ITU enhances G.709 Optical Transport Network standards series

The International Telecommunication Union’s Telecommunication Standardization Sector (ITU-T), through its Study Group 15, has updated the ITU G.709 series of Optical Transport Network (OTN) standards. The enhancements focus on stronger forward error correction (FEC) for long-reach applications and additional security for short-reach scenarios.

The first upgrade comes via a revision to ITU G.709.3/Y.1331.3 “Flexible OTN long-reach interfaces.” The revision enables a stronger FEC option for 100-, 200-, and 400-Gbps Flexible OTN (FlexO) 450-km interfaces. The revision also describes practices for the direct multiplexing of different OTUCn signals into the FlexO payload area. It’s “a shift from providing the physical layer for a single OTUCn,” according to Steve Gorshe of Microchip Technology, who is Rapporteur for the Q11/15 working group responsible for the new specifications.

Meanwhile, ITU G.709.1/Y.1331.1 (Amendment 2) “Flexible OTN short-reach interfaces” enables additional FlexO security with encryption and authentication for FlexO links. The two new updates follow what ITU-T terms “a key extension” of ITU G.709.4 “OTU25 and OTU50 short-reach interfaces,” which is a new ITU standard designed by the Q11/15 working group to support IMT-2020/5G transport. ITU G.709.4 defines nominally 25G and 50G OTN interfaces optimized for carrying Ethernet 25GBASE-R and 50GBASE-R client signals.

“These are the rates becoming popular in 5G radio access networks,” Gorshe explains. “The ITU G.709.4 interfaces make it much easier for carriers to continue to base their radio access networks on OTN technology.”

ITU G.709.4 carries an index that also defines lower-rate OTN interfaces that operate at the same rates as Ethernet 25GBASE-R and 50GBASE-R signals, which enables the use of these OTN interfaces in applications where the network operator wants direct reuse of Ethernet optical modules.

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