Alignment of parity bits to eliminate errors in switching from an active to a standby processing circuit

• US 5,838,698 A
• Filed: 04/28/1995
• Issued: 11/17/1998
• Est. Priority Date: 04/28/1995
• Status: Expired due to Fees

• Current Assignee: AT&T IPM Corp. (AT&T, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Hammer, Michael Paul, Doubler, James Arthur
• Primary Examiner(s): Gordon, Paul P.
• Assistant Examiner(s): BROWN, THOMAS
• Application Number:
  US08/430,627
• Time in Patent Office: 1,299 Days
• Field of Search: 371/5.1, 371/48, 371/49.1, 371/49.2, 371/49.3, 371/49.4, 371/51.1, 371/68.2, 371/50.1, 371/67.1, 371/68.1, 371/69.1, 371/70, 370/13, 370/14, 370/16, 364/184-187
• US Class Current: 714/800
• CPC Class Codes: G06F 11/10 Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's
• CPC Class Codes: G06F 11/20 using active fault-masking, e.g. by switching out faulty elements or by switching in spare elements
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/22 using redundant apparatus to increase reliability

Abstract

Glitchless switching between active and standby telecommunication apparatus having hierarchical nested parity bits is provided. A higher order parity bit is calculated based on defined data as well as a lower order parity bit. A method is provided for aligning each parity bit generated by a standby processor with a corresponding parity bit independently generated by an active processor. This alignment is accomplished prior to output frames of data being supplied by the standby processor in order to provide glitchless switching such that the first frame of data supplied by the standby processor contains parity bits which are in agreement with the corresponding data in the frame.

Claims

1. In a telecommunication apparatus having first and second processing devices where the first device processes sequential frames of data in an active mode and the second device operates in a standby mode ready to take over the processing of the frames of data from the first device, each of the sequential frames of data including a plurality of hierarchical generated parity bits, a method for aligning the parity bits during a change of processing of the frames of data from the first device to the second device comprising the steps of:

(a) determining whether the lowest rank parity bit in a first frame of data processed by the second device has the same polarity as the lowest rank parity bit processed by the first device during the first frame;

(b) inverting the polarity of the lowest rank parity bit in the first frame of data processed by the second device if its polarity is not the same as the polarity of the corresponding parity bit processed by the first device during the first frame;

(c) for parity bits processed by the second device, determining for each parity bit of a higher rank than the lowest rank parity bit if a polarity inversion of a lower ranked parity bit has occurred;

(d) if the determination of step (c) is true for a one of the higher rank parity bits, selecting one inversion sequence from a set of inversion sequences to control inversions of the parity of said one parity bit, said selection of the one inversion sequence based on the number of inversions of lower rank parity bits.

2. The method according to claim 1 wherein step (d) further comprises the step of said selection of said one inversion sequence also based on whether the polarity of said one parity bit processed by the second device is not the same as the polarity of the corresponding parity bit processed by the first device.

3. The method according to claim 1 further comprising a step following step (d) of claim 1 of determining whether the highest rank parity bit in a frame of data processed by the second device has the same polarity as the highest rank parity bit processed by the first device during the corresponding frame, and inverting the polarity of the highest rank parity bit in the frame of data processed by the second device if its polarity is not the same as the polarity of the corresponding parity bit processed by the first device during the corresponding frame.

4. The method according to claim 1 wherein said hierarchical parity bits are nested.

5. The method according to claim 1 further comprising the step of the second device sequential frames of data following the first frame of data and aligning the parity bits in the data for each frame.

6. The method according to claim 1 wherein said first and second devices process synchronous formatted data.

7. The method according to claim 1 further comprising the step of said second device beginning to process the frames of data with said first frame of data, and where the second device does not have access to prior history of the state of the parity bits for data previously processed by the first device.

8. The method according to claim 1 further comprising the steps of first and second data streams of the frames of data being generated by the first and second devices, respectively, an output data stream being selected from the first and second data streams, selecting the second data stream as the output data stream only after all ranked parity bits in frames of data in the second data stream have been aligned to be the same as corresponding parity bits in frames of data in the first data stream.

9. In a telecommunication apparatus having first and second processing devices where the first device processes sequential frames of data in an active mode and the second device operates in a standby mode ready to take over the processing of the frames of data from the first device, each of the sequential frames of data including a plurality of hierarchical generated parity bits, the improvement of aligning the parity bits during a change of processing of the frames of data from the first device to the second device comprising:

(a) first means for determining whether the lowest rank parity bit in a first frame of data processed by the second device has the same polarity as the lowest rank parity bit processed by the first device during the first frame;

(b) means responsive to said first means for inverting the polarity of the lowest rank parity bit in the first frame of data processed by the second device if its polarity is not the same as the polarity of the corresponding parity bit processed by the first device during the first frame;

(c) second means for determining if a polarity inversion of a lower ranked parity bit has occurred for each parity bit of a higher rank than the lowest rank parity bit;

(d) means for selecting one inversion sequence from a set of inversion sequences to control inversions of the parity of said one parity bit if the determination of said second determining means is true for one of the higher rank parity bits, said selecting means making the selection based on the number of inversions of lower rank parity bits.

10. The apparatus according to claim 9 wherein said selecting means further comprises selecting said one inversion sequence based on whether the polarity of said one parity bit processed by the second device is not the same as the polarity of the corresponding parity bit processed by the first device.

11. The apparatus according to claim 9 further comprising means for determining whether the highest rank parity bit in a frame of data processed by the second device has the same polarity as the highest rank parity bit processed by the first device during the corresponding frame, and means for inverting the polarity of the highest rank parity bit in the frame of data processed by the second device if its polarity is not the same as the polarity of the corresponding parity bit processed by the first device during the corresponding frame.

12. The apparatus according to claim 9 wherein said hierarchical parity bits are nested.

13. The apparatus according to claim 9 further comprising means for processing sequential frames of data following the first frame of data in order to align the parity bits in the data processed by the second device with the parity bits in the data processed by the first device.

14. The apparatus according to claim 9 wherein said first and second devices process synchronous formatted data.

15. The apparatus according to claim 9 wherein said second device begins processing the frames of data with said first frame of data, and wherein the second device does not have access to prior history of the state of the parity bits for data previously processed by the first device.

16. The apparatus according to claim 9 wherein first and second data streams of the frames of data are generated by the first and second devices, respectively, and further comprising means for generating an output data stream being selected from the first and second data streams, said output generating means selecting the second data stream as the output data stream only after all ranked parity bits in frames of data in the second data stream have been aligned to be the same as corresponding parity bits in frames of data in the first data stream.

17. A telecommunication apparatus adapted to receive first and second streams of data where the first and second streams of data include frames of data with each frame having hierarchical generated parity bits, the apparatus comprising:

means for comparing hierarchical parity bits of equal rank in corresponding frames of data in said first and second streams of data;

means coupled to said comparing means for inverting the polarity of ones of the parity bits in the second stream when;

(a) the polarity of said ones are not equal to the corresponding polarity of a parity bit of equal rank in the first data stream, and (b) the polarity of a lower rank parity in the second data stream has been inverted as a result of condition (a), said inverting means selecting ones of predetermined inversion sequences dependent upon conditions (a) and (b).

18. The apparatus according to claim 17 further comprising another means coupled to said inverting means for comparing at least the polarity of all equal rank parity bits in a corresponding frame of data in the first and second streams of data, and means coupled to said another means for routing the second data stream to an output only if the results of the comparison by said another means indicates that all of the equal rank parity bits in the first and second streams of data have the same polarity.

19. In a telecommunication system that receives first and second streams of data where the first and second streams of data includes frames of data having hierarchical parity bits, the system transmitting one of the first and second streams of data, a method for preventing parity mismatch when changing from transmitting the one to the other of the first and second streams of data comprising the steps of:

comparing hierarchical parity bits of equal rank in corresponding frames of data in said first and second streams of data;

selectively inverting the polarity of ones of the parity bits in the second stream of data based on said comparing step in order prevent an interframe mismatch of the polarity of the hierarchical parity bits in the second data stream relative to the hierarchical parity bits in the first data stream.

20. The method according to claim 19 wherein the comparing and selectively inverting steps are performed prior to the change from transmitting the one to the other of the first and second streams of data, and the hierarchical parity bits are nested.