Optical transport networks are a type of Layer one network, which are also called digital wrapper. The capacity hierarchies that OTN supports today include ODU0 (Gigabit Ethernet), ODU1 (2.5 Gb/s), ODU2 (10 Gb/s), ODU3 (40 Gb/s) and ODU4 (100 Gb/s). OTN generally has very flexibility encapsulation capability, which is able to support various types of client services, for example, storage area network service such as fiber channel, traditional SDH/SONET services such as OC-3, STM-4, and so on, as well as carrier Ethernet services such as Gigabit Ethernet and 10 Gigabit Ethernet.