Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1999-08-30
2003-06-24
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S429000
Reexamination Certificate
active
06584069
ABSTRACT:
This application is based on an application No. H10-245729 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention applies to a packet filtering apparatus that filters packets In particular, the invention relates to an apparatus, such as that used by a set-top box (hereafter, STB) for receiving a broadcast, that extracts required packets from a plurality of packets that are transferred as a broadcast.
(2) Prior Art
Several techniques for transferring video and audio information as digital information have been developed. Such techniques can be used in broadcasting and other fields, and transfer such digital information as packets that are obtained by dividing the digital information into units of a suitable length and adding information required for transfer. A packet is therefore a processing unit that is indicated to both the transmitter and receiver in advance. The information required for transfer includes the type, size, and transfer destination of each packet. In many cases, such information forms the first part of each packet, and so is called the header information.
The transferred packets are received by a reproduction apparatus (such as an STS that receives a broadcast or a personal computer connected to the Internet) that uses the information in them to reproduce video and audio. In order to extract the video and audio from the packets, the reproduction apparatus first has to select only the required packets out of the various packets it receives. This processing for selecting the right packets can be achieved exclusively by software that is executed by the CPU in the reproduction apparatus. However, to reduce the processing load of the CPU, this packet selecting will generally be executed by specialized packet selecting hardware (hereafter, a filtering apparatus) that is independent of the CPU.
In digital broadcasts (and digital communication in general), a field denoting a version number showing the position of a packet in the order of packets is given at a specified position in header information. For certain kinds of packets (such as those including information for a list of broadcast programs), the same information is broadcast consecutively and cyclically to guarantee that the reproduction apparatus will be able to immediately obtain the latest information, even if the reproduction apparatus has been switched on midway through a broadcast.
In general, a packet with the same content as a preceding packet with the same packet type will be given the same version number. Conversely, a packet with the same packet type but a content that follows the preceding packet will be given a version number that is one greater than that of the preceding packet. Such version number is reset to zero on exceeding a maximum value.
A conventional filtering apparatus that is provided in a reproduction apparatus passes (i.e., selects) packets that are consecutively transmitted according to a filter condition whereby the version number has to match a specific value. When version numbers are used for packets, the filtering apparatus will only select a packet of a specified type if the version number of the packet follows the version number of the previously received packet of that type. The selected packet is then used by the reproduction apparatus in the processing it performs thereafter.
The following is a detailed description of the selection of packets by a conventional filtering apparatus in detail, with reference to
FIGS. 1
to
6
.
FIG. 1
is a block diagram showing the construction of a conventional filtering apparatus
131
.
FIG. 2
shows examples of the filtering conditions stored in the filtering condition storage unit
1314
. Here, assume that the construction and operation of the reproduction apparatus that includes the filtering apparatus
131
are fundamentally the same as those of the STB
3
explained in the “Description of the Preferred Embodiments” with reference to
FIGS. 8 and 9
, etc.
As shown in
FIG. 1
, the conventional filtering apparatus
131
includes a packet obtaining unit
1311
, a filtering unit
1312
, a packet outputting unit
1313
, a filtering condition storage unit
1314
and a filtering condition setting unit
1315
.
The packet obtaining unit
1311
obtains a packet from a broadcasting center via a wired or wireless transfer path, and sends the packet to the filtering unit
1312
. The filtering control unit indicates the filtering conditions to the filtering condition setting unit
1315
, which then stores the indicated filtering conditions in the filtering condition storage unit
1314
.
As shown in
FIG. 2
, each filtering condition stored in the filtering condition storage unit
1314
is composed of a filtering condition number for specifying the filtering condition, a comparison data position, and comparison data. The filtering condition number is composed of a one-byte integer, while the comparison data position and comparison data are each composed of an eight-byte integer. All these values are expressed in hexadecimal. Note that the comparison data position and comparison data are explained later in this text.
The filtering unit
1312
operates as follows. When a packet is received from the packet obtaining unit
1311
, the filtering unit
1312
applies the filtering conditions stored in the filtering condition storage unit
1314
, judges whether the obtained packet is necessary, and sends only the packets it has judged to be necessary to the packet outputting unit
1313
. The packet outputting unit
1313
stores the packets transferred in this way into a buffer memory. This buffer memory has a plurality of areas, with packets being stored into different areas according to which filtering condition they satisfy. Video and audio reproduction then take place using the packets that have been stored into the buffer memory.
The following is a detailed description of the control procedure by which the above conventional filtering apparatus
131
performs filtering by judging whether the obtained packets are necessary.
FIG. 3
is a flowchart showing the control procedure for the filtering of packets by a conventional filtering apparatus
131
(shown in FIG.
1
).
FIG. 4
shows the actual packets that are obtained by the packet obtaining unit
1311
.
In the example shown in
FIG. 4
, the packet obtaining unit
1311
obtains packets
501
to
509
one at a time in that order. In each packet, one-byte units of data are successively obtained in the order shown from left to right (1A, 3F, 05, AB . . . ) in FIG.
4
.
The following describes the filtering by the filtering apparatus
131
. First, a packet to be stored in the buffer memory is specified according to an indication from the filtering control unit. In accordance with this packet, filtering conditions, such as those shown in
FIG. 2
, are set by the filtering condition setting unit
1315
and are stored in the filtering condition storage unit
1314
(S
201
). After this, the packet obtaining unit
1311
obtains the next packet to arrive via the transfer path (S
202
), and one of the filtering conditions stored in the filtering condition storage unit
1314
is selected (S
203
).
Suppose here that the plurality of filtering conditions are applied one a time in order of the filtering condition numbers to packet
501
that has been obtained by the packet obtaining unit
1311
, Tn such case, filtering condition#
1
is selected, and it is judged whether packet
501
satisfies this filtering condition. After this, filtering condition#
2
is selected as the next filtering condition and the judgement is performed again for packet
501
.
A logical AND is taken for the comparison data position of the selected filtering condition and the first eight bytes of the packet obtained by the packet obtaining unit
1311
, and the result is substituted into the variable x (S
204
). The comparison data is substituted into the variable y (S
205
).
In an actual example, the value 0000000000000090 is substituted int
Kagemoto Hideki
Kakiuchi Takashi
Okamura Kazuo
Takao Naoya
Emdadi Kamran
Matsushita Electric Industrial Co. LTD
Yao Kwang Bin
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