream; and

(ii) determining from the extracted mapping information which of the subframe data streams contains the selected program.

15. A method according to claim 13 wherein each subframe of each subframe data stream has a format comprising a plurality of successive lines, a first group of lines in each subframe defining a transport layer region of that subframe and a second group of lines defining a program data region, and wherein the program data region of each subframe is partitioned into a plurality of program data packets and different portions of each program data packet are allocated to different ones of said programs, and further wherein the transport layer region of each subframe contains a program multiplex control packet that specifies which portions of each program data packet in that subframe are allocated to which programs and the subframe multiplex map in each subframe specifies the location, within the transport layer region, of the program multiplex control packet for that subframe, and still further wherein step (d) comprises performing the following steps for each subframe:

(i) extracting the subframe multiplex map from the subframe and determining therefrom the location of the program multiplex control packet within the transport layer region of the subframe;

(ii) extracting the located program multiplex control packet from the transport layer region;

(iii) identifying, based upon the extracted program multiplex control packet, which portion of each program data packet of the subframe is allocated to the selected program; and

(iv) extracting the portion identified in step (d)(iii) from each of the program data packets in the subframe.

16. An encoder apparatus for combining a plurality of digital programs into a multiplex data stream, wherein each program comprises a single bit stream containing a combination of related digital services, said encoder comprising:

a control computer for controlling the operation of the encoder;

a plurality of subframe multiplexers, each coupled to the control computer and each being coupled to receive a respective group of said programs, each subframe multiplexer being operative to multiplex its respective group of programs to form a subframe data stream having a format comprising a continuous sequence of subframes wherein different portions of each subframe are allocated to different ones of said respective group of programs, each subframe multiplexer being further operative to insert, in each subframe, a subframe multiplex map that specifies, at least indirectly, which portions of each subframe are allocated to which programs; and

a superframe multiplexer coupled to each of said subframe multiplexers for receiving said subframe data streams and for multiplexing selected ones of said subframe data streams to generate said multiplex data stream, said multiplex data stream having a format comprising a continuous sequence of superframes, each superframe containing at least one subframe from at least one of said selected subframe data streams, said superframe multiplexer being further operative to generate, for each superframe in the multiplex data stream, a superframe map that specifies the location of each subframe contained in that superframe, and to insert the superframe map in that superframe.

17. An encoder according to claim 16 wherein each subframe has a format comprising a plurality of lines, a first group of lines in each subframe defining a subframe transport layer region and a second group of lines defining a program data region, and wherein each subframe multiplexer comprises:

a subframe controller coupled to the control computer for generating, for each subframe, the subframe multiplex map and at least one program multiplex control packet;

a program multiplexer coupled to the subframe controller and responsive to said program multiplex control packets for multiplexing said respective group of programs in a time-division manner to produce a continuous sequence of program data packets, different portions of each program data packet being allocated to different ones of said group of programs; and

a subframe builder coupled to the subframe controller and to said program multiplexer for constructing each subframe in accordance with the subframe multiplex map generated for that subframe, wherein for each subframe, the subframe builder is operative;

(i) to insert a number of consecutive program data packets in the program data region of the subframe, (ii) to insert the program multiplex control packet for that subframe in the transport layer region of the subframe at a location specified by the subframe multiplex map for that subframe, and (iii) to insert the subframe multiplex map at a beginning of the subframe.

18. An encoder according to claim 17 wherein, for each program data packet to be inserted in a particular subframe, the program multiplex control packet generated for that subframe by the subframe controller specifies which portions of each program data packet are to be allocated to which programs, and wherein the program multiplexer is responsive to the multiplex control packet for generating each of the program data packets in accordance with the information specified therein.

19. An encoder according to claim 17 wherein the subframe builder is further operative to insert a subframe synchronization word (SFSYNC) in a first line of each subframe and to insert the subframe multiplex map in each frame such that the subframe multiplex map immediately follows the subframe synchronization word (SFSYNC).

20. An encoder according to claim 17 wherein the control computer is further operative to construct a plurality of system related data packets including system data packets (SDP'"'"'s), system teletext packets (STT'"'"'s), addressable data packets (ADP'"'"'s), service seed packets (SSP'"'"'s) and program virtual channel map packets (PVCMP'"'"'s), said subframe builder in each subframe multiplexer inserting selected ones of said system related data packets in the transport layer regions of each subframe, the subframe multiplex map generated for each subframe by the subframe controller specifying the number and location of each system related data packet to be inserted in the transport layer region of that subframe.

21. An encoder according to claim 18 wherein each of said digital programs has a respective data rate and wherein said portions of each program data packet are allocated to said programs in proportion to the respective data rates of each program.

22. An encoder according to claim 21 wherein said subframe multiplexer is further operative to adjust, on a per subframe basis, the size of each portion of each program data packet allocated to a particular program as the respective data rates of each program change.

23. An encoder according to claim 16 wherein said superframe multiplexer comprises:

a superframe controller coupled to the control computer for generating said superframe map; and

a superframe builder coupled to the superframe controller and coupled to receive successive subframes from each subframe multiplexer for constructing each superframe in accordance with the superframe map generated by the superframe controller, and for inserting each superframe map in its respective superframe.

24. An encoder according to claim 23 wherein said superframe multiplexer further comprises an interleaver coupled to an output of said superframe builder for interleaving portions of each superframe to reduce burst errors during subsequent transmission of the multiplex data stream to a remote location.

25. An encoder according to claim 23 wherein each superframe has a format comprising an adjustable number of successive blocks, a first group of blocks in each superframe defining a superframe transport layer region of that superframe and a second group of blocks defining a subframe data region, said superframe builder including:

means for inserting a block syncrhonization byte (BSYNC) in a first portion of each block; and

means for inserting a superframe syncrhonization word (FSYNC) in a first block of each superframe.

26. An encoder according to claim 25 wherein the superframe multiplexer further comprises block error coding means for generating a block error code for each block and appending the block error code to the block.

27. An encoder according to claim 23 wherein the control computer is further operative to generate a subframe virtual channel map packet that contains information that specifies, for each program, which subframe data stream contains that program, and wherein the superframe builder of the superframe multiplexer further comprises means for periodically inserting the subframe virtual channel map packet in the transport layer regions of selected superframes, the superframe map for each superframe into which the subframe virtual channel map packet is inserted further specifying the location of the subframe virtual channel map packet within that superframe.

28. A decoder for use at a remote location to decode a multiplex data stream received at that location, said received multiplex data stream containing a multiplexed combination of digital programs and having a format comprising a continuous sequence of superframes each comprising a predetermined number of blocks, a first group of blocks in each superframe defining a transport layer region of that superframe and a second group of blocks defining a subframe data region, the subframe data region of each superframe comprising a multiplexed combination of subframes, different portions of each subframe being allocated to different ones of said digital programs and at least one subframe in each superframe containing data for a different group of said programs than another subframe in that superframe, said decoder comprising:

a receiver for receiving successive superframes of the multiplex data stream;

a selector for selecting at least one of said digital programs for extraction from said received multiplexed data stream;

a superframe demultiplexer comprising;

a superframe map extractor for locating and extracting a superframe map from a received superframe of the received multiplex data stream, said superframe map specifying the location of each subframe contained within that superframe; and

a subframe extractor at least indirectly responsive to the extracted superframe map for identifying which subframe in the received superframe contains data for the selected program and for extracting that subframe from the received superframe; and

a subframe demultiplexer coupled to the superframe demultiplexer for receiving the extracted subframe from the superframe demultiplexer, said subframe demultiplexer comprising;

a subframe multiplex map extractor for extracting a subframe multiplex map from the extracted subframe that specifies, at least indirectly, which portions of the subframe are allocated to which digital programs; and

a program extractor responsive to the extracted subframe multiplex map for identifying, based at least in-part upon information contained in the subframe multiplex map, which portion of the subframe is allocated to the selected program, and for extracting the identified portion from the subframe.

29. A decoder according to claim 28 wherein the multiplex data stream contains mapping information that specifies, for each program, which subframe data stream contains that program, and wherein the superframe demultiplexer further comprises means for extracting the mapping information from the received multiplex data stream and identifying therefrom which subframe in the received superframe contains data for the selected program.

30. A decoder for use at a remote location to decode a multiplex data stream received at that location, said received multiplex data stream containing a multiplexed combination of digital programs and having a format comprising a continuous sequence of superframes each containing a multiplexed combination of subframes, each subframe comprising a transport layer region and a program data region, the program data region of each subframe being partitioned into a plurality of program data packets, different portions of each program data packet being allocated to different ones of said digital programs, at least one subframe in each superframe containing data for a different group of said programs than another subframe in that superframe, the transport layer region of each subframe containing a program multiplex control packet that specifies, for each program data packet within that subframe, which portions of each program data packet are allocated to which programs, the transport layer region of each subframe further containing a subframe multiplex map which specifies, for that subframe, the location of the program multiplex control packet contained in the transport layer region of that subframe, said decoder comprising:

a receiver for receiving successive superframes of the multiplex data stream;

a selector for selecting at least one of said digital programs for extraction from said received multiplexed data stream;

a superframe demultiplexer comprising;

a superframe map extractor for locating and extracting a superframe map from a received superframe of the received multiplex data stream, said superframe map specifying the location of each subframe contained within that superframe; and

a subframe extractor at least indirectly responsive to the extracted superframe map for identifying which subframe in the received superframe contains data for the selected program and for extracting that subframe from the received superframe; and

a subframe demultiplexer coupled to the superframe demultiplexer for receiving the extracted subframe from the superframe demultiplexer, said subframe demultiplexer comprising;

a subframe multiplex map extractor for extracting the subframe multiplex map from the received subframe and for identifying therefrom the location of the program multiplex control packet within the transport layer region of that subframe;

means for extracting the program multiplex control packet from the transport layer region of the received subframe; and

a program extractor responsive to the extracted program multiplex control packet for identifying, based upon information contained in the extracted program multiplex control packet, which portion of each program data packet in the received subframe is allocated to the selected program, and for extracting the identified portion from each program data packet.

31. A decoder according to claim 30 wherein the multiplex data stream contains mapping information that specifies, for each program, which subframe data stream contains that program, and wherein the superframe demultiplexer further comprises means for extracting the mapping information from the received multiplex data stream and identifying therefrom which subframe in the received superframe contains data for the selected program.

32. A method comprising the steps of:

a) receiving a plurality of multiplex data streams, each multiplex data stream containing a multiplexed combination of subframe data streams wherein each subframe data stream comprises a continuous sequence of subframes, said received multiplex data streams each having a format comprising a continuous sequence of superframes, each superframe in a particular multiplex data stream containing at least one subframe from at least one of the subframe data streams contained in that multiplex data stream and each superframe further containing a superframe map that specifies the location of each subframe within that superframe;

b) for each received multiplex data stream, demultiplexing and separating the subframe data streams contained in that multiplex data stream and providing each subframe data stream in a separate channel;

c) selecting a plurality of said demultiplexed and separated subframe data streams, at least one of said selected subframe data streams having been demultiplexed and separated from a different multiplex data stream than others of said selected subframe data streams;

d) multiplexing said selected subframe data streams to generate a new multiplex data stream having a format comprising a continuous sequence of superframes wherein each superframe comprises at least one subframe from at least one of said selected subframe data streams;

e) generating, for each superframe in the new multiplex data stream, a superframe map that specifies the location of each subframe within that superframe, and inserting the superframe map in that superframe; and

f) transmitting the new multiplex data stream to at least one reception site.

33. A method according to claim 32 wherein for each received multiplex data stream step (b) comprises:

(i) for each successive superframe of the received multiplex data stream, extracting the superframe map from the superframe, and based upon information contained therein, locating, extracting and separating the subframes contained in that superframe; and

(ii) combining each subframe extracted from a particular superframe with corresponding subframes extracted from previous superframes to reproduce each subframe data stream and provide each subframe data stream on a separate channel.

34. A method according to claim 32 wherein each superframe of said new multiplex data stream and each of said received multiplex data streams has a format comprising an adjustable number of successive blocks, a first portion of each block comprising a block synchronization byte (BSYNC), a second portion of each block comprising a data portion, and a last portion of each block comprising a block error code generated in accordance with a block error coding scheme.

35. A method according to claim 32 wherein a first group of blocks in each superframe of the new multiplex data stream define a superframe transport layer region of that superframe, and a second group of blocks define a subframe data region, the superframe map generated in step (c) for each superframe of the new multiplex data stream being inserted in the superframe transport layer region of that superframe.

36. A method according to claim 32 further comprising the step of inserting, in a first block of each superframe of the new multiplex data stream a superframe synchronization word (FSYNC), and wherein step (e) comprises inserting the superframe map for each superframe at a location immediately following the superframe synchronization word.

37. A method according to claim 32 wherein step (f) comprises transmitting successive superframes of said new multiplex data stream at a constant rate.

38. A method according to claim 34 wherein each block comprises a predetermined number of bits, and wherein step (f) comprises transmitting successive superframes of said new multiplex data stream at a constant rate such that the new multiplex data stream is transmitted at a bit rate equal to F_SF (n)(B) bits per second, where F_SF is the rate at which successive superframes are transmitted, n is the number of blocks in each superframe, and B is the number of bits in each block.

39. A headend installation comprising:

a plurality of receivers each tuned to receive a different one of a plurality of multiplex data streams transmitted from at least one encoder site, each multiplex data stream containing a multiplexed combination of subframe data streams wherein each subframe data stream comprises a continuous sequence of subframes, said received multiplex data streams each having a format comprising a continuous sequence of superframes, each superframe in a particular multiplex data stream containing at least one subframe from at least one of the subframe data streams contained in that multiplex data stream and each superframe further containing a superframe map that specifies the location of each subframe within that superframe;

a plurality of superframe demultiplexers each coupled to a respective one of said receivers for demultiplexing and separating the subframe data streams contained in the multiplex data streams received by that receiver and for providing each of the separated subframe data stream on a separate channel;

re-routing means for selecting a plurality of said demultiplexed and separated subframe data streams, at least one of said selected subframe data streams having been demultiplexed and separated from a different multiplex data stream than others of said selected subframe data streams; and

a superframe multiplexer coupled to receive each of said selected subframe data streams for multiplexing said selected subframe data streams to generate a new multiplex data stream, said new multiplex data stream having a format comprising a continuous sequence of superframes, each superframe containing at least one subframe from each of said selected subframe data streams, said superframe multiplexer being further operative to generate, for each superframe in the multiplex data stream, a superframe map that specifies the location of each subframe contained in that superframe, and to insert the superframe map in that superframe.

40. A headend installation according to claim 39 wherein said superframe multiplexer comprises:

a superframe controller for generating the superframe map for each superframe; and

a superframe builder coupled to the superframe controller and coupled to receive successive subframes from each subframe multiplexer for constructing each superframe in accordance with the superframe map generated by the superframe controller, and for inserting each superframe map in its respective superframe.

41. A headend installation according to claim 40 wherein said superframe multiplexer further comprises an interleaver coupled to an output of said superframe builder for interleaving portions of each superframe to reduce burst errors during subsequent transmission of the multiplex data stream to a remote location.

42. A headend installation according to claim 40 wherein each superframe of the new multiplex data stream has a format comprising an adjustable number of successive blocks, a first group of blocks in each superframe defining a superframe transport layer region of that superframe and a second group of block defining a subframe data region, said superframe builder including:

means for inserting a block synchronization byte (BSYNC) in a first portion of each block; and

means for inserting a superframe synchronization word (FSYNC) in a first block of each superframe.

43. A headend installation according to claim 42 wherein the superframe multiplexer further comprises block error coding means for generating a block error code for each block and appending the block error code to the block.

44. A headend installation according to claim 39 further comprising a transmitter coupled to said superframe multiplexer for transmitting successive superframes of said new multiplex data stream at a constant rate.

45. A headend installation according to claim 42 wherein each block comprises a predetermined number of bits, and wherein said headend installation further comprises a transmitter coupled to said superframe multiplexer for transmitting successive superframes of said new multiplex data stream at a constant rate such that the multiplex data stream is transmitted at a bit rate equal to F_SF (n)(B) bits per second, where F_SF is the rate at which successive superframes are transmitted, n is the number of blocks in each superframe, and B is the number of bits in each block.

46. A headend installation according to claim 39 wherein each superframe demultiplexer comprises:

a superframe map extractor for locating and extracting a superframe map from a superframe of the received multiplex data stream, said superframe map specifying the location of each subframe contained within that superframe;

a subframe extractor coupled to the superframe map extractor and at least indirectly responsive to the extracted superframe map for determining the location of each subframe within the superframe and for extracting and separating each subframe from the superframe.

47. A digital data stream containing a multiplexed combination of digital programs wherein each program comprises a combination of related digital services, said data stream comprising a continuous sequence of superframes,

each superframe containing a plurality of subframes, and each superframe containing a superframe map that specifies for that superframe the location of each of the subframes in that superframe,

each subframe in each superframe containing a multiplexed combination of data from a subset of said digital programs wherein different portions of each subframe are allocated to different ones of said programs of said subset, at least one of the subframes in a particular superframe containing a multiplexed combination of digital programs from a different subset than another subframe in that superframe, each subframe further containing a subframe multiplex map that at least indirectly specifies which portions of that subframe are allocated to which programs of said subset.

48. A digital data stream according to claim 47 wherein each subframe in each superframe has a format comprising a plurality of lines, a first group of lines in each subframe defining a subframe transport layer region and a second group of lines defining a program data region, the program data region of each subframe being portioned into a plurality of program data packets, and wherein different portions of each program data packet in each subframe are allocated to different ones of the programs of said subset.

49. A digital data stream according to claim 48 wherein the transport layer region of each subframe in each superframe contains a program multiplex control packet that specifies which portions of each program data packet in that subframe are allocated to which programs of said subset.

50. A digital data stream according to claim 48 wherein each of said digital programs has a respective data rate, and wherein different portions of each program data packet in each subframe are allocated to different ones of said programs of said subset in proportion to the respective data rates of said programs of said subset.

51. A digital data stream according to claim 48 wherein the transport layer region of each subframe in each superframe contains a plurality of system related data packets including system data packets (SDP'"'"'s), system teletext packets (STT'"'"'s), addressable data packets (ADP'"'"'s), service seed packets (SSP'"'"'s) and program virtual channel map packets (PVCMP'"'"'s), and wherein the subframe multiplex map in each subframe specifies the location of each system related data packet in the transport layer region of that subframe.

52. A digital data stream according to claim 47 wherein each superframe has a format comprising an adjustable number of successive blocks, a first portion of each block comprising a block synchronization byte (BSYNC), a second portion of each block comprising a data portion, and a last portion of each block comprising a block error code generated in accordance with a block error coding scheme.

53. A digital data stream according to claim 52 wherein a first group of blocks in each superframe define a superframe transport layer region of that superframe, and a second group of blocks define a subframe data region, the superframe map of each superframe being located in the superframe transport layer region of said each superframe.

54. A digital data stream according to claim 53 wherein each subframe has a format comprising a plurality of lines, and wherein the data portion of each block in the subframe data region of each superframe contains a single line of one of the subframes in that superframe.

55. A digital data stream according to claim 52 wherein a first block of each superframe contains a superframe synchronization word (FSYNC), and wherein the superframe map for each superframe is located in the superframe immediately following the superframe synchronization word.