Optical transmission network with asynchronous mapping and demapping and digital wrapper frame for the same
View Patent ↗An optical transmission network is inherently asynchronous due to the utilization of a variable overhead ratio (V-OHR). The network architecture makes extensive use of OEO regeneration, i.e., deals with any electronic reconditioning to correct for transmission impairments, such as, for example, FEC encoding, decoding and re-encoding, signal reshaping, retiming as well as signal regeneration. The optical transmission network includes a plesiochronous clocking system with intermediate nodes designed to operate asynchronously with a single local frequency clock without complicated network synchronization schemes employing high cost clocking devices such as phase locked loop (PLL) control with crystal oscillators and other expensive system components. The asynchronous network operation provides for asynchronous remapping or remapping of any client signal utilizing any type of transmission protocol where the line side rate or frequency is always the same frequency for the payload signal and the local frequency at an intermediate node is set to a local reference clock in accordance with the payload type and its overhead ratio, i.e., the overhead ratio is varied to meet the desired difference between the line rate or frequency and the desired client signal payload rate or frequency for the particular client signal payload type.
1. A method of providing a single line frequency rate operation between node elements (NEs) of a communication transmission network receiving a multitude of different client signals of different payload types with different client signal payload rates which client signals are propagated at the single line frequency rate between NEs of the network, comprising the steps of:
providing a constant line rate between node elements regardless of the client signal payload rates;
establishing at a node element an overhead ratio (OHR) between the line rate and an effective payload rate where the effective payload rate is determined from a payload offset size from an actual client signal payload size for a particular client signal payload type;
buffering ingress of the client signals at node element where the client signal payload is clocked into the node element at the higher line frequency rate and clocked within the node element at the client signal payload rate; and
utilizing the established effective payload rate at the node element to generate the client signal payload clock for clocking the client signals through the node element at the client signal payload rate.
2. The method of claim 1 wherein the line rate is a higher frequency than the client signal payload rate.
3. The method of claim 1 wherein the step of buffering is performed with the use of a first FIFO buffer or a first delay line.
4. The method of claim 1 comprising the further steps of:
buffering egress of the client signals out of the node element where the client signal payload is clocked out of the node element from the lower client signal payload clock into the higher line rate for output from the node element.
5. The method of claim 4 wherein the step of buffering is performed with the use of a second FIFO buffer or a second delay line.