Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2000-05-12
2004-11-30
Duong, Frank (Department: 2666)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S395500, C370S395640
Reexamination Certificate
active
06826185
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a system for transporting and broadcasting encoded audiovideo streams and, more particularly, to a piece of equipment for remultiplexing such streams, that is to say a unit to extract from a stream containing several programs the information related to specific programs and their re-organization into an output stream to be transmitted to users.
BACKGROUND OF THE INVENTION
It is known that an increasing number of encoded audio-video programs (television programs in particular) are transmitted by cable or satellite. The techniques for transporting such programs are governed by international standards, among which series ETS 300 4xx ETSI standards (“Digital broadcasting systems for television, sound and data services . . . ”) are mentioned as an example. These standards concern the transmission on the same cable or on the same satellite channel of a certain number of encoded and multiplexed programs in conformity with the procedures established by recommendation ITU-T H222 or standard ISO/IEC 13818, “Information Technology—Generic Coding of Moving Pictures and Associated Audio Information”, commonly known as the MPEG2 Standard. This standard defines syntax both for encoded SPTS Single Program Transport Streams and multiplexed MPTS Multiprogram Transport Streams. The standard also specifies the rules for transporting the information on stream content, in particular the PSI/SI Program Specific Information/System Information table. Transport streams consist of 188 byte fixed-length packets that include a header and a data field or payload that can contain either elementary audio-video or table data. In its turn, the header includes a Packet Identifier (PID) whose value is univocally assigned to single elementary streams for the entire duration of a program. A special PID value identifies packets carrying a specific Program Association Table (PAT) containing the information required to
identify the Program Map Table (PMT), which in its turn contains information on the single elementary streams inside a single program. The packet header also contains synchronization information transmitted periodically, including the Program Clock Reference (PCR), which plays an interesting role within this invention.
In conventional cable or satellite broadcastings, the entire stream of multiprograms reaches the home of the user, who selects a program with a special set top box.
The audio-video business is also becoming interesting for telecommunications operators, since optical fiber-based long distance lines feature the capability required for transporting several multiprogram streams on the one hand, and the use of XDSL techniques (Cf. standard ITUT G.992 for the ADSL technique for instance) for transmission on user lines has made capabilities in the range of Mbit/s to some tens of Mbit/s available for supplying users with single audio programs or a limited number of programs on the other. Specification DAVIC 1.1 that can be consulted at Internet site www.davic.org sets the features of a possible service known as Switched Digital Video Broadcasting (SDVB) that telecommunications operators can offer users through fixed web infrastructures.
Program selection in this type of service cannot be allocated to the user unit but must be made by centralized bodies, such as access web nodes for instance, receiving user selection commands and having the capability of identifying and extracting the program elementary streams inside the multiprogram transport stream, and compressing them into a single program stream, then associating this latter with the service information required for proper user decoding and sending it to the user. These operations are completed at one or several points of the web by Broadcast Control Units (BCU) allocated to user command receipt and processing jointly with an Replication Unit (RU) receiving multiprogram streams and distributing them to individual users. The operation whereby a multiprogram stream is split into single program streams or more generally into lower capacity streams is commonly known as remultiplexing.
The devices featuring this function, if necessary jointly with the multiplexing of independent programs in a transport stream or with the addition of programs to a transport stream, are documented and available commercially. U.S. Pat. No. 5,835,493 is mentioned as an example, which describes in detail the problems associated with the remultiplexing of transport streams of the TokenMux unit produced by the Philips Company of Eindhoven, Holland.
The creation of a switched video transmission service further requires adapting MPEG transport streams from service suppliers to the transport technique adopted on the web. A convenient and nearly natural choice for transport is using the ATM technique by inserting each program into a virtual channel. In particular, the choice was made to use the so-called ATM Adaptation Layer level AAL
5
defined in ITU-T Recommendation 1.363. In transferring program packets to ATM virtual channels the need arises to check that the peak band for each channel on each of these lines does not exceed the band available on the line itself (typically 8 Mbit/s if an ADSL connection is used). This requires control, known as shaping or leveling, of output streams to level off traffic peaks.
Known remultiplexing devices do not provide direct remultiplexing of MPEG transport streams into ATM virtual channels and the purpose of the invention is to supply an unit capable of transferring an MPEG multiprogram transport stream to an ATM virtual channel and multiplexing virtual channels into virtual itineraries, bearing the band control needs mentioned above in mind.
SUMMARY OF THE INVENTION
The invention provides equipment for remultiplexing encoded audio-video streams transmitted within a switched digital video broadcasting system, each containing multiple programs (multiprogram transport streams), in which program information is transmitted in packets each including a packet identifier supplying information as to the program identity the packet refers to and a payload containing program data or stream structure service information. This equipment comprises syntactical analysis and reception means-circuits (AS; FLI . . . FLn, MSI . . . MSn) suitable to receive a plurality of such streams, separate in each flow packets which can be forwarded directly to
output stream generation means (CF; AA, MC, TU), from packets which must be forwarded to the said control device (MP) to be submitted to processing, in particular for updating service information to reflect the composition of output streams. Means (ME) for temporary storage of data packets is provided separately for each input stream.
The output stream generation means circuits (CA; AA, MA, TU) generates and sends to users output streams obtained starting from the packets stored in such said temporary memories (ME) and from the processed service packets, such output streams being single or multi-program streams at a lower band than input streams.
The control device (MP) is suitable to receive the service packets from syntactical analysis and reception means (AS; FL
1
. . . FLn, MS
1
. . . MSn), to identify individual streams making up the multiprogram streams, to perform updating of service information and drive temporary memory means (ME) and output stream generation means-circuits (CF; AA, MC, TU) so as to enable the creation of single or multi-program streams for different users.
According to the invention such output stream generation means (CA; AA, MA, TU) are suitable to create ATM streams by transferring packets related to the same program or group of programs to ATM cells related to one or more virtual channel and multiplexing such virtual channels into multiple itineraries each containing programs of the same input stream. The output stream generation means circuits (CF; AA, MC, TU) is suitable to perform, during ATM stream generation, a two-step control of the band associated to each ATM stream by reading the packets allocated to different virtua
Montanaro Achille
Mori Luigi
Pilati Luciano
Turolla Maura
Dubno Herbert
Duong Frank
Jagannathan Melanie
Telecom Italia Lab S.p.A.
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