G.709

Internet protocol suite
Application layer
Transport layer
Internet layer
Link layer
G.709
Interfaces for the Optical Transport Network (OTN)"
StatusIn force
Year started2001
Latest version6.0
June 2020
OrganizationITU-T
LicenseFreely available
Websitehttps://www.itu.int/rec/T-REC-G.709

ITU-T Recommendation G.709 Interfaces for the Optical Transport Network (OTN) describes a means of communicating data over an optical network.[1] It is a standardized method for transparent transport of services over optical wavelengths in DWDM systems. It is also known as Optical Transport Hierarchy (OTH) standard. The first edition of this protocol was approved in 2001.[2]

The G.709 OTUk signal is positioned as a server layer signal for various client signals, e.g. SDH/SONET, ATM, IP, Ethernet, Fibre Channel and OTN ODUk (where k=0, 1, 2, 2e, 3, 3e2, 4 or flex).[3] Work on support for InfiniBand and Common Public Radio Interface client signals is currently[when?] in progress.

The frame structure defined in G.709 is constructed of 4 areas:

  1. OPUk[3] is the area in which payload is mapped.
  2. ODUk[3] contains the OPUk with additional overhead bytes (e.g. TTI, BIP8, GCC1/2, TCM etc.).
  3. OTUk[3] is the section and includes framing, TTI, BIP8 and GCC0 bytes.
  4. FEC – The standard FEC code (described in G.975) is a Reed–Solomon coding calculated across the payload (OPU) columns. This allows detection and correction of bit errors due to signal impairments during transmission. The FEC code also extends the distance the optical signal can travel before requiring regeneration.

G.709 offers advanced OAM&P capabilities such as Tandem Connection Monitoring (TCM), End to End performance monitoring, connectivity monitoring, signal quality supervision and General Communication Channel (GCC).

Typical client signals and corresponding G.709 rates

Client Signal Type Client Signal OTN Line Signal (G.709) OTUk Line Rate (kbit/s)[4] OPUk Payload Rate (kbit/s)[4] OTUk frame period (μs) OTUk frequency accuracy (ppm)
SONET/SDH STS-48/STM-16 OTU1 2,666,057 2,488,320 48.971 ± 20
SONET/SDH STS-192/STM-64 OTU2 10,709,225 10,037,629 12.191 ± 20
Ethernet/Fibre Channel 10GBASE-R/10GFC OTU2e 11,095,727 10,356,012 11.766 ±100
SONET/SDH/Ethernet STS-768/STM-256/Transcoded 40GBASE-R OTU3 43,018,413 40,150,519 3.034 ±20
Ethernet Up to 4 10GBASE-R OTU3e2 44,583,355 41,611,131 2.928 ±20
Ethernet 100GBASE-R OTU4 111,809,973 100,376,298 1.167 ±20

Unlike SDH/SONET, the line rate is increased by maintaining the G.709 frame structure (4 rows x 4080 columns) and decreasing the frame period (in SDH/SONET the frame structure is increased and the frame period of 125 μs is maintained).

Notes and references

  1. ^ "ITU standards enhance capabilities of the Optical Transport Network". www.itu.int. Archived from the original on 2021-04-09. Retrieved 2021-04-09.
  2. ^ "G.709: Interfaces for the optical transport network". www.itu.int. Archived from the original on 2021-06-15. Retrieved 2021-06-15.
  3. ^ a b c d The letter k represents the ODUk data rate as follows:
    0 = ~1.24 Gbit/s
    1 = ~2.50 Gbit/s
    2 = ~10.04 Gbit/s
    2e = ~10.40 Gbit/s
    3 = ~40.32 Gbit/s
    3e2 = 41.79 Gbit/s
    4 = ~104.79 Gbit/s
    flex = a multiple of ~1.24 Gbit/s
  4. ^ a b Fractional portion is truncated

See also