Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2000-05-18
2004-02-17
Ton, David (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C709S237000
Reexamination Certificate
active
06694470
ABSTRACT:
BACKGROUND OF THE INVENTION
Definitions
The following definitions are employed throughout the following discussion:
carrier set—a set of one or more frequencies associated with a PSD mask of a particular xDSL Recommendation;
downstream—direction of transmission from the xTU-C to the xTU-R;
Galf—an octet having the value 81
6
; i.e., the ones complement of an HDLC flag;
initiating signal—signal which initiates a startup procedure;
initiating station—DTE, DCE and other associated terminal equipment which initiates a startup procedure;
message—framed information conveyed via modulated transmission;
metallic local loop—communication channel
5
, the metallic wires that form the local loop to the customer premise;
responding signal—signal sent in response to an initiating signal;
responding station—station that responds to initiation of a communication transaction from the remote station;
session—active communications connection, measured from beginning to end, between computers or applications over a network;
signal—information conveyed via tone based transmission;
signaling family—group of carrier sets which are integral multiples of a given carrier spacing frequency;
splitter—combination of a high pass filter and a low pass filter designed to split a metallic local loop into two bands of operation;
transaction—sequence of messages, ending with either a positive acknowledgment [ACK(
1
)], a negative acknowledgment (NAK), or a time-out;
terminal—station; and
upstream: The direction of transmission from the xTU-R to the xTU-C.
Abbreviations
The following abbreviations are used throughout the following discussion:
ACK—Acknowledge Message;
ADSL—Asymmetric Digital Subscriber Line;
CDSL—Consumer Digital Subscriber Line;
DSL—Digital Subscriber Line;
FSK—Frequency Shift Keying;
HDSL—High bit rate Digital Subscriber Line;
HSTU-C—handshaking portion of the xDSL central terminal unit (xTU-C);
HSTU-R—handshaking portion of the xDSL remote terminal unit (xTU-R).
ITU-T—International Telecommunication Union—Telecommunication Standardization Sector;
NAK—Negative Acknowledge Message;
POTS—Plain Old Telephone Service PSD—Power Spectral Density;
PSTN—Public Switched Telephone Network;
RADSL—Rate Adaptive DSL;
RTX—Request Retransmit;
VDSL—Very high speed Digital Subscriber Line;
XDSL—any of the various types of Digital Subscriber Lines (DSL);
xTU-C—central terminal unit of an xDSL; and
xTU-R—remote terminal unit of an xDSL.
1. Field of the Invention
The present invention is directed to a high speed communications device, such as, for example, but not limited to, a modem, a cable modem, an xDSL modem, a satellite communication system, a point-to-point wired, or a wireless communication system, that includes a handshaking or initializing protocol, and in particular, to an apparatus and method that provides error free communication by detecting errors and requesting the retransmission of errored communication messages.
2. Discussion of Background and Other Information
Recently, new communication methods are being proposed and/or developed to transmit data on a local twisted wire pair that uses a frequency spectrum above a traditional voice band (e.g., 4 kHz bandwidth). For example, various “flavors” (variations) of digital subscriber line (DSL) modems have been/are being developed, such as, but not limited to, for example, DSL, ADSL, VDSL, HDSL, SHDSL and SDSL (the collection of which is generally referred to as xDSL). Each particular xDSL technology requires a robust start-up or initialization technique.
The ITU-T has published several recommended procedures for initiating a data communication, the following subject matter of which is expressly incorporated herein by reference in their entireties:
1) Recommendation V.8, entitled “Procedures For Starting Sessions Of Data Transmission Over The General Switched Telephone Network”, published in September, 1994;
2) Recommendation V.8 bis, entitled “Procedures For The Identification And Selection Of Common Modes Of Operation Between Data Circuit-Terminating Equipments (DCEs) And Between Data Terminal Equipments (DTEs) Over The General Switched Telephone Network”, published in August, 1996; and
3) Recommendation G.994.1, entitled “Handshake Procedures For Digital Subscriber Line (DSL) Transceivers”, published in June 1999. It is noted that this document is the final version of Temporary Document MA-006, that was published in March, 1999.
Documents (1) and (2), above, pertain to procedures for initiating a data communication over voice band channels. Document (3), above, pertains to initiating a data communication over xDSL channels.
Unfortunately, if a data reception error occurs in a message, even if the error is only a single bit in length, the data communication devices must completely restart, from the beginning, a handshake (initialization) procedure. Since initialization procedures often involve a plurality of messages or transactions, and thus, restarting a transmission from the beginning results in a significant loss of information and time. Thus, there is a need for an apparatus and method that minimizes an initialization recovery procedure, by retransmitting only the errored portion of a session instead of completely restarting the initialization procedure.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to develop a retransmission mechanism that retransmits an errored message that occurs during handshaking or initializing procedure. In a disclosed embodiment, the procedure is implemented as an extension to an xDSL handshaking and selection procedure (such as, but not limited to, for example, the above-noted ITU-T Recommendations G.994.1, V.8, and V.8 bis). According to the instant invention, if a communication device receives an errored message during a session, the communication device indicates the last correctly received message and requests a retransmission of the errored message. In addition, an optional feature of the present invention enables the retransmission request messages to suggest the length of a message frame to be used by a communication device in order to help reduce the occurrence of frames with errors.
According to an object of the invention, a communication device is disclosed that minimizes a retransmission of signals and messages when an errored message is received during a communication handshaking procedure. The communication device has a receiving section that receives signals from an initiating communication device, in order to detect when an errored message is received, and a retransmission request device that transmits, to the initiating communication device, a retransmission request message indicating that the errored message was received. The receiving section includes an error detecting device that operates to detect errored messages.
According to a feature of the invention, the retransmission request message may indicate which correct message was lastly received by the communication device. In addition, the retransmission request message can include information related to, for example, a suggested length of subsequent message frames to be transmitted, or a frame number of a multi-segmented message.
According to another object of the current invention, a method is disclosed for minimizing a retransmission of signals and messages when an errored message is received during a handshaking procedure of a communication session. According to this method, the handshaking procedure is monitored to determine whether a received signal contains an errored message. When the monitored handshake procedure determines that an errored message was received, a retransmission request message is transmitted to request retransmission of a portion of the handshaking procedure.
According to an advantage of the invention, data related to a Frame Check Sequence is examined to determine whether an errored message was received.
According to another advantage of the invention, the retransmission request message may, for example, indicate a last correctly received message, or, indicate a segment index number
Greenblum & Bernstein P.L.C.
Panasonic Communications Co. Ltd.
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