Through-timing of data transmitted across an optical communications system utilizing frequency division multiplexing

1. In an optical fiber communications system, a method for maintaining jitter tolerance of data transmitted across the communications system, the method comprising:

receiving a tributary complying with a jitter tolerance;

recovering data from the tributary;

receiving a reference clock;

retiming the recovered data according to the reference clock;

converting the recovered data into at least two intermediate-speed data channels, wherein each intermediate-speed data channel is timed by a first clock based on the reference clock;

converting each intermediate-speed data channel into at least two low-speed data channels, wherein the low-speed data channels in aggregate contain the recovered data and each low-speed data channel is timed by a second clock based on the reference clock;

modulating each low-speed data channel to generate a corresponding low-speed symbol channel; and

frequency division multiplexing the low-speed symbol channels to produce an electrical high-speed channel for transmission in optical form across the communications system.

2. The method of claim 1 wherein the tributary and the jitter tolerance conform to a SONET protocol.

3. The method of claim 2 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the SONET protocol; and

a payload which does not conform to the SONET protocol.

4. The method of claim 3 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-3 protocol; and

a payload which does not conform to the STS-3 protocol.

5. The method of claim 3 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-48 protocol; and

a payload which does not conform to the STS-48 protocol.

6. The method of claim 1 wherein the step of converting the recovered data into at least two intermediate-speed data channels comprises:

recovering a clock from the tributary;

phase aligning the reference clock to the recovered clock;

retiming the recovered data using the phase-aligned reference clock; and

time division demultiplexing the retimed, recovered data into the intermediate-speed data channels.

7. The method of claim 6 wherein the step of converting each intermediate-speed data channel into at least two low-speed data channels comprises:

dividing the phase-aligned reference clock to produce the first clock;

retiming the recovered data in the intermediate-speed data channels using the first clock;

time division demultiplexing the intermediate-speed data channels into the low-speed data channels.

8. The method of claim 1 further comprising:

converting the electrical high-speed channel to an optical high-speed channel;

transmitting the optical high-speed channel across a fiber;

receiving the optical high-speed channel;

converting the received optical high-speed channel to a receive-side electrical high-speed channel;

frequency division demultiplexing the receive-side electrical high-speed channel into at least two receive-side low-speed symbol channels;

demodulating each receive-side low-speed symbol channel to generate a corresponding receive-side low-speed data channel;

recovering a clock and data from each receive-side low-speed data channel;

generating a receive-side reference clock synchronized to the receive-side recovered data;

converting the receive-side low-speed data channels into at least two receive-side intermediate-speed data channels; and

converting the receive-side intermediate-speed data channels into a receive-side tributary, wherein the receive-side tributary contains all of the receive-side recovered data, and the receive-side tributary is timed by a clock based on the receive-side reference clock and complies with the jitter tolerance.

9. The method of claim 8 wherein the tributary, the receive-side tributary and the jitter tolerance conform to a SONET protocol.

10. The method of claim 8 wherein the step of converting the receive-side low-speed data channels into at least two receive-side intermediate-speed data channels comprises:

storing the recovered data from each receive-side low-speed data channel;

aligning a timing for the receive-side low-speed data channels; and

time division multiplexing the receive-side recovered data from the receive-side low-speed data channels into the at least two receive-side intermediate-speed data channels according to the aligned timing.

11. The method of claim 10 wherein the step of converting the receive-side intermediate-speed data channels into the tributary comprises:

storing the recovered data from each receive-side intermediate-speed data channel;

aligning a timing for the receive-side intermediate-speed data channels; and

time division multiplexing the stored recovered data from the receive-side intermediate-speed data channels according to the aligned timing.

12. In an optical fiber communications system, a method for maintaining jitter tolerance of data transmitted across the communications system, the method comprising:

receiving an optical high-speed channel containing data transmitted across the communications system, the data from a tributary complying with a jitter tolerance before said transmission;

frequency division demultiplexing an electrical high-speed channel into at least two low-speed symbol channels, wherein the electrical high-speed channel is derived from the optical high-speed channel;

demodulating each low-speed symbol channel to generate a corresponding low-speed data channel;

recovering data from each low-speed data channel;

generating a reference clock synchronized to the recovered data;

storing the recovered data from each low-speed data channel;

aligning a timing for the low-speed data channels;

time division multiplexing the recovered data from the low-speed data channels into at least two intermediate-speed data channels according to the aligned timing;

aligning a timing for the intermediate-speed data channels; and

converting the intermediate-speed data channels into a tributary, wherein the tributary contains all of the recovered data, and the tributary is timed by a clock based on the reference clock and complies with the jitter tolerance.

13. The method of claim 12 wherein the tributary and the jitter tolerance conform to a SONET protocol.

14. The method of claim 13 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the SONET protocol; and

a payload which does not conform to the SONET protocol.

15. The method of claim 14 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-3 protocol; and

a payload which does not conform to the STS-3 protocol.

16. The method of claim 14 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-48 protocol; and

a payload which does not conform to the STS-48 protocol.

17. The method of claim 12 wherein the step of aligning a timing for the low-speed data channels comprises:

generating a framing pulse for each low-speed data channel; and

aligning the framing pulses.

18. The method of claim 12 wherein the step of converting the intermediate-speed data channels into the tributary comprises:

storing the recovered data from each intermediate-speed data channel;

aligning a timing for the intermediate-speed data channels; and

time division multiplexing the stored recovered data from the intermediate-speed data channels according to the aligned timing.

19. The method of claim 18 wherein the step of aligning a timing for the intermediate-speed data channels comprises:

generating a framing pulse for each intermediate-speed data channel; and

aligning the framing pulses.

20. An optical fiber communications system for maintaining jitter tolerance of data transmitted across the communications system, the communications system comprising:

a local oscillator for generating a reference clock conforming to a jitter tolerance;

a clock and data recovery circuitry coupled to the local oscillator for recovering data from a received tributary and for retiming the recovered data according to the reference clock;

a first time division demultiplexer coupled to the clock and data recovery circuitry for time division demultiplexing the recovered data into at least two intermediate-speed data channels, wherein each intermediate-speed data channel is timed by a first clock based on the reference clock;

a second time division demultiplexer coupled to the clock and data recovery circuitry for time division demultiplexing the intermediate-speed data channels into at least two low-speed data channels, wherein each low-speed data channel is timed by a second clock based on the reference clock;

a modulator coupled to the time division demultiplexer for modulating each low-speed data channel to generate a corresponding low-speed symbol channel; and

a frequency division multiplexer coupled to the modulator for frequency division multiplexing the low-speed symbol channels to produce an electrical high-speed channel for transmission in optical form across the communications system.

21. The communications system of claim 20 wherein the tributary and the jitter tolerance conform to a SONET protocol.

22. The communications system of claim 21 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the SONET protocol; and

a payload which does not conform to the SONET protocol.

23. The communications system of claim 22 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-3 protocol; and

a payload which does not conform to the STS-3 protocol.

24. The communications system of claim 22 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-48 protocol; and

a payload which does not conform to the STS-48 protocol.

25. The communications system of claim 20 further comprising:

an E/O converter coupled to the frequency division multiplexer for converting the electrical high-speed channel to an optical high-speed channel and for transmitting the optical high-speed channel across a fiber;

an O/E converter for receiving the optical high-speed channel and for converting the received optical high-speed channel to a receive-side electrical high-speed channel;

a frequency division demultiplexer coupled to the O/E converter for frequency division demultiplexing the receive-side electrical high-speed channel into at least two receive-side low-speed symbol channels;

a demodulator coupled to the frequency division demultiplexer for demodulating each receive-side low-speed symbol channel to generate a corresponding receive-side low-speed data channel;

a receive-side data recovery circuitry coupled to the demodulator for recovering data from each receive-side low-speed data channel;

a phase-locked loop coupled to the receive-side data recovery circuitry for generating a receive-side reference clock synchronized to the receive-side recovered data; and

a first time division multiplexer coupled to the receive-side data recovery circuitry and the phase-locked loop for generating at least two intermediate-speed data channels; and

a second time division multiplexer coupled to the first time division multiplexer for generating a receive-side tributary, wherein the receive-side tributary contains all of the receive-side recovered data, and the receive-side tributary is timed by a clock based on the receive-side reference clock and complies with the jitter tolerance.

26. The communications system of claim 25 wherein the tributary, the receive-side tributary and the jitter tolerance conform to a SONET protocol.

27. The communications system of claim 25

wherein the first time-division multiplexer comprises:

a state machine for aligning a timing for the receive-side intermediate-speed data channels;

buffers for storing the recovered data from each receive-side intermediate-speed data channel and releasing the stored recovered data according to the aligned timing; and

multiplexers for combining the released data; and

wherein the second time-division multiplexer comprises:

a state machine for aligning a timing for the receive-side low-speed data channels;

buffers for storing the recovered data from each receive-side low-speed data channel and releasing the stored recovered data according to the aligned timing; and

multiplexers for combining the released data.

28. An optical fiber communications system for maintaining jitter tolerance of data transmitted across the communications system, the communications system comprising:

a receiver for receiving an optical high-speed channel containing data transmitted across the communications system, the data from a tributary complying with a jitter tolerance before said transmission;

a frequency division demultiplexer coupled to the receiver for frequency division demultiplexing an electrical high-speed channel into at least two low-speed symbol channels, wherein the electrical high-speed channel is derived from the optical high-speed channel;

a demodulator coupled to the frequency division demultiplexer for demodulating each low-speed symbol channel to generate a corresponding low-speed data channel;

a clock and data recovery circuitry coupled to the demodulator for recovering data from each low-speed data channel and for generating a reference clock synchronized to the recovered data; and

a first time division multiplexer coupled to the clock and data recovery circuitry for generating at least two intermediate-speed data channels, wherein the first time division multiplexer comprises:

circuitry for aligning a timing according to the reference clock for the receive-side low-speed data channels;

circuitry for storing the recovered data from each receive-side low-speed data channel, and for releasing stored recovered data from the low-speed data channels according to the aligned timing; and

circuitry for combining the released data from the low-speed data channels;

wherein the intermediate-speed data channels are timed by a first clock based on the reference clock and comply with the jitter tolerance; and

a second time division multiplexer coupled to the clock and data recovery circuitry for generating a tributary, wherein the tributary contains all of the recovered data, and the tributary is timed by a second clock based on the reference clock and complies with the jitter tolerance.

29. The communications system of claim 28 wherein the tributary and the jitter tolerance conform to a SONET protocol.

30. The communications system of claim 29 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the SONET protocol; and

a payload which does not conform to the SONET protocol.

31. The communications system of claim 30 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-3 protocol; and

a payload which does not conform to the STS-3 protocol.

32. The communications system of claim 30 wherein each low-speed data channel includes:

a framing header and a data rate which conforms to the STS-48 protocol; and

a payload which does not conform to the STS-48 protocol.

33. The communications system of claim 28 wherein the second time division multiplexer comprises:

a state machine for aligning a timing for the receive-side intermediate-speed data channels;

buffers for storing the recovered data from each receive-side intermediate-speed data channel and releasing the stored recovered data from the intermediate-speed data channels according to the aligned timing; and

multiplexers for combining the released data from the intermediate-speed data channels.