Optical network system with quality control function

• US 6,990,294 B2
• Filed: 06/28/2001
• Issued: 01/24/2006
• Est. Priority Date: 01/25/2001
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Sakano, Shinji, Ikoma, Yoshiaki, Miyagami, Masaki
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): CURS, NATHAN M
• Application Number:
  US09/894,017
• Publication Number:
  US 20020097460A1
• Time in Patent Office: 1,671 Days
• Field of Search: 398/9, 398/16, 398/25, 398/26, 398/27, 398/30, 398/33, 398/34
• US Class Current: 398/16
• CPC Class Codes: H04B 10/00 Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04J 14/0305 in end terminals
• CPC Class Codes: H04L 43/00 Arrangements for monitoring or testing data switching networks
• CPC Class Codes: H04L 43/0811 by checking connectivity
• CPC Class Codes: H04L 43/0823 Errors, e.g. transmission errors
• CPC Class Codes: H04L 43/50 Testing arrangements

Abstract

To ensure transmission in a flexible optical network system, a digital test signal generation/comparison circuit is incorporated in an electrical signal processing portion of a transponder. The optical network system provides transparent wavelength-division multiplex service regardless of the signal type in client optical signals. Prior to connecting a client optical line to the optical system, a selective insertion unit and a selective extraction unit enable quality assessment of the client optical line.

Claims

1. An optical network system with quality control function in the optical network system wherein a signal to be transmitted is converted to an optical signal of a prescribed wavelength and transmitted over an optical transmission path by a transmit-end wavelength convener;

and said optical signal from said optical transmission path is received and wavelength-converted by a receive-end wavelength converter, for regenerating the signal to be transmitted, the optical network system comprising;

said transmit-end wavelength converter for a transmit end with a first transponder further comprising;

an optical signal input unit for inputting an optical signal to be transmitted;

a test signal generator circuit ultimately connected to said optical signal input unit for generating a test signal for testing optical transmission quality, said test signal generator circuit further comprising;

a clock generator for generating a clock signal indicative of a bit rate to be added to the test signal;

an ‘

all 1s and all 0s’

generator circuit for generating ‘

all 1s and all 0s’

signals; and

a scrambler circuit connected to said ‘

all 1s and all 0s’

generator circuit for scrambling the ‘

all 1s and all 0s’

signals to generate a scrambled test signal;

an insertion circuit connected to said optical signal input unit and said test signal generator circuit for outputting an output signal by selectively inserting the test signal from said test signal generator circuit into the transmission path formed between the transmit end and a receive end; and

a converter connected to said insertion circuit for converting the output signal of said insertion circuit to a predetermined optical wavelength; and

said receive-end wavelength converter at the receive end with a second transponder further comprising;

an extraction circuit for selectively extracting the test signal in the optical signal from said transmission path;

a test comparison circuit connected to said extraction circuit for determining the optical transmission quality based on the test signal extracted by said extraction circuit, said test comparison circuit further comprising;

a clock extraction circuit for extracting the clock signal from the test signal that is received at the receive end in order to synchronize with the bit rate of the selected test signal;

a descrambler circuit connected to said clock extraction circuit for using the clock component for descrambling the scrambled test signal to generate descrambled signals;

a selector circuit connected to said descrambler unit for selecting one of the descrambled signals from said descrambler circuit; and

a comparison test circuit connected to said selector circuit for performing a test signal comparison and a bit error count/computation of the selected descrambled signal.

2. The optical network system with quality control function according to claim 1 wherein said test signal generator circuit further comprises a pseudo-random signal generator circuit.

3. The optical network system with quality control function according to claim 1 further comprising:

a switch for initiating the test signal comparison for assessing the quality of the transmission path prior to transmitting the signal to be transmitted; and

if the quality of the transmission path is less than a predetermined transmission path quality level, another transmission path is established, and another test signal comparison being performed for the quality of said another transmission path.

4. An optical transponder in connection with a client line and an optical transmission line, comprising:

a first optical to electronic (O/E) converter for converting an optical signal from the client line to an electronic signal;

a signal testing unit connected to said first O/E converter for selectively adding a scrambled test signal to the electronic signal so as to generate a test-signal-contained electronic signal, said signal testing unit further comprising;

a clock generator for generating a clock signal indicative of a bit rate of a scrambled test signal to be added to the electronic signal;

an ‘

all 1s and all 0s’

generator circuit for generating ‘

all 1s and all 0s’

signals; and

a scrambler circuit connected to said ‘

all 1s and all 0s’

generator circuit for scrambling the ‘

all 1s and all 0s’

signals to generate the scrambled test signal

a first electronic to optical (E/O) converter connected to said signal testing unit for converting the test-signal-contained electronic signal to generate a test-signal-contained optical signal to be transmitted in the optical transmission line;

a second optical to electronic (O/E) converter connected to said signal testing unit for converting a received test-signal-contained optical signal from the optical transmission line to a second test-signal-contained electronic signal, wherein said signal testing unit determines the quality of transmission in the optical transmission line based upon the second test-signal-contained electronic signal, said signal testing unit further comprising;

a clock extraction circuit for extracting the clock signal from the second test signal contained electronic signal in order to synchronize with the bit rate of the electronic test signal;

a descrambler circuit connected to said clock extraction circuit for using a clock signal component for descrambling a scrambled test signal component of the second test-signal-contained electronic signal to generate descrambled signals;

a selector circuit connected to said descrambler unit for selecting one of the descrambled signals from said descrambler circuit;

a comparison test circuit connected to said selector circuit for performing a test signal comparison and a bit error count/computation of the selected descrambled signal; and

a second electronic to optical (E/O) converter connected to said signal testing unit for converting the second test-signal-contained electronic signal to generate received optical signal for the client line.

5. The optical transponder according to claim 4 wherein said signal testing unit further includes a random signal generation unit for generating a random signal as the scrambled test signal.

6. The optical transponder according to claim 4 wherein said signal testing unit further includes a predetermined signal generation unit for generating a predetermined sequence of 0 and 1 signals.

7. The optical transponder according to claim 4 wherein said signal testing unit further includes an error count unit for counting a number of errors or bit errors based upon the second test-signal-contained electronic test signal.

8. The optical transponder according to claim 4 wherein said first O/E converter and said second O/E converter each convert from a predetermined single wavelength, and wherein said first E/O converter and said second E/O converter each convert to a predetermined single wavelength.

9. The optical transponder according to claim 4 wherein said first O/E converter converts from a predetermined wavelength optical signal to an electronic signal and said second O/E converter converts from an optical signal with a variable wavelength to an electronic signal, and wherein said first E/O converter converts from an electronic signal to an optical signal with a variable wavelength and said second E/O converter converts from an electronic signal to a predetermined wavelength optical signal.

10. An optical signal network in connection with client lines and an optical network transmission line, a plurality of nodes each connected to a corresponding one of the client lines and the optical network transmission line, the client lines each having an optical signal at a predetermined optical wavelength, the optical network transmission line having an optical signal comprising multiplexed wavelengths, each of said nodes comprising:

an optical wavelength separator connected to the optical network transmission line for separating a desired wavelength from the optical signal comprising multiplexed wavelengths;

an optical wavelength combiner connected to the client lines and the optical network transmission line for creating the optical signal comprising multiplexed wavelengths; and

a transponder connected to said optical wavelength separator and said optical wavelength combiner for converting an optical signal at a first wavelength to a second wavelength, said transponder further comprising a set of optical-to-electronic converters, electronic-to-optical converters and a transmission quality testing unit connected between an optical-to-electronic converter and an electronic-to-optical converter for testing a transmission quality of the optical network transmission line, said transmission quality testing unit further comprising;

a test signal generator circuit for generating a test signal for testing optical network transmission line quality, said test signal generator circuit further comprising;

a clock generator connected to said test signal generator circuit for generating a clock signal indicative of a bit rate of the test signal from said test signal generator circuit;

an ‘

all 1s and all 0s’

generator circuit for generating ‘

all 1s and 0s’

signals;

a scrambler circuit connected to said ‘

all 1s and all 0s’

generator circuit for scrambling the ‘

all 1s and all 0s’

signals to generate a scrambled test signal;

a test comparison circuit for determining the optical network transmission line quality based on a test signal received from other nodes, said test comparison circuit further comprising;

a clock extraction circuit for extracting a clock signal from a separated wavelength signal in order to determine the bit rate of the separated wave length signal,

a descrambler circuit connected to said clock extraction circuit for using the clock signal for descrambling a received scrambled test signal to generate descrambled signals;

a selector circuit connected to said descrambler unit for selecting one of a test signal comparison and a bit error count/computation of a selected descrambled signal.

11. The optical signal network according to claim 10 wherein said optical wavelength separator is an optical demultiplexer.

12. The optical signal network according to claim 10 wherein said optical wavelength combiner is an optical multiplexer.

13. The optical signal network according to claim 10 further comprising an optical switch matrix located between said optical wavelength separator and said optical wavelength combiner.

14. The optical signal network according to claim 10 further comprising a monitor control unit connected to said transmission quality testing unit for monitoring and controlling said transmission quality testing unit.

15. The optical signal network according to claim 10 wherein said optical wavelength separator is an optical wavelength add/drop module.

16. The optical signal network according to claim 10 wherein said optical wavelength combiner is an optical wavelength add/drop module.

17. The optical signal network according to claim 10 wherein a plurality of said transponders each receive a predetermined optical wavelength signal from said optical wavelength separator for any combination of desired wavelengths.

18. The optical signal network according to claim 10 wherein a plurality of said transponders receives optical signals from the client lines in any combination of desired wavelengths to output to said optical wavelength combiner.

19. A method of testing transmission quality in an optical network having optical transmission lines and client lines connected to the optical transmission lines, comprising:

converting an optical signal at a first wavelength from one of the client lines to an electrical signal in a transponder;

generating a test signal for testing optical transmission line quality;

specifying a bit rate of the test signal by adding a clock signal to a test signal generator;

adding the electrical signal and the test signal in the transponder to create a sum signal;

scrambling the sum signal to generate a scrambled test signal;

converting the scrambled test signal to an optical signal at a second wavelength in the transponder to be transmitted in the optical transmission lines;

converting an optical signal at the second wavelength from the optical transmission lines to a second electrical signal in the transponder;

extracting a clock signal from the second electrical signal;

descrambling the second electrical signal based upon the extracted clock signal to generate descrambled signals;

selecting one of the descrambled signals;

performing a test signal comparison and a bit error count/computation with the selected descrambled signal;

synchronizing the bit rate of the test signal with the clock signal;

determining transmission quality based upon the test signal comparison in the transponder; and

converting the second electrical signal to an optical signal at the first wavelength in the transponder to be outputted to the one of the client lines.

20. The method of testing transmission quality in an optical network according to claim 19 further comprising selecting the client lines based on the transmission quality.

21. The method of testing transmission quality in an optical network according to claim 19 further comprising selecting the optical transmission lines based upon the transmission quality.

22. The method of testing transmission quality in an optical network according to claim 19 further comprising multiplexing a plurality of wavelengths to form an optical signal for a transmission line, wherein said transmission quality is determined for each of the wavelengths of the optical signal.

23. The method of testing transmission quality in an optical network according to claim 19 further comprising demultiplexing an optical signal received from the optical transmission lines into a plurality of wavelengths including the first wavelength;

and

selecting at least a part of the plurality of wavelengths that includes the first wavelength in order to determine transmission quality.

24. The method of testing transmission quality in an optical network according to claim 23 wherein the selected part of the plurality of wavelengths of the demultiplexed optical signal is remotely selected for determining the transmission quality.