Multiplex communications – Communication techniques for information carried in plural... – Byte assembly and formatting
Reexamination Certificate
1998-11-05
2002-11-05
Vincent, David (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Byte assembly and formatting
C370S503000
Reexamination Certificate
active
06477181
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to data communication methods and systems which, via a communication network, transmit a plurality of data, such as digital audio data, arranged in a time series of a predetermined period. More particularly, the present invention relates to a data communication method and system in which data are arranged at a transmitting end in such a format that allows a receiving end to accurately reproduce a time-positional relationship between the individual data.
The present invention also relates to data transmitter/receiver devices and data communication systems which communicate time-stamped data via a communication network.
The present invention further relates to data communication systems which receive time-stamped data from a segment on a communication network and then transfer the received data to another segment on the communication network.
Furthermore, the present invention relates to methods of and devices for synchronizing network data.
BACKGROUND ART
Data communication systems using a communication network can be classified roughly into synchronous and asynchronous types. The synchronous-type data communication system allows the transmitting end and receiving end to operate synchronously with each other and hence is well suitable for use in an audio data transmission that requires an accurate reproduction, at the receiving end, of time positions of received data. However, the conventionally-known synchronous-type data communication system only has a very limited use because it needs particular arrangements to permit synchronization between the two ends, such as provision of a separate synchronizing signal line, and also has to statically maintain a communication band due to the synchronization. This would result in the communication band unnecessarily remaining reserved even when a synchronized communication is not required at all, and therefore a significant problem would be encountered that the no other information can be transmitted through the communication band.
In contrast, the asynchronous-type data communication system can avoid the above-mentioned problem encountered by the synchronous-type data transmission by dynamically reserving a necessary communication band, but would present another problem of reduced communication efficiency unless communication overheads are reduced by organizing together some pieces of information relatively densely in each asynchronous packet to be issued. Such a packet with the densely organized information would, however, often lose information indicative of original time positions of the individual data. To avoid this problem, it has been proposed, in the packet-based data transmission, to transmit data along with additional information indicative of time positions of the data; namely, the data and time information—commonly called “time stamp”—indicative of respective time positions of the individual data are included together in a packet to be sent from the transmitting end.
However, the proposed approach of attaching the time information to each individual data would lead to very poor efficiency because of a significant increase in the total data quantity.
As another communication scheme for communicating data via a communication network, there has been known an “isochronous” data communication system, which can be referred to as a compromise between the above-mentioned synchronous-type data communication system characterized by successive transmission of same-period signals between the transmitting and receiving ends and the asynchronous-type data communication system characterized by intermittent communication of predetermined information units. This isochronous data communication system permits data communication with increased real-time responsiveness where possible time delays are well compensated for by securing a necessary frequency band in advance.
The following paragraphs describe in more detail the isochronous data communication system with reference to FIG.
25
. This figure shows exemplary arrangement of packets on a system bus called “IEEE1394 high-speed serial bus”; specifically, three different kinds of packets, i.e., a cycle start packet
101
, isochronous packet
102
and asynchronous packet
103
, are provided on a communication network. Each dotted line in
FIG. 5
denotes a first timing signal (cycle synch) indicating reference timing in the system, which has a period of 125 &mgr;sec. (8 KHz).
The cycle start packet
101
is sent from one of a plurality of nodes connected to the bus which is called a cycle master node, and a new data transmission cycle is initiated with the cycle start packet
101
. The has a precise clock pulse source that generates the first timing signal. The cycle start packet
101
is normally transmitted at time intervals corresponding to generation timing of the first timing signal; however, when another packet is being transmitted, transmission of the cycle start packet
101
is waited or delayed until transmission of the other packet has been completed. Reference numeral
104
denotes a delay time with which transmission of the cycle start packet
101
is delayed (start delay time), and this start delay time is included in the cycle start packet
101
in coded form and sent to each of the nodes. It is guaranteed that each packet sent from the node at a given clock period is received by another node within the same clock period.
Each of the nodes is provided with a 32-bit cycle timer register. The cycle timer register uses its lower 12 bits to count 24.576 MHz clock pulse signals (with a period of 40.7 nsec.), which are generated as system's reference clock pulses, modulo 3,072. The cycle timer register uses other 13 bits, higher in position than the lower 12 bits, to count the above-mentioned 8kHz reference cycles, and also uses its uppermost seven bits to count seconds. Using the cycle start packet
101
, the above-mentioned cycle master allows stored contents of its own register to be copied into the cycle timer registers of all the nodes, and also allows all the nodes to be synchronized with each other to within a given phase difference. Thus, in the communication network, a common time standard is provided.
The isochronous packet
102
is a data channel used to transfer data requiring precise timing reference, such as digital sound, video and performance data, and it is guaranteed that each of the isochronous packets
102
is transmitted within a predetermined transmission cycle associated therewith; for example, it is guaranteed that each of the isochronous packets
102
is transmitted, within the associated transmission cycle, to up to 63 channels for a maximum time period of 100 &mgr;sec.
Further, the asynchronous packet
103
is a packet which is transmitted asynchronously when there is an empty time in the associated transmission cycle after completion of the transmission of the above-mentioned isochronous packet
102
. It is assumed here that the asynchronous packet has a maximum length of 75 &mgr;sec. The asynchronous packet continues to be transferred until all the data of the packet have been completely transferred, so that it is likely that the transfer of this packet will continue beyond the period of the cycle timer.
In order to guarantee reproducibility of data on the time axis in transmitting time-serial data, such as sound, video or performance data using any of various networks, the data are transmitted along with a time stamp indicative of a particular time point when the data are to be reproduced, if the transmission path is not capable of a completely synchronous communication. In this case, the receiving end refers to the time stamp and initiates the reproduction of the data upon arrival at the time point indicated by the time stamp.
Each time stamp used on such a communication network must be interpreted in one meaning. Namely, the time stamp requires a cyclic period greater than a time length that is considered to be appropriate to some extent and therefore requires a great amount of information. Whe
Abe Tatsutoshi
Fujimori Junichi
Inagaki Yoshihiro
Kuribayashi Hirotaka
Ohtani Yasushi
Morrison & Foerster / LLP
Vincent David
Yamaha Corporation
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