Multiplex communications – Communication techniques for information carried in plural... – Assembly or disassembly of messages having address headers
Reexamination Certificate
1998-09-15
2002-04-16
Vincent, David R. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Assembly or disassembly of messages having address headers
C370S395650
Reexamination Certificate
active
06373856
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communications system and method for communicating compression coded image data, audio data, and additional information via a transmission path such that a temporal sequence of the data can be correctly reconstructed even after a transmission path error occurs.
2. Description of the Prior Art
The development of communication systems using optical fibers and other high speed transmission paths has greatly increased communication capacity. This has spurred the development of digital communication systems, which are now used not only for digital computer data, but also for transmitting digitized image signals, audio signals, and related additional information.
Asynchronous transfer mode (ATM) systems, for example, can operate at speeds in excess of 155 megabits/second, and practical ATM systems for communicating digital data are now available.
Formal standards for ATM systems have been adopted by the International Telecommunication Union—Telecommunication Standardization Sector (ITU-T) and the ATM Forum, for example, and numerous related publications have been issued.
Japanese Patent Laid-Open Publication 8-307859 (referred to below as prior art example 1), for example, teaches a means for transmitting image, audio, and related data coded for commercial digital VCR use over an ATM network. A method for allocating the moving picture data of this digital VCR data stream to ATM cells is disclosed in this prior art example 1.
More specifically, as shown in
FIG. 10
, an 80-byte DIF (digital interface) block is split into two 40-byte parts, and the remaining 8-byte part of the 48-byte ATM cell payload is used for e.g. error correction parity. Alternatively, a 4-byte portion of the remaining 8 bytes is used for error detection code. In another method of the above-noted prior art example 1, three 80-byte DIF blocks are joined to form a single 240-byte data block, which is then split into five 48-byte ATM cells.
A further method for writing moving picture data to ATM cells is a so-called “MPEG over ATM” method taught in “Video On Demand Specification 1.0, af-saa-0049.000”, issued by The ATM Forum Technical Committee on Audiovisual Multimedia Services in December 1995 (referred to below as prior art example 2). Numerous descriptions of this specification have also been published. Basically, MPEG over ATM is a method for joining two continuous MPEG
2
Single Program Transport Streams (STPS), each 188 octets long, into one 376 octet stream to which an 8-byte AAL 5 trailer is added, and then allocating this 384-byte stream to be split into eight ATM cells, each cell corresponding to a 48-octet payload, for data transmission.
A further another method for writing moving picture data to ATM cells is disclosed in U.S. Pat. No. 5,533,021 (referred to as prior art example 3, hereinafter). In this prior art example 3, a transport system (TS) packet stream sequence is split into a plurality of packets in the ATM adaptation layer and mapped into a cell size AAL-5 Protocol Data Units (PDUs). In this example, however, there is no suggestion or teaching of a feature of appending time information to every packet for identifying the location thereof.
These conventional methods are, however, involved with problems or drawbacks as to be described below.
Specifically, in these conventional methods, temporal information or time code data indicating when each payload was coded is not contained in each payload. As a result, when an error occurs in the communications network, the receiver is unable to determine the time of error recovery, resulting in disruption of reproduction of images associated with the payload in which the error occurred.
This problem is described more specifically with reference to accompanying FIG.
11
.
The top row
111
in
FIG. 11
represents three continuous frames of data to be transmitted where the frames are identified as frame n, frame n+1, and frame n+2. The places at which an error occurs during transmission over the communications network are indicated with hatching in rows
112
,
113
, and
114
.
For example, when a transmission load increases to a point exceeding a processing capacity of an ATM switch on an ATM communications network, a problem of cell loss is caused. When cell loss occurs, an error in successive bursts as indicated in
FIG. 11
occurs.
The error is confined within frame n+1 in row
112
, but expands to frame n and n+1 in row
113
, and moreover in row
114
starts in frame n, continues through frame n+1, and extends into frame n+2. When an error occurs as shown in FIG.
11
and the error is recovered, there is no means available for identifying at what point in these successive frames error recovery occurred. More specifically, if error recovery occurs in frame n+1 in row
112
, frame n+1 in row
113
, or frame n+2 in row
114
, there is no method for determining to which frame the data received immediately after error recovery belongs. As a result, the data for frames n and n+1 in row
113
may be merged into one frame of data, and data for frames n and n+2 in row
114
may be merged. In addition, error recovery may occur in the same frame in which the error occurred in row
112
, for example, but there is no means of determining that the data before and after error recovery can be processed as coming from the same frame because there is no means of detecting that the error and error recovery occurred in the same frame.
When the segment in which an error occurred is re-transmitted, it is necessary to determine where the error occurred. This error determination is, however, not possible with the method according to the prior art example 1. It is therefore necessary to re-transmit the entire data block. It should be noted that the above-described problems with prior art example 1 occur regardless of the length of the error.
The above-described problem in the conventional method is involved due to lack of the time code data or time information in each cell payload, for identifying where or to what period in the image signal stream the image information contained in a given cell payload belongs.
In the conventional method using MPEG
2
encoding which is a combination of interframe predictive motion compensation coding and discrete cosine transform (DCT) coding, when an error in the code stream occurs as a result of an error on the communications network, the error is propagated to a macroblock coding unit. This means that, because of interframe predictive coding, the error is propagated along the time base.
The problem with MPEG
2
coding likewise occurs due to the reason because relatively large macroblocks are used as the encoding unit and because interframe predictive coding is used.
With regard to the aforementioned problems, there is a need for a communication apparatus which allows to determine a time period or frame number in the image signal stream to which every successfully received packet belongs even when an error occurs in a communication network. There is a further need for a communication apparatus which surely prevents propagation of errors in the communication network.
SUMMARY OF THE INVENTION
To meet the above described needs, an essential object of the present invention is to provide a novel communications system for transmitting a stream of multimedia digital data over a distribution communications network via a transmission path by way of a transmitter.
The communications system of the present invention comprises: a data stream generator for coding image data, audio data, other associated additional information in a unit of an image data group and generating a continuous data stream thereof together with temporal information indicative of a temporal location of the image data group; a packetizer for segmenting the data stream into a plurality of data packets; a packet header adding device for adding the temporal information as a packet header to each data packet to thereby produce a transmission p
Vincent David R.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Communications system for transmission of multimedia digital... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Communications system for transmission of multimedia digital..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Communications system for transmission of multimedia digital... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2857360