Telephonic communications – Reception of calling information at substation in wireline... – Having broadband premise equipment
Reexamination Certificate
1996-06-19
2002-09-10
Hoosain, Allan (Department: 2645)
Telephonic communications
Reception of calling information at substation in wireline...
Having broadband premise equipment
C379S201110, C379S088130, C379S088220, C379S114290, C379S219000, C379S221020, C379S102030
Reexamination Certificate
active
06449352
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a packet generating method when transmitting by multiplexing one program composed of digital image, digital sound, digital data or the like, or multiplexing plural programs, a data multiplexing method using the same, and an apparatus for coding and decoding the transmission data.
This packet multiplexing method is also employed in MPEG (Moving Picture Experts Group), an international standard for data compression, and is designed to compress and encode the image data and sound data, in every frame for image or in every specific number of samples such as 1024 for sound (also called frame in the case of sound in MPEG), and generate a packet called PES packet by assembling one frame or plural frames.
FIG. 19
shows an outline of format of PES packet; a PES packet has a header, and the header includes information such as stream ID showing whether the succeeding data area is image data, sound data, or other data, or trick mode flag showing data for trick playback. It also contains a timing signal showing when to decode and reproduce in the frame unit of image data and sound data.
Each PES packet transmits by further dividing into a plurality of 188-byte long TS packets (transport packets) described below.
FIG. 21
shows an outline of format of TS packet. FIG.
21
(
a
) shows the state of a PES packet divided into plural TS packets to be continuous TS packets.
As shown in FIG.
21
(
b
), a TS packet is divided into a header, an extension header or adaptation field, and a payload for storing the compressed image or sound data.
The header contains, as shown in FIG.
21
(
c
), packet identifier PID, adaptation field control flag, and counter. The PID has a same value when data of same sequence is included in the payload. The adaptation field control flag indicates presence or absence of adaptation field and payload. The TS packet includes both or either one of adaptation field and payload. The counter shows the sequence of TS packets having same PID. The counter value is expressed in four bits, and is increased one by one, returning to o after
15
.
FIG.
21
(
d
) is an explanatory diagram of adaptation field, which includes, as shown in the diagram, random access instruction flag showing random access is enabled, discontinuity flag showing the TS packet is discontinuous, and PCR flag showing presence or absence of coding of reference time clock called PCR (program clock reference) necessary when decoding. In MPEG2, the clock frequency of multiplexing apparatus and separating apparatus is specified at 27 MHz, and in order to synchronize the clock of the multiplexing apparatus and separating apparatus, the clock of the multiplexing apparatus is counted at 27 MHz, and the obtained numerical value is sent as PCR. The separating apparatus reproduces the clock synchronized with the multiplexing apparatus from the received PCR. This PCR is not always required to be transmitted, but is transmitted at interval necessary for synchronization of the multiplexing apparatus and separating apparatus, for example, once in about 0.1 sec. Therefore, in the adaptation field, structurally, it may be allowed to be sent or not to be sent as optional field.
Thus constituted image decoder for decoding image data from the packet data is required to detect a special code called sequence start code in the first place. In the TS packet for transmitting image compressed data, when the random access instruction flag is 1, it is clear that the sequence start code is present in the payload.
The discontinuity flag indicates that discontinuity occurs in the value of counter or PCR shown in FIG.
21
(
c
).
This is description about the packet composition for multiplexing, transmitting or recording image data, sound data, or the like of one program, whereas plural programs can be multiplexed in the TS packet row shown in FIG.
21
(
a
). An example of such packet row is shown in FIG.
20
. In
FIG. 20
, aside from the packet of image, sound and data, there is also multiplexed a table packet for identifying each program when plural programs are multiplexed. Each packet contains identifier (PID) and counter. Multiplexing of plural programs is described below.
When selecting and decoding one program from the TS packet row containing plural programs, it is necessary to refer to the tables called PMT (program map table) and PAT (program association table) in order to identify and select plural programs.
The PMT is a table showing the PID of TS packet including image and sound data contained in one program as shown in FIG.
22
(
a
).
The PAT is a table containing the PID of PMT for each program as shown in FIG.
22
(
b
).
The PMT and PAT are multiplexed in the payload of the TS packet.
FIG. 23
shows an example of packet multiplexing apparatus for multiplexing and transmitting by such conventional MPEG2 multiplexing system, and multiplex data decoding apparatus for reproducing data by separating the input multiplex data. First, the operation of a multiplexing unit
1203
is described. A packet row stored in a first memory device
1201
is put into a first buffer
12031
of the multiplexing unit
1203
, and a packet row stored in a second memory device
1202
is put into a second buffer
12032
. A table packet is stored in a memory
12033
.
A CPU
12033
monitors the buffers
12031
,
12032
, and tilts a multiplex switch
12035
to the buffer side having input of TS packet, and issues the TS packet. The CPU
12033
also multiplexes and transmits the table packet in the TS packet at a specific interval.
The operation of a separating unit
1204
is described below. An input TS packet is first stored in a buffer
12041
. A CPU
12042
operates according to the flowchart shown in
FIG. 24
, and first receives the PAT and extracts the PID of the TS packet including the PMT of the program to be decoded, and then receives the PMT, and extracts the PID of the PS packet including the image and sound data of a selected program. In the input TS packet, a packet including PCR is sent to a clock control unit
1205
, and reproduces reference clock necessary for decoding of image and sound signals. The TS packet including image and sound data is issued into decoders
1206
,
1207
, respectively through a separation switch
12043
. In the decoders
1206
,
1207
, using the reproduced reference clock, image and sound data is decoded and expanded, and the program is reproduced.
The above international MPEG standard is, for example, ISO/IEC JETC1/SC29/WG11, N801, “ISO/IEC 13818-1 International Standard: INFORMATION TECHNOLOGY—GENERIC CODING OF MOVING PICTURES AND ASSOCIATED AUDIO SYSTEMS,” November 1994.
In such constitution alone, however, various problems occur in the decoding apparatus.
First, in the multiplexing apparatus, if the program is skipped halfway and transmitted, in the decoding apparatus, the counter of the TS packet in FIG.
21
(
c
) is discontinuous, and the decoding apparatus recognizes an error when detecting discontinuity of the counter, and the TS packet is discarded, and normal decoding may be disabled.
Or, if sequence start code is included in the image data, the random access instruction flag may not be always set at 1, and hence the separating unit in
FIG. 23
must search the image data in order to judge presence or absence of sequence start code. Therefore, the CPU requires high processing capacity, and the multiplex data decoding apparatus may be expensive.
Thus, when decoding one program, since identifier (flag) for processing securely is not disposed in a proper position in the packet row, data discarding, long processing time, or other inconvenience may occur.
When a packet row is fed by multiplexing plural programs, by referring to the table packet in the procedure shown in
FIG. 23
as mentioned above, only the packets composing one program can be selected and decoded. However, considering to change a program in the midst of reception in the multiplex data decoding apparatus, it is necessary to analyze by obtaining PAT and PMT again, and it takes a cert
Matsui Yoshinori
Takahashi Toshiya
Hoosain Allan
Matsushita Electric - Industrial Co., Ltd.
McDermott & Will & Emery
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