Optical Transport Network


defines an Optical Transport Network as a set of Optical Network Elements connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals. An ONE may Re-time, Re-Amplify, Re-shape but it does not have to be 3R it can be purely photonic.

Standards

OTN was designed to provide support for optical networking using wavelength-division multiplexing unlike its predecessor SONET/SDH.
ITU-T Recommendation G.709 is commonly called Optical Transport Network . As of December 2009, OTN has standardized the following line rates.
SignalApproximate data rate Applications
OTU12.66Transports SONET OC-48 or synchronous digital hierarchy STM-16 signal
OTU210.70Transports an OC-192, STM-64 or wide area network physical layer for 10 Gigabit Ethernet
OTU2e11.09Transports a 10 Gigabit Ethernet local area network PHY coming from IP/Ethernet switches and routers at full line rate. This is specified in G.Sup43.
OTU2f11.32Transports a 10 Fibre Channel.
OTU343.01Transports an OC-768 or STM-256 signal or a 40 Gigabit Ethernet signal.
OTU3e244.58Transports up to four OTU2e signals
OTU4112Transports a 100 Gigabit Ethernet signal

The OTUk is an information structure into which another information structure called ODUk is mapped. The ODUk signal is the server layer signal for client signals. The following ODUk information structures are defined in ITU-T Recommendation G.709
SignalData Rate Typical Applications
ODU01.24416Transport of a timing transparent transcoded 1000BASE-X signal or a stream of packets using Generic Framing Procedure
ODU12.49877512605042Transport of two ODU0 signals or a STS-48/STM-16 signal or a stream of packets using Generic Framing Procedure.
ODU210.0372739240506Transport of up to eight ODU0 signals or up to four ODU1 signals or a STS-192/STM-64 signal or a WAN PHY or a stream of packets using Generic Framing Procedure
ODU2e10.3995253164557Transport of a 10 Gigabit Ethernet signal or a timing transparent transcoded Fibre Channel 10GFC signal
ODU340.3192189830509Transport of up to 32 ODU0 signals or up to 16 ODU1 signals or up to four ODU2 signals or a STS-768/STM-256 signal or a timing transparent transcoded 40 Gigabit Ethernet signal or a stream of packets using Generic Framing Procedure
ODU3e241.7859685595012Transport of up to four ODU2e signals
ODU4104.794445814978Transport of up to 80 ODU0 signals or up to 40 ODU1 signals or up to ten ODU2 signals or up to two ODU3 signals or a 100 Gigabit Ethernet signal
ODUflex x client bit rateTransport of a constant bitrate signal such as Fibre Channel 8GFC, InfiniBand or Common Public Radio Interface
ODUflex any configured rateTransport of a stream of packets using Generic Framing Procedure

Equipment

At a very high level, the typical signals processed by OTN equipment at the Optical Channel layer are:
A few of the key functions performed on these signals are:
The OTN signals at all data-rates have the same frame structure but the frame period reduces as the data-rate increases. As a result, the Time-Slot Interchange technique of implementing SONET/SDH switch fabrics is not directly applicable to OTN switch fabrics. OTN switch fabrics are typically implemented using Packet Switch Fabrics.

FEC Latency

On a point-to-point OTN link there is latency due to forward error correction processing.