Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
1998-04-17
2001-06-05
Decady, Albert (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S757000
Reexamination Certificate
active
06243846
ABSTRACT:
COPYRIGHT
A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
MICROFICHE APPENDIX
This patent document includes a microfiche appendix, containing one sheet of microfiche and a total of 45 frames.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to packet switched telecommunications networks and more particularly to a system for correcting loss of data packets in such a network.
2. Description of the Related Art
In a packet switched network, a message to be sent is divided into blocks, or data packets, of fixed or variable length. The packets are then sent individually over the network through multiple locations and then reassembled at a final location before being delivered to a user at a receiving end. To ensure proper transmission and re-assembly of the blocks of data at the receiving end, various control data, such as sequence and verification information, is typically appended to each packet in the form of a packet header. At the receiving end, the packets are then reassembled and transmitted to an end user in a format compatible with the user's equipment.
A variety of packet switching protocols are available, and these protocols range in degree of efficiency and reliability. Those skilled in the art are familiar, for instance, with the TCP/IP suite of protocols, which is used to manage transmission of packets throughout the Internet. One of the protocols within the TCP/IP suite, for example, is TCP.
TCP is a reliable connection-oriented protocol, which includes intelligence necessary to confirm successful transmission between sending and receiving ends in the network. According to TCP, each packet is marked in its header with a sequence number to allow the receiving end to properly reassemble the packets into the original message. When a packet arrives at the destination, the receiving TCP entity should send back to the sending entity a packet bearing an acknowledgement number equal to the next sequence number that it expects to receive. If the sending entity does not receive an acknowledgement within a specified time period, it will re-transmit the package of data.
Generally speaking, this acknowledgment and re-transmission system works well to correct packet loss in the Internet. However, the system can unfortunately delay the complete transmission of a data stream. For the transmission of packets representing pure data signals such as e-mail messages, transmission delay is not ideal, although it is of secondary concern compared to an unrecoverable loss of information. Real-time media signals (especially compressed signals), however, are by definition highly sensitive to delay and will appear jumpy, interrupted or otherwise distorted if parts of the signal do not flow continuously to the receiving end. Therefore, although the loss of packets in a real time media transmission over the Internet has been correctable, the resulting signals have often nevertheless been of unacceptable quality.
SUMMARY OF THE INVENTION
The present invention provides a computationally simple yet powerful system for handling packet loss that may arise in the communication of data or real time media signals, such as digitized voice, video or audio, in a packet switched network. The invention generates and transmits into the network one or more forward error correction codes, or parity packets, at least one of which is defined by taking a cross-wise XOR sum of a predetermined number of preceding payload packets. In turn, a receiving end may extract lost payload from this redundant information and may correct for the loss of multiple packets in a row.
Various features and advantages of the present invention will become apparent to those of ordinary skill in the art by reading the following detailed description, with appropriate reference to the accompanying drawings.
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Borella Michael
Mahler Jerry
Schuster Guido M.
Sidhu Ikhlaq
3Com Corporation
De'cady Albert
McDonnell & Boehnen Hulbert & Berghoff
Ton David
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