The OTN frame structure based on ITU-TG.709 can support various customer signals mapping and transparent transmission, such as SDH, ATM, and Ethernet. Currently, standard encapsulation and transparent transmission can be achieved for SDH and ATM, but there are differences in the support for Ethernet at different rates. ITU-TG.sup43 provides supplementary suggestions for achieving different levels of transparent transmission for 10GE services, while the standardized mapping method for GE, 40GE, 100GE Ethernet, Fibre Channel (FC) for dedicated network service, and Gigabit Passive Optical Network (GPON) for access network service into the OTN frame is currently under discussion.
The electrical layer bandwidth granules defined by OTN are optical channel data units, namely ODU1 (2.5Gbit/s), ODU2 (10Gbit/s) and ODU3 (40Gbit/s). Compared with the scheduling granules of VC-12/VC-4 in SDH, the grain size of the OTN system for multiplexing, cross-connection and configuration is significantly larger, resulting in significantly improved efficiency in adapting and transmitting high-bandwidth customer data services.
OTN provides overhead management capabilities similar to SDH, and the OTN frame structure of the optical channel (OCh) layer greatly enhances the digital monitoring capabilities of the OCh layer. In addition, OTN also provides 6-layer nested tandem connection monitoring (TCM) function, which makes it possible to perform performance monitoring simultaneously across end-to-end and multiple segments when constructing OTN systems.
Through the introduction of the OTN frame structure, ODUk cross-connection and multidimensional reconfigurable optical add-drop multiplexer, the networking capability of optical transmission networks is greatly enhanced, changing the current situation of providing large-capacity transmission bandwidth based on SDHVC-12/VC-4 scheduling bandwidth and WDM point-to-point transmission. Adopting forward error correction (FEC) technology significantly increases the transmission distance of the optical layer. In addition, OTN systems will provide more flexible business protection functions based on the electrical layer and optical layer, such as photon network connection protection (SNCP) and shared ring network protection based on ODUk layer, and optical channel or multiplex segment protection based on the optical layer, but shared ring network technology has not yet been standardized.
From the electrical domain perspective, OTN systems retain many effective aspects of traditional digital transmission systems (SDH). At the same time, OTN expands new capabilities and fields, such as supporting transparent transmission of larger-grained 2.5G, 10G, and 40G services, supporting synchronous mapping and transparent transmission of both business and timing through asynchronous mapping, supporting FEC off-band, and supporting the monitoring of multi-layer and multi-domain network connections.