Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1997-03-12
2001-05-15
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S517000
Reexamination Certificate
active
06233256
ABSTRACT:
BACKGROUND OF THE INVENTION
The increasing demand for digital video/audio information presents an ever increasing problem of monitoring the transmission or storage of data in data communication. As the transmission bandwidth increases in response to greater demand, it becomes increasingly more difficult to monitor the enormous amount of transmitted information in real time.
Generally, the data streams contain video, audio, timing and control data which are packaged into various “packets”. A packet is a group of binary digits that include data and control elements which are switched and transmitted as a composite whole. The data, control elements and other information are arranged in various specific formats.
Examples of such formats are disclosed in the ISO/IEC international Standards 11172 (1994) (generally referred to as MPEG-1) and 13818 (Jan. 20, 1995 draft) (generally referred to as MPEG-2), which are incorporated herein in their entirety by reference. In general, MPEG defines a packet as consisting of a header followed by a number of contiguous bytes from an “elementary data stream”. An elementary stream is simply a generic term for one of the coded video, coded audio or other coded bitstreams. More specifically, a MPEG-2 “transport stream” packet comprises a header, which may be four (4) or more bytes long with a payload having a maximum length of 184 bytes. Transport stream packets are part of one or more programs which are assembled into a transport stream. The transport stream is then transmitted over a channel with a particular transfer rate.
Thus, in order to monitor and evaluate the status of a transport stream in real time, a method or apparatus must be able to handle the high transfer rate of the transmission channel. To illustrate, if data from the transport stream is arriving at a rate of 5 Mega-bytes per second and a processing unit operates at 20 Mega-instructions per second, then the processing unit must perform, on average, a READ operation every fourth instruction. This requirement is computationally expensive and increases the cost of performing real time packet analysis. In fact, since time is such a scarce resource in real time packet analysis, it may become prohibitively expensive. Although it may be more cost effective to capture the data in the transport stream into storage and then analyze the data at a later time, the benefit of real time analysis is lost. These benefits may include the detection of packet framing errors, jitters, inconsistent time base information or network wide errors that may affect a plurality of channels.
Therefore, a need exists in the art for a method and apparatus for performing real time packet analysis without the associated high computational expense. Specifically, a need exists for a method and apparatus for detecting errors, verifying the consistencies of time base information and displaying important packet stream information.
SUMMARY OF THE INVENTION
The present invention is a method and apparatus for analyzing and monitoring packet streams. The apparatus, a packet analyzer, comprises an input buffer, a real-time analysis unit, a non-real-time analysis unit, a graphics unit and a monitor. A packet stream is received into the input buffer where the data is read by the real-time analysis unit. Messages are passed between the real-time analysis unit and the non-real-time analysis unit to report on detected errors or to update packet stream information. In turn, real time packet stream information are displayed and updated on a display via the graphic unit.
The present invention incorporates a method of detecting framing errors in a packet stream by setting a 9th bit in the input buffer for each byte of data in a packet. Depending on this 9th bit value and the position of its associated byte of data (i.e., first byte in the packet, second, third, or etc.), the packet analyzer is able to detect packet framing errors, such as long packet, short packet, or bad data.
The present invention also minimizes the number of bytes that are processed by the real-time analysis unit by implementing a “flushing” circuit and method. This flushing method distinguishes payload carrying scrambled data in video and audio packets from those packets carrying important control data such as adaptation information relating to time base. Since the access of scrambled data is often limited, they provide little information in packet analysis except for the fact that a packet of this type has been transmitted and received. As such, the data bytes in such packets are flushed from the input buffer, thereby reducing significantly the number of bytes of data that the real-time analysis unit must process.
Furthermore, the present invention incorporates a plurality of methods in verifying the consistency of time base information. Specifically, the difference in program clock reference (PCR) values, the bit rate between PCR values and the difference in the arrival time of the PCR values are compared in different combinations with each other to determine the degree of PCR jitter in the packet stream.
Finally, various packet stream information are grouped and shown on a display for monitoring the packet stream. The displayed information are grouped in a manner to easily alert an operator as to potential problems in a packet stream or a network of packet streams.
REFERENCES:
patent: 4775973 (1988-10-01), Tomberlin et al.
patent: 4887260 (1989-12-01), Carden et al.
patent: 5212724 (1993-05-01), Nazarenko et al.
patent: 5247517 (1993-09-01), Ross et al.
patent: 5309435 (1994-05-01), Hirome
patent: 5315580 (1994-05-01), Phaal
patent: 5323426 (1994-06-01), James et al.
patent: 5394395 (1995-02-01), Nagai et al.
patent: 5535216 (1996-07-01), Goldman et al.
patent: 5544172 (1996-08-01), Abbas
patent: 5565924 (1996-10-01), Hasket et al.
patent: 5592476 (1997-01-01), Calamvokis et al.
patent: 5640388 (1997-06-01), Woodhead et al.
patent: 5650825 (1997-07-01), Naimpally et al.
patent: 5668841 (1997-09-01), Hasket et al.
patent: 5694397 (1997-12-01), Burton
patent: 5729530 (1998-03-01), Kawaguchi et al.
patent: 5751695 (1998-05-01), Ohashi
patent: 5767746 (1999-03-01), Dieterich
patent: 5768326 (1999-03-01), Koshiro et al.
patent: 5790543 (1998-08-01), Cloutier
patent: 5881114 (1999-03-01), Moon
Copy of International Search Report dated Jun. 09, 1997 from corresponding International Application No. PCT/US97/04009.
Jander, M., “A Handy Way to Analyze LAN Stats/ Star-Tek's hand-held device filters, captures, and analyzes packets from Ethernets and token rings”, Data Communications, US McGraw-Hill, NY, 21, (14), pp. 45-46, 1992.
Dieterich Charles Benjamin
Greenberg Arthur Lee
Burke William J.
Nguyen Chau
Nguyen Phuongchau Ba
Sarnoff Corporation
Silverio John V.
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