Network element for signals of the optical transport network (OTN)
View Patent ↗A crossconnect for asynchronous OTN signals operates synchronously internally at an internal clock rate. Received OTN signals are synchronized to an internal frame format by stuffing. The synchronized signals are parallelized and switched with a switching matrix comprising synchronously operating integrated circuits that operate at the internal clock rate. At the output, the synchronized signals are again destuffed and are transmitted again at the original bit rate.
1. A network element for asynchronous optical communications signals that are assembled in accordance with a multiplex specification and have a bit rate within a specified bit-rate range, the network element comprising:
optical-to-electrical converters for converting received asynchronous optical signals into electrical signals;
bit stuffing devices for adapting the bit rates of the electrical signals to an integral multiple of an internal clock rate that is higher than the upper limit of the specified bit-rate range;
serial/parallel converters for converting the bit stuffed signals into a specified number of parallel signals having the internal clock rate; and
a synchronous electrical switching matrix that operates at the internal clock rate for switching the parallel signals from any to any port.
2. The network element according to claim 1 , which is designed as an optical cross connect.
3. The network element according to claim 1 , which is designed for optical communication signals in accordance with ITU-T G.709.
4. The network element according to claim 1 , the network element having a second redundant switching matrix to which the first switching matrix is switched over in an interruption-free manner in the fault condition.
5. The network element according to claim 1 , wherein the internal clock frequency is chosen in such a way that the bit stuffing rate is between 0 and 1.
6. The network element according to claim 1 , having a clock generator for generating a clock signal that is an integral multiple of the internal clock rate, and having a divider for generating an internal clock signal.
7. The network element according to claim 6 , wherein the clock generator is a free-running oscillator having a frequency position of about ±20 ppm or less.
8. The network element according to claim 6 , wherein the clock generator can be externally synchronized.
9. The network element according to claim 6 , wherein the divider generates a gapped clock having the internal clock rate by blocking individual clock pulses of the clock signal generated by the clock generator.
10. The network element according to claim 6 , the network element comprising:
first bit stuffing devices for adapting the bit rates of electrical signals of a lower hierarchy level to a first integral multiple including 1 of the internal clock rate; and
second bit stuffing devices for adapting the bit rates of the electrical signals of a middle hierarchy level to a second integral multiple of the internal clock rate, which is greater than the first multiple.
11. The network element according to claim 10 , wherein the lowest multiplex level corresponds to OTU 1 and the middle multiplex level to OTU 2 in accordance with ITU-T G.709.
12. The network element according to claim 10 , further comprising a third bit stuffing device for adapting the bit rates of electrical signals of a highest hierarchy level to a third integral multiple of the internal clock rate that is greater than the second multiple.
13. A method of switching asynchronous optical communications signals that are assembled in accordance with a multiplex specification and have a bit rate within a specified bit-rate range, the method comprising:
converting of received asynchronous optical signals into electrical signals;
adapting of the bit rates of the electrical signals by bit stuffing to an integral multiple of an internal clock rate, which multiple is higher than the upper limit of the specified bit-rate range; and
converting the bit stuffed signals into a specified number of parallel signals having the internal clock rate; and
switching -the parallel signals with a synchronous electrical switching matrix -that operates at the internal clock rate from any to any port in an arbitrary controlled manner.