Connectors and Cages

Electronics, optics, and copper wires are housed in metal shell plugs called form-factor plugs. Plugs have a cage counterpart that is in the network switch front panels and on top of network adapters. The metal plugs have many code name extensions based on the single-channel; small-form-factor plug (SFP).

SFP can be proceeded by Q for quad or 4-channels (QSFP) and for 8-channels, quad-double density (QSFP-DD), and octal (OSFP). NVIDA created an 8-channel transceiver called the twin-port OSFP that has 8 electrical channels and two optical 4-channel ports. Numbers at the end indicate the maximum Gb/s speed rating of the connector e.g., 28, 56, 112 e.g., QSFP56, QSFP112 to contain the signal EMI noise. Also note that InfiniBand and Ethernet use slightly lower speed ratings than the connector maximum speed e.g. QSFP56 supports 50G rates, and QSFP112 uses 100G rates.

The octal small form-factor plug, or OSFP, has become the preferred form-factor for high-speed applications such as artificial intelligence and HPC networking as it offers future expansion with more channels, more space for components, and higher power dissipation capabilities. The twin-port OSFP 800G plug has 8-channels of electrical signaling for the switch and two 400Gb/s engines inside the transceiver that exit to two 400G optical or copper ports. Extra cooling fins are used on top to support 17-Watt transceivers– hence the name “2x400G twin-port OSFP finned-top”.

The 800G twin-port OSFP is also offered in a flat top version and a 400Gb/s single-port, flat-top OSFP is offered. These are all the same size, but the twin-port OSFP finned top version is taller due to the heat sink.

The three OSFP versions are:

• 800G finned-top, twin-port, 8-channel, 2x400G OSFP for Quantum-2 and Spectrum-4 SN5600 Ethernet air-cooled switches.

• 800G flat-top, twin-port, 8-channel, 2x400G OSFP for linking DGX H100 Cedar7 GPU links which use internal cage riding, air-cooled, heat sinks for liquid-cooled systems. This has the same internals as the finned top version.

• 400G flat-top, single-port, 4-channel, OSFP for ConnectX-7/OSFP network adapters using cage riding heat sinks.

800G twin-port OSFP finned-top connectors area also used to construct passive copper cables, active copper cables, and active optical cables using twin-port OSFP, OSFP, QSFP112, and QSFP56 connector ends. These parts are available in various combinations including 800G twin-port OSFP with flat tops instead of fins.

Lastly, a long reach single mode, 2km twin-port OSFP called 2xFR4 transceiver will be available at the end of 2023 that uses a finned-top but with a lid on top of the fins creating a closed channel for additional cooling.

Twin-port OSFP Open Finned Top Closed Finned Top

QSFP112 form-factor is a single-port, 4-channel, 400G device specifically for ConnectX-7/QSFP112 adapters and BlueField-3/QSFP112 DPUs.

• QSFP112 has a flat top without cooling fins on top and uses the cooling fins located on the adapter and DPU connector cages.

• QSFP112 cannot be used in twin-port OSFP switch cages or single-port OSFP ConnectX-7 adapters.

Twin-port OSFP, OSFP, and QSFP112 connector plugs

Twin-port 2x400G finned-top OSFP	Twin-port 2x400G flat-top OSFP	Single-port OSFP	Single-port QSFP112

Twin-port OSFP for Switches, OSFP, and QSFP112 ConnectX-7, and BlueField-3 DPUs

50G-PAM4 modulation enables 400GbE with 8-channels and 200GbE and 200G HDR InfiniBand with 4-channels.

• 400G QSFP-DD has two rows of 4-channel electrical lanes, hence the name Double Density. Based on 8-channels of 50G-PAM4, QSFP-DD is used only in Spectrum-3 SN4000 400G Ethernet and Spectrum-4 SN5400 switches.

• 200G QSFP56 is used for 4-channels of 50G-PAM4 for HDR InfiniBand and 200GbE Spectrum-2 Ethernet networking.

The NVIDIA Spectrum SN2000 series switches and ConnectX-5 adapters use the QSFP28 plug and some models SFP28. These parts date back to 2015 but are still in widespread use.

• 100G QSFP28 is used for 4-channels of 25G-NRZ for EDR InfiniBand and Ethernet 100GbE networking.

• 40G QSFP+ is used for 4-channels of 10G-NRZ for QDR InfiniBand and Ethernet 40GbE networking.

• 25G SFP28 is used for 1-channel of 25G-NRZ for Ethernet (not used for InfiniBand).

• 10G SFP+ is used for 1-channel of 10G-NRZ for Ethernet (not used for InfiniBand).

Backwards Compatibility

The QSFP evolved over many years and generations and offers backwards compatibility of newer cages with older devices. QSFP-DD plug is the same height and width as the 4-channel QSFP56 and QSFP28 used for 200G and 100G systems, but longer to support two rows of 4-channel electrical pins creating 8-channels. This enables the QSFP-DD cages in switches to support backwards compatibility to 4-channel QSFP56, QSFP28, and QSFP+ devices, which engage only the first row of 4 pins in the 8-channel QSFP-DD cage supporting 4-channels.

• QSFP-DD is not used for InfiniBand systems as of 2023 and not for 100G-PAM4 Ethernet systems.

• QSFP-DD cages in switches can accept QSFP112, QSFP56, and QSFP28 devices using 50G-PAM4 or 25G-NRZ modulation.

• QSFP112 cages in adapters and DPUs can accept QSFP56, QSFP28, and QSFP+ cables and transceivers.

• QSFP56 cages devices in switches and adapters accept QSFP28, QSFP+ cables and transceivers.

• ConnectX-6/7 and BlueField-2/3 are not offered using QSFP-DD cages –- only for switches.

• NVIDIA does not offer a QSA port adapter to convert QSFP112 devices to be inserted into twin-port OSFP cages.

• NVIDIA does offer a QSA+ and QSA28 port adapter enabling SFP devices to be inserted into QSFP cages and passing through one channel. QSA56 is not offered.

QSFP-DD, QSFPxx, and SFPxx connector plugs

QSFP-DD
QSFP112, QSFP56
QSFP28, QSFP+
SFP28, SFP+
QSA28, QSA+