Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
2001-11-29
2003-06-10
Olms, Douglas (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S464000
Reexamination Certificate
active
06577646
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a transmitting apparatus to transmit video and audio signals between digital video/audio apparatuses, acquiring a part of a bandwidth of a transmitting medium before communication.
TECHNICAL BACKGROUND
Nowadays, standardization is proceeded for a bandwidth compression system of a digital video signal and a digital audio signal. The system is called MPEG (Moving Picture Experts Group) and is divided into two groups, MPEG1 subject to storage media at a low rate and MPEG2 which realizes a high picture quality for broadcast and can correspond to different picture sizes. In MPEG2, because compression ratio is variable for a picture size or a required picture quality, the data size per time is variable for broadcast programs and contents.
Further, in MPEG2, standardization is also proceeded for data transmission system used for broadcast. In this transmission system, one program is called stream and the data size is variable in each stream (variable rate) and a system to transmit a plurality of streams all together is standardized. Especially, in the case in which a reproducing apparatus to reproduce compressed video audio signals has to isochronize with the broadcast station which makes compression, like in a case to receive a broadcast wave, a stream called transport stream is used. In this transport stream, a device to make the reproducing apparatus possible to isochronize is included, using a parameter in the stream. In the transport stream, the data is transmitted with a axed length packet (transport stream packet, hereafter) and data necessary for isochronization is also transmitted with the same kind of packet. It is described in a reference, coding of moving picture and associated audio information Part 1, System″ of ISO/IEC International Standard 13818-1, International Technology.
In the case of transmitting a plurality of streams, it is possible to vary the data size per stream if necessary although the bandwidth of the entire transmission medium is fixed. It is possible to effectively use the bandwidth of the determined transmission medium by allocating a broad bandwidth to a stream which a high rate is required and suppressing the rates of the other streams, not equally sharing the bandwidth of the entire transmission medium to each stream.
On the other hand, in the case in which broadcast signal is once received, a specific stream is selected and is transmitted or recorded again, a bandwidth for transmission or recording has to be secured on the basis of the maximum rate in the selected stream. For such a purpose, a method indicating a buffer for smoothing a stream (smoothing buffer, hereafter) and a bandwidth necessary for transmission or recording with a reading rate from the smoothing buffer (leak rate, hereafter) is adopted in MPEG2. The smoothing buffer memory size and the leak rate are shown by parameters included in the stream.
In the method using smoothing buffer and leak rate, the received stream is once stored in a smoothing buffer memory and is read from here at the leak rate. As long as a smoothing buffer memory having a size expressed by a parameter in the stream and a leak rate are used, the smoothing buffer memory is guaranteed not to overflow. Therefore, in the case of being transmitted or recorded again, transmission or recording becomes possible by securing the bandwidth equal to the leak rate. Because by once smoothing the rate, it becomes unnecessary to secure the bandwidth equal to the maximum rate which rarely occurs, the bandwidth at transmitting or recording the stream with a variable rate can be minimum and it is possible to effectively use a transmitting medium or recording medium.
However, because timing information of each transport stream packet is deteriorated by once storing the stream in a smoothing buffer memory, the reproducing apparatus of video and audio signals cannot isochronize. Therefore, in the case of transmission or recording, timing information written in the smoothing buffer memory is added to each packet. On the other hand, at the receiving or reproducing apparatus, the timing information is reproduced by once storing each transport stream packet in a packet having the same size as a smoothing buffer memory and outputting the output based on timing information added to each transport stream packet and as a result, it becomes possible to isochronize at the reproducing apparatus of video and audio signals.
Thus, in order to transmit a MPEG2 transport stream, it is necessary to be able to reproduce the timing of each transport stream packet in the receiving apparatus of the transport stream packet. As such a transmission medium which can reproduce the timing, there is P1394 interface. P1394 is a high speed serial interface for the next generation multimedia which is studied at IEEE. It is described in the reference, High Performance Serial Bus P1394/Draft 7.1v1″.
P1394 is a transmitting medium of serial bus type and all nodes connected to a bus have isochronized timing information. When a transport stream packet of MPEG2 is transmitted, the timing of each transport stream packet is secured using the timing information.
An apparatus connected to P1394 (node, hereafter) is connected in a tree structure having branches and a node having a plurality of terminals relays the signal by outputting a signal received from one of the terminals to another terminal. Accordingly, it is secured to arrive to every node connected with data outputted from any node. As a result, P1394 works as a bus theoretically although it has a tree structure.
However, because P1394 realizes a bus by relaying a plurality of nodes, there occurs a propagation delay depending on the number of relaying nodes as well as a propagation delay determined by the length of the transmission medium. Further, in P1394, it is secured that a plurality of nodes do not simultaneously transmit, by that only one node assigns buses.
Thus, an identifier to identify the node (node ID, hereafter) is added to each node composed as a bus. The addition of the node ID is automatically done by initializing a bus generated when a new node is added to the bus or on the contrary, when a node is separated from the bus (bus reset, hereafter). When a bus reset is generated, a node connected to the bus outputs a packet indicating a connection state of the node (self ID packet, hereafter) to the bus according to a predetermined order. The node ID is determined by the output order of the self ID packet and the self ID packet includes the node ID determined at outputting to the self ID packet and information whether the other nodes are connected to each terminal or not. As for the node on the bus, the tree structure composing the bus can be known by receiving and analyzing all of self ID packets outputted from each node.
In P1394, two kinds of transfer, a isochronous transfer used for transferring the data which is necessary of real time such as a MPEG2 transport stream or a digital video signal and an asynchronous transfer used for outputting data which is unnecessary of real time are possible. P1394 works on the basis of every 125 microsecond period (cycle, hereafter) and is used for isochronous transfer at a first half of each cycle and for asynchronous transfer at a second half.
When a isochronization transfer is done, time (bandwidth) used during one cycle is acquired in the node controlling the bandwidths before communication. P1394 has a node controlling bandwidth used with isochronous transfer and a bandwidth to be used is acquired from the bandwidth controlling node. The node to execute a isochronous transfer can transfer the data in a range of the acquired bandwidth and the data transmitted with isochronous transfer is outputted as a packet specified by P1394. In a isochronous transfer, it is possible to transfer real time data by secure the transfer of the data size predetermined at every cycle.
The bandwidth to be acquired before transmission is a summation of overhead parts such as a bandwidth necessary for transferring the
Litsuka Hiroyuki
Nishimura Takuya
Takeda Hidetoshi
Yamada Masazumi
Matsushita Electric - Industrial Co., Ltd.
Olms Douglas
Pizarro Ricardo M.
RatnerPrestia
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