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400G QSFP Transceiver Types and Fiber Connections

Updated on April 19, 2022
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400G QSFP has become one of the most popular form factors in the next-generation network. And different types of modules have appeared in the 400G optical transceiver market. What are 400G QSFP-DD transceiver types? What fiber cables could be used with these 400G optical modules? What about the answers to frequently asked questions about 400G QSFP? This post will illustrate them thoroughly.

400G QSFP Transceiver Types

400G QSFP transceivers are introduced respectively in the following table according to the two transmission types (over multimode fiber and single-mode fiber) they support.

Transmission Type QSFP-DD Product Description Reach Optical Connector Wavelength Optical Modulation Protocol
Multimode fiber 400G QSFP-DD SR8 up to 100m over OM4 or OM5
up to 70m over OM3
MTP-16/MPO-16 850nm 50G PAM4

IEEE P802.3c

IEEE 802.3cd

Single-mode fiber 400G QSFP-DD DR4 up to 500m over parallel SMF MTP-12/MPO-12 1310nm 100G PAM4 IEEE 802.3bs
400G QSFP-DD XDR4/DR4+ up to 2km over parallel SMF MTP-12/MPO-12 1310nm 100G PAM4 /
400G QSFP-DD FR4 up to 2km over duplex SMF LC CWDM4 wavelength 100G PAM4 100Glambda MSA
400G QSFP-DD 2FR4 up to 2km over duplex SMF CS CWDM4 wavelength 50G PAM4 IEEE 802.3bs
400G QSFP-DD LR4 up to 10km over duplex SMF LC CWDM4 wavelength 100G PAM4 100Glambda MSA
400G QSFP-DD LR8 up to 10km over duplex SMF LC CWDM4 wavelength 50G PAM4 IEEE 802.3bs
400G QSFP-DD ER8 up to 40km over duplex SMF LC 1310nm 50G PAM4 IEEE 802.3cn

Fiber Connections for 400G QSFP Transceivers

QSFP 400G SR8

  • A QSFP-DD SR8 can interop with another QSFP-DD SR8 over an MTP-16/MPO-16 cable. This is the most popular connection using an MTP-16/MPO-16 cable to connect two QSFP-DD SR8 transceivers directly.

  • QSFP-DD SR8 Connection
  • 400G QSFP-DD SR8 breaks out to 2× 200G SR4.

  • QSFP-DD SR8 to 2× 200G SR4 Breakout Connection
  • QSFP-DD SR8 interops with 8× 50G SR over MPO-16 to 8× LC duplex fiber cables.


QSFP 400G DR4

  • QSFP-DD DR4 interops with QSFP-DD DR4 over an MPO-12 trunk cable.

      QSFP-DD DR4 Connection
  • 400G QSFP-DD DR4 interops with 4× 100G DR over MPO-12 to 4× LC duplex breakout cable.

QSFP-DD DR4 to 4x 100G Breakout Connection

QSFP 400G XDR4/DR4+

  • QSFP-DD XDR4/DR4+ interops with QSFP-DD XDR4/DR4+ over an MPO-12 trunk cable.

      QSFP-DD XDR4 Connection
  • 400G QSFP-DD XDR4 interops with 4× 100G FR modules over an MPO-12 to 4× Duplex LC cable.

QSFP 400G FR4

QSFP-DD FR4 interops with QSFP-DD FR4 over a duplex LC cable.

QSFP-DD FR4 Connection

QSFP 400G 2FR4

QSFP-DD 2FR4 interops with 2× 200G FR4 over 2× CS to 2× LC duplex cable.

QSFP-DD 2FR4 Connection

QSFP 400G LR4

QSFP-DD LR4 interops with QSFP-DD LR4 over an LC duplex cable.

QSFP-DD LR4 Connection

QSFP 400G LR8

QSFP-DD LR8 interops with QSFP-DD LR8 over an LC duplex cable.

QSFP-DD LR8 Connection

QSFP 400G ER8

QSFP-DD ER8 interops with QSFP-DD ER8 over an LC duplex cable.

QSFP-DD ER8 Connection

400G QSFP Transceivers: Q&A

Q: What does "SR8", "DR4", "XDR4", "FR4", "LR4", and "LR8" mean in QSFP 400G modules?

A: "SR" refers to short-range, and "8" implies there are 8 optical channels. "DR" refers to 500m reach using single-mode fiber, and "4" implies there are 4 optical channels. "XDR4" is short for "eXtended reach DR4". And "LR" refers to 10km reach using single-mode fiber.

Q: Can I plug a QSFP-DD transceiver module into an OSFP port?

A: No. QSFP-DD and OSFP are totally different form factors. For more information about OSFP transceivers, you can refer to the 400G OSFP Transceiver Types Overview. You can use only one kind of form factor in the corresponding system. Eg, if you have a QSFP 400G system, QSFP-DD transceivers and cables must be used.

Q: Can I plug a 100G QSFP28 module into a 400G QSFP port?

A: Yes. A QSFP28 module can be inserted into a QSFP-DD port (without a mechanical adapter). When using a QSFP28 module in a QSFP-DD port, the QSFP-DD port must be configured for a data rate of 100G instead of 400G.

Q: What other breakout options are possible apart from using the 400G QSFP-DD modules mentioned above?

A: 400G QSFP-DD DACs & AOCs are possible for breakout 400G connections. See 400G Direct Attach Cables (DAC & AOC) Overview for more information about 400G DACs & AOCs.

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