MXPA00006181A - Scrambling unit for a digital transmission system - Google Patents

Abstract

An independant scrambling unit (1) for a digital audiovisual transmission system, the scrambling unit (1) comprising an input for receiving an assembled transport packet stream from a physically seperate multiplexer (4), a scrambling device for scrambling the received transport stream according to a randomising control word and an output for sending the scrambled transport stream to a transmitter means for subsequent transmission. The scrambling unit (1) may also be used to introduce other packet data in the data stream.

Description

A MIXING DATA FOR A MISIÓ N DIG ITAL SYSTEM The present invention relates to a mixing unit for a digital audiovisual transmission system, in particular for a digital television transmission system, together with a mixing system. which includes said mixing unit. The transmission of mixed or encrypted data is well known in the field of digital pay television systems, where the mixed audiovisual information is transmitted to a number of subscribers, each subscriber has a decoder or receiver / decoder capable of separating the transmitted program for its subsequent observation. The mixing of the data is commonly carried out by the multiplexer device also responsible for joining the transmitted transport data stream. The multiplexer receives digital video, audio or other digital data and conjuncts it into a single transport packet stream. Each packet in the transport stream is commonly of a predetermined length and contains a header and a payload. The package header includes a packet identification or PID that identifies the packet and corresponds to the type of data (video, audio, etc.) in the packet. The payload of the packet contains the audio, video or any other data such as application data processed by the receiver / decoder to provide additional functions, for example to generate a program guide, etc. Conventionally, the payload data is mixed by a rapidly changing random control word generated by the multiplexer. This control word is then sent to the receiver / decoder in an ECM, or Authorization Control Message inserted in the transport packet stream in conjunction with the mixed data. The Authorization Control Message contains other information such as access rights and is encrypted by an encryption key before transmission. The commonly-encrypted Authorization Control Message is that produced by a separate access control system, exclusive of a particular service channel or provider. The access control system receives the mixing control word from the multiplexer, inserts the control word into an Authorization Control Message, encrypts the Authorization Control Message complete with the current encryption key and sends the Control Message to the control message. Encrypted authorization back to the multiplexer. Then, the multiplexer inserts the encrypted Authorization Control Message in the transport stream together with the mixed data. The mixed data and the encrypted Authorization Control Message are transmitted to a receiver / decoder that has access to an equivalent of the encryption key to decrypt the Authorization Control Message and thus obtain the control word to separate the transmitted data. The trading key changes regularly and a decoder belonging to a paid subscriber will usually receive in a monthly M M (Authorization Administration Message) the operating key necessary to decrypt the Encrypted Authorization Control Message for that month. The advantage of mixing the data with a control word generated by the multiplexer is that the system can be expanded to simultaneously mix data for a number of access control systems in parallel. This may be necessary, for example, when the content provider is transmitting to a mixed park of decoders, different epochs, characteristics, etc. Each access control system receives the control word used at that time by the multiplexer and, subsequently, generates its own exclusive Authorization Control Message, which is sent to the multiplexer for incorporation into the transport packet stream. These systems of "Multiply encryption" uses the same control word to mix all the data. Although systems of this type are relatively simple in terms of their implementation, the administration of communications between the multiplexer and the access control systems can be difficult to implement. Additionally, the security level is generally limited by the complexity of the algorithm used by the multiplexer to generate the mixing control word. An object of the present invention in its various aspects and modalities is to solve some or all of the problems of the systems of the prior art. In accordance with the present invention, a mixing unit for a digital audio-visual transmission system is provided, the mixing unit comprises an input for receiving a bundled transport packet stream from a physically separate multiplexer, a mixing device for mixing the transport stream received in accordance with a random control word and an output for sending the mixed transport stream to a transmitting medium for subsequent transmission in order to allow mixing of the transport pack stream by the mixing unit independently of the operations of the multiplexer. Unlike the prior art systems, in which the data is mixed by the multiplexer while multiplexing together the different data streams to form a single transport stream, the present invention proposes an entirely different solution in which a discrete mixing unit receives, via a dedicated input, the transport stream already joined. This solution facilitates the management of communications between each of the elements of the system through the division of functionality between separate mixing and multiplexing parts of the system. Additionally, as the mixing unit is not constrained by the usual limitations of the multiplexer mixer devices, the level of complexity of the mixing algorithm can be increased. The mixing device can be adapted to carry out mixing in some or all of the payloads of selected packets of the transport stream pack. For example, at a high "transport stream" mixing level, the entire payload of a given transport stream pack can be mixed. Alternatively, only part of the payload of a packet can be mixed. In addition to the mixing device, the mixing unit may also comprise a packet insertion means for inserting transport packet data into the transport stream. for example, the mixing unit can be used to introduce packages containing the mixing control word into encrypted Authorization Control Messages. Other types of data can also be inserted into the transport stream to make full use of the available bandwidth, regardless of the limitations of the multiplexer downstream of the unit. In one embodiment, the packet insertion means may act to insert a packet of data into the transport stream by detecting the presence of a null packet and replacing this packet with the packet to be inserted. A null packet is a packet generated during the multiplexer's operation cycle that does not contain data. Conventionally it is identified by a characteristic packet identification value. Additionally, the mixing unit may comprise a packet filter means for identifying and copying to a memory part or all of a predetermined transport packet. For example, the filter may be pre-programmed to identify certain transport packets by their packet identification value which contain data to be modified by the mixer, such as user-specific tables or the like. Filtering can also be carried out in part of a package, for example by looking at the identification of the table in the payload of the transport package, etc. Conveniently, the mixing unit may also comprise a packet elimination means for removing a predetermined packet, for example, transforming the packet identification to that of a null packet. For example, when the packet is to be filtered for its packet identification value and is to be replaced by a modified packet with the same packet identification value, it will be necessary to remove the original packet with this packet identification to avoid generation of multiple packages with the same package ID. The packet to be deleted will then become a null packet, which will later be ignored or replaced with another packet introduced by the packet insert. Preferably, the mixing unit also comprises a packet counting means for counting the number of packets of a predetermined packet identification value in the received transport data stream. For example, the packet counting means can be used to count the number of null packets in the data stream to allow evaluation of the space available in the transport stream for inserting Authorization Control Message packets, etc. It can also be used to detect the presence of a particular packet identification or calculate a bitrate of a packet identification. Preferably, the mixing unit also comprises a means of repetition of packet identification map formation to change the packet identification value assigned to a predetermined plurality or to a series of packets. This can be used to eliminate the risk of any conflict between the packet identification value of an inserted packet and that of a packet already present in the transport stream by changing the packet identification value to one that does not occur in the incoming stream or one that leaks. The mixing unit described above can operate in a stand-alone mode. Alternatively, the unit may be part of a mixing system, the system additionally comprising a central control means for generating a control word sent to and received by the mixing unit for mixing the transport stream. The central control means may be implemented by a single personal computer or a personal computer that acts as a central control station in combination with a second personal computer and smart card to generate the control word. Preferably, the mixing system further comprises one or more access control systems connected to the central control means and adapted to receive a control word provided by the central control means and to send an encrypted message back to the central control means. , for example an Authorization Control Message containing the control word. In this way, the central control means can coordinate the generation of an Authorization Control Message based on the same control word by a plurality of access control systems, in accordance with the principle of "simultaneous encryption", and transmit r Authorization Control Messages and their control word associated with the mixer, for the synchronized insertion of the Authorization Control Messages into the transport stream and mixing of the transport data in accordance with the control word. Preferably, some or all of the data sent from the central control means to the relay unit is authenticated by the central control means by generating an authorization in accordance with a secret encryption key. In the case where a public / private encryption configuration is used, the mixing unit has an equivalent public key that allows the mixer to verify the origin of the data. In particular, all control word data sent to the mixer must be authenticated, to avoid the possibility of falsification of the control word by violation of the connection between the two. It is also possible to introduce additional security measures, for example to encrypt all the transmitted data in accordance with a symmetric algorithm, the central control means and the mixing unit each having the necessary keys for message encryption and decryption. The embodiment of the aforementioned mixing system has been described in relation to a single mixing unit, a single central control means, etc. However, for reasons of reliability it may be desired to have at least one reservation or support of each of the elements of the system and, in a preferred embodiment, the system comprises a plurality of mixing units and central control means associated with the generation of the transport current. In this way, the system can switch between control means and mixing units in the event of failure or erroneous operation of the relevant part of the system. Conveniently, the or each mixing unit in a system of this type is adapted to operate autonomously in the case of disconnection of the central control means, for example, periodically storing its operating configuration characteristics and / or word value. of current control (or a default control word value). In the context of the present application, the term "digital audiovisual transmission system" refers to all transmission systems for transmitting mainly digital audio-visual or multimedia data. Although the present invention is particularly applicable to a digital broadcast television system, the present invention can also be used in filtering data sent by a fixed telecommunication network for multimedia Internet applications, etc. The term MPEG refers to the standards of data transmission developed by the working group of the International Standards Organization "Group of Cinematographic Film Experts" and principally the MP EG-2 standard developed for digital television applications and established in documents ISO 1 3818-1, ISO 1 381 8-2, ISO 1 381 8-3 and I OS 1 381 8-4. In the context of the present patent application, the term includes all variants, modifications or developments for the basic PEG M formats applicable to the field of digital data transmission. A number of embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows the elements of a mixing system of one embodiment of the invention.; Figure 2 shows in detail the mixing unit of Figure 1; and Figure 3 shows a further embodiment of the present invention. Referring now to Figure 1, a mixing system for the central digital television control station 2 and a control word generator 3 is shown. The control word generator 3 can be, as shown, a computer type personal computer including a smart card reader adapted to receive a smart card that contains an encryption key to authorize data (see below). Alternatively, the control word generator may be a console-type unit, an add-on card for inserting into the co-trol station 2, etc. The mixing unit 1 receives unmixed transport packets from a multiplexer 4 at its input and passes a mixed transport stream to a modulator 5 for preparation before transmission via a suitable satellite transmission link or the like. The multiplexer 4 may be any conventional multiplexer in accordance with the MPEG standard and capable of receiving digital video, audio, teletext, etc. information. and producing an unencrypted transport packet stream of this data. In a conventional MPEG transmission system the video, audio data, etc. they can be provided to the multiplexer in the form of a PES (elementary stream formed in packets). Other packet data can also be multiplexed in the transport stream. The output of the multiplexer comprises a sequence of transport packets comprising a header and a payload containing the elementary stream formed in packets or other data. Depending on the data provided to the multiplexer and the efficiency of the multiplexer, the packet stream may also comprise a greater or lesser number of so-called null packets that do not contain data. Other types of data in the data stream provided to the multiplexer can be divided into sections. In addition or alternatively, data may also be provided to the multiplexer in the form of a number of tables or modules, the receiver / decoder unloads and joins the tables at another end of the transmission system to form the complete application. In a manner similar to the packets in the transport packet stream, the tables can be identified by a table identification or TI value D. In the data stream, the data packets are identified by their packet identification, the Video data have a packet identification value, another audio data, etc. In the MPEG standard, the null data packets have the Oxi FFF package identification value. In contrast, the packet identification value assigned to a given data type (audio, video, etc.) can be determined by the content provider. For more details on the package structure of an MPEG transport stream, the shape of the elementary stream formed into packets and the sectioned and tabulated data, the reader can consult the documents of the international standard ISO 13818-1, ISO 13818- 2, ISO 13818-3 and ISO 13818-4. These standards also establish the characteristics of the physical interface layer to ensure compatibility between MPEG devices, and provide as an example the use of an Asynchronous Serial Interface (ASI). Other links or interfaces are possible, for example, SPI, LVDS, G703, etc. The modulator 5 can be of any conventional type necessary to convert the digital transport packet stream into a form suitable for transmission via a telecommunications link such as a satellite, cable, network link, etc. The mixing unit 1 is additionally connected to receive the Authorization Control Message and control word data of the central control station 2, which in turn is connected to the control word generator 3 and to one or more access systems conditional 6, 7. The control word generator 3 comprises a personal computer type computer capable of generating a random control word stream and includes a card reader for reading a smart card containing a private key to authorize the word data Random control generated.

The central control station 2 may also comprise a personal computer or the like and, in fact, may even be integrated with the control word generator 3. In accordance with the principles of a "simultaneous encryption" system the same control word it is used to encrypt transmissions for a number of access control systems. Each access control system encrypts the control word and other data with its own encryption key to prepare an Authorization Control Message for transmission to subscribers using this access control system. Therefore, the central control station 2 is configured to pass the data of the control word via a suitable communication link to the access systems 6, 7 which prepare the encrypted Authorization Control Messages that are sent back. to the central control station 2. Then, the central control station 2 sends the Authorization Control Messages (in the form of one or more transport packets) and the associated control word data via, for example, a TCP / IP link to the mixing unit 1 . To avoid the possibility of the communication link being compromised and the data of the control word being replaced by other data originating outside the system, the control word data is authorized at the time of generation by means of a private key contained in the smart card associated with the generator 3, as mentioned above. The mixing unit 1 has an equivalent public key that can be used to authenticate the authorized data, in accordance with private / public key authentication methods. In the event that the control word data is not properly authenticated, the mixing unit may refuse to carry out the mixing of the transport packet stream. Encryption of past communications between the control station 2 and the mixing unit 1 can also be carried out, for example through the use of a symmetric encryption scheme and a pair of private keys contained in the central control means and the mixing unit. Referring now to Figure 2, the structure of the mixing unit of Figure 1 will now be described in detail. As will be understood, some of the elements shown here represent functional blocks in the decoder that can be implemented in the form of computer or computer programs or in a combination thereof. The mixing unit 1 receives via the inputs 10, 1 1 the output of the unencrypted transport stream of the multiplexer. To provide a degree of security against problems in the link between the multiplexer and the mixing unit, a double connection is provided, with the same transport current received in each of the inputs 10, 1 1. The connection can also be used to handle the redundancy of data streams that originate from different multiplexer sources. The information on synchronization and timing of the packets in the MPEG packet stream is provided to a central microprocessor 15 via the decoder and the synchronization elements 12, 1 3. The decoder and the synchronization elements detect that the data correspond to a M PEG current at a physical level (clock presence, correct Asynchronous Serial Interface or other interface characteristics, etc.). The synchronization element retrieves the PEG M synchronization byte to ensure the synchronous synchronous processing of the data. These elements are conventional and are found, for example, in the MPEG receiver / decoder units as an element of the decryption link. In the case of any failure in the current received via one of the inputs, the microprocessor controls a switching element 14 to change to the received current via the other input. As will be seen, given the need to maintain a continuous fl ow of data transmitted, this type of redundancy can be repeated at other levels in the mixing system. As will be described, the output of the transport stream via the outputs 1 8, 1 9 is normally mixed. However, to provide an unaltered and unmixed output of the unit, either for testing purposes or to divert the mixing circuits in the event of a fault, the unit additionally includes the bypass switches 16, 17 which they can be operated manually and allow the transport packet stream (received via one or both inputs) to pass directly through the unit. As shown in the cross connection 20, the input / output link in the bypass mode can be switched so that the current received via the input 1 0 emerges via the output 18, while that received via input 1 1 emerges via output 1 9. Alternatively, by changing the configuration of connection 20, input 10 may be connected to output 19 and input 1 1 to output 1 8. cross section 20 can be implemented, for example, by external tips connected in the unit, whose configuration can be changed as desired. This cross-connection again makes it easier to verify the individual communication channels. The advantage of this implementation is that the deviation is completely passive so that the signal can pass through the unit, even in the case of a power failure. If activated by a relay, the bypass can be activated automatically when a power failure occurs. The operation of the elements of the packet identification counter 21, the packet identification filter 22, the packet identification elimination unit 23, the pack identification map repetition unit 24, the packet identification unit package 25 and mixer 26 will be described below. As will be evident, some of these elements such as the packet identification filter 22 and the packet identification counter 21 are known in the context of a receiver / decoder where they are used in the demultiplexing and separation operations carried out in a received transport stream. Likewise, elements such as the mixer 26, the packet insertion unit 25, the pack identification map repetition unit 24 and the pack identification identification unit 23 are known in the context of a conventional combined multiplexer / mixing device. Although there will therefore be no difficulty for those skilled in the art of assembling and constructing these elements, it will nevertheless be appreciated that the specific combination and juxtaposition of such elements in the context of an external unit as described is, however, completely original . The packet identification counter 21 programmable by the microprocessor 15 can be used to verify the presence or absence of packets with a predetermined packet identification value in the transport packet stream as well as to count the number of packets having this value of package identification that are present in a given block of transport packets. In particular, the packet identification counter 21 can be used to count the number of null packets present in the transport stream (MPEG packet identification value: OxI FFF) to evaluate the bit rate available for insertion of additional packets (see below). Alternatively, the packet identification counter 21 may be used to detect the presence of a packet such as a packet of private or similar data that is to be modified or deleted by the unit. To more fully analyze the data stream, a packet identification filter and demultiplexer unit 22 is used to filter packet sequences of a given packet identification value and to copy these packets to the memory 27. The filter unit 22 also it can be used to carry out filtering at a lower level in the transport packet stream, for example, a filtering of sections and / or data tables in the payload of a transport packet. As in conventional filter units used in a receiver / decoder, the filter 22 can be programmed to recognize table identification values, table identification extension values, section data, etc. The configuration of the filter 22 is established by the microprocessor 15, which in turn is connected via a network adapter 28 and a TCP / IP link to the central control station shown in Figure 2. The central control station can then select which packets filter the data stream. A packet accessed or filtered in the data stream is copied by the filter 22 into the memory 27 associated with the microprocessor 15. The packet stored in the memory can then be transmitted via the TCP / IP link to the central control station for analysis and additional modifications. The central control station can decide, for example, to filter certain private data packets from a given packet identification value for modification or may require modification of the packets used to describe the contents of the transport stream in the case that fully new packets with a new value of package identification will be inserted into the transport stream. As will be understood, the fact that a given packet has been filtered and copied into memory does not mean that the packet has been physically removed from the transport stream, therefore, in the case that packets of a packet identification value Given that they are going to be inserted in the transport stream, it will be necessary to delete the present packages that have this value to avoid a collision. To do this, the packet elimination unit is adapted to transform packets of a given packet identification value into null packets, by changing, inter alia, the package identification value of the packets to the packet identification value of a packet. null. Specifically, in the case of an MPEG standard package, the following changes must be made to the package header: Forced package identification value to 0x1 FFF Forced transport mixed control to 00 Forced adaptation field control to 01 Forced payload unit start indicator to 0 Forced continuity counter to 0 (optional) As will be understood, the null packets in the transport stream are not read because they supposedly do not contain payload and the transformed packets are for all the purposes eliminated. Additionally, as will be described, the packet insert unit 25 is in fact adapted to detect and replace any null packets by packets contained in the memory for insertion into the transport stream. In addition, and in the same way that the deletion unit 23 eliminated certain packet identification packets to null packets by changing their packet identification value, a packet identification map repetition unit may be provided to change any identification of the packet. package given a new package identification value. This may require circumventing the limitations of the original multiplexer that provides the multiplexed transport stream to the mixing unit and / or to avoid packet identification conflicts with new packets to be inserted in the transport stream.

For example, the unit can be configured as follows: incoming PID value PID value re-mapped 0x20 0x0100 0x21 0x01 01 0x22 0x0200 00xx2233 0x0201 Only the packet identification field in the transport packet header is modify. Transport packages not designated by these packet identification values remain unchanged. As with the elimination unit, the configuration of the packet identification map repetition unit is determined in practice by the central control station. In the event that the packet insertion unit 25 has been programmed to insert packets of a packet identification value not present in the original transport stream, the repetition of map formation of packet identification values may not be necessary . In contrast, in the event that a potential conflict has been detected, the packet identification map formation repetition unit will re-map the conflicting packet identification value in the original transport stream to a new value. Returning now to the packet insertion unit 25, this unit is adapted to insert a transport packet contained in the memory 27 to replace any null packets present in the transport stream. No change or handling of the packet identification values of the inserted packets is performed by unit 25. As mentioned above, potential packet identification conflicts are handled by the packet identification map 24 repetition unit. and the packet identification elimination unit 23. Packages can be inserted into the transport stream in a number of different ways: 1. I n ser ction of cyclical data. This can be used, for example, to enter static tables of data. In this case, the packets are stored in a queue in the memory 27, a programmer reads each of the queues at regular intervals to enter the packet data cyclically into the stream, a packet is introduced in each occurrence of the packet. a package n ulo. The programmer handles the continuity counter (that is, the sequential number of the packet) in the packet sequence to ensure the correct numbering of the transmitted sequence. 2. Synchronized insertion of Authorization Control Message. In this case, Authorization Control Messages are received from the control station together with the associated control word data. The Authorization Control Messages are inserted as cyclic data, synchronized with the mixing operation carried out by the mixer 26 using the control word data. 3. Insertion of data of a shot. In this case, a packet sequence is inserted only once in the transport stream. The sequence is stored in a queue of first-in, first-out memory, the next packet in the queue is inserted in the occurrence of the next null packet. In this case, the continuity counter of the packets in the sequence can be previously established before being received by the mixing unit. The one-shot data insertion can be used to insert data received from the control station 2, or from other sources, such as Authorization Control Message generators. The packets or packet sequences sent from the central control station 2 to the mixing unit 1 in any of these operations can be identified with an associated identity value, so that the central control station can override or call back to the insertion of a packet or sequence of packets into the transport stream. The transport packet stream, modified and including the desired Authorization Control Messages is then passed to the mixer 26. The mixer 26 can conform to a digital mixer as used in any conventional mixer / muitiplexer device. In order to carry out the mixing of the transported data (but not of the Authorization Control Messages) the mixer has the necessary package identification information to prepare groups of packages that have package identification values indicating that they are to be mixed . The mixing can be carried out at a transport current level, that is, in the total payload of a transport packet, or (for example, for audiovisual type data) at an elementary stream current level formed in packets, that is, in the payload of the packets of the elementary stream formed in packets contained in the transport packets. Any type of mixing can be desired in accordance with the requirements of the service provider. The mixer performs the mixing of the data in accordance with the control word provided by the central control station 1. As mentioned above, control word data is authorized at the central control station by a private key and the control word and authorization are sent to unit 1. Unit 1 includes a smart card reader adapted to read a smart card 29 containing the equivalent public key. At the same time that the control word passes to the mixer 26, the microprocessor 15 verifies the authorization using the public key, as shown. In case there is a failure in the authentication process, the mixer 26 may be instructed to terminate the mixing process or to ignore the control word that has been received. As mentioned above, the communications between the central control station and the mixing unit can be further encrypted by a symmetric algorithm and, in this case, the smart card 29 can also contain the necessary key to decrypt the data communicated before the step of authentication. Further, in the case where the mixing unit is adapted to receive data sent from other sources independent of the central control station (e.g., a source of Authorization Control Messages) the network used to send messages from the control station Central control to the mixing unit may be physically separated from the network used to receive messages received from other sources. In this case, the network adapter 28 will include two separate network interfaces, the interface for receiving data from other sources that are "read only" to prevent the unit from being reprogrammed by sources external to the mixing system. As shown, the mixing unit 1 additionally includes outputs 30, 31 to allow a clear transport current output to be read from the unit. Unlike the output obtained by the diverter switches 16, 17, the outputs 30, 31 represent the transport current after modification by the insertion / deletion of packets, etc. , but before the mixing is carried out. These outputs can be used to monitor the operation of the unit and monitor the result of clear operations. In addition, the unit may include a standard RS232 interface 32 to allow interrogation of the microprocessor for testing purposes, network configuration, or basic data insertion (file transfer capacity) per terminal. Figure 3 shows a further embodiment of the present invention, in which a number of the elements of the system of Figure 1 have been duplicated to provide a degree of security through the redundancy of the elements. In particular, a central reserve control unit 2a and a control word generator 3a together with a reserve mixing unit 1 a have been indicated.

The parts of the access control systems relating to the generation of an Authorization Control Message have also been duplicated and this has been indicated by reference numerals 6a, 7a. Audio, video, etc. signals they can also be passed through a backup multiplexer 4a. Additionally, a second transmission channel for generating an MPEG transport channel can also be handled by the present system. This has been indicated by the multiplexer 40 (and its backup multiplexer 40a), the mixing unit 41 (and its backup mixing unit 41 a) and the modulator 42. The redundancy of the various elements in the system can be managed by a communication link between the control stations 2, 2a and / or a link to a remote supervisor or terminal indicated by line 43. In particular, a "heartbeat" signal may be provided from station 2 to the station 2a, the control station 2a acts to take control of the generation of Authorization Control Messages and control word data in the case of the interruption of this signal. Likewise, the mixing units 1, 1 a can be related to the control stations to allow the transfer of functions between the two in case of failure of one to the other mixing unit. In addition, each mixing unit 1, 1 a can be adapted to store, for example a reusable memory, the operating configuration of the unit and / or the value of the control word at predetermined intervals so that the units 1, 1 a they can continue to operate in the event of disconnection of the control stations 2, 2a and / or after an interruption in the power supply. Alternatively, a fixed predetermined configuration and control word value can be put into the memory, to be used in case of disconnection and / or power interruption. The values of the configuration can include identifications of packages that the unit is going to suppress or replace, etc.

Claims (16)

1. REVIVAL DICATIONS l. A mixing unit for a digital audio-visual transmission system, the mixing unit comprises an input for receiving a transport packet stream formed from a physically separate multiplexer, a mixing device for mixing the transport stream received in accordance with a random control word and an output for sending the mixed transport stream to a transmitting medium for subsequent transmission, in order to allow mixing of the transport packet stream by the mixing unit independently of the multiplexer operations .
2. 2. A mixing unit according to claim 1, wherein the mixing device is adapted to carry out mixing in part or all of the payload of selected packages of the transport stream package.
3. 3. A mixing unit according to claim 1 or 2, further comprising a packet insertion means for inserting transport packet data into the transport stream.
4. 4. A mixing unit in accordance with the claim 3, wherein the packet insertion means inserts a data packet into the transport stream detecting the presence of a null packet and replacing a null packet with the packet to be inserted.
5. A mixing unit according to any one of the preceding claims, further comprising a packet filtering means for identifying and copying to a memory part or all of a predetermined transport packet.
6. 6. A mixing unit according to any of the preceding claims, further comprising a means of eliminating packets to eliminate a predetermined packet or a series of packets.
7. 7. A mixing unit according to claim 6, wherein the packet elimination means removes a packet transformed from the packet identification of the packet to that of a null packet.
8. A mixing unit according to any of the preceding claims, further comprising a packet counting means for counting the number of packets of a predetermined packet identification value in the received transport data stream.
9. A mixing unit according to any one of the preceding claims, further comprising a means of repetition of package identification map mapping to change the package identification value assigned to a predetermined package or a series of packages.
10. A mixing system comprising a mixing unit according to any of the preceding claims together with a central control means for generating a control word sent to and received by the mixing unit for mixing the transport stream. eleven .
11. A mixing system according to claim 10, further comprising one or more access control systems connected to the central control means and adapted to receive a control word provided by the central control means and to send back to the medium of central control an encrypted message containing the control word.
12. 12. A mixing system according to claim 10 or 1, in which part or all of the data sent from the central control means to the mixing unit is authenticated by the central control means by generating an authorization in accordance with a secret encryption key.
13. 13. A mixing system according to any of claims 10, 11 or 12 comprises a plurality of mixing units and central control means associated with the generation of a single transport stream.
14. A mixing system according to any of claims 10 to 13, wherein the or each mixing unit is adapted to store its operating configuration characteristics and / or the value of the current control word.
15. 15. A mixing unit substantially as described herein with reference to and as illustrated in the accompanying drawings.
16. 16. A mixing system substantially as described herein with reference to and as illustrated in the accompanying drawings. RESU MEN An independent mixing unit (1) for a digital audio-visual transmission system, the mixing unit (1) comprises an input for receiving a bundled transport packet stream from a physically separate multiplexer (4), a mixing device for mixing the received transport stream in accordance with a random control word and an output for sending the mixed transport stream to a transmitting medium for subsequent transmission. The mixing unit (1) can also be used to introduce other data packets in the data stream.