Scrambling and descrambling control word control in a remultiplexer for video bearing transport streams

• US 6,148,082 A
• Filed: 01/14/1998
• Issued: 11/14/2000
• Est. Priority Date: 01/14/1998
• Status: Expired due to Term

• Current Assignee: Skystream Networks Incorporated (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Skystream Corporation
• Inventors: Slattery, William, Gratacap, Regis
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US09/007,199
• Time in Patent Office: 1,035 Days
• Field of Search: 370/426, 370/474, 370/394, 370/412, 370/521, 380/212, 380/217, 380/239, 380/269, 709/246, 709/247, 348/385, 348/465, 713/160, 713/162
• US Class Current: 380/212
• CPC Class Codes: H04N 21/23106 involving caching operations prefetching while addressing of a memory level in which the access to the desired data or data block requires associative addressing means within memory systems or architectures G06F12/0862; caching at an intermediate stage in a data network H04L67/568
• CPC Class Codes: H04N 21/23608 Remultiplexing multiplex streams, e.g. involving modifying time stamps or remapping the packet identifiers
• CPC Class Codes: H04N 21/23611 Insertion of stuffing data into a multiplex stream, e.g. to obtain a constant bitrate synchronisation arrangements in time-division multiplex systems using bit stuffing for systems with different or fluctuating information rates H04J3/073
• 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 21/23895 involving multiplex stream encryption
• CPC Class Codes: H04N 21/242 Synchronization processes, e.g. processing of PCR [Program Clock References] arrangements for synchronising broadcast or distribution via plural systems in broadcast distribution systems H04H20/18

Abstract

A method and system are provided for remultiplexing program bearing data. The remultiplexing method and system are applicable to MPEG-2 compliant transport streams carrying video programs. A descriptor based system is used for scheduling the timely output of transport packets wherein each descriptor records a dispatch time as well as a receipt time for each transport packet. The receipt time is used for estimating program clock reference adjustments, but final program clock reference adjustment is performed in hardware in relation to the precise output timing of each transport packets. A descriptor and transport packet caching technique is used for decoupling the synchronous receipt and transmission of transport packets from any asynchronous processing performed thereon. The descriptors can also be used for managing scrambling and descrambling control words (encryption and decryption keys). Remultiplexing functions may be distributed across a network. The remultiplexer can furthermore optimize the bandwidth of transport streams by replacing null transport packets with transport packet data to be inserted into the output transport stream. Program data transmitted via asynchronous communication links is re-timed and assistance is provided for outputting program data on such asynchronous communication links to reduce a variation in end-to-end delay incurred by the program data. Remultiplexing and program specific information can be seamlessly dynamically varied without stopping, or introducing a discontinuity in, the flow of outputted transport packets. A technique is also provided for locking multiple internal reference clock generators.

Claims

1. A method for descrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said method comprising the steps of:

(a) defining a sequence of one or more processing steps to be performed on each transport packet and ordering the step of descrambling processing within said sequence,

(b) allocating one unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, one or more processing indications and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) setting said one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on each of said allocated descriptors,

(e) sequentially accessing each allocated descriptor, and

(f) for each accessed descriptor pointing to a memory location for storing a to-be-descrambled transport packet, descrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor, only if said one or more processing indications of said accessed descriptor are set to indicate that descrambling processing may be performed on said accessed descriptor and transport packet stored in said memory location to which said accessed descriptor points.

2. The method of claim 1 wherein said control word information is a base address of a control word table.

3. The method of claim 2 further comprising the steps of:

(g) during said step of descrambling, locating a control word table using said base address and retrieving a control word from an entry of said control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet.

4. The method of claim 3 wherein said step of locating further comprises using an odd/even control word indication of said transport packet for retrieving said control word.

5. The method of claim 3 further comprising the steps of:

(g) maintaining a control word table containing said control words for descrambling contents of said transport packets.

6. The method of claim 1 further comprising the steps of:

(g) writing descrambled transport packet data into a transport packet storage location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-descrambling data of said transport packet, and

(h) after examining each descriptor containing processing indications that indicate that descrambling processing may be performed, setting one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on said descriptor, and transport packet to which said descriptor points.

7. A method for scrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said method comprising the steps of:

(a) defining a sequence of one or more steps to be performed on each transport packet and ordering scrambling processing within said sequence,

(b) allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, one or more processing indications and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) setting said one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on each of said allocated descriptors,

(e) sequentially accessing each allocated descriptor, and

(f) for each accessed descriptor pointing to a memory location storing a to-be-scrambled transport packet, scrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor, only if said one or more processing indications of said accessed descriptor are set to indicate that scrambling processing may be performed on said accessed descriptor and transport packet stored in said memory location to which said accessed descriptor points.

8. The method of claim 7 wherein said control word information is a control word corresponding to contents of each transport packet.

9. The method of claim 8 further comprising the steps of:

(g) during said step of allocating, retrieving said control word from an entry of a control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet, and

(h) storing said retrieved control word in said control word storage location of said descriptor.

10. The method of claim 9 further comprising the steps of:

(i) maintaining a control word table containing said control words for scrambling contents of said transport packets.

11. The method of claim 7 further comprising, for each of one or more descriptors allocated for a to-be-scrambled transport packet, the steps of:

(g) writing scrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-scrambled data of said transport packet, and

(h) after examining said descriptor containing one or more processing indications that indicate that scrambling processing may be performed, setting one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on said descriptor, and transport packet stored in said memory location to which said descriptor points.

12. A remultiplexer for descrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said remultiplexer comprising:

a processor for defining a sequence of one or more processing steps to be performed on each transport packet and for ordering descrambling processing within said sequence,

a data link control circuit for allocating one unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, one or more processing indications and a control word information field, and for setting said one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on each of said allocated descriptors, and

a descrambler for sequentially accessing each allocated descriptor, and, for each accessed descriptor pointing to a memory location storing a to-be-descrambled transport packet, descrambing said transport packet pointed to by said accessed descriptor using control word information in said accessed descriptor, only if said one or more processing indications of said accessed descriptor are set to indicate that descrambling processing may be performed on said accessed descriptor and transport packet stored in said memory location to which said accessed descriptor points,

wherein said processor also stores control word information associated with the contents of received transport packets in said control word information fields of corresponding ones of said descriptors.

13. The remultiplexer of claim 12 wherein said control word information is a base address of a control word table.

14. The remultiplexer of claim 13 wherein said descrambler locates a control word table using said base address and retrieves a control word from an entry of said control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet.

15. The remultiplexer of claim 14 wherein said descrambler locates said control word using an odd/even indicator of said transport packet to index said control word table.

16. The remultiplexer of claim 14 wherein said processor maintains a control word table containing said control words for descrambling contents of said transport packets.

17. The remultiplexer of claim 12 wherein, for each of one or more descriptors allocated for a to-be-descrambled transport packet, said descrambler writes descrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-descrambling data of said transport packet, and, after examining said descriptor containing processing indications that indicate that descrambling processing may be performed, sets one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on said descriptor and transport packet stored in said memory location to which said descriptor points.

18. A remultiplexer for scrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said remultiplexer comprising:

a processor for defining a sequence of one or more processing steps to be performed on each transport packet, for ordering scrambling processing within said sequence, for allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, one or more processing indications and a control word information field, storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors, and for setting one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on each of said allocated descriptors, and

a scrambler for sequentially accessing each allocated descriptor, and, for each accessed descriptor pointing to a memory location storing a to-be-scrambled transport packet, scrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor, only if said one or more processing indications of said accessed descriptor are set to indicate that scrambling processing may be performed on said accessed descriptor and transport packet stored in said memory location to which said accessed descriptor points.

19. The remultiplexer of claim 18 wherein said control word information is a control word corresponding to contents of each transport packet.

20. The remultiplexer of claim 19 wherein said processor retrieves said control word from an entry of a control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet, and stores said retrieved control word in said control word storage location of said descriptor.

21. The remultiplexer of claim 20 wherein said processor maintains a control word table containing said control words for scrambling contents of said transport packets.

22. The remultiplexer of claim 18 wherein, for each of one or more descriptors allocated for a to-be-scrambled transport packet, said scrambler writes scrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-scrambled data of said transport packet, and, after examining said descriptor containing one or more processing indications that indicate that scrambling processing may be performed, sets one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on said descriptor and transport packet stored in said memory location to which said descriptor points.

23. A transport stream containing descrambled transport packets, said transport packets containing elementary stream data of one or more video programs, said transport stream being produced by the steps of:

(a) defining a sequence of one or more processing steps to be performed on each transport packet and ordering descrambling processing within said sequence,

(b) allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, one or more processing indications and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) setting one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on each of said allocated descriptors,

(e) sequentially accessing each allocated descriptor, and

(f) for each accessed descriptor pointing to a memory location storing a to-be-descrambled transport packet, descrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor, only if said one or more processing indications of said accessed descriptor are set to indicate that descrambling processing may be performed on said accessed descriptor and transport packet stored in said memory location to which said accessed descriptor points.

24. A transport stream containing scrambled transport packets, said transport packets containing elementary stream data of one or more video programs, said transport stream being produced by the steps of:

(a) defining a sequence of one or more processing steps to be performed on each transport packet and ordering scrambling processing within said sequence,

(b) allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, one or more processing indications and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) setting one or more of said processing indications to indicate that the next step of processing of said sequence may be performed on each of said allocated descriptors,

(e) sequentially accessing each allocated descriptor, and

(f) for each accessed descriptor pointing to a memory location storing a to-be-scrambled transport packet, scrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor, only if said one or more processing indications of said accessed descriptor are set to indicate that scrambling processing may be performed on said accessed descriptor and transport packet stored in said memory location to which said accessed descriptor points.

25. A method for descrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said method comprising the steps of:

(a) defining a sequence of one or more processing steps to be performed on each transport packet and ordering the step of descrambling processing within said sequence,

(b) allocating one unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated, and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) sequentially accessing each allocated descriptor, and

(e) for each accessed descriptor pointing to a memory location for storing a to-be-descrambled transport packet, descrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor.

26. The method of claim 25 wherein said control word information is a base address of a control word table.

27. The method of claim 26 further comprising the steps of:

(f) during said step of descrambling, locating a control word table using said base address and retrieving a control word from an entry of said control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet.

28. The method of claim 27 wherein said step of locating further comprises using an odd/even control word indication of said transport packet for retrieving said control word.

29. The method of claim 27 further comprising the steps of:

(f) maintaining a control word table containing said control words for descrambling contents of said transport packets.

30. The method of claim 25 further comprising, for each of one or more descriptors allocated for a to-be-descrambled transport packet, the steps of:

(f) writing descrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-descrambling data of said transport packet, and

(g) performing any processing steps subsequent to said descrambling processing step on said descrambled transport packet stored in said memory location pointed to by said allocated descriptor.

31. A method for scrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said method comprising the steps of:

(a) defining a sequence of one or more steps to be performed on each transport packet and ordering scrambling processing within said sequence,

(b) allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) sequentially accessing each allocated descriptor, and

(e) for each accessed descriptor pointing to a memory location storing a to-be-scrambled transport packet, scrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor.

32. The method of claim 31 wherein said control word information is a control word corresponding to contents of each transport packet.

33. The method of claim 32 further comprising the steps of:

(f) during said step of allocating, retrieving said control word from an entry of a control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet, and

(g) storing said retrieved control word in said control word storage location of said descriptor.

34. The method of claim 33 further comprising the steps of:

(h) maintaining a control word table containing said control words for scrambling contents of said transport packets.

35. The method of claim 31 further comprising, for each of one or more descriptors allocated for a to-be-scrambled transport packet, the steps of:

(f) writing scrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-scrambled data of said transport packet, and

(g) performing any processing steps subsequent to the scrambling processing step on said scrambled transport packet stored in said memory location pointed to by said pointer of said allocated descriptor.

36. A remultiplexer for descrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said remultiplexer comprising:

a processor for defining a sequence of one or more processing steps to be performed on each transport packet and for ordering descrambling processing within said sequence,

a data link control circuit for allocating one unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated and a control word information field, and

a descrambler for sequentially accessing each allocated descriptor, and, for each accessed descriptor pointing to a memory location storing a to-be-descrambled transport packet, descrambling said transport packet pointed to by said accessed descriptor using control word information in said accessed descriptor,

wherein said processor also stores control word information associated with the contents of received transport packets in said control word information fields of corresponding ones of said descriptors.

37. The remultiplexer of claim 36 wherein said control word information is a base address of a control word table.

38. The remultiplexer of claim 37 wherein said descrambler locates a control word table using said base address and retrieves a control word from an entry of said control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet.

39. The remultiplexer of claim 38 wherein said descrambler locates said control word using an odd/even indicator of said transport packet to index said control word table.

40. The remultiplexer of claim 38 wherein said processor maintains a control word table containing said control words for descrambling contents of said transport packets.

41. The remultiplexer of claim 36 wherein, for each of one or more descriptors allocated for a to-be-descrambled transport packet, said descrambler writes descrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-descrambling data of said transport packet, and, wherein any processing steps subsequent to said descrambling processing step are performed on said descrambled transport packet stored in said memory location pointed to by said allocated descriptor.

42. A remultiplexer for scrambling transport packets of a transport stream, said transport packets containing elementary stream data of one or more video programs, said remultiplexer comprising:

a processor for defining a sequence of one or more processing steps to be performed on each transport packet, for ordering scrambling processing within said sequence, for allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated and a control word information field, and for storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors, and

a scrambler for sequentially accessing each allocated descriptor, and, for each accessed descriptor pointing to a memory location storing a to-be-scrambled transport packet, scrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor.

43. The remultiplexer of claim 42 wherein said control word information is a control word corresponding to contents of each transport packet.

44. The remultiplexer of claim 43 wherein said processor retrieves said control word from an entry of a control word table indexed by a packet identifier of said transport packet, each packet identifier uniquely indicating the elementary stream data contained in said transport packet, and stores said retrieved control word in said control word storage location of said descriptor.

45. The remultiplexer of claim 44 wherein said processor maintains a control word table containing said control words for scrambling contents of said transport packets.

46. The remultiplexer of claim 42 wherein, for each of one or more descriptors allocated for a to-be-scrambled transport packet, said scrambler writes scrambled transport packet data into said memory location pointed to by said pointer of said allocated descriptor, thereby overwriting pre-scrambled data of said transport packet, wherein any processing steps subsequent to the scrambling processing step are performed on said scrambled transport packet stored in said memory location pointed to by said pointer of said allocated descriptor.

47. A transport stream containing descrambled transport packets, said transport packets containing elementary stream data of one or more video programs, said transport stream being produced by the steps of:

(a) defining a sequence of one or more processing steps to be performed on each transport packet and ordering descrambling processing within said sequence,

(b) allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocateds and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) sequentially accessing each allocated descriptor, and

(e) for each accessed descriptor pointing to a memory location storing a to-be-descrambled transport packet, descrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor.

48. A transport stream containing scrambled transport packets, said transport packets containing elementary stream data of one or more video programs, said transport stream being produced by the steps of:

(a) defining a sequence of one or more processing steps to be performed on each transport packet and ordering scrambling processing within said sequence,

(b) allocating a unique descriptor of a queue for each transport packet, each allocated descriptor containing a pointer to a memory location for storing said transport packet for which said descriptor is allocated and a control word information field,

(c) storing control word information associated with contents of said transport packet in said control word information field of selected ones of said allocated descriptors,

(d) sequentially accessing each allocated descriptor, and

(e) for each accessed descriptor pointing to a memory location storing a to-be-scrambled transport packet, scrambling said transport packet stored in said memory location pointed to by said accessed descriptor using said control word information in said accessed descriptor.