400GBASE-SR4.2 Application Overview

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400GBASE-SR4, 400GBASE-VR4, and 400GBASE-SR4.2
400GBASE-SR4.2: 400 Gb/s PAM4 parallel, bidirectional WDM transmission at 850 nm and 910 nm over 8 multimode optical fibers, with reach up to at least 100 m

400GBASE-SR4.2 supports short wavelength 4‑level pulse amplitude modulated (PAM4) parallel bidirectional 2‑wavelength division multiplexing (WDM) transmission over four lanes (8‑fibers) of multimode optical fiber cabling. The application’s equivalent symbol rate is 106.25 GBd per lane (PAM4 maps pairs of bits into a single symbol and two transmission wavelengths double the symbol rate) and the supported distance varies according to the type of multimode cable used. Network equipment interface connections include a multi‑fiber push on (MPO) connector and a standard socket into which a physical (PHY) layer transceiver module may be plugged.

  • Connector type: MPO/MTP
  • Transceiver module: QSFP-DD
  • Defined in clause 150 of the IEEE 802.3 Standard for Ethernet
  • Initially published as IEEE Std 802.3cm™: Physical Layer and Management Parameters for 400 Gb/s over Multimode Fiber in 2020

Optical Fiber Cabling (Channel) Characteristics:

400GBASE-SR4.2
Parameter OM3 OM4 OM5 Unit
Operating wavelengths: 850 and 910 nm
Modal bandwidth at 850 nm (min): 2,000 4,700 4,700 MHz∙km
Modal bandwidth at 953 nm (min): not specified 2,470 MHz∙km
Operating range: 0.5 to 70 0.5 to 100 0.5 to 150 m
Insertion loss (max): 1.7 1.8 2.0 dB
Cabling skew (max): 79 ns
Cabling skew variation: 2.4 ns

Key Application Capabilities:

  • Defines a four-lane 400 Gb/s PHY using two WDM lanes for operation over at least 100 m of MMF
  • Supports full-duplex operation only
  • Preserves the Ethernet frame format utilizing the Ethernet MAC
  • Preserves minimum and maximum FrameSize of current 802.3 Standard for Ethernet
  • Provides appropriate support for optical transport networks (OTNs)
  • Supports a BER of better than or equal to 10-13 at the MAC/PLS service interface (or the frame loss ratio equivalent)
  • Supports optional Energy-Efficient Ethernet operation

Related Applications:

The IEEE P802.3cm Task Force also specified the following PAM4, 26.5625 GBd symbol rate 400 Gb/s Ethernet application:

Application    Operating    Wavelength Media Operating Range1
400GBASE-SR8 850 nm Multimode up to 100 m
1 Supported distance varies according to the type of optical fiber cable used.

Back to TIA FOTC IEEE 802.3 Multimode Optical Fiber Ethernet Standards Explorer