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OTN - Optical Transport Network overview



What is the OTN (Optical Transport Network)?

ITU-T (Telecommunication Standardization Sector) defines an Optical Transport Network (OTN) as a set of Optical Network Elements (ONE) connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals.

ITU-T Recommendation G.709 is commonly called Optical Transport Network (OTN).  As of December 2009 OTN has standardized the following line rates.

Signal
Approximate data rate (Gbit/s)
Applications
OTU1
2.66
Transports SONET OC-48 or synchronous digital hierarchy (SDH) STM-16 signal
OTU2
10.70
Transports an OC-192STM-64 or wide area network (WAN) physical layer (PHY) for 10 Gigabit Ethernet (10GBASE-W)
OTU2e
11.09
Transports a 10 Gigabit Ethernet local area network (LAN) PHY coming from IP/Ethernet switches and routers at full line rate (10.3 Gbit/s). This is specified in G.Sup43.
OTU3
43.01
Transports an OC-768 or STM-256 signal or a 40 Gigabit Ethernet signal.[2]
OTU3e2
44.58
Transports up to four OTU2e signals
OTU4
112
Transports a 100 Gigabit Ethernet signal

Why use OTN?
OTN offers the following advantages relative to SONET/SDH:
·         Stronger Forward Error Correction
·         More Levels of Tandem Connection Monitoring (TCM)
·         Transparent Transport of Client Signals

·         Switching Scalability

OTN Equipment Type
At a very high level the typical signals that OTN equipment at the Optical Channel layer processes are:
·         OTN
·         SONET/SDH
·         Ethernet/Fiber Channel
·         Packets
A few of the key functions performed on these signals are:
·         Protocol processing of all the signals. Some of the more complex processes are:
§  Forward error correction (FEC) on OTN signals
§  Multiplexing and de-multiplexing of OTN signals
§  Mapping and de-mapping of non-OTN signals into and out of OTN signals
·         Packet processing in conjunction with mapping/de-mapping of packet into and out of OTN signals

OTN Layer


The basic OTN Layer is consisting of the following information.
·         OCh:  Optical Channel
OCh is consist of the end-to-end transparent transmission functions, including re-arranging OCh connection to implement flexible network routing, processing OCh overheads to achieve the completeness of OCh adaption information, and monitoring OCh to implement the running and management of the network section.
·         OMS: Optical Multiplex Section
It provides multi-wavelength signals with network functions, including re-arranging OMS connection to implement flexible multi-wavelength network routing, processing OMS overheads to achieve the completeness of multi-wavelength OMS adaption information, and monitoring OMS to implement the running and management of the section.
·         OTS: Optical Transmission Section
It transmits optical signals over various fibers as well as detects and controls the optical amplifiers.

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