This standard specifies a flexible Optical Service Unit (OSU) path layer for optical networks to provide 2 Mb/s to 100 Gb/s services. The main features of the OSU path layer are providing massive OSU connections to carry packet and Constant Bit Rate (CBR) services with guaranteed performance, enabling the flexible hitless bandwidth adjustment (e.g. n × 10 Mb/s) for each OSU connection, with the capabilities of high-bandwidth efficiency, large capacity and low latency. The OSU path layer can be carried on different server layers, e.g. OTN, PON, etc.