Multiplexing low-order to high-order ODU signals in an optical transport network
View Patent ↗A method and apparatus are provided for multiplexing one or more Low-Order (LO) ODUj/ODUflex clients into a High-Order (HO) ODUk in an Optical Transport Network (OTN). LO bytes are multiplexed in accordance with a tributary slot assignment for a selected LO ODUj of the HO ODUk stream using a permutation matrix. In an implementation, each byte on each ingress port of a W-port space-time-space switch is configurably assigned to an associated timeslot of an associated egress port, using time-division multiplexing. The number of TribSlots assigned to an ODUflex may be increased and decreased hitlessly. A Clos-like Space-Time-Space switch is used to interleave bytes from Low-Order ODUk words into High-Order ODUk words.
1. A system for multiplexing a plurality of Low-Order (LO) optical channel data unit (ODUj) data words into a High-Order (HO) ODUk carrier in an Optical Transport Network (OTN) comprising:
an apparatus configured to insert pad words among the plurality of LO ODUj data words, to justify the plurality of LO ODUj data words and to create expanded LO ODUj data words which together form an optical channel data tributary unit (ODTUjk); and
a space-time-space (STS) switch including a permutation matrix for re-arranging and multiplexing bytes in the expanded LO ODUj data words into HO ODUk words in accordance with a tributary slot assignment for a selected LO ODUj of the HO ODUk carrier;
wherein the STS switch comprises:
a plurality of ingress multiplexers and a plurality of egress multiplexers implementing space stages of the STS switch; and
a plurality of random access memories (RAMs) implementing a time stage of the STS switch, the RAMs configured to control the plurality of ingress multiplexers and the plurality of egress multiplexers.
2. The system of claim 1 wherein, for a W-byte LO ODUj cycle, where W is a positive integer, a multiplexer selects one of 2*W−1 RAMs to store received LO ODUj data words.
3. The system of claim 1 wherein, for each received byte, the STS switch determines an egress word and a byte within the determined egress word on which the received bye will be sent out.
4. The system of claim 3 wherein the STS switch comprises W ports, where W is a positive integer, and configurably assigns each byte on each ingress port of the W-port STS switch to an associated timeslot of an associated egress port.
5. The system of claim 1 wherein the re-arranged bytes comprise m bytes of the selected LO ODUj client when the selected LO ODUj client occupies m tributary slots in the HO ODUk.
6. The system of claim 1 wherein the plurality of LO ODUj clients comprises LO ODUflex clients.
7. The system of claim 1 wherein the expander block inserts generic mapping procedure (GMP) pad bytes among GMP data bytes.
8. The system of claim 7 wherein each GMP pad and GMP data word occupies the same number of bytes as the number of HO ODUk tributary slots occupied by the LO ODUj stream.
9. The system of claim 1 wherein the STS switch is configured to multiplex the plurality of LO ODUj clients to a plurality of HO ODUks, the STS switch further comprising a set of permutation matrices comprising one permutation matrix for each of the plurality of HO ODUks.
10. The system of claim 1 wherein the permutation matrix is reconfigurable for additions or removals of LO ODUj/ODUflex clients within the HO ODUk carrier.
11. The system of claim 1 further comprising a standby page of configuration settings in the permutation matrix, the standby page being updated with new settings that take effect at a next server multi-frame boundary, ensuring that existing LO ODUj/ODUflex clients are hitless during a change.
12. The system of claim 1 wherein the expander block inserts end of multiframe (EOMF) padding bytes that complete the final buffer of the permutation matrix for that multiframe, allowing for LO ODUj/ODUflex addition or removal of LO ODUj/ODUflex clients while remaining hitless on other LO ODUj/ODUflex clients.