Abstract:
Disclosed is a system and method for sending and receiving information of digital cable broadcasting, which comprises: a headend unit for assigning a packet identifier (PID) from within a range of PIDs to tables carrying data according to inclusion of service information (SI), constructing a transport packet (TP), and sending it using an MPEG communication method; and a receiving unit for receiving the TP from the headend unit, checking the PID of the TP to determine whether the TP includes SI, and determining how to process the TP depending on inclusion states of SI in the TP. The PID discriminates a TP including SI from a TP including other messages in transmission of MPEG-2 TPs from the headend unit to the receiving unit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (a) Field of the Invention  
           [0002]    The present invention relates to a system and method for sending and receiving information of digital cable broadcasting. More specifically, the present invention relates to a system and method for sending and receiving information of digital cable broadcasting that is to more rapidly process service information than any other messages transferred on out-of-band channels.  
           [0003]    (b) Description of the Related Art  
           [0004]    In general, digital cable broadcasting is a system for converting analog broadcast signals to digital codes similar to those used in computers and sending the digital codes to a digital TV picture receiver, which displays the received digital codes to viewers. The digital cable broadcasting employs digital equipment in all processes related to production, sending, and receiving of broadcast programs, and it makes use of its advantageous functions, such as high resolution and data broadcasting.  
           [0005]    There are two communication methods using out-of-band channels that are prescribed in the current digital cable broadcasting.  
           [0006]    One method uses MPEG-2 (Motion Picture Experts Group 2) transport packets for downward communication from a headend to a subscriber-receiver, and an ATM (Asynchronous Transfer Mode) cell format for upstream communication from the subscriber-receiver to the headend.  
           [0007]    MPEG-2 is an image compression method that was standardized as ISO 13818 in 1994 and is now widely used for computer media service (e.g., DVD), broadcasting service (direct satellite broadcasting, cable broadcasting, high-definition TV, etc.), movies, and advertisement editions.  
           [0008]    The other method utilizes an SL-ESF (Signaling Link-Extended Super Frame) format for downward communication from the headend to the subscriber-receiver, and an ATM cell format for upstream communication from the subscriber-receiver to the headend.  
           [0009]    In the downward communication of the MPEG-2 transport packets using the former method, the subscriber-receiver extracts the received MPEG-2 transport packets based on the packet identifier (PID) included in the transport packets. Subsequently, the messages in the data link layer are reconstructed from the data extracted from the private section of the MPEG-2 transport packets.  
           [0010]    To reconstruct the MPEG-2 transport packets, use is made of a payload unit start indicator (PUSI) bit included in the header of the MPEG-2 transport packets. It is then determined from the address-type portion of the header if the messages thus constructed are transmitted to a single cast address or a broadcast address.  
           [0011]    The single cast address is for data transmission to an individual set-top-box and the broadcast address is for data transmission to all set-top-boxes.  
           [0012]    For a message transmitted to the single cast address, the receiver compares the single cast address with it&#39;s own private address and determines whether the message is for it. If the message is destined for the private address, the receiver processes the corresponding message in the next step; otherwise, it discards the message.  
           [0013]    For a message transmitted to the broadcast address, the receiver receives the message unconditionally and checks the reception state by a cyclic redundancy check (CRC).  
           [0014]    In this manner, the receiver constructs a protocol data unit (PDU) and combines more than one PDU to construct a service data unit (SDU).  
           [0015]    The SDU thus constructed has an Internet protocol (IP) datagram form. The receiver extracts the payload portion from the IP datagram to take the message sent from the headend.  
           [0016]    In transmission of service information on out-of-band channels by the above procedures, the conventional method for sending and receiving information of digital cable broadcasting encounters several problems related to inefficient transmission, as follows.  
           [0017]    The service information refers to a set of additional information in a table format that enables the viewers to see and hear the programs. The service information allows the viewers to choose a desired program via one of at least 100 channels supported in the digital cable broadcasting.  
           [0018]    In communication of the service information, the headend receives the service information included in the IP datagram from an application server and inserts additional information before the header of the IP datagram in order to interpret the message in the data link layer of the receiver prior to division of the IP datagram into MPEG-2 transport packets.  
           [0019]    The additional information comprises message type, address type, message length, and message version fields, and it has a variable length depending on the address type. But the service information can also be transmitted normally without additional information.  
           [0020]    The message type field enables the PID to determine if the message contains the service information, because the service information is transmitted via the private section of the MPEG-2 transport packets. The service information, which is transmitted to the broadcast address, requires no address field.  
           [0021]    The message length field is used to construct medium access control (MAC) packets in the data link layer of the receiver and becomes useless when there is no need for forming the MAC packets. The message version field is normally set to “zero” and is thus meaningless. Accordingly, the headend performs an unnecessary process of inserting additional information in transmission of the service information that makes the transmission inefficient. In the case where the headend inserts the IP datagram independently into the 184-byte payload other than the 4-byte header of the MPEG-2 transport packet, the receiver has to extract the IP datagram from the received MPEG-2 transport packet and then extract the payload from the IP datagram so as to acquire service information in the MPEG-2 private section format. As the headend also transmits the IP datagram, a problem related to the inefficient transmission occurs in that the receiver performs an unnecessary step of extracting the data.  
           [0022]    On the other hand, U.S. Pat. No. 5,892,910 discloses a communication method for a bidirectional cable TV system, in which the data between the sender&#39;s headend equipment are communicated according to the IP protocol and all messages are multiplexed for MPEG-2 communication and sent to the receiver, which then extracts the data from the MPEG-2 transport messages.  
           [0023]    Such a communication method for a bidirectional cable TV system has some problems in regard to the complexity of the receiver circuit as well as difficulty in managing the service information in a rapid and efficient manner, because the communication protocol message format for data transmission is too complex and all the data sent to the receiver are multiplexed by the MPEG2 communication system.  
         SUMMARY OF THE INVENTION  
         [0024]    It is an object of the present invention to provide a system and method for sending and receiving information of digital cable broadcasting that is to more rapidly process service information than any other messages transferred on out-of-band channels from a headend to a receiver in digital cable broadcasting.  
           [0025]    In one aspect of the present invention, there is provided a system for sending and receiving information of digital cable broadcasting that includes: a headend unit for assigning a packet identifier (PID) from within a range of PIDs predefined by the system to tables carrying data according to inclusion of service information, constructing a transport packet, and sending the constructed transport packet using a motion picture experts group (MPEG) communication method; and a receiving unit for receiving the transport packet from the headend unit, checking the PID of the transport packet to determine whether the transport packet includes service information, and deciding how to process the transport packet depending on inclusion of service information in the transport packet.  
           [0026]    The headend unit and the receiving unit designate the PID of the transport packet containing service information excepting an aggregate event information table (AEIT) and an aggregate extended text table (AETT) as a first specified number, and the PID of the transport packet containing service information including the AEIT or AETT as a second specified number within a defined range of PIDs excepting the first specified number.  
           [0027]    The headend unit includes: a service information generator for generating the tables including the service information in MPEG private section format and sending them on an IP datagram; and a transport packet generator for receiving the IP datagram from the service information generator, assigning a PID to construct a transport packet, and outputting the constructed transport packet.  
           [0028]    The service information generator uses a PID predefined by the system exclusively for the transport packet including service information so as to discriminate the transport packet including service information from transport packets including other messages.  
           [0029]    The service information generator adds an indicator bit to a header of the transport packet so as to discriminate between IP datagrams including different service information.  
           [0030]    The service information generator constructs a master guide table (MGT) that provides a version, size, and PID of all other tables, among the tables including service information.  
           [0031]    The transport packet generator extracts a payload from the IP datagram received from the service information generator and assigns the PID of the transport packet as the first specified number for the table containing service information excepting the AEIT and the AETT, and as the second specified number for the table containing service information including the AEIT or AETT.  
           [0032]    The transport packet generator extracts a payload of the IP datagram received from the service information generator and adds a transport packet header of a predetermined size to construct the final transport packet.  
           [0033]    The transport packet generator determines the PID with reference to the MGT received from the service information generator.  
           [0034]    The receiving unit includes: a PID checker for checking the PID of the transport packet received from the headend unit and determining whether the PID is in a range of PIDs predefined by the system, to discriminate a transport packet including service information from a transport packet not including service information; a table constructer for receiving the transport packet including service information from the PID checker, extracting the service information from the transport packet, and constructing various tables; and a link layer packet constructer for receiving the transport packet not including service information from the PID checker and constructing a protocol data unit (PDU) and a service data unit (SDU).  
           [0035]    The PID checker checks the PID of the transport packet received from the headend unit and decides that the transport packet includes service information when the PID is identical to the first specified number; that the transport packet includes the AEIT or AETT when the PID is identical to the second specified number; or that the transport packet does not include service information when the PID is identical to neither of the first specified number nor the second specified number.  
           [0036]    The table constructer extracts service information messages from a private section of the transport packet received from the PID checker and constructs various tables using a table identifier of the extracted service information messages.  
           [0037]    In another aspect of the present invention, there is provided a method for sending and receiving information of digital cable broadcasting that includes: (a) a headend assigning a packet identifier (PID)s from within a range of PIDs predefined by the system to tables carrying data according to inclusion of service information, constructing a transport packet, and sending the constructed transport packet to a receiver using a motion picture experts group (MPEG) communication method; and (b) upon reception of the transport packet in the step (a), the receiver checking the PID of the transport packet to determine whether the transport packet includes service information, and deciding how to process the transport packet depending on inclusion of service information in the transport packet.  
           [0038]    The step (a) includes the headend and the receiver designating the PID of the transport packet containing service information excepting an aggregate event information table (AEIT) and an aggregate extended text table (AETT) as a first specified number, and the PID of the transport packet containing service information including the AEIT or AETT as a second specified number within a defined range of PIDs excepting the first specified number. The step (a) includes: generating the tables including service information in MPEG private section format and sending them on an IP datagram; and receiving the IP datagram from the service information generating step, assigning a PID to construct a transport packet and sending the constructed transport packet to the receiver.  
           [0039]    The transport packet generating step includes: extracting a payload from the IP datagram, and assigning the first specified number for the table containing service information excepting the AEIT and the AETT, and the second specified number for the table containing service information including the AEIT or AETT. The step (a) includes: assigning a PID excepting the first and second specified numbers to the messages not including service information and constructing the transport packet.  
           [0040]    The step (b) includes: checking the PID of the transport packet received from the step (a) and determining whether the PID is predefined by the system; when the PID is predefined by the system, deciding that the transport packet includes service information, extracting service information messages from the transport packet, and constructing tables; and when the PID is not predefined by the system, deciding that the transport packet does not include service information, and processing the transport packet in a data link layer.  
           [0041]    The PID checking step includes: determining whether the PID of the transport packet corresponds to the first specified number; deciding that the transport packet contains service information excepting the AEIT and the AETT when the PID corresponds to the first specified number; determining whether the PID corresponds to the second specified number when the PID does not correspond to the first specified number; deciding that the transport packet contains service information including the AEIT or AETT when the PID corresponds to the second specified number; and deciding that the transport packet does not include service information when the PID corresponds to neither of the first specified number nor the second number.  
           [0042]    The link layer processing step includes: receiving the transport packet not including service information; constructing a protocol data unit; and combining more than one protocol data unit to construct a service data unit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention:  
         [0044]    [0044]FIG. 1 is a block diagram showing the construction of a headend unit in a system for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention;  
         [0045]    [0045]FIG. 2 illustrates the structure of an MPEG-2 transport packet generated from the headend unit;  
         [0046]    [0046]FIG. 3 is a block diagram showing the construction of a receiving unit of digital cable broadcasting in accordance with an embodiment of the present invention;  
         [0047]    [0047]FIG. 4 is a flow chart showing a method for sending information from the headend unit in the method for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention; and  
         [0048]    [0048]FIG. 5 is a flow chart showing a method for receiving information at the receiving unit in the method for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0049]    In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.  
         [0050]    A system according to an embodiment of the present invention comprises a headend unit for constructing MPEG-2 transport packets, and a receiving unit for receiving the MPEG-2 transport packets to construct various information tables and processing information.  
         [0051]    [0051]FIG. 1 is a block diagram showing the construction of the headend unit in a system for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention.  
         [0052]    As shown in FIG. 1, the headend unit  10  comprises a service information generator  11  for generating tables including service information in a MPEG-2 private section format and sending them on an IP datagram, and a transport packet generator  13  for receiving the IP datagram from the service information generator  11  and assigning a PID to the IP datagram to construct and output MPEG-2 transport packets.  
         [0053]    Hence, the headend unit  10  extracts the service information in the MPEG-2 private section format from the payload of the IP datagram without including the IP datagram in the MPEG-2 transport packets, and adds a  4 -byte header to the MPEG-2 private section to construct the MPEG-2 transport packets.  
         [0054]    [0054]FIG. 2 illustrates the structure of the MPEG-2 transport packet generated from the headend unit.  
         [0055]    As shown in FIG. 2, the IP datagram  20  comprises a header  21  and service information  22 , and the private section  30  comprises a table identifier  31 , a section syntax indicator  32 , a private indicator  33 , a section length  35 , and service information  36 .  
         [0056]    A transport packet stream  40  comprises a sync byte  41 , a transport error indicator  42 , a payload unit start indicator  43 , a transport priority  44 , a PID  45 , a transport scrambling device  46 , an adaptation field control  47 , a continuity counter  48 , and service information  49 .  
         [0057]    The transport packet generator  13  extracts the payload of the IP datagram received from the service information generator  11  and adds 4-byte MPEG-2 transport packet headers  41  to  48  and 184-byte service information  49  to construct the 188-byte MPEG-2 transport packet  40 .  
         [0058]    The PID  45  is assigned to the MPEG-2 transport packet  40  having a 4 byte header, and it is used to discriminate the MPEG-2 transport packets including service information from those including other messages.  
         [0059]    In the system according to an embodiment of the present invention, the PID for a transport packet including service information has a first specified number designated as 0x1FFC, lest it should be used for transport packets including messages other than the service information.  
         [0060]    When the application server of the headend unit  10  generating the service information constructs a master guide table (MGT), the PID for an MPEG-2 transport packet including an aggregate event information table (AEIT) and an aggregate extended text table (AETT) has a second specified number designated with a value other than that of the first specified number, within a defined range.  
         [0061]    The MGT provides version, size, and PID for all tables except a system time table (STT). The AEIT provides information for events on a virtual channel, and the AETT provides a detailed description of the virtual channel and the events.  
         [0062]    The transport packet generator  13  uses the payload unit start indicator&#39;s bit included in the header of the MPEG-2 transport packet to discriminate the IP datagram including the service information from those including other service information.  
         [0063]    [0063]FIG. 3 is a block diagram showing the construction of the receiving unit of the system of digital cable broadcasting in accordance with an embodiment of the present invention.  
         [0064]    As shown in FIG. 3, the receiving unit  50  comprises a PID checker  51  for checking the PID from the MPEG-2 transport packet received from the transport packet generator  13  of the headend unit  10  via the out-of-band channel and determining if the transport packet includes service information; a table constructer  53  for, upon receipt of a transport packet including service information, extracting service information from the transport packet received from the PID checker  51  and constructing various tables; and a link layer packet constructer  52  for, upon receipt of a transport packet not including service information, constructing a protocol data unit (PDU) according to the regulation of the SCTE DVS  178  and combining more than one PDU to construct a service data unit (SDU).  
         [0065]    The receiving unit  50  separately manages the first and second specified numbers for PIDs of the MPEG-2 transport packet including service information on agreement with the headend unit  10 .  
         [0066]    The PID checker  51  checks whether the PID of the MPEG-2 transport packet is identical to the first specified number, 0x1FFC. If the PID is 0x1FFC, the PID checker  51  determines that the MPEG-2 transport packet includes service information, and sends the transport packet to the table constructer  53 .  
         [0067]    If the PID is not identical to the first specified number, the PID checker  51  checks whether the PID corresponds to the second specified number separately assigned for AEIT and AETT.  
         [0068]    When the PID of the MPEG-2 transport packet is identical to the second specified number, the PID checker  51  sends the MPEG-2 transport packet to the table constructor  53 . Otherwise, when the PID is not the first or second specified number, the PID checker  51  determines that the MPEG-2 transport packet does not include service information, and sends the MPEG-2 transport packet to the link layer packet constructer  52 .  
         [0069]    Accordingly, the receiving unit  50  can discriminate the transport packet including AEIT and AETT from other transport packets received via out-of-band channels.  
         [0070]    The table constructer  53  extracts service information messages from the private section of the MPEG-2 transport packet received from the PID checker  51  and uses the table identifiers of the extracted service information messages to construct a network information table (NIT), a network text table (NTT), a short-form virtual channel table (S-VCT), a long-form virtual channel table (L-VCT), and a system time table (STT).  
         [0071]    Next, a description will be given to an operation of the system for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention with reference to FIGS. 4 and 5.  
         [0072]    [0072]FIG. 4 is a flow chart showing a method for sending information from the headend unit in the method for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention.  
         [0073]    As shown in FIG. 4, the service information generator  11  of the headend unit  10  determines in step S 11  whether the data-carrying tables include service information. The service information generator  11  generates tables including service information in the MPEG-2 private section format, in step S 12 , and sends the generated service information tables on the IP datagram  20  to the transport packet generator  13 , in step S 13 .  
         [0074]    The transport packet generator  13  extracts the payload of the IP datagram  20  received from the service information generator  11 , in step S 14 , and determines in step S 15  whether the service information tables include an AEIT/AETT.  
         [0075]    If the AEIT/AETT is not included, the transport packet generator  13  assigns a first specified number, 0x1FFC as a PID, in step S 16 . Otherwise, if the AEIT/AETT is included, the transport packet generator  13  examines the PID from the MGT and assigns a second specified number, in step S 17 .  
         [0076]    In constructing the MGT among the service information tables, the transport packet generator  13  assigns the PID of the AEIT/AETT as the second specified number within a predefined range of PIDs on agreement between the headend unit  10  and the receiving unit  50 . Once the PID is assigned, the transport packet generator  13  adds a 4 byte transport packet header to the private section  30  to construct a 188-byte MPEG-2 transport packet  40 , in step S 18 .  
         [0077]    If the service information generator  11  determines in step S 11  that the tables do not include service information, the transport packet generator  13  constructs the transport packet using a PID of other than the first and second specified numbers so as to discriminate it from those including service information, in step S 18 .  
         [0078]    Once the MPEG-2 transport packet construction is completed, the transport packet generator  13  sends the transport packet to the receiving unit  50  via the out-of-band channel, in step S 19 .  
         [0079]    [0079]FIG. 5 is a flow chart showing a method for receiving information at the receiving unit in the method for sending and receiving information of digital cable broadcasting in accordance with an embodiment of the present invention.  
         [0080]    As shown in FIG. 5, the PID checker  51  receives an MPEG-2 transport packet through a physical layer, in step S 21 , and checks the PID of the transport packet, in step S 22 .  
         [0081]    The PID checker  51  determines in step S 23  whether the PID of the transport packet is identical to the first specified number. If so, the PID checker  51  considers that the transport packet includes service information, and sends the transport packet to the table constructer  53 , in step S 24 .  
         [0082]    If the PID of the transport packet is not identical to the first specified number, the PID checker  51  determines in step S 25  whether the PID corresponds to the second specified number. If so, the PID checker  51  considers that the transport packet includes an AEIT/AETT among the service information tables, and sends the transport packet to the table constructor  53 , in step S 26 .  
         [0083]    Upon receiving the transport packet from the PID checker  51 , the table constructer  53  extracts service information messages from the private section of the MPEG-2 transport packet, in step S 27 , and uses the table identifiers of the extracted service information messages to construct various tables, in step S 28 .  
         [0084]    If the PID does not correspond to the second specified number, the PID checker  51  considers that the MPEG-2 transport packet does not include service information, and sends the MPEG-2 transport packet to the link layer packet constructer  52 , in step S 29 .  
         [0085]    The link layer packet constructer  52  constructs a PDU in the data link layer, in step S 30 , and combines more than one PDU to construct an SDU, in step S 31 .  
         [0086]    While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.  
         [0087]    The system and method for sending and receiving information of digital cable broadcasting according to the present invention makes use of a PID predefined by the system to discriminate the transport packet including service information from the transport packet including other messages in transmission of MPEG-2 transport packets from the headend unit to the receiving unit.  
         [0088]    The receiving unit gives a priority to the transport packet including service information using the PID predefined by the system in extraction to construct a table including service information, decides that the transport packet having a PID not predefined by the system does not include service information, and processes the transport packet not including service information in the data link layer.  
         [0089]    Accordingly, the present invention eliminates a step of disassembling and reconstructing frames in the data link layer of the receiving unit and enables processing of the messages including service information more rapidly than any other messages and simplifies the circuit of the receiving unit.