Optical Transport Network (OTN): Rate Standards Guide

Posted on Apr 9, 2024 by

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In the ever-evolving telecommunications landscape, Optical Transport Networks (OTN) have emerged as a game-changer for transmitting data across vast distances. At the heart of OTN's success lies its meticulous rate standards, pivotal for ensuring flawless data transmission. This article takes an in-depth dive into the realm of OTN rate standards, exploring their evolution, significance, and their indispensable role in shaping modern telecommunications infrastructure.

OTN Rate Standards Background and Basics

OTN rate standards originated from the growing demands on traditional communication networks and advancements in data transmission technology. As data volume and transmission distances increased, SONET/SDH technologies showed limitations in meeting bandwidth needs and network complexity. This led to the emergence of OTN, offering higher bandwidth, flexible transmission, and robust fault tolerance. Standardization bodies like ITU-T developed OTN rate standards to regulate optical transmission across different data rates, driving OTN's development and adoption.

The following basic information has been presented to provide a brief introduction to the OTN Rate Standard:

Definition: An Optical Transport Network (OTN) is a sophisticated digital framework engineered to encapsulate data frames, enabling the seamless transmission of multiple data sources over a unified channel.

Functionality: OTN creates dedicated optical networks for each client signal, following ITU-T standards. It includes interconnected optical elements linked by fiber optics, handling tasks like transport, multiplexing, switching, and monitoring, ensuring reliable data transmission.

Distinction: OTN differs from SONET/SDH by offering an effective mechanism for managing multiplexed wavelengths within Dense Wavelength Division Multiplexing (DWDM) systems. If you want to know more about the differences between the OTN and SONET/SDH, you can check out this article: OTN VS SONET/SDH.

OTN Standard Line Rates

ITU-T Recommendation G.709 is often referred to as OTN, also known as digital wrapper technology or optical channel wrapper. By December 2009, OTN had standardized the following line rates.

Signal	Marketing data Rate(Gbit/s)	True Signal rate (OTU)(Gbit/s)	# of ODU0, 1.2G	# of ODU1, 2.5G	# of ODU2, 10G	# of ODU2, 10.4G	# of ODU25, 26.4G	# of ODU3, 40.3G	# of ODU50, 52.8G	# of ODU4, 104G	Applications
OTU1	2.5	2.66	2	1	0	0	0	0	0	0	Transports SONET OC-48 or synchronous digital hierarchy (SDH) STM-16 signal.
OTU2	10	10.7	8	4	1	0	0	0	0	0	Transports an OC-192, STM-64 or wide area network (WAN) physical layer (PHY) for 10 Gigabit Ethernet (10GBASE-W).
OTU2e	10.5	11.1	8	4	1	1	0	0	0	0	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.
OTU25	25	26.4	20	10	2	2	1	0	0	0	Transports a 25 Gigabit Ethernet signal.
OTU3	40	43	32	16	4	3	1	1	0	0	Transports an OC-768 or STM-256 signal or a 40 Gigabit Ethernet signal.
OTU3e1/2	41	44.5	32	16	4	3	1	1	0	0	Develop for transport of 10G LAN PHY, and one for 10G WAN PHY, over SDH and OTN.
OTU50	50	52.8	40	20	5	5	2	1	1	0	Transports a 50 Gigabit Ethernet signal.
OTU4	100	111.8	80	40	10	10	2	2	2	1	Transports a 100 Gigabit Ethernet signal.
OTUCn	n x 100	n x 105.2	Total bandwidth / ODU size. e.g. 200G Channel support 4xODU3 and 4xODU2								Instances of a logically interleaved 100G (C=100) frame format are used for data transmission.

OTN Signal Mapping

In an OTN, signal mapping involves the process of mapping client signals onto appropriate server-layer signals for transmission within the network. The OTUk (where k=1/2/2e/3/3e2/4) serves as an information structure for mapping ODUk signals. These ODUk signals function as the server-layer signals, capable of accommodating data from different clients. Through necessary processing and encapsulation as defined in ITU-T Recommendation G.709, this signal mapping ensures effective data transmission and management within the OTN, while maintaining network flexibility and reliability.

The following ODUk information structures are defined in ITU-T Recommendation G.709：

Signal	Data Rate (Gbit/s)	Typical Applications
ODU0	1.24416	Transport of a timing transparent transcoded (compressed) 1000BASE-X signal or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure.
ODU1	2.49877512605042	Transport of two ODU0 signals or a STS-48/STM-16 signal or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure.
ODU2	10.0372739240506	Transport of up to eight ODU0 signals or up to four ODU1 signals or a STS-192/STM-64 signal or a WAN PHY (10GBASE-W) or a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure.
ODU2e	10.3995253164557	Transport of a 10 Gigabit Ethernet signal or a timing transparent transcoded (compressed) Fibre Channel 10GFC signal.
ODU3	40.3192189830509	Transport 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 (such as Ethernet, MPLS or IP) using Generic Framing Procedure.
ODU3e2	41.7859685595012	Transport of up to four ODU2e signals.
ODU4	104.794445814978	Transport 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 (CBR)	239/238 x Client Bit Rate	Transport of a constant bitrate signal such as Fibre Channel 8GFC, InfiniBand or Common Public Radio Interface.
ODUflex (GFP)	Any Configured Rate	Transport of a stream of packets (such as Ethernet, MPLS or IP) using Generic Framing Procedure.

FS OTN Solution for Data Center

FS offers a customized 1.6T transponder solution designed to address the demanding requirements for high-speed and high-bandwidth interconnections within data centers. Leveraging the TSP16 device, this solution integrates 8 200G CFP2 modules on the line side and 16 100G QSFP28 modules on the client side, facilitating the transmission of 1.6T of business capacity. Moreover, it features a 40CH DWDM MUX/DEMUX, capable of supporting up to 8T of business capacity transmission. These versatile devices are well-suited for both short-distance interconnections between data centers and long-distance business transmissions across backbone networks, providing robust support for enabling extensive information exchange.

In conclusion

In conclusion, OTN represents a vital component of contemporary telecommunications infrastructure, fundamentally changing the transmission of data across extensive distances. The meticulous rate standards integral to OTN are pivotal in enabling seamless data transmission, ensuring the reliability and efficiency of communication networks. As technology continues its advancement, OTN rate standards will remain crucial in meeting the escalating demands for data transmission and shaping the trajectory of telecommunications. This guide offers insights into the evolution and significance of OTN rate standards, underscoring their indispensable role in driving innovation and progress within the telecommunications sector.