NZ286352A

NZ286352A - Error correction code inserted in transmitted signal if error rate threshold at receiver exceeded

Info

Publication number: NZ286352A
Application number: NZ286352A
Authority: NZ
Inventors: Ivan Todorov Popov
Original assignee: Alcatel Australia
Priority date: 1995-04-20
Filing date: 1996-04-11
Publication date: 1997-05-26
Also published as: ZA96778B; AU698574B2; AU5068496A

Description

<div class="application article clearfix" id="description"> Priority Date(s): Jta.lM-.l35? Complete Specification Filsd: Claw: (6) 2'B'MY'Wy Publication Date:........ P.O. Journal No: /.hh.'.fe CQpy NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION 'TRANSMISSION NETWORK ERROR CORRECTION" WE, ALCATEL AUSTRALIA LIMITED, ooo oo5 S43 A Company of the State of New South Wales, of 280 Botany Road, Alexandria, New South Wales, 2015, Australia, hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of correcting data errors and to an apparatus therefore. More particularly, the invention relates to a method of and to an apparatus for correcting errors in a data stream of a digital data transmission network. The quality of transmission networks varies widely, The quality of a transmission network is affected by the choice of transmission medium, as well as by the presence of faulty components on the network, such as end node equipment. The quality of the network may also exhibit temporary fluctuations due to factors such as weather conditions, time of day, or interference caused by industrial activity. The number of transmission errors occurring in the network increases as the quality of the network deteriorates. Various methods are available to detect and to minimise the effects of errors in transmission networks. For example, error detection and correction may be performed on a continuous basis by means of dedicated electronic circuits or by means of firmware, at each node of ht network. This method is disadvantageous as it increases the cost of network node equipment, and it does not differentiate between periods of acceptable and unacceptable network quality. Another method involves the detection of a transmission error by means of the network application software. When an error is detected in a network data packet, the entire data packet is retransmitted on the network with the expectation 28 S3" that the error will not occur in the retransmitted data packet. Alternatively, the handshaking procedure between different nodes on the transmission network is reinitialised. This type of high-level error correction technique is unsatisfactory as it can cause long time out periods during which the data packets are retransmitted or handshaking is re-initialised, thereby consuming additional network capacity. Extended time-out periods also render the performance of the network application software unacceptable to users. It is an object of this invention to provide a method of error correction, and an apparatus therefor which will, at least partially, alleviate the abovementioned difficulties. In accordance with this invention, there is provided a method for correcting data errors in a transmission network having a sending node and at least one receiving node, comprising the steps of: buffering at least a portion of a network data packet transmitted by the sending node and received by the receiving node; detecting the number of errors present in the buffered data; determining the error rate of the transmission network at the receiving node, as a function of the number of errors detected in the buffered data; and activating the insertion of error correction code in further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving 2 ;m IS '•% node exceeds a predetermined threshold. Further features of the invention provide for de-activating the insertion of error correction code in the further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving node does not exceed the predetermined threshold, for activating the insertion of error correction code by transmitting an activation request data packet from the receiving node to the sending node, and for de-activating the insertion of error correction code by transmitting a de-activation request data packet from the receiving node to the sending node. There is also provided for separately buffering at least a portion of a data packet to be transmitted from the receiving node to the sending node, for activating the insertion of error correction code in the data packet to be transmitted from the receiving node to the sending node upon reception of an activation request data packet from the sending node, and for de-activating the insertion of error correction code in the data packet to be transmitted from the receiving node upon reception of a de-activation request data packet from the sending node. There is also provided for the insertion of error correction code by means of one or more of the techniques of bit interleaving, byte interleaving, cyclic redundancy check control, linear, BCH or convolutional codes. The invention extends to an apparatus for correcting data errors in a transmission network having a sending node and at least one receiving node, comprising: buffering means for buffering at least a portion of a network data packet transmitted by the sending node and received by the receiving node; detector means for detecting the number of errors present in the buffered data; monitoring means for continuously determining the error rate of the transmission network at the receiving node, as a function of the number of errors detected in the buffered data; and activating means for activating the insertion of error correction code in further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving node exceeds a predetermined threshold. There is also provided for the apparatus to include de-activating means for de-activating the insertion of error correction code in further network data packets transmitted by the sending node when the error ra'e of the transmission network at the receiving node does not exceed the predetermined threshold, for the activating means to be a transmitter for transmitting an activation request data packet from the receiving node to the sending node, for the de-activating means to b e a transmitter for transmitting a de-activation request data packet from the receiving node to the sending node, and for the activating and de-activating means to be the same transmitter. There is also provided for separate buffering means for buffering at least a portion of a data packet to be transmitted from the receiving node to the sending node, for the apparatus to include insertion means for inserting error correction code in the data packet to be transmitted from the receiving node, for the insertion means to be activatable upon reception of an activation request data packet from the sending node, and for the insertion means to be de-adivatable upon reception of a de-activation request data packet from the sending node. Preferably, the insertion means inserts error correction code in the data packet by means of one or more of the techniques of bit interleaving, byte interleaving, cyclic redundancy check control, linear, BCH or convolutional codes. The invention extends further to a transmission network having at least two nodes with the error correcting apparatus above described. A preferred embodiment of the invention is describe below, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a schematic representation of a transmission network including error correcting apparatus according to the invention; and Figure 2 is a more detailed schematic representation of an error correcting apparatus on the transmission network of Figure 1, according to the invention. Referring to Figure 1, a transmission network is indicated generally by reference number (11). The network comprises a transmission medium (12) such as a copper or fibre-optic cable and two network nodes (1 3a and 1 3b). Each network node (13a and 13b) is equipped with an apparatus (i), according to the invention, for correcting data errors at the respective network nodes. In this embodiment, for convenience, node (1 3a) will be referred to as a receiving node and node (13b) will be described as a sending node, but each network node (13a and 13b) can received and transmit data packets across the transmission medium (12). Turning now to Figure 2, the apparatus for correcting data errors at a node of the transmission network (1 1) is indicated generally by reference numeral (1). The error-correcting apparatus (1) is connectable at (2a and 2b) to the transmission medium (12) of the transmission network (11) and is further connectable at (3a and 3b) to one of the network nodes (13a and 1 3b) are equipped with an identical error-correcting apparatus (1). The connections at (2) and (3) are bi-directional, enabling data packets to be received at (2a) from the transmission medium (12) and forwarded to the node equipment at (3a), while data packets originating from the node equipment are received at (3b) and forwarded at (2b) to the transmission medium (12). The error-correcting apparatus (1) includes a received data buffer (4) for buffering data packets received from the network transmission medium (12). The error-correcting apparatus (1) also includes a transmit data buffer (5) for buffering data packets originating from the node equipment (1 3a or 1 3b). An error detection and correction circuit (6) is connected to the output of the received data buffer (4). The outputs of the received data buffer and of the error detection and correction circuit (6) are switchably connected to the node equipment by means of a switch (7). A controller (9) is connected to the received data buffer (4) as well as to the error detection and correction circuit (6). In use, a data packet received by the receiving node (13a) from the sending node (13b) on the network (11) is buffered in the received data buffer (4). Errors such as single bit, multiple bit or block errors in the buffered received data are detected by the controller (9). The controller (9) computes a received error rate for the transmission network (11) at the receiving node (13a), as a function of the number of detected received data errors. This computed received error rate is a measure of the instantaneous quality of the transmission network at the receiving node (1 3a). When the received error rate exceeds a predetermined threshold, the controller (9) causes a request to be transmitted to the error-correcting apparatus (1) of the sending node (13b) to enable error handling at that node. Conversely, if error handling is enable at the sending node (13b), and the received error rate drops below the predetermined threshold, indicating that the quality of the transmission network (11) has improved, the controller (9) in the receiving node (1 3a) causes a request to be transmitted to the sending node (1 3b) to disable the error handling at the sending node. Data packets to be transmitted on the transmission network (11) by the sending node (13b) are buffered in a transmit data buffer (5). During periods when error handling is disabled, the contents of ht transmit data buffer (5) are transmitted on the network (11) without any modification thereto. When error handling has been requested by the receiving node (13a), the controller (9) in the error-correcting apparatus (1) of the sending node (13b) causes the contents of the transmit data buffer (5) to be modified by means of a transmit data processor (8) to contain an error correction code and associated control. The insertion of the error correction code and control will, of necessity, consume a portion of the bandwidth of the network (11), thereby reducing the throughput of data on the network. The error correction code and control inserted at the sending node (13b) is detected by the error detection and correction circuit (6) at the receiving node (13a) and any errors such as single bit error present in the buffered received data packet are corrected base on the code. The controller (9) also controls the switch (7) to cause the contents of the receive data buffer (4) to be passed directly to the node equipment when error handling is disabled, and to cause the error corrected contents of the received data (4) to be passed to the node equipment during periods when error handling is enable. The error correction described above is not performed on a continuous basis, but only during periods where the quality of the transmission network has deteriorated to a predetermined level. Furthermore, the activation of error handling for each direction of data transfer on the transmission medium (12) can be individually activated and deactivated by the respective receiving nodes, although when the network quality is unacceptable, the error rates in both directions on the network (11) are likely to be unsatisfactory. The error handling between the receiving node (1 3a) and the sending node (13b) on the transmission network (ii) can be achieved by means of any one or more of the known techniques of bit interleaving, byte interleaving, cyclic redundancy checks and linear, BCH or convolutional error correction codes. The techniques used may be chosen to suit the needs of a particular application. The error-correction circuit (1) and it operation is independent of the transmission medium (1 2) used for the transmission network, such as copper cable, fibre optic cable, and includes radio, microwave and infrared transmission. The invention therefore provides an inexpensive and effective solution for the reduction of errors occurring in a transmission network which will minimize the additional network traffic utilised for error correction purposes. t 10 </div>

Claims

<div class="application article clearfix printTableText" id="claims"> What we claim is:

1. A method for correcting data errors in a transmission network having a sending node and at least one receiving node, comprising the steps of: buffering at least a portion of a network data packet transmitted by the sending node and received by the receiving node; detecting the number of errors present in the buffered data; determining the error rate of the transmission network at the receiving node, as a function of the number of errors detected in the buffered data; and activating the insertion of error correction code in further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving node exceeds a predetermined threshold.

2. A method for correcting data errors as claimed in claim 1, including the further step of de-activating the insertion of error correction code in the further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving node does not exceed the predetermined threshold.

3. A method for correcting data errors as claimed in claim 1, wherein the insertion of error correction code is activated by transmitting an activation request data packet from the receiving node to the sending node.

4. A method for correcting data errors as claimed in claim 2 in wherein the insertion of error correction code is deactivated by transmitting a de-activation f 11 28 P3 request data packet from the receiving node to the sending node.

5. A method for correcting data errors as claimed in any one of the preceding claims, including the further step of separately buffering at least a portion of a data packet to be transmitted from the receiving node to the sending node.

6. A method for correcting data errors as claimed in claim 5, including the further step of activating the insertion of error correction code in the data packet to be transmitted from the receiving node to the sending node upon reception of an activation request data packet fro the sending node.

7. A method for correcting data errors as claimed in claim 6, wherein the insertion of error correction code in the data packet to be transmitted from the receiving node is deactivated upon reception of a de-activation request data packet from the sending node.

8. A method for correcting data errors as claimed in any one of the preceding claims, wherein error correction code is inserted by means of one or more of the techniques of bit interleaving, byte interleaving, cyclic redundancy check control, linear, BCH or convolutional codes.

9. An apparatus for correcting data errors in a transmission network having a sending node and at least one receiving node, comprising: buffering means for buffering at least a portion of a network data packet transmitted by the sending node and received by the receiving node; detector means for detecting the number of errors present in the buffered t 12 ck^ j; monitoring means for continuously determining the error rate of the transmission network at the receiving node, as a function of the number of errors detected in the buffered data; and activating means for activating the insertion of error correction code in further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving node exceeds a predetermined threshold.

10. An apparatus as claimed in claim 9 which includes de-activating means for de-activating the insertion of error correction code in further network data packets transmitted by the sending node when the error rate of the transmission network at the receiving node does not exceed the predetermined threshold.

11. An apparatus as claimed in claim 1 0, wherein the activating means is a transmitter for transmitting an activation request data packet from the receiving node tot he sending node.

12. An apparatus as claimed in claim 1 1, wherein the de-activating means is a transmitter for transmitting a de-activation request data packet from the receiving node to the sending node.

13. A apparatus as claimed in claim 12, wherein the activating and de-activating g means are the same transmitter.

14. An apparatus as claimed in any one of claims 9 to 13, including separate t 13 buffering means for buffering at least a portion of a data packet to be transmitted from the receiving node to the sending node.

15. An apparatus as claimed in claim 14 which including insertion means for inserting error correction code in the data packet to be transmitted from the receiving node.

1 6. An apparatus as claimed in claim 1 5, wherein the insertion means is activatable upon reception of an activation request data packet from the sending node.

1 7. An apparatus as claimed in claim 16, wherein the insertion means is de-activatable upon reception of a de-activation request data packet from the sending node.

1 8. An apparatus as claimed in any one of claims 1 5 to 1 7 in which the insertion means inserts error correction code in the data packet by means of one or more of the techniques of bit interleaving, byte interleaving, cyclic redundancy check control, linear, BCH or convolutional codes.

1 9. A transmission network having at least two nodes including the apparatus for correcting data errors as claimed in any one of claims 9 to 18.

20. A method for correctino data errors, substantially as herein described with reference to and as illustrated in the accompanying drawings.

21. An apparatus for correcting data errors, substantially as herein described with reference to and a illustrated in the accompanying drawings. 2 r* b v.-.

22. A transmission network, substantially as herein described with reference to and as illustrated in the accompanying drawings. ALCATEL AUSTRALIA LIMITED B. O'Connor Authorized Agent P5/1/1 703 END OF CLAIMS </div>