Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2001-02-09
2004-11-23
Iqbal, Nadeem (Department: 2184)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C714S018000, C714S020000
Reexamination Certificate
active
06823470
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to network communication systems, and more particularly to the correction of data communicated by such systems.
BACKGROUND OF THE RELATED ART
Communication systems are generally used to transmit information between entities that use such information. Such communication systems may be any system that transmits or receives information such as voice data, video data, or data for use by an entity. An entity may be, for example, a computer, networking device, telephone or other device, that receives and transmits information to another entity.
Such information or data is generally transmitted over a network. A network may include, for example, a communication channel upon which signals are transmitted and received. This communication channel may include one or more transmission media, such as copper or fiber optic cable, air, or other medium suitable for transmitting and/or receiving data between entities.
A communication system typically includes one or more communication interfaces that receive and/or transmit data, and are coupled to other communication systems or devices by one or more communication channels. Communication systems generally communicate using one or more communication protocols as is known in the art. For example, communication systems may communicate using a network protocol such as TCP/IP, and transmit information over a communication channel using a data-link and physical protocols such as SONET, Ethernet, or other protocol. Also, these communication systems may be physically connected to each other by fiber-optic interfaces and may have connections by one or more fiber optic cables.
It should be appreciated that there are many different types of communication interfaces and protocols used for transmitting data.
Data communication is an imperfect process. That is, errors may occur in the transmission of data between a sending entity and receiving entity. Error detection is a process of detecting errors in received data. This may be performed by determining, for a received data signal, whether one or more bits of the received signal have been changed during transmission. Error detection may be performed by one or more methods including those known in the art, such as performing parity checks, using checksums to check received signals, comparing received signals to expected signals, and other methods. Error correction is a process for correcting detected errors in received data so that the received data may be used by the receiving system. For example, a transmitting system may transmit additional information such as code words according to an encoding protocol having a group of predefined codewords. A receiving system inspects received signals, and determines whether the received signals include codewords that are members of the group of predefined codewords.
Communication systems modulate information by mapping information into codewords, also referred to as symbols, that can be efficiently transmitted over a communication channel, such as a cable, air, or other communication medium. The modulated information can experience noise signals from external sources, from the medium, or even from interference with the modulated information itself. These noise signals may change the modulated information so as to be considered incorrect or indiscernible from a receiver of the modulated information. Also, degradation of transmission components such as optical components, or transmission component error, may give rise to errors in received information. The receiver of the modulated information must be able to detect and correct these erroneous signals, and, if necessary, request the transmitter to resend the information.
Communications systems may perform error detection and/or error correction when transmitting and/or receiving data. The use of error correction codes is a common solution for detecting and correcting errors in received information. More particularly, the nature of error correction codes allow a receiver of information to determine the presence of and correct, errors in received information.
Hamming codes are a type of well-known binary error correction block codes used for error detection and correction in communication systems. In a Hamming code, a group of binary code words are defined that are valid. Signals are encoded using the valid code words at a transmitting system, and these code words are transmitted to a destination system where they are decoded. More particularly, the received signals are organized into code word blocks and a determination is made whether a received block belongs to the set of valid codewords. If the received block does not belong, there has occurred an error in one or more locations of the received block. Depending on the group of codewords selected, the destination system may be able to correct one or more bit errors in the received data.
There are many other types of codes used to encode and decode data. BCH and Reed-Solomon codes are well-known types of codes used to detect and correct errors in received information. These and other codes are discussed more fully in various texts, such as the book entitled “Error Control Systems for Digital Communication and Storage” by Stephen B. Wicker, Prentice Hall, Upper Saddle River, N.J. (1995), incorporated herein by reference.
Error detection and correction improves the bit error rate of a particular communication channel by allowing a communication system to detect and correct a finite amount of errors. Forward Error Correction (FEC) is a type of error correction code wherein the algebraic structure of the error correction code is used to determine which of the valid code words is most likely to have been sent, given the erroneous received word. As discussed above, Hamming and other codes provide this capability.
Many types of conventional communication use error detection and correction in their operation. For example, PPP and HDLC communication protocols have a frame structure having a header and trailer, wherein the trailer includes information used for error detection and correction of the frame. Other communication systems employ what is known in the art as a frame check sequence (FCS) or cyclic redundancy check (CRC) codes. For example, Ethernet, Fast Ethernet, and Gigabit Ethernet frames implement a CRC code that is appended to the end of a frame. CRC information used in SDH is a bit interleaved parity CRC polynomial referred to as BIP-8 wherein a parity calculation is calculated for a current frame and transmitted in a subsequent frame over the same physical connection. The BIP-8 error monitoring function is discussed more fully in the book entitled “Broadband Networking: ATM, SDH and SONET” by Mike Sexton and Andy Reid, Artech House, Boston, Mass. (1997).
All of the aforementioned types of communication systems transmit the error correction as part of the transmitted frame or in a subsequent frame, increasing overhead of the frame and decreasing the effective throughput of the communication system. To increase throughput of the communication system, some types of communication systems remove error correction and detection altogether, or rely on higher layers of communication to determine whether data is in error.
SUMMARY
Communication systems exist that have redundant or “backup” data paths that are used in situations where the “primary” or working path is unavailable for transferring data. A backup or redundant data path is a data path that is parallel to the working path between a source and destination of data. A data path may include one or more physical components such as copper, fiber, or other active or passive components. In some network configurations, the redundant path carries a copy of data transmitted on the working path, may not carry data under normal operating conditions, or other configuration wherein the redundant path is not relied on in a normal operating condition for transmitting working data. Data channels may be defined between a source and a destination which use one or more data paths.
Francis, Jr. James T.
Reeve, III Howard C.
Smith Douglas Edward
Bonura Timothy M
Iqbal Nadeem
Sycamore Networks, Inc.
Wolf Greenfield & Sacks P.C.
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