Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2003-06-09
2004-05-04
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C375S240270
Reexamination Certificate
active
06732313
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data transmission methods, data transmission apparatuses, data receiving apparatuses, and a packet data structure and, more particularly, to a process of performing data transmission in packet units between a distribution server and a terminal while successively reproducing the data of received packets at the terminal.
BACKGROUND OF THE INVENTION
For transmission of video (audio and video) data on the Internet, a download type transmission method and a stream type transmission method are currently employed.
In the download type transmission method, a video file transmitted from a distribution server is once copied at the terminal and, thereafter, data of the video file (video data) is reproduced. So, the terminal cannot perform data reproduction until the file transmission is completed. Therefore, the download type transmission method is not suitable for long-hours reproduction of video data or the like.
On the other hand, in the stream type transmission method, while video data or the like is transmitted from a distribution server to a terminal, received data is reproduced at the terminal.
Recently, a stream type transmission method using a protocol called RTP (Real-time Transport Protocol) which is defined in IETE RFC 1889, has mainly been used.
FIG.
28
(
a
) is a diagram for explaining a video data transmission method according to the RTP.
With reference to FIG.
28
(
a
), a distribution server (transmitting end) and a terminal (receiving end) such as a personal computer are connected by a cable in the Internet, such as modem, ISDN, or LAN, and transmission of video data is carried out between the server and the terminal by using the RTP.
In the data transmission according to the RTP, processes for the respective packets are synchronized between the transmitting end and the receiving end by using time stamps: as time information, and asynchronous (late arrival) packets and packets affected by transmission errors are discarded at the receiving end. Further, discarded or lost packets are detected at the receiving end, according to the absence of sequence numbers given to these packets.
On the other hand, Internet applications utilizing mobile phones, for example, mail access and text information service, are advancing now, and infrastructure for high-speed radio data communication (high-speed packet communication of ~384 kbps) is under preparation for practical use of the third generation mobile communication (W-CDMA: Wide band-Code Division Multiple Access).
FIG.
28
(
b
) is a diagram illustrating a communication network for the above-described W-CDMA visual terminal.
Such communication network includes a radio transmission section. For example, when performing data transmission between a video distribution server and a visual terminal through a relay server, the section between the distribution server and the relay server is a cable transmission section by the Internet, but the section between the relay server and the visual terminal is a radio transmission section by a mobile phone network such as the W-CDMA.
However, the bit error rate in the radio transmission section is 10
−3
while the bit error rate in the cable transmission section is 10
−5
~10
−7
, and the radio transmission quality becomes a problem in the RTP type data transmission method in which the reproduction quality depends on the end-to-end (server-to-terminal) transmission quality.
SUMMARY OF THE INVENTION
The present invention is made to solve the above-described problems and has for its object to provide a data transmission method, a data transmission apparatus, and a data receiving apparatus, which can improve the transmission quality in a radio section in real-time transmission.
Other objects and advantages of the invention will become apparent from the detailed description that follows. The detailed description and specific embodiments described are provided only for illustration since various additions and modifications within the scope of the invention will be apparent to those of skill in the art from the detailed description.
According to a first aspect of the present invention, there is provided a data transmission method for performing continuous data transmission from the transmitting end to the receiving end in units of packets, each packet having additional information relating to its sequence number, priority, and data reproduction time at the receiving end, while successively reproducing data of packets received at the receiving end. This method comprising the steps of: at the transmitting end, giving priority information to each packet to be transmitted; and storing, as retransmission data, only data of packets the priorities of which are equal to or higher than a predetermined value, in a retransmission buffer; at the receiving end, when a transmission error is detected, detecting the priority information of an error packet; and when the detected priority is equal to or higher than the predetermined value, outputting a retransmission request for the error packet to the transmitting end by indicating the sequence number of this error packet; at the transmitting end, only when the data of the packet having the sequence number which is indicated by the retransmission request from the receiving end is stored in the retransmission buffer, retransmitting the data of this packet to the receiving end; and discarding the data stored in the retransmission buffer in order starting from a packet which cannot be in time for data reproduction at the receiving end. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a second aspect of the present invention, in the data transmission method of the first aspect, when the retransmission buffer is filled up to its capacity, an updating process is performed, in which the retransmission data are retained while the data stored in the retransmission buffer are discarded in order, starting from a packet of the earliest reproduction time, on the basis of the reproduction time of each packet stored in the retransmission buffer. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a third aspect of the present invention, in the data transmission method of the first aspect, when the data transmitted from the transmitting end to the receiving end is video data based on MPEG, a packet which contains data corresponding to frames coded by utilizing intra-frame correlation is regarded as a packet having a high priority. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a fourth aspect of the present invention, in the data transmission method of the first aspect, at the transmitting end, the additional information relating to the sequence number and the priority of a predetermined packet is also embedded in a subsequent packet to be transmitted after the predetermined packet; and at the receiving end, in the case where a transmission error has occurred in the predetermined packet and the additional information of the predetermined packet has an error, a retransmission request for the predetermined packet as an error packet is made on the basis of the additional information of the predetermined packet which is embedded in the subsequent packet, when the subsequent packet transmitted after the predetermined packet is received. Therefore, the transmission quality in a radio section in real-time transmission is improved and, further, the number of retransmission times is reduced.
According to a fifth aspect of the present invention, in the data transmission method of the fourth aspect, at the transmitting end, the process of embedding the sequence number of a predetermined high priority packet in a subsequent packet which follows the predetermined high priority
Fukushima Hideaki
Hagai Makoto
Horii Seiji
Matsui Yoshinori
Miyazaki Akihiro
Britt Cynthia H
De'cady Albert
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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